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Encyclopedia of Electronic Circuits

Encyclopedia of Electronic Circuits Selected by Rudolf F. Graf & William Sheets, © 1999 McGraw-Hill & Mental Automation, Inc.

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SuperCAD is a program which is specialized for drawing electronic circuits. The lite version of SuperCAD allows you to draw A and B size schematics, using a large library of nearly 1000 symbols. With SuperCAD lite you can edit any of the on-line encyclopedia schematics, as well as make entirely new schematics. Because of our association with McGraw-Hill in producing the Encyclopedia of Electronic Circuits CD ROM , the SuperCAD schematic editor is fast becoming a standard for schematic entry.

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Contents Volume 2

Audio Circuits

Consumer Circuits

Display

General Electronics

Measurement and Sensor Electronics

Power and Battery Circuits

Radio Circuits

Signal Generation

A B C	Topics in Alphabetical Order


Audio Circuits

AMPLIFIER (MISCELLANEOUS)

AMPLIFIERS (AUDIO)

AMPLIFIERS, POWER

AUDIO EFFECTS CIRCUITS

AUDIO MIXER CIRCUITS

TONE CONTROL CIRCUITS


Consumer Circuits

AUTOMOTIVE CIRCUITS

AUTOMOTIVE SECURITY CIRCUITS

BUGGING CIRCUITS

COMPUTER CIRCUITS

ELECTRONIC LOCK CIRCUITS

GAME CIRCUITS

INTERCOM CIRCUITS

LIGHT CONTROL CIRCUITS

LIGHT CONTROLLED CIRCUITS

MEDICAL ELECTRONICS CIRCUITS

METRONOME CIRCUITS

MODEL AND HOBBY CIRCUITS

MUSICAL CIRCUITS

PHOTOGRAPHY RELATED CIRCUITS

TAPE RECORDER CIRCUITS

TELEPHONE RELATED CIRCUITS

TIMER CIRCUITS

TOUCH-CONTROL CIRCUITS

WEATHER RELATED CIRCUITS


Display

ALARM AND SECURITY CIRCUITS

ANNUNCIATOR CIRCUITS

FLASHER AND BLINKER CIRCUITS

INDICATOR CIRCUITS


General Electronics

AGC AND ALC CIRCUITS

AMPLIFIER (INSTRUMENTATION) CIRCUITS

AMPLIFIER (OPERATIONAL) CIRCUITS

ANALOG TO DIGITAL CONVERTERS

BUFFER CIRCUITS

CARRIER CURRENT CIRCUITS

CLOCK CIRCUITS

COMPARATOR CIRCUITS

COMPRESSOR/EXPANDER CIRCUITS

CONTROLLER CIRCUITS

CONVERTER CIRCUITS

COUNTER CIRCUITS

DECODER CIRCUITS

DESCRAMBLER AND DECODER CIRCUITS

DIGITAL CIRCUITS

DIGITAL TO ANALOG CONVERTER CIRCUITS

DRIVER CIRCUITS

FIBER-OPTICS CIRCUITS

FILTER CIRCUITS

INFRARED CIRCUITS

INTERFACE CIRCUITS

LASER CIRCUITS

LIGHT BEAM COMMUNICATION CIRCUITS

LIMITER CIRCUITS

LOGIC CIRCUITS

MISCELLANEOUS TREASURES

MOTOR CONTROL CIRCUITS

NOISE REDUCTION CIRCUIT

OPTICAL CIRCUITS

PIEZO CIRCUITS

RELAY CIRCUITS

SAMPLE AND HOLD CIRCUITS

SWITCHING CIRCUITS

TEMPERATURE CONTROLLER CIRCUITS

TESLA COIL CIRCUITS

ULTRASONIC CIRCUITS

WINDOW COMPARATOR/DISCRIMINATOR CIRCUITS


Measurement and Sensor Electronics

CRYSTAL TEST CIRCUITS

FIELD STRENGTH METER CIRCUITS

FREQUENCY MEASURING CIRCUITS

GAS AND SMOKE DETECTOR CIRCUIT

HALL EFFECT CIRCUITS

ION GENERATOR AND DETECTOR CIRCUITS

LIQUID LEVEL DETECTOR CIRCUITS

MEASURING AND TEST CIRCUITS (HIGH FREQUENCY AND RF)

MEASURING AND TEST CIRCUITS (SOUND)

MEASURING AND TEST CIRCUITS - CABLE

MEASURING AND TEST CIRCUITS - CAPACITANCE

MEASURING AND TEST CIRCUITS - CURRENT

MEASURING AND TEST CIRCUITS - FREQUENCY

MEASURING AND TEST CIRCUITS - MISCELLANEOUS

MEASURING AND TEST CIRCUITS - POWER

MEASURING AND TEST CIRCUITS - RESISTANCE

MEASURING AND TEST CIRCUITS - SEMICONDUCTOR

MEASURING AND TEST CIRCUITS - VOLTAGE

METAL DETECTOR CIRCUITS

MOISTURE AND FLUID DETECTOR CIRCUITS

MOTION AND PROXIMITY DETECTOR CIRCUITS

PROXIMITY SENSOR CIRCUITS

RADIATION DETECTOR CIRCUITS

TEMPERATURE SENSOR CIRCUITS

THERMOMETER CIRCUITS


Power and Battery Circuits

BATTERY CHARGERS

BATTERY TEST AND MONITOR CIRCUITS

CURRENT SOURCES AND SINK CIRCUITS

OSCILLATORS (RF)

POWER SUPPLIES (VARIABLE)

POWER SUPPLY CIRCUITS (FIXED)

POWER SUPPLY CIRCUITS - DC-DC

POWER SUPPLY CIRCUITS - HIGH VOLTAGE

POWER SUPPLY CIRCUITS - MULTIPLE OUTPUT

POWER SUPPLY MONITOR CIRCUITS

PROTECTION CIRCUITS

REGULATOR CIRCUITS

REMOTE CONTROL CIRCUITS


Radio Circuits

AMATEUR CIRCUITS

AMATEUR TELEVISION (ATV) CIRCUITS

ANTENNA CIRCUITS

CODE PRACTICE CIRCUITS

CRYSTAL RADIO CIRCUITS

DETECTOR, DEMODULATOR AND DISCRIMINATOR CIRCUITS

MIXER AND MULTIPLEXER CIRCUITS

MODULATOR CIRCUITS

RADAR DETECTOR CIRCUITS

RADIO CIRCUITS

RECEIVING CIRCUITS

TRANSMITTER CIRCUITS

VIDEO CIRCUITS


Signal Generation

FREQUENCY MULTIPLIER AND DIVIDER CIRCUITS

FUNCTION AND SIGNAL GENERATOR CIRCUITS

MULTIVIBRATOR CIRCUITS

NOISE GENERATOR CIRCUITS

OSCILLATOR (AUDIO)

OSCILLATOR (SINE WAVE) CIRCUITS

OSCILLATORS (MISCELLANEOUS)

OSCILLATORS (VOLTAGE-CONTROLLED)OSCILLOSCOPE CIRCUITS

PHASE SEQUENCE AND PHASE SHIFT CIRCUITS

SAWTOOTH GENERATOR CIRCUIT

SIRENS, WARBLERS, WAILERS AND WHOOPERS CIRCUITS

SOUND EFFECT CIRCUITS

SOUND- AND VOICE-CONTROLLED CIRCUITS

SQUARE-WAVE GENERATOR CIRCUITS

STAIRCASE GENERATOR CIRCUITS

STROBE CIRCUITS

TONE CIRCUITS


A

AGC AND ALC CIRCUITS

ALARM AND SECURITY CIRCUITS

AMATEUR CIRCUITS

AMATEUR TELEVISION (ATV) CIRCUITS

AMPLIFIER (INSTRUMENTATION) CIRCUITS

AMPLIFIER (MISCELLANEOUS)

AMPLIFIER (OPERATIONAL) CIRCUITS

AMPLIFIERS (AUDIO)

AMPLIFIERS, POWER

ANALOG TO DIGITAL CONVERTERS

ANNUNCIATOR CIRCUITS

ANTENNA CIRCUITS

AUDIO EFFECTS CIRCUITS

AUDIO MIXER CIRCUITS

AUTOMOTIVE CIRCUITS

AUTOMOTIVE SECURITY CIRCUITS

B

BATTERY CHARGERS

BATTERY TEST AND MONITOR CIRCUITS

BUFFER CIRCUITS

BUGGING CIRCUITS

C

CARRIER CURRENT CIRCUITS

CLOCK CIRCUITS

CODE PRACTICE CIRCUITS

COMPARATOR CIRCUITS

COMPRESSOR/EXPANDER CIRCUITS

COMPUTER CIRCUITS

CONTROLLER CIRCUITS

CONVERTER CIRCUITS

COUNTER CIRCUITS

CRYSTAL RADIO CIRCUITS

CRYSTAL TEST CIRCUITS

CURRENT SOURCES AND SINK CIRCUITS

D

DECODER CIRCUITS

DESCRAMBLER AND DECODER CIRCUITS

DETECTOR, DEMODULATOR AND DISCRIMINATOR CIRCUITS

DIGITAL CIRCUITS

DIGITAL TO ANALOG CONVERTER CIRCUITS

DRIVER CIRCUITS

E

ELECTRONIC LOCK CIRCUITS

F

FIBER-OPTICS CIRCUITS

FIELD STRENGTH METER CIRCUITS

FILTER CIRCUITS

FLASHER AND BLINKER CIRCUITS

FREQUENCY MEASURING CIRCUITS

FREQUENCY MULTIPLIER AND DIVIDER CIRCUITS

FUNCTION AND SIGNAL GENERATOR CIRCUITS

G

GAME CIRCUITS

GAS AND SMOKE DETECTOR CIRCUIT

H

HALL EFFECT CIRCUITS

I

INDICATOR CIRCUITS

INFRARED CIRCUITS

INTERCOM CIRCUITS

INTERFACE CIRCUITS

ION GENERATOR AND DETECTOR CIRCUITS

L

LASER CIRCUITS

LIGHT BEAM COMMUNICATION CIRCUITS

LIGHT CONTROL CIRCUITS

LIGHT CONTROLLED CIRCUITS

LIMITER CIRCUITS

LIQUID LEVEL DETECTOR CIRCUITS

LOGIC CIRCUITS

M

MEASURING AND TEST CIRCUITS (HIGH FREQUENCY)

MEASURING AND TEST CIRCUITS (SOUND)

MEASURING AND TEST CIRCUITS - CABLE

MEASURING AND TEST CIRCUITS - CAPACITANCE

MEASURING AND TEST CIRCUITS - CURRENT

MEASURING AND TEST CIRCUITS - FREQUENCY

MEASURING AND TEST CIRCUITS - MISCELLANEOUS

MEASURING AND TEST CIRCUITS - POWER

MEASURING AND TEST CIRCUITS - RESISTANCE

MEASURING AND TEST CIRCUITS - SEMICONDUCTOR

MEASURING AND TEST CIRCUITS - VOLTAGE

MEDICAL ELECTRONICS CIRCUITS

METAL DETECTOR CIRCUITS

METRONOME CIRCUITS

MISCELLANEOUS TREASURES

MIXER AND MULTIPLEXER CIRCUITS

MODEL AND HOBBY CIRCUITS

MODULATOR CIRCUITS

MOISTURE AND FLUID DETECTOR CIRCUITS

MOTION AND PROXIMITY DETECTOR CIRCUITS

MOTOR CONTROL CIRCUITS

MULTIVIBRATOR CIRCUITS

MUSICAL CIRCUITS

N

NOISE GENERATOR CIRCUITS

NOISE REDUCTION CIRCUIT

O

OPTICAL CIRCUITS

OSCILLATOR (AUDIO)

OSCILLATOR (SINE WAVE) CIRCUITS

OSCILLATORS (MISCELLANEOUS)

OSCILLATORS (RF)

OSCILLATORS (VOLTAGE-CONTROLLED)

OSCILLOSCOPE CIRCUITS

P

PHASE SEQUENCE AND PHASE SHIFT CIRCUITS

PHOTOGRAPHY RELATED CIRCUITS

PIEZO CIRCUITS

POWER SUPPLIES (VARIABLE)

POWER SUPPLY CIRCUITS (FIXED)

POWER SUPPLY CIRCUITS - DC-DC

POWER SUPPLY CIRCUITS - HIGH VOLTAGE

POWER SUPPLY CIRCUITS - MULTIPLE OUTPUT

POWER SUPPLY MONITOR CIRCUITS

PROTECTION CIRCUITS

PROXIMITY SENSOR CIRCUITS

R

RADAR DETECTOR CIRCUITS

RADIATION DETECTOR CIRCUITS

RADIO CIRCUITS

RECEIVING CIRCUITS

REGULATOR CIRCUITS

RELAY CIRCUITS

REMOTE CONTROL CIRCUITS

S

SAMPLE AND HOLD CIRCUITS

SAWTOOTH GENERATOR CIRCUIT

SIRENS, WARBLERS, WAILERS AND WHOOPERS CIRCUITS

SOUND EFFECT CIRCUITS

SOUND- AND VOICE-CONTROLLED CIRCUITS

SQUARE-WAVE GENERATOR CIRCUITS

STAIRCASE GENERATOR CIRCUITS

STROBE CIRCUITS

SWITCHING CIRCUITS

T

TAPE RECORDER CIRCUITS

TELEPHONE RELATED CIRCUITS

TEMPERATURE CONTROLLER CIRCUITS

TEMPERATURE SENSOR CIRCUITS

TESLA COIL CIRCUITS

THERMOMETER CIRCUITS

TIMER CIRCUITS

TONE CIRCUITS

TONE CONTROL CIRCUITS

TOUCH-CONTROL CIRCUITS

TRANSMITTER CIRCUITS

U

ULTRASONIC CIRCUITS

V

VIDEO CIRCUITS

W

WEATHER RELATED CIRCUITS

WINDOW COMPARATOR/DISCRIMINATOR CIRCUITS


AGC AND ALC CIRCUITS

AGC AUDIO PREAMP

AUDIO LEVELER

DIGITAL AUTOMATIC LEVEL CONTROL (ALC)


AGC AUDIO PREAMP
AGC AUDIO PREAMPFF1-1

The circuit uses an easily obtained 741 op amp set for an internal gain of about 200. A portion of the op amp's output signal is rectified by the 1N4148 diodes, then filtered and fed to the gate of the FET input shunting circuit.  As the output rises, more and more input shunting takes place. That is, more of the input signal is bypassed, effectively keeping the output level constant.

The circuit offers a 100:1 limiting action.  The input level can change over a 100:1 ratio with little or no effect on the output level.  The output level itself can be set from less than unity all the way up to nearly the gain of the amplifier, making the circuit usable in other applications as well.

(QST , 2/95, p. 58)


K AUDIO LEVELER
AUDIO LEVELERFF1-4

A low power programmable compandor chip, the Signetics NE577 IC is used. Incoming audio is compressed, rectified and conditioned so that the input signal level always remains about the noise level. The compressor is an ALC circuit that outputs a constant level and the expander part of the IC is not used. (1994 Experimenters Handbook, p. 113)


K DIGITAL AUTOMATIC LEVEL CONTROL (ALC)
DIGITAL AUTOMATIC LEVEL CONTROL (ALC)FE7-1

This approach to automatic level control (ALC) makes use of digitally switched audio attenuators in the signal path. The output level of the system is sensed, compared to a reference, and audio pads are inserted via analog switches. This method is nearly instantaneous and eliminates the compromises necessary in conventional RC network ALC systems using fast attack, slow-decay approaches. (Reprinted with permission from 73 Amateur Radio Today, 8/92, p.36)


ALARM AND SECURITY CIRCUITS

555-BASED ALARM

BURGLAR ALARM CIRCUIT

CLOSED-LOOP ALARM

HEAT- OR LIGHT-ACTIVATED ALARM

INTRUDER ALARM

LATCHING BURGLAR ALARM

MULTI-LOOP PARALLEL ALARM

NO-DOZE ALARM

PARALLEL LOOP ALARM

SAFER SECURITY SYSTEM

SEMICONDUCTOR FAIL-SAFE ALARM

SIMPLE BURGLAR ALARM

LATCHING BURGLAR ALARM


K 555-BASED ALARM
555-BASED ALARMFE1-15

The alarm circuit has a single 555 oscillator/timer (U1) performing double duty; serving both in the alarm-trigger circuit and the entry-delay circuit.  In this application, the trigger input of U1 at pin 2 is held high via R1.  A normally-closed sensor switch, S1, supplies a positive voltage to the junction of R2 and C1, and lights LED1. With both ends of C1 tied high, there is no charge on C1. But, when S1 opens, C1 (initially acting as a short) momentarily pulls pin 2 of U1 low, triggering the timed delay cycle.  At the beginning of the timing cycle, U1 produces a positive voltage at pin 3, which charges C4 to near the positive voltage at pin 3, which charges C4 to near the positive supply voltage.  Transistor Q1 is heavily biased on by R3, keeping its collector at near ground level.  With Q1 on, SCR1's gate is clamped to ground, holding it off.  When the delay circuit times out, pin 3 of U1 goes low and ties the positive end of C4 to ground.  That turns Q1 off.

When Q1 turns off, the voltage at the gate of SCR goes positive, turning on the SCR and sounding the alarm. The delay time is adjustable from just a few seconds (R6 set to its minimum resistance) to about one minute (R6 adjusted to its maximum resistance).  (Reprinted with permission from Popular Electronics, 2/92, p. 66, (c) Copyright Gernsback Publications, Inc., 1992)


K BURGLAR ALARM CIRCUIT
BURGLAR ALARM CIRCUITFF3-1

This alarm circuit is built around a single 4081 (CMOS) quad AND gate. It offers an exit and entry delay (around automatically reset two minutes after tripping, provided that the trip input is not left high).

The arming switch must go high to arm or low to disarm. After arming, U1-a begins to charge C1 via R6. Around 20 seconds later (after the exit delay), C1 has a sufficient charge to produce a high at the pin-5 input of U1-b. Also, when the circuit is armed, Ql is turned on to indicate arming, and one input of U1-d is brought high.

After the exit delay times out, if the trip input opens, it causes an output on gate U1-b. Transistor Q1 is turned on, lighting the trip indicator (LED3), C2 instantly charges, and the output of U1-c goes high. At that point, C3 begins charging to provide the entry delay.

After 20 seconds, C3 has sufficient charge to produce a high at pin 13 of U1-d. That forces U1-d's output high, turning Q3 and Q4 on, which activates the alarm indicator (LED2) and sounder (BZ1), respectively. If disarmed after a trip pulse, but before the 20-second, entry delay time out, pin 12 of U1-d goes low, so the gate's output does not go high and the alarm does not sound.

Components C2 and R10 hold Ul-c on-for around 2 minutes and 20 seconds to provide the two-minute alarm. After C2's charge drops below half of the supply voltage, U1-c's output goes low, awaiting another trip pulse to set it off again. (Reprinted with permission from Popular Electronics, 9/94, p. 26. Copyright Gernsback Publications, Inc., 1994)


K CLOSED-LOOP ALARM
CLOSED-LOOP ALARMFE1-5

A string of three series-connected, normally closed switches are connected across the gate of an SCR.  When one opens, the SCR triggers via R1, sounding an alarm. The alarm should be of the noninterrupting type.  (Reprinted with permission from Popular Electronics, 1/92, p. 79, (c) Copyright Gernsback Publications, Inc., 1992)


K HEAT- OR LIGHT_ACTIVATED ALARM
HEAT- OR LIGHT-ACTIVATED ALARMFE1-12

The tone generated by a 555 oscillator can be turned on (activated) by heat or light.  That causes Ql to conduct transistor W2 (TIP 3055).Q2 (TIP 3055) acts as an audio amplifier and speaker driver. (William Sheets)


K INTRUDER ALARM
INTRUDER ALARMFG2

The circuit triggers a pulsed-tone alarm when anyone passes by, and several of these units may be littered around premises to give burglars the impression that they are being monitored! It is guaranteed to drive any burglar bananas. Two photodiodes, D1 and D2, are used as shown to ensure sensitivity over a very wide range of lighting conditions, though the circuit will be less effective in diffuse light. IC1 is connected as a differential amplifier. As the voltage at point "A" swings high the response at pin 2 of IC1 is slowed by capacitor C1, and the voltage swings high at the output (pin 6). Capacitor C3 charges up and transistor TR1 level-shifts the signal to enable the oscillator section formed from IC2, a quad NAND Schmitt. Piezo disc Xl will pulse accordingly. C3 determines the duration of the pulsed tone. and resistor R8 determines the pitch. Photodiodes Dl and D2 should be mounted a small distance apart for best effect. The circuit draws a mere 0.5mA. (Everyday Practical Electronics, September 1996, p. 711)


LATCHING BURGLAR ALARM
LATCHING BURGLAR ALARMFA1-19

Closing the protective circuit (i.e., R1 to R2) applies positive voltage to the gate of SCR1 and sounds the alarm. It can only be turned off with S1. (101 Electronic Projects, 1977, #65)


MULTI-LOOP PARALLEL ALARM
MULTI-LOOP PARALLEL ALARMFE1-2

This alarm has status LEDs connected across each inverter output to indicate the status of its associated sensor. S8 is used to monitor the switches via the LEDs, or to trigger an alarm via Ql and SCR1. BZ1 should be a suitable alarm of the noninterrupting type. (Reprinted with permission from Popular Electronics, 1/92. (C) Copyright Gernsback Publications, Inc., 1992)


NO-DOZE ALARM
NO-DOZE ALARMFE1-11

This circuit sends out a loud tone if the input switch (S2) is not retriggered at preset intervals. If you fall asleep and miss retriggering the circuit, it will sound until you press S2. (Reprinted with permission from Popular Electronics, 12/92, p.68. (C)Copyright Gernsback Publications, Inc.,1992)


PARALLEL LOOP ALARM
PARALLEL LOOP ALARMFE1-4

Four parallel switches are used to monitor four positions.  When a closure occurs on any switch, SCR1 triggers, which sounds the alarm. The alarm should be of the noninterrupting type.  (Reprinted with permission from Popular Electronics, 1/92, p. 79, (c) Copyright Gernsback Publications, Inc., 1992)


SAFER SECURITY SYSTEM
SAFER SECURITY SYSTEMFG1

Many security systems use a closed loop of wires and switches arranged so that whenever a door or window is opened, the loop will be broken and the alarm will sound.  An obvious problem is that someone can tamper with the system, short out the loop, and later on, come back and burglarize the premises without sounding the alarm. Hiding a known resistance in the loop is a very good idea. That way, the alarm can distinguish a short circuit from a correctly functioning closed loop. The Figure shows a circuit that does the job. It's a somewhat unusual application of a National Semiconductor LM3915 IC, normally used to drive LED bargraph displays. That chip happens to contain the right combination of comparators and logic circuits to do what you need.  Step 1 is to translate the loop resistance into a voltage. That's done by putting a voltage divider with resistors Rl and R2. Capacitor C2 protects the circuit against electromagnetic noise - important because burglar alarms use long wires, often running near heavy electrical equipment. Step 2 is to translate the voltage into a logic signal indicating whether it's in the correct range. Normally, the LM3915 would drive ten LEDs, one for each of then small ranges of voltage.  To obtain logic-level outputs, we have it driving 1 K resistors instead of LEDs. Since we only need to distinguish three situations, we tie some of the outputs together. The LM3915 has open-collector outputs that can be paralleled in that way.  The truth table in Fig. 2 shows how the outputs work. Note that they use negative logic (0V for "yes", +5V for "no"), the opposite of ordinary logic circuits. You can use inverters such as the 74HC04 to produce positive logic signals if that's what you need. Finally, note that the circuit will actually work with any supply voltage for 3 to 25 volts.

 (Electronics Now, December 1996, p. 10)


SEMICONDUCTOR FAIL-SAFE ALARM
SEMICONDUCTOR FAIL-SAFE ALARMFC2-3

False alarms produced by semiconductor failure are impossible with this burglar-alarm circuit equipped with relays. What's more, the circuit is virtually immune to false triggering. With a standby cur rent of less than 0.1 mA, the circuit offers all the features an alarm needs: entry and exit delays, a timed alarm period, and automatic reset after an intrusion.

One CMOS CD4093B quad NAND gate, ICI, supplies both logic and analog timing functions with the aid of Schmitt-trigger switching action. Relays make the circuit fail-safe in the alarm-active mode, even when the semiconductors fail. The relays are 12-V, with coil resistances of 250Ω or more.

Closing switch Sl initiates circuit operation. Capacitor C2 begins charging through resistor R2 and arming indicator LED1 lights. When pin 2 of ICla reaches its switching point, its output decreases, extinguishing LED1 and indicating that the exit delay has ended. That output also drives the base of Ql low, so that if the emitter circuit completes to the VDD line, Ql conducts. The circuit is now armed, and current drain drops to less than 0.1 mA.

When the vehicle is entered, relay RY1 contacts close momentarily, completing the emitter circuit of Ql and causing the RY2 contacts to close. Charging C4 through R7 determines the entry-delay period. If the system isn't turned off by opening Sl during this period, the oscillator circuit of IClc and ICld activates, and a rapid on/off horn-honking cycle kicks on with the aid of Q2 and RY3.

The alarm cycle ends after about a minute, when C2 charges through R3 to the threshold voltage of ICla at pin 1. This voltage resets the timing circuit, readying it for another entry/alarm cycle.

RY1 is connected for vehicles that use door switches connected to + 12 V. For vehicles that use grounding door switches, the bottom of the RY1 coil should connect to + 12 V instead of ground. In the latter case, the polarity of C7 should be reversed.

For home use, the R3C3 time constant should be increased to give a longer alarm.

(Reprinted with permission from Electronic Design, Copyright 1988 Penton Publishing)


SIMPLE BURGLAR ALARM
SIMPLE BURGLAR ALARMFD16-3

A simple circuit using either NO or NC sensors uses an RC delay circuit (R2/C2 or R1/C2) to drive emitter-follower Q1, switching SCR1 and buzzer (or bell) BZ1.  S1 is used for activation and reset.  (Reprinted with permission from Popular Electronics, 12/90, p. 41-42, (c) Copyright Gernsback Publications, Inc., 1990)


TAMPER-PROOF BURGLAR ALARM
LATCHING BURGLAR ALARMFA1-9

When the protective circuit is interrupted (opened), the alarm sounds.  To set the circuit, adjust R2 (with protective circuit open) for 1 V across R1. (101 Electronic Projects, 1977.  #64)


AMATEUR CIRCUITS

FOUR-STAGE 75-METER SSB SUPERHET RECEIVER

ONE-WATT CW TRANSMITTER

RF LINE SAMPLER/COUPLER

SIMPLE IDENTIFIER

TWO METER HT BASE STATION ADAPTER

WAVEMETER AMPLIFIER FOR 10 GHZ HAM USE

WWV TO 75 METER BAND CONVERTER


FOUR-STAGE 75-METER SSB SUPERHET RECEIVER
FOUR-STAGE 75-METER SSB SUPERHET RECEIVERFF4-4

A simple superhet receiver for SSB reception in the 75-meter amateur band is shown. Y1 acts as a crystal filter. (QST 5/89 pp. 25-27)


ONE-WATT CW TRANSMITTER
ONE-WATT CW TRANSMITTERFF4-10

C6,C7	Ll
820 pF disc ceramic (160 meters)	33 turns, #30, T37-2 (160 meters)
470 pF disc ceramic (80 meters)	23 turns, #30, T37-2 (80 meters)
220 pF disc ceramic (40 meters)	17 turns, #26, T37-2 (40 meters)
150 pF disc ceramic (30 meters)	14 turns, #26, T37-2 (30 meters)
100 pF disc ceramic (20 meters)	12 turns, #26, T37-2 (20 meters)
82 pF disc ceramic (17 meters)	10 turns, #26, T37-2 (17 meters)
(QST 10/94, p.65)


RF LINE SAMPLER/COUPLER
RF LINE SAMPLER/COUPLERFF4-15

Suitable for RF line sampling, this coupler is useful where an indirect measurement of line current is needed. A 10:1 turn ratio yields a secondary current about 1/10 (ideally) of the line current. A 5l-Ω resistor terminates the secondary. Insertion loss in the main line is negligible, < 0.1 dB. For higher power levels, use proportionately larger core for T1. (William Sheets)


SIMPLE IDENTIFIER
SIMPLE IDENTIFIERFF4-17

This identifier uses a PIC16C54 microcomputer which must be programmed for your desired identifier. (QST, 10/94, p. 42)


TWO METER HT BASE STATION ADAPTER
TWO METER HT BASE STATION ADAPTERFG3

This device mates up with a small handie-talkie (HT) and provides power and speaker interface as well as charging capability. It was designed for an Icom 02-AT but can be adapted for other makes and models as well. (QST, December 1996, p. 68)


WAVEMETER AMPLIFIER FOR 10 GHZ HAM USE
WAVEMETER AMPLIFIER FOR 10 GHZ HAM USEFG4

Schematic diagram for the wavemeter amplifier that is connected to the microwave, waveguide detector. This circuit operates on a single 9-volt transistor radio battery for simplicity. (73 Amateur Radio Today, August 1996;, p. 54)


WWV TO 76 METER BAND CONVERTER
WWV TO 75 METER BAND CONVERTERFG5

This circuit for an HF-band converter will convert the 10-MHz WWV signal to the 75-meter ham band. The local oscillator section of NE-602 is available on pins 6 (base)and 7 (emitter). In this circuit, a 6.00-MHz crystal oscillator is provided by the NE-602. Capacitors Cl and C2 form the feedback network. The junction of C2 and XTAL1 can be connected to either the +5-VDC line or ground (the former is shown here). The difference frequency between WWV's 10 MHz and the 6.00-MHz crystal frequency is 4.00 MHz, which is found at the top end of the 75-meter ham band. Other-frequency crystals will produce other output sum or difference frequencies, so tune the receiver appropriately if something other than 6.00 MHz is used. (Popular Electronics, July, 1996, pp. 62-63)


AMATEUR TELEVISION (ATV) CIRCUITS

1.3GHz ATV TRANSMITTER

5-W ATV TRANSCEIVER

5-W ATV TRANSMITTER FOR 440 MHz

AMATEUR TELEVISION TRANSMITTER

ATV LINE SAMPLER

DUMMY LOAD AND VIDEO DETECTOR FOR TRANSMITTER TESTS

MINI ATV TRANSMITTER

UHF ATV DOWNCONVERTER FOR 900 AND 1300 MHZ


1.3GHz ATV TRANSMITTER
1.3GHz ATV TRANSMITTERFG8

This TV transmitter operates from a +1 2V source and produces about 1 watt peak power on sync tips. Output frequency is 1240 to 1300 MHz but operation is possible to 1325 MHz (for U.K. band). Video interface is 1 V p-p/75 Ω neg sync, audio is 5 mv to 1 volt @ Z = 5 kΩ. For PAL operation, reduce the number of turns on L16 to 11 turns for 5.5 MHz sound. A complete kit of parts. including, PC board, is available from North Country Radio, P.O. Box 53,  Wykagyl Station, New Rochelle NY 10804-0053A (William Sheets, 1995)


5-W ATV TRANSCEIVER
5-W ATV TRANSCEIVERFF5-2

For the transmitter schematic (part of this transceiver), see entry entitled "5-W ATV Transmitter for 440 MHz." The down converter portion is shown here. This transmitter contains both a video and sound section. Five to six watts PEP on synch tips of NTSC video are produced. Three channels are available. Channel switching is via PIN diodes. Power supply voltage is 12 to 14 Vdc. The receiver function is provided with a downconverter circuit and is tunable. A relay is used for T-R switching. A complete kit of parts, including PC board, is available from North Country Radio, P.O.Box 53, Wykagyl Station, New Rochelle, NY 10804-0053A. (Reprinted with permission from Electronics Now, 7/94, p. 39. (C)Copyright Gernsback Publications, Inc.,1994)


5-W ATV TRANSMITTER FOR 440 MHz
5-W ATV TRANSMITTER FOR 440 MHzFF5-1

The circuit will produce typically 6 W RF output on synch tips. A crystal oscillator drives a doubler to produce a 220-MHz output. Another doubler produces 440 MHz to drive the power amplifier. A high-level series modulator provides the video modulation capability. A sound subcarrier is generated using a VCO circuit and combined with the video information. A complete kit of parts, including the PC board, is available from North Country Radio, P.O.Box 53, Wykagyl Station, New Rochelle, NY 10804-0053A. (reprinted with permission from Radio-Electronics, 7/94, p.34. (C)Copyright Gernsback Publications, Inc.,1994)


AMATEUR TELEVISION TRANSMITTER
AMATEUR TELEVISION TRANSMITTERFD93-3

Although the unit was designed for 2 W operation, Q6 and Q7 stages and associated components can be omitted and about 1 to 30 mW of RF can be obtained by a link coupling to L9. A complete set of parts, including PC board is available from North Country Radio, P.O.Box 53, Wykagyl Station, New Rochelle, NY 10804. (Reprinted with permission from Radio-Electronics, 6-7/89, p. 45-50. (C)Copyright Gernsback Publications, Inc., 1989)


ATV LINE SAMPLER
ATV LINE SAMPLERFG6

This device can be used to recover demodulated video from the output of an ATV transmitter. A small sample of the signal on the antenna feeder is tapped off and detected and the resultant video is fed to an emitter follower. Cl is chosen for 1 V p-p under normal transmit conditions. This circuit was intended for 440 MHz AM TV signals. It will not work for FM and for 900 MHz or 1300 MHz. A stripline directional coupler can be used to sample the RF line without introducing an impedance bump. (QST, December 1996, p. 41)


DUMMY LOAD AND VIDEO DETECTOR FOR TRANSMITTER TESTS
DUMMY LOAD AND VIDEO DETECTOR FOR TRANSMITTER TESTSFF5-4

This circuit is useful as a video modulation monitor for testing low-power video transmitters. For higher power inputs, use a suitable attenuator between the detector and source. The detector should be connected to scope with as short a cable as possible to preserve video bandwidth. (William Sheets)


MINI ATV TRANSMITTER
MINI ATV TRANSMITTERFF5-3

This low-power NTSC video and sound transmitter is useful for amateur radio, video handie-talkie, R/C and surveillance purposes. A crystal oscillator-multiplier RF power amplifier. Video modulation is via a three-transistor series modulator. The sound subcarrier is generated with a VCO circuit and is combined with the video information. The output is 0.4 to 1.2 W with supply voltages of  9 to 14 volts. A complete kit of parts, including PC board, is available from North Country Radio, P.O.Box 53, Wykagyl Station, New Rochelle, NY 10804-0053A. (Reprinted with permission from Electronics Now, 7/94. (C)Copyright Gernsback Publications, Inc.,1994)


UHF ATV DOWNCONVERTER FOR 900 AND 1300 MHZ
UHF ATV DOWNCONVERTER FOR 900 AND 1300 MHZFG7

This downconverter is tunable and can cover either 902-928 MHz or 1240-1300 MHz for receiving amateur television transmissions or other wideband signals. A NEC 25139 low noise RF amplifier feeds a BFR 90 mixer driven by a BFR90 tunable LO operating 61 or 67 MHz below the received frequency. A pair of 2N3563 transistors are used as a post IF amplifier. Overall gain is 37 to 40 dB with around 1.5 dB noise figure. AGC control voltage may be used on gate 2 of the RF stage to reduce RF gain on strong signals, about -3 volts needed to reduce RF gain by >30 dB. Either on board tuning via pot R24 or remote tuning via 10 to 20 volt variable DC supply on the IF coaxial cable may be used. Note that striplines are different for 900 or 1300 MHz and this requires separate models for each band, although physical layout and circuit diagrams are identical. A complete kit of parts, including PC board. is available from North Country Radio, P.O. Box 53, Wykagyl Station, New Rochelle, NY 10804-0053A. (Electronics Now, June, 1996, pp. 38-75)


AMPLIFIERS (AUDIO)

2 WATT STEREO AMPLIFIER FOR PORTABLE CD AND CASSETTE PLAYERS

8-W AUDIO AMPLIFIER

BASIC TRANSISTOR AMPLIFIER CIRCUITS

COMPRESSION AMPLIFIER

DUAL PREAMP

ELECTRET MIKE PREAMP WITH PTT CIRCUIT

LOW-VOLTAGE MICROPHONE PREAMP

MAGNETIC PHONO AMPLIFIER

NB FM AUDIO AMPLIFIER

PERSONAL STEREO AUDIO AMP

SIMPLE AUDIO OUTPUT AMPLIFIER

SIMPLE GUITAR AMPLIFIER WITH DUAL INPUTS

SIMPLE HIGH-GAIN AUDIO AMPLIFIER

SIMPLE TAPE PLAYBACK AMPLIFIER

SINGLE-ENDED HI-ZMICROPHONE PREAMP

STEREO PRE-AMP

STEREO PREAMPLIFIER

VACUUM TUBE AUDIO AMPLIFIER


2 WATT STEREO AMPLIFIER FOR PORTABLE CD AND CASSETTE PLAYERS
2 WATT STEREO AMPLIFIER FOR PORTABLE CD AND CASSETTE PLAYERSFG12

The amplifier is built around a ULN2274B, dual, audio power amp and provides a maximum of 2 watts of quality sound. Since the amplifier is comprised of two identical subcircuits, only one subcircuit will be covered. Resistor R5 sets the tone and may be replaced with a variable unit; lower values of that resistor produce more bass. The bias is set by R6 and C4, and R7, R9, and C5 are feedback elements. For a more wholesome sound, R8 and C3 were are used to roll off the high frequencies, Capacitor C6 is a DC-blocking capacitor. The circuit chip is content with anything from 6-26 VDC without distortion. (Popular Electronic, December 1994, p. 31)


8-W AUDIO AMPLIFIER
8-W AUDIO AMPLIFIERFD7-6

This audio power amp (built around an LM383 8-W, audio power amplifier) can be used to boost an audio signal to a sufficient level so that it can be heard in a high-noise environment. Note that LM383 should be heatsinked. (Reprinted with permission from Popular Electronics, 10/90, p. 90. Copyright Gernsback Publications, Inc., 1990)


BASIC TRANSISTOR AMPLIFIER CIRCUITS
BASIC TRANSISTOR AMPLIFIER CIRCUITSFA9-2

Typical component values are given for use at audio frequencies, where these circuits are used most often. The input and output phase relationships are shown. (No reference)


COMPRESSION AMPLIFIER
COMPRESSION AMPLIFIERFG14

Here's a compression-type amplifier that can be used to keep the volume level of an organ constant.  Unlike compressors used for public-address-system applications, the Organ-Leveler can respond to the entire range of frequencies generated by the organ without coloring the voice.  It can handle large fluctuations in input signal without clipping. It also works well as a microphone-leveler.  (Popular Electronics, April 1997, pp. 58-59)


DUALPREAMP
DUAL PREAMPFE6-8

If you wish to amplify low-level signals, such as the output of a turntable, the signal must first be fed to this preamp. (Reprinted with permission from R-E Experimenters handbook, 1987, p.74)


ELECTRET MIKE PREAMP WITH PTT CIRCUIT
ELECTRET MIKE PREAMP WITH PTT CIRCUITFG13

Schematic of mike element and amplifier circuit. All resistors are 1/4 W units. The mike connector is an RS 274-284. (QST, December 1996, p. 69)


MAGNETIC PHONO AMPLIFIER
MAGNETIC PHONO AMPLIFIERFC7-9

(Popular Electronics Fact Card No. 110)


LOW-VOLTAGE MICROPHONE PREAMP
LOW-VOLTAGE MICROPHONE PREAMPFF6-16

A microphone amplifier is shown. The reference, with a 500-kHz unity-gain bandwidth, is used as a preamplifier with a gain of 100. Its output is fed through a gain-control potentiometer to the op amp, which is connected for a gain of 10. The combination gives a 60-dB gain with a 1 0-kHz bandwidth, unloaded, and 5 kHz loaded at 500. Input impedance is 10 k.

Potentially, using the reference as a preamplifier in this fashion can cause excess noise. However, because the reference voltage is low, the noise contribution, which adds root-mean-square, is likewise low. The input noise voltage in this connection is 440-500 nV Hz, about equal to that, of the op amp.

(Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 501)


NB FM AUDIO AMPLIFIER
NB FM AUDIO AMPLIFIERFF10-3

This audio system amplifies, limits, and filters an audio voice signal for use with an FM modulator or VCO. It has pre-emphasis of 6-dB/octave 300-3000 Hz. Almost any suitable op amp can be used. (William Sheets)


PERSONAL STEREO AUDIO AMP
PERSONAL STEREO AUDIO AMPFF10-5

You can make your personal stereo do double duty as a small room stereo by adding this 2-watt amplifier. (Reprinted with permission from Popular Electronics, 12/94, p. 31. Copyright Gernsback Publications, Inc.,1994)


SIMPLE AUDIO OUTPUT AMPLIFIER
SIMPLE AUDIO OUTPUT AMPLIFIERFG10

Audio amplifier circuit has a gain of about 20. A supply of 3 to 12 volts may be used. Output is up to about 1 watt depending on load impedance and supply voltage. (Electronic Experimenters Handbook, 1996, p. 26)


SIMPLE GUITAR AMPLIFIER WITH DUAL INPUTS
SIMPLE GUITAR AMPLIFIER WITH DUAL INPUTSFG11

This amplifier uses an LM386 IC and has two inputs, for guitar and a separate audio input for a second guitar or mike, etc. Power is supplied by a 9 volt battery. While headphones are indicated, the amplifier will drive a small speaker. Output is around 300-500 mw depending on load and battery voltage. (Popular Electronics, October, 1996, p. 6)


SIMPLE HIGH-GAIN AUDIO AMPLIFIER
SIMPLE HIGH-GAIN AUDIO AMPLIFIERFF10-15

This amplifier has a very high gain in the audio range and is approximately the product of the current gains of the three transistors multiplied by the ratio of RL to (Rin + Rs). Rin is approximately equal to:

(BQ1+1)(26)

IEQ1

(William Sheets)


SIMPLE TAPE PLAYBACK AMPLIFIER
SIMPLE TAPE PLAYBACK AMPLIFIERFD8-2

This circuit uses an LM381/1A as a tape preamp.  The feedback network includes NAB Equalization.  (Reprinted with permission from Radio-Electronics, 2/90, p. 56 (c) Copyright Gernsback Publications, Inc)


SINGLE-ENDED HI-ZMICROPHONE PREAMP
SINGLE-ENDED HI-Z MICROPHONE PREAMPFF10-10

This low noise circuit works on a +5-V supply. Gain range is 20 to 40 dB and bandwidth is 20kHz with the AD820. THD is 0.05% with 1 V RMS into a 2-kΩ load. Noise output with the input shorted is less than 200 μV. (Analog Devices, Analog Dialogue Vol. 27, No. 2 (1993), p. 22)


STEREO PRE-AMP
STEREO PRE-AMPFG9

The output of the audio source is fed to the left and right inputs of the circuit (Jl and J2). Potentiometers R1 and R2 control the volumes of the input signals, while potentiometer R17 is a balance control. The incoming signals are coupled through capacitors Cl and C2 to the non-inverting inputs of op-amps ICl-a and ICl-b. Because IC1 operates as a single-supply amplifier, its output signal fluctuates above and below half of the supply voltage. The output signals of the op-amps are coupled to the bases of two 2N2222 transistors (Ql and Q2), which further amplify the left and right signals. Then, the outputs of the transistors are coupled to the bases of two more 2N2222 transistors (Q3 and Q4), further boosting the left and right signals. The transistor pairs also act as buffers. (Popular Electronics, July, 1996, p. 66)


STEREO PREAMPLIFIER
STEREO PREAMPLIFIERFB6-3

The circuit provides better than 20-dB gain in each channel.  A better op-amp type will give a better noise figure and bandpass.  In this circuit the roll-off is acute at 20,000 Hertz.  (Hands-on Electronics, Jul/Aug 1986, p. 16)


VACUUM TUBE AUDIO AMPLIFIER
VACUUM TUBE AUDIO AMPLIFIERFF10-1

This schematic is for a tubehead amplifier. The output from transformer Tl is positive half- wave ac rectified by D1 and filtered by Cl, C2, and R1 for a +15-V supply. A -15-V supply is available from D2, C3, C4, and R3. The plate supply for the 12AX7 tubes is produced by a voltage multiplier. Some listeners prefer the sound of a vacuum tube audio system. Although this is rather subjective and a personal preference, this circuit can be used to simulate the "tube sound" preferred by these listeners. (Reprinted with permission from Electronics Now, 6/94, p. 34. (C)Copyright Gernsback Publications, Inc.,1994)


AMPLIFIER (INSTRUMENTATION) CIRCUITS

DIFFERENTIAL-INPUT INSTRUMENTATION AMPLIFIER

HIGH INPUT-IMPEDANCE INSTRUMENTATION AMPLIFIER

INSTRUMENTATION AMPLIFIER

INSTRUMENTATION AMPLIFIER

INSTRUMENTATION METER DRIVER

LOW-NOISE INSTRUMENTATION AMPLIFIER

LOW-POWER INSTRUMENTATION AMPLIFIER

STRAIN GAGE INSTRUMENTATION AMPLIFIER

ULTRA-LOW-NOISE SINGLE-SUPPLYINSTRUMENTATION AMPLIFIER


DIFFERENTIAL-INPUT INSTRUMENTATION AMPLIFIER
DIFFERENTIAL-INPUT INSTRUMENTATION AMPLIFIERFF41-5

(Reprinted with permission from Popular Electronics, Fact Card 248, (c) Copyright Gernsback Publications, Inc)


HIGH INPUT-IMPEDANCE INSTRUMENTATION AMPLIFIER
HIGH INPUT-IMPEDANCE INSTRUMENTATION AMPLIFIERFF41-6

(Reprinted with permission from Popular Electronics, Fact Card 247, (c) Copyright Gernsback Publications, Inc)


INSTRUMENTATION AMPLIFIER
INSTRUMENTATION AMPLIFIERFF41-11

(Linear Technology, 2/95)


INSTRUMENTATION AMPLIFIER
INSTRUMENTATION AMPLIFIERFF41-2

(Linear Technology, 2/95)


INSTRUMENTATION METER DRIVER
INSTRUMENTATION METER DRIVERFB46-4

Three op amps Ul, U2, and U3 are connected in the basic instrumentation amplifier configuration. Operating from ± 5 V, pin 8 of each op amp is connected directly to ground and provides the ac performance desired in this application (high bias mode). Pl is for offset error correction and P2 allows adjustment of the input common mode rejection ratio. The high input impedance allows megohms without loading. The resulting circuit frequency response is 200 kHz at -3 dB and has a slew rate of 4.5 V/us. (Texas Instruments, Linear and Interface Circuits Applications Vol. 1, 1985, p. 3-18)


LOW-NOISE INSTRUMENTATION AMPLIFIER
LOW-NOISE INSTRUMENTATION AMPLIFIERFF41-8

A Maxim MAX412 IC amplifier is used in this circuit.  The supply current is ± 5V at 5 mA.  (Maxim, Vol. III, New Releases Data Book, 1994, p.3-33)


LOW-POWER INSTRUMENTATION AMPLIFIER
LOW-POWER INSTRUMENTATION AMPLIFIERFF41-9

This amplifier requires less than 20mA from a ± 15-V supply. (Maxim, Vol. III, New Releases Data Book, 1994, p.3-69)


STRAIN GAGE INSTRUMENTATION AMPLIFIER
STRAIN GAGE INSTRUMENTATION AMPLIFIERFC46-2

This circuit has an overall gain of 320. More gain can easily be obtained by lowering the value of R2. Untrimmed Vos is 10 μV, and Vos tempco is less than 0.1 μV/ºC. In many circuits, the OP07 can be omitted, with the two MAX421 differential outputs connected directly to the differential inputs of an integrating a /d. (Maxim, Maxim Advantage, p. 45)


ULTRA-LOW-NOISE SINGLE-SUPPLYINSTRUMENTATION AMPLIFIER
ULTRA-LOW-NOISE SINGLE-SUPPLY INSTRUMENTATION AMPLIFIERFF41-10

(Analog Devices, Analog Dialogue, Vol. 27, No. 1 (1993), p. 20)


AMPLIFIER (MISCELLANEOUS)

ABSOLUTE VALUE AMPLIFIER

BUFFER AMPLIFIER WITH MODULATOR

COMPOSITE AMPLIFIER

CURRENT DIFFERENCE AMPLIFIER

DIFFERENCE AMPLIFIER

FAST SUMMING AMPLIFIER

GENERAL PURPOSE WIDEBAND PREAMP

HIGH INPUT-IMPEDANCE AC AMPLIFIER

IMPROVED RF ISOLATION AMPLIFIER

INVERTING AMPLIFIER

INVERTING SUMMING AMPLIFIER

MOSFET WIDEBAND AMPLIFIER

NONINVERTING ac AMPLIFIER

NONINVERTING AMPLIFIER

OPERATIONAL TRANSCONDUCTANCE AMPLIFIER WITH BOOSTER

REAR SPEAKER AMBIENCE (4-CHANNEL) AMPLIFIER

WIDE-BAND AGC AMPLIFIER

WIDER BANDWIDTH PHOTODIODE AMPLIFIER

X 1000 AMPLIFIER CIRCUIT


ABSOLUTE VALUE AMPLIFIER
ABSOLUTE VALUE AMPLIFIERFA3-10

The circuit generates a positive output voltage for either polarity of input. For positive signals it acts as a noninverting amplifier and for negative signals, as an inverting amplifier. The accuracy is poor for input voltages under 1 V, but for less stringent applications it can be effective. (Signetics Analog Data manual, 1983, p. 10-100)


BUFFER AMPLIFIER WITH MODULATOR
BUFFER AMPLIFIER WITH MODULATOR FD76-16

A 40673 MOSFET is used as a wideband buffer amplifier (to 20 Mhz). If desired, the amplifier can be modulated, considering that the gate 2 voltage of a MOSFET can be used to vary the gain of the stage. (Reprinted with permission from Popular Electronics, 11/90, p.69. (C) Copyright Gernsback Publications, Inc.,19902)


COMPOSITE AMPLIFIER
COMPOSITE AMPLIFIERFC3-5

A composite configuration greatly reduces dc errors without compromising the high-speed, wideband characteristics of HA-2539. The HA-2540 could also be used, but with slightly lower speeds and bandwidth response.

The HA-2539 amplifies signals above 40 kHz which are fed forward via C2; R2 and R5 set the voltage gain at - 10. The slew rate of this circuit was measured at 350 V/μs.  Settling time to a 0.1% level for a 10-V output step is under 150 ns and the gain bandwidth product is 300 MHz.

The HA-5170 amplifies signals below 40 kHz, as set by Cl and R1, and controls the dc input characteristics such as offset voltage, drift, and bias currents of the composite amplifier. Therefore, it has an offset voltage of 100 μV, drift of 2 μV/ degree C, and bias currents in the 20-pA range.  The offset voltage can be externally nulled by connecting a 20-K ohm pot to pins 1 and 5, with the wiper tied to the negative supply.  The dc gains of the HA-5170 and HA-2539 are cascaded; this means that the dc gain of the composite amplifier is well over 160 dB.

The excellent ac and dc performance of this composite amplifier is complemented by its low noise performance, 0.5-μV rms from 0.1 Hz to 100 Hz.  It is very useful in high-speed data acquisition systems.

(Harris, Analog Product Data Book, 1988 p. 10-95)


CURRENT DIFFERENCE AMPLIFIER
CURRENT DIFFERENCE AMPLIFIERFG16

Here is a practical 20-dB gain AC amplifier built using the LM3900 CDA.  (Popular Electronics, July 1996, p. 51)


DIFFERENCE AMPLIFIER
DIFFERENCE AMPLIFIERFE2-1

By using two inputs as shown, a difference amplifier yielding the differential between U1 and U2, times a gain factor results.  (Reprinted with permission from Popular Electronics, Fact Card 255, (c) Copyright Gernsback Publications, Inc)


FAST SUMMING AMPLIFIER
FAST SUMMING AMPLIFIERFA3-27

(Intersil Data Book, 5/83, p. 5-36)


GENERAL PURPOSE WIDEBAND PREAMP
GENERAL PURPOSE WIDEBAND PREAMPFG35

This preamp has a gain of 35 dB at 100 kHz, 30 dB at 10 MHz, and 17 dB gain at 100 MHz and draws 15 mA at 12 V. (73 Amateur Radio Today, November 1995, p. 34)


HIGH INPUT-IMPEDANCE AC AMPLIFIER
HIGH INPUT-IMPEDANCE AC AMPLIFIERFF6-14

This figure shows an op amp used as an ac amplifier. It is unusual in that dc bootstrapping is used to obtain high input resistance without requiring high-value resistors. In theory, this increases the output offset because the op amp offset voltage is multiplied by the resistance boost. But when conventional resistor values are used, it is practical to include R5 to eliminate bias-current error.  This gives less output offset than if a single, large resistor were used.  C1 is included to reduce noise.  (Reprinted with permission of National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 594)


IMPROVED RF ISOLATION AMPLIFIER
IMPROVED RF ISOLATION AMPLIFIERFB85-8

This wideband RF isolation amplifier has a frequency response of 0.5 to 400 Mhz ±0.5 dB. This two stage amplifier can be used in applications requiring high reverse isolation, such as receiver intermediate-frequency (IF) strips and frequency distribution systems. Both stages use complementary-symmetry transistor arrangements. The input stage is a common-base connection for the complementary circuit. The output stage, which supplies the positive gain, is a common-emitter circuit using emitter degeneration and collector-base feedback for impedance control. (NASA, Tech Briefs, Spring 1984, p. 322)


INVERTING AMPLIFIER
INVERTING AMPLIFIERFC3-7

(Hands-on Electronics, Fact Card No. 29)


INVERTING SUMMING AMPLIFIER
INVERTING SUMMING AMPLIFIERFE2-4

The output of Ul is the sum of V1, V2, and V3, multiplied by R1/R4, R2/R4 and respectively. R1, R2, R3 are selected as required for individual gains. R4 affects gain of all these inputs.  (Reprinted with permission from Popular Electronics, Fact Card 253, (c) Copyright Gernsback Publications, Inc)


MOSFET WIDEBAND AMPLIFIER
MOSFET WIDEBAND AMPLIFIERFD76-21

For high impedance (7500 Ω) applications, this amplifier will provide a voltage gain of approximately -gm/ZL where ZL is the  load impedance in ohms and gm is ~ 12 x 10-³ for the 40673 FET. The G2 voltage can be used to control the gain. (Reprinted with permission from Popular Electronics, 1/90, p.74. (C) Copyright Gernsback Publications, Inc.,1990)


NONINVERTING ac AMPLIFIER
NONINVERTING ac AMPLIFIERFE2-3

A general-purpose noninverting ac amplifier for audio of other low-frequency applications is shown.  Design equations are in the figure. Almost any general-purpose op amp can be used for Ul.  (Reprinted with permission from Popular Electronics, Fact Card 254, (c) Copyright Gernsback Publications, Inc)


NONINVERTING AMPLIFIER
NONINVERTING AMPLIFIERFC3-8

(Hands-on Electronics, Fact Card No. 29)


OPERATIONAL TRANSCONDUCTANCE AMPLIFIER WITH BOOSTER
OPERATIONAL TRANSCONDUCTANCE AMPLIFIER WITH BOOSTERFF6-1

Implementing a bidirectional precision current amplifier in an operational transconductance amplifier (OTA) can boost the OTAs output current. To accomplish this task, two diodes and a complementary stage are added to this otherwise simple design. (Reprinted with permission from Electronic Design, 11/93, p. 102. Copyright 1993, Penton Publishing, Inc)


REAR SPEAKER AMBIENCE (4-CHANNEL) AMPLIFIER
REAR SPEAKER AMBIANCE (4-CHANNEL) AMPLIFIERFB71-8

Rear channel "ambiance" can be added to an existing stereo system to extract a difference signal (R - L or L - R) which, when combined with some direct signal (R or L), adds fullness, or "concert hall realism" to the reproduction of recorded music. Very little power is required at the rear channels, hence an LM1877 suffices for most "ambiance" applications. The inputs are merely connected to the existing speaker output terminals of a stereo set, and two more speakers are connected to the ambiance circuit outputs. The rear speakers should be connected in the opposite phase to those of the front speakers, as indicated by the ± signs. (National Semiconductor Corporation, Audio/Radio Handbook 1980, p. 4-20).


WIDE-BAND AGC AMPLIFIER
WIDE-BAND AGC AMPLIFIERFC3-11

The NE592 is connected in conjunction with a MC1496 balanced modulator to form an excellent automatic gain control system. The signal is fed to the signal input of the MC1496 and rc-coupled to the NE592.  Unbalancing the carrier input of the MC1496 causes the signal to pass through unattenuated.  Rectifying and filtering one of the NE592 outputs produces a dc signal which is proportional to the ac signal amplitude.  After filtering, this control signal is applied to the MC1496, causing its gain to change.  (Signetics, 1987 Linear Data Manual Vol. 2:Industrial,2/87, p. 4-243)


WIDER BANDWIDTH PHOTODIODE AMP
WIDER BANDWIDTH PHOTODIODE AMPLIFIERFG15

Many photodiode applications require high gain and wide bandwidth. A dc-restored photodiode amplifier (Fig. 1) is useful in situations where a time-varying light signal of interest competes with unwanted ambient background light. To extend the amplifier's bandwidth, the design can be modified to provide current-to-voltage conversion with subsequent voltage gain (Fig. 2). Current from the low-capacitance photodiode flows through Rag and establishes a voltage at the noninverting terminal. This voltage then receives a gain equal to 1 + RF/Rl. With the values shown in figure 2., the equivalent transimpedance Rag(l+Rf/Rl) is equal to 10 ohms. The design uses an inverting integrator to drive a restoration current through Rag. This low-frequency current cancels current from the photodiode at frequencies below the low-frequency cutoff pole. The low-frequency pole in figure 2. is given by: f-3dB = (1/2(Pi)(1 +Rf/Rl).  For the values shown, it's equal to 159 Hz. Resistor Rag helps determine the equivalent transimpedance and provides the path for the low-frequency restoration current.  The measured high-frequency cut-off for the circuit in Fig. 1 is 4.9 kHz, with a total in-band noise of 370uV rms. In Fig.2, the high-frequency cut-off is extended to 1 l.7 kHz, with a total in-band noise of 589 uV rms. (Electronic Design, August 19, 1996, pp. 113-114)


X 1000 AMPLIFIER CIRCUIT
X 1000 AMPLIFIER CIRCUITFA3-12

(Courtesy of Fairchild Camera & Instrument Corporation, Linear Databook, 1982, p. 9-17)


AMPLIFIER (OPERATIONAL) CIRCUITS

BASIC OP-AMP AUDIO AMPLIFIER

BASIC OP-AMP CIRCUITS

OP AMPS WITH LONG RC TIME CONSTANTS

OP-AMP OFFSET NULL

OP-AMP RESISTANCE MULTIPLICATION CIRCUIT

SINGLE-SUPPLY OP-AMP APPLICATIONS

TWO CA3100 WIDEBAND OPERATIONAL AMPLIFIERS


BASIC OP-AMP AUDIO AMPLIFIER
BASIC OP-AMP AUDIO AMPLIFIERFF60-4

Any general-purpose op amp can be used in this application.  (Reprinted with permission from Radio-Electronics, June 1987, p. 75. (c) Copyright Gernsback Publications, Inc., 1987)


BASIC OP-AMP CIRCUITS
BASIC OP-AMP CIRCUITSFF60-1

The two simplest op-amp configurations are the inverting (A) and the noninverting (B).  Resistor R3 is needed only if C1 is used in the noninverting circuit. (Reprinted with permission from Radio-Electronics, June 1987, p69. (C)Copyright Gernsback Publications, Inc.,1987)


OP AMPS WITH LONG RC TIME CONSTANTS
OP AMPS WITH LONG RC TIME CONSTANTSFF60-2

This circuit multiplies RC time constant to 1000 seconds and provides low output impedance. Cost is lowered because of reduced resistor and capacitor values. (Reprinted with permission of National Semiconductor Corporation, National Semiconductor Linear Application Handbook, 1991, p. 578)


OP-AMP OFFSET NULL
OP-AMP OFFSET NULLFF60-3

Offset problems can occur in the best of circuits (and often do) without regard to whether the circuit is inverting (A), or noninverting (B).  Offset-nulling potentiometers are useful in correcting the output to zero, but their effectiveness will vary under different conditions.  (Reprinted with permission from Radio-Electronics, June 1987, p. 70 (c) Copyright Gernsback Publications, Inc., 1987)


OP-AMP RESISTANCE MULTIPLICATION CIRCUIT
OP-AMP RESISTANCE MULTIPLICATION CIRCUITFF60-10

Equivalent feedback resistance is 10 GΩ, but only standard resistors are used. Even though the offset voltage is multiplied by 100, output offset is actually reduced because error is dependent on offset current, rather than bias current, Voltage on summing junction is less than 5 mV. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 578).


SINGLE-SUPPLY OP-AMP APPLICATIONS
SINGLE-SUPPLY OP-AMP APPLICATIONSFF60-8

An op amp that normally needs two supplies can be used when only a single supply needed. The value of V+ should be twice the minimum allowable values of the positive and negative voltages normally needed. For example, a 12-V single-supply application would require an op amp capable of ±6V operation. (Reprinted with permission from Radio-Electronics, June 1987, p. 75. (C)Copyright Gernsback Publications, Inc.,1987)


TWO CA3100 WIDEBAND OPERATIONAL AMPLIFIERS
TWO CA3100 WIDEBAND OPERATIONAL AMPLIFIERSFD76-18*

These circuits use the RCA CA3100 wideband amplifier IC. The gain is:

Av=1 + R2/R1

These circuits are useful for video applications to 10 Mhz. The 3.3-pF capacitors are compensation capacitors. Capacitors on pins 7 and 4 are bypass capacitors to prevent self-oscillations. Figure (a) is noninverting and Fig. (b) is an inverting configuration. (Reprinted with permission from Popular Electronics, 1/90, p. 74, (c) Copyright Gernsback Publications, Inc., 1990)


AMPLIFIERS, POWER

10-WATT AUDIO AMPLIFIER

16-W BRIDGE AMPLIFIER

18-W BRIDGE AUDIO AMPLIFIER

22W AMPLIFIER FOR 12V SYSTEMS

25 WATT SOLID STATE LINEAR AMPLIFIER

40-W AMPLIFIER

6-W AUDIO AMPLIFIER WITH PREAMP

6OW SWITCHING AMPLIFIER

A 33-W BRIDGE COMPOSITE AMPLIFIER

AUDIO POWER AMPLIFIER

AUDIO POWER AMPLIFIER, 1.5 W, 12V

AUDIO POWER BOOSTER

BRIDGE CONNECTION OF TWO POWER OP AMPS

HYBRID POWER AMPLIFIER

MINIATURE AUDIO POWER AMPLIFIER

POWERED SUBWOOFER

WIDEBAND AMPLIFIER


10-WATT AUDIO AMPLIFIER
10-WATT AUDIO AMPLIFIERFF11-3

This circuit is a general-purpose 10-W audio amplifier for moderate-power PA or modulator use in an AM transmitter.  With higher voltages and a change in bias resistors, up to 30 W can be obtained. (William Sheets)


16-W BRIDGE AMPLIFIER
16-W BRIDGE AMPLIFIERFF11-9

This circuit delivers 16 W RMS audio into a 4-Ω load (RL). The ICs are LM383s. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Application Specific ICs Handbook 1993, p. 1-14)


18-W BRIDGE AUDIO AMPLIFIER
18-W BRIDGE AUDIO AMPLIFIERFE5-12

Two LM383 IC devices are used in a bridge circuit that is useful for auto sound applications. (Reprinted with permission from Popular Electronics, Fact Card 243. (C) Copyright Gernsback Publications, Inc)


22W AMPLIFIER FOR 12V SYSTEMS
22W AMPLIFIER FOR 12V SYSTEMSFG33

The schematic for the 22-watt amplifier is shown. Power for the circuit (+12volts) is provided by a connection to the host vehicle's battery. A connection is also provided for the vehicle's ground. Capacitors Cl and C2 provide decoupling of any signal riding on the supply voltage, while capacitor C3, working in conjunction with IC1, provides ripple rejection. The incoming audio signal is coupled to IC1 by capacitors C4 and C5. Those 10-μF capacitors are used to avoid rolling off of the low audio frequencies. Resistor R1 and capacitor C6 feed the mute switch circuit (included in ICl), providing the delay that eliminates turn-on pop. Their R/C time constant is about 1.4 seconds. None of the component values external to IC1 are critical, but major value substitutions should not be made. Pin 14 (the mute switch) of IC1 must have at least 8.5 volts for the amplifier to be on, or be held below 3.3 volts to ensure the chip stays in the mute condition. Current requirements at this pin are on the order of 40 μA in the on condition, and 100 μA for standby. The Rl/C6 combination used here (47μF and 39,000 ohms) provides enough delay to eliminate turn-on pop without having an excessive wait for normal operation. In addition to this slight delay, pin 14 gradually comes up above the 8.5-volt threshold as C6 charges up, rather than coming on instantly as it would if a simple switch were used. Values for C6 and R1 aren't critical but R1 should be no larger than 100,000 ohms and the Rl/C6 time constant should be on the order of a second or two. Too short a time constant may not eliminate the turn-on pop; too long a time constant does no harm except causing an irritating delay.

(Popular Electronics, February 1997, p. 28)


25 WATT SOLID STATE LINEAR AMPLIFIER
25 WATT SOLID STATE LINEAR AMPLIFIERFG21

Schematic diagram of the 25 watt linear amplifier. Decimal value capacitors are in μF. Others are in pF. Polarized capacitors are electrolytic or tantalum, 16 volts or greater. Resistors other than R5 are 1/4 watt carbon-composition or carbon-film units. (CQ Magazine January, 1996, p. 60)


40-W AMPLIFIER
40-W AMPLIFIERFE5-2

This circuit uses two LM1875 devices and a dc servo loop. This circuit provides a 40-W output. IC3 and IC5 must be heatsinked. (Reprinted with permission from Electronics Now, 11/92, p. 42. (C) Copyright Gernsback Publications, Inc.,1992)


6-W AUDIO AMPLIFIER WITH PREAMP
6-W AUDIO AMPLIFIER WITH PREAMPFC72-6

This monolithic IC, class-B, audio amplifier circuit is a 6-W car radio amplifier for use with 4-ohm and 2-ohm load impedance.  (Signetics, 1987 Linear Data Manual Vol. 1:Communications, 11/6/86, p. 7-246)


6OW SWITCHING AMPLIFIER
6OW SWITCHING AMPLIFIERFG20

The schematic for the Switching Amplifier is shown. A separate 51-volt-DC source is required to power the Amplifier circuit. The 51-volt-DC source is fed to a pair of Zener diodes, D5 and D6, and is filtered by capacitors Cl1 and Cl2 to provide a 12-volt-DC source for part of the circuit. Also, part of the 51-volt-DC source bypasses the Zeners to power the sections of the circuit that require a high voltage. The right and left signals are input to the Amplifier through jacks J1 and J2, respectively. Two sections of a TL074 op amp, IC1-c and IC1-d ,generate a 4-V p-p, 50-kHz triangular refence waveform. The generated waveform is then fed to potentiometer R19. That enables the amplifier to use input signals with amplitudes ranging from 1 V p-p to 4 V p-p. The other two op-amp sections, IC1-a and IC1-b, function as comparators to produce the pulse-width-modulating output for the left and right channels of the amplifier. In the right channel of the amplifier, the output of the voltage comparator is coupled to the bipolar translating circuit-limiting resistor,R5. The translating cicuit has a positive and negative "leg;" Q1, D1, and R7 make up the positive leg, and Q3, D3, and R11 make up the negative leg. Both legs are tied to ground through the emitters of Q1 and Q3, providing a reference point for the translator. The translator arrangement result in 17 V being present across Q1, Q3, and zener diodes D1 and D3. Sufficient current is then present to overcome the power MOSFET gate capacitance; that rapidly switches on and off the power MOSFET complementary push-pull ouput stage, composed of Q5 and Q7. Resistor R3 keeps the output swing centered at the midpoint of the supply voltage. Without R3, the square- wave output drifts down toward the negative rail. The RC network, composed of R9 and C5, which connects to both N- and P-channel gates, minimizes switching noise and sharpens the square-wave output. Note that both channels contain power-supply elements to split the incoming single- polarity voltage in half. Capacitors C3, C4, C7, and C8 make up a series-parallel circuit that converts the 51-Vdc supply to 25.5 Vdc. The output can feed full-range 60-W rms speakers, which demodulate the signal and produce an amplified audio output. (At peak output power, the current draw for an 8 ohm dynamic load is approximately 1.2 A at 51 Vdc.)


A 33-W BRIDGE COMPOSITE AMPLIFIER
A 33-W BRIDGE COMPOSITE AMPLIFIERFE5-6

Two LM1875 ICs provide 33 W of audio. IC4 is used as a phase inverter. IC6 and IC2 must be heatsinked. (Reprinted with permission from Electronics Now, 11/92, p. 41. (C) Copyright Gernsback Publications, Inc.,1992)


AUDIO POWER AMPLIFIER
AUDIO POWER AMPLIFIERFC72-5

The single speaker amplifier circuit uses current feedback, rather than the more popular voltage feedback. The feedback loop is from the junction of the speaker terminal and a 0.5-ohm resistor, to the inverting input of the NE5534.  When the input to the amplifier is positive, the power supply supplies current through the TIP32 and the load to ground.  Conversely, with a negative input, the TIP31 supplies current through the load to ground.  The gain is set to about 15 (gain = SPKR 8 ohm/0.5 ohm feedback).  The 0.22-uF capacitor across the speaker rolls off its response beyond the frequencies of interest.  Using the 0.22-uF capacitor specified, the amplifier current output is 3 dB down at 90 kHz where the speaker impedance is about 20 ohm. To set the recommended class A output collector current, adjust the value of either 130-ohm resistor.  An output current of 50 to 100 mA will provide a good operating midpoint between the best crossover distortion and power dissipation.  (Texas Instruments, Linear and Interface Circuits Applications, 1985, Vol. 1, p. 3-14)


AUDIO POWER AMPLIFIER, 1.5 W, 12V
AUDIO POWER AMPLIFIER, 1.5 W, 12VFF11-1*

Although ICs have largely replaced circuits such as this, this circuit still finds use where flexibility of a discrete device design is desirable. Parts are easy to obtain and the problem of IC obsolescence is eliminated. The TIP31A can be heatsinked to a small metal heatsink, if desired. (William Sheets)


AUDIO POWER BOOSTER
AUDIO POWER BOOSTERFG19

The Audio Power Booster is based on two TDA2006 audio IC power amplifiers. Power amplifier IC1 is used as what is virtually a non-inverting amplifier, with the non-inverting input of the device being biased to half the supply voltage by R2 and R3. R5 provides 100-percent negative feedback from the output to the inverting input of ICl at DC so that the circuit has unity voltage gain and the output is biased to the required level of half the supply voltage, C2 and R4 remove some of the feedback at audio frequencies and this gives a voltage gain of about 18 times at these frequencies, R1 is used at the input of the amplifier to reduce the sensitivity to a more suitable level, and Cl simply provides DC blocking at the input. IC2 is used in virtually the same configuration, but its non-inverting input is not fed with an audio signal, and only receives the DC bias signal from R9 and R10. Resistor R1 couples the output signal of IC1 to the inverting input of IC2, and the value of R11 is chosen to give IC2 an effective voltage gain of unity. However, as the input signal is coupled to IC2's inverting input there is a phase inversion through this section of the amplifier, giving the required anti-phase relationship at the two outputs. Diodes Dl to D4 are protection diodes for the two IC's, while R6 plus C4 helps to prevent instability. Components C3, C5 and C7 are all supply decoupling capacitors. (Electronic Experimenters Handbook, 1996, p.63)


BRIDGE CONNECTION OF TWO POWER OP AMPS
BRIDGE CONNECTION OF TWO POWER OP AMPSFF11-18

These bridge connections provide differential outputs that approach twice the total supply voltage. Diode bridge clamps output to the supplies. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 1059)


HYBRID POWER AMPLIFIER
HYBRID POWER AMPLIFIERFC72-7

The input is ac coupled to the amplifier through C2, which blocks dc signals that might also be present at the input. The Rl/Cl combination forms a low-pass filter, which eliminates unwanted high-frequency signals by bypassing them to ground when they appear at the circuit input, which has an impedance of about 52 Ω. The gain of the amplifier is set at about 26 dB by resistors R3 and R4. The R5/C5/C7 combination on the positive supply and its counterpart R6/C6/C8 on the negative supply provides power-supply decoupling. R7 and C9 together prevent oscillation at the output of the amplifier. From that point, the amplifier's output signal is direct coupled to the speaker through a 3-A fuse, Fl. The dc output of the amplifier at pin 7 is 0 V, so no dc current flows through the speaker. Should there be a catastrophic failure of the output stage, fuse Fl, which should be a fast-acting type, prevents dc from flowing through the speaker. (Hands-On Electronics, 8/86, p. 43)


MINIATURE AUDIO POWER AMPLIFIER
MINIATURE AUDIO POWER AMPLIFIERFG18

A compact audio power amplifier with low current drain has many applications. These are the design basis for the mini amplifier. It continues working satisfactorily with a battery voltage down to 1.5 V. Its quiescent current drain is about 1 mA, and its efficiency is a worthwhile 70 per cent. It provides an output power of 500 mW into 8Ω (or 800 mW into 4 ohms), has a sensitivity of 400 mV, and its distortion is never high than 1.2 percent. Since the output transistors have no emitter resistor, the voltage is determined solely by the knee voltage of T3 and T4- With a load of 4-8Ω, these voltages are limited to 0.2-0.3 V, so that the transistors can be driven virtually up to the supply voltage. The overall bandwidth of the amplifier is limited to not less than 21 kHz at the maximum amplification of x5. With a 4Ω load, the peak output current is 700 mA. A 315 mA fuse in series with the output is, therefore, a simple but effective short-circuit protection. At maximum drive with a music signal, the average current is only 50 mA. In practice the drive will never be continuously maximum, so that the actual current drain will be much lower. A set of four penlight batteries should last about 200 hours. (Elektor Electronics, July-August 1996, p. 96)


POWERED SUBWOOFER
POWERED SUBWOOFERFG17

The power supply consists of a center-tapped 48-volt transformer, bridge rectifier, and filter capacitors. The rectified and filtered output is about ±35 volts. The power supply for opamp IC1 is regulated to ±15 volts by Zener diodes Dl and D2 and resistors R19 and R20. The input circuit consists of a mixer and voltage divider formed by resistors Rl and R2, potentiometer R3, and unity-gain buffer ICl-a. Potentiometer R3 is provided to adjust the output of the subwoofer to the desired level. Op-amp IC1-b provides a 12 dB per octave high-pass filter with capacitors C2 and C3, and resistors R5 and R6. The cut-off frequency for this filter is 1/2πRC, or about 34 Hz with the values shown. Resistors R8 and R7 set the gain and Q of the filter. Capacitor Cl and resistor R4 form an additional 6-dB-per-octave high-pass filter at about 20 Hz. A 12-dB-per-octave low-pass filter at about 20 Hz. A 12-dB-per-octave low-pass filter is formed by ICl-c, C4 and C5, and R9 and R10. The values shown set the low-pass cutoff at 72 Hz. The gain and Q of this stage are set by R11 and R12. These two filters, connected back-to-back, form a bandpass filter. When operated with ±l5-volt supplies, the output of op-amp ICl-d can swing about 10 volts peak to drive transistors Q1 and Q2. Resistors R17 and R18 provide negative feedback, and set the gain of the output stage at about three. Hence, the output can swing to about 30 volts peak. As long as the transistors are the high-beta types specified, the peak power output into an 8-ohm load is (30x30/8)/2 = 56 watts RMS. The overall gain of the amplifier is set by resistor Rl3 and feedback resistor Rl4. (Electronics Now, October 1995, p. 37)


WIDEBAND AMPLIFIER
WIDEBAND AMPLIFIERFD76-15

Using a Signetics NE5205, this circuit gives about + 16-dB gain from LF to 600 Mhz. The π minimizes load impedance and source-impedance variations and aids stability. (Reprinted with permission from Popular Electronics, 1/90, p.98. (C)Copyright Gernsback Publications, Inc.,1990)


ANALOG TO DIGITAL CONVERTERS

10-BIT A/D CONVERTER

16-BIT A/D CONVERTER

A/D CONVERTER FOR PCs

HIGH SPEED 3-BIT A/D CONVERTER

SUCCESIVE APPROXIMATION A?D CONVERTER

TRACKING ADC


10-BIT A/D CONVERTER
10-BIT A/D CONVERTERFB3-5

The converter has a 60 ms conversion time, consumes 460 uA from its 1.5 V supply and maintains 10 bit accuracy over a 15 degree C to 35 degree C temperature range.  A pulse applied to the convert command line causes Q3, operating in inverted mode, to discharge through the 10 k ohm diode path, forcing its collector low. Q3's inverted mode switching results in a capacitor discharge within 1 mV of ground.  During the time the ramps' value is below the input voltage, C1A's output is low. This allows pulses from C1B, a quartz stabilized oscillator, to modulate Q4.  Output data appears at Q4's collector.  When the ramp crosses the input voltages value C1A's output goes high, biasing Q4 and output data ceases. The number of pulses at the output is directly proportional to the input voltage.  To calibrate apply 0.5 V to the input and trim the 10 k ohm potentiometer for exactly 1000 pulses out each time the convert command line is pulsed.  (Linear Technology Corp., Linear Databook.  1986. p. 5-17)


16-BIT A/D CONVERTER
16-BIT A/D CONVERTERFB3-3

The A/D converter, made up of A2, a flip-flop, some gates and a current sink, is based on a current balancing technique. Once again, the chopper-stabilized LTC1052's 50 nV/°C input drift is required to eliminate offset errors in the A/D. (Linear Technology Corp., Linear Applications Handbook, 1987, p. AN15-2)


A/D CONVERTER FOR PCs
A/D CONVERTER FOR PCsFF7-2

An ADC0804 A/D converter converts analog data to digital. This is fed to a 74165 8-bit shift register and converted to serial data. U3 provides a baud-rate clock. U4A and U4B are used to generate start and stop bits needed at beginning and end of each data word. (Reprinted with permission from Popular Electronics, 4/94, p. 47. (C) Copyright Gernsback Publications, Inc., 1994)


HIGH SPEED 3-BIT A/D CONVERTER
HIGH SPEED 3-BIT A/D CONVERTERFA4-11

(Courtesy of Fairchild Camera & Instrument Corporation, Linear Databook, 1982, p. 5-32)


SUCCESIVE APPROXIMATION A/D CONVERTER
SUCCESSIVE APPROXIMATION A/D CONVERTERFA4-2

A bipolar input, high-speed A/D converter uses two AM25L03s to form a 14-bit successive approximation register. The comparator is a two stage circuit with an HA2605 front-end amplifier used to reduce settling time problems at the summing node. Careful offset-nulling of this amplifier is needed. (Intersil Data Book, 5/83, p. 4-83)


TRACKING ADC
TRACKING ADCFC4-2

The analog input is fed into the span resistor of a DAC. The analog input voltage range is selectable the same way as the output voltage range of the DAC. The net current flow through the ladder termination resistance; i.e., 2 KΩ for HI-562A; produces an error voltage at the DAC output. This error voltage is compared with 1/2 LSB by a comparator. When the error voltage is within ± 1/2 LSB range, the Q output of the comparators are both low, which stops the counter and gives a data ready signal to indicate that the digital output is correct. If the error exceeds the ± 1/2 LSB range, the counter is enabled and driven in an up or down direction depending on the polarity of the error voltage.

The digital output changes state only when there is a significant change in the analog input. When monitoring a slowly varying input, it is necessary to read the digital output only after a change has taken place. The data ready signal could be used to trigger a flip-flop to indicate the condition and reset it after readout. The main disadvantage of the tracking ADC is the time required to initially acquire a signal; for a 12-bit ADC, it could be up to 4096 clock periods. The input signal usually must be filtered so that its rate of change does not exceed the tracking range of the ADC-1 LSB per clock period.

(Harris Analog Data Book, 1988, p. 10-48)


ANNUNCIATOR CIRCUITS

ELECTRONIC DOOR BUZZER 1

ELECTRONIC DOOR BUZZER 2

ELECTRONIC DOORBELL


ELECTRONIC DOOR BUZZER 1
ELECTRONIC DOOR BUZZER 1FE27-3

This simple electronic door buzzer draws no quiescent current When Sl is pressed the speaker produces a tone. The NE555 (Ul) generates signal.(.Reprinted with permission from Popular Electronics, 6/93, p. 63. Copyright Gernsback Publications, Inc., 1993)


ELECTRONIC DOOR BUZZER 2
ELECTRONIC DOOR BUZZER 2FD3-1

When Sl is depressed, an initial positive voltage is placed on C2 and the non-inverting terminal of Ul. The circuit oscillates at a low frequency. As C2 charges up through R3, a rapid increase in frequency of oscillation results, producing (at SPKR1) a rapidly rising pitched sound. This sound is easily recognized over ambient noise. (Hands-On Electronics, 8/87, p. 94)


ELECTRONIC DOORBELL
ELECTRONIC DOORBELLFE27-1

When the doorbell switch is pressed, the two monostable stages are activated in sequence, applying bias to a pair of voltage-controlled resistor stages. These then modulate the outputs from a pair of tone generators. The resulting signals are fed to an audio amplifier, then to the speaker. (Reprinted with permission from Popular-Electronics, 9/93. (C)Copyright Gernsback Publications, Inc.,1993)


ANTENNA CIRCUITS

ACTIVE ANTENNA FOR UHF SCANNERS

ACTIVE ANTENNA I OOKHZ - 3OMHZ -

ANTENNA NOISE BRIDGE DETECTOR

ANTENNA TUNING INDICATOR

FM AUTO RADIO DIVERSITY ANTENNA

FM AUTO RADIO DIVERSITY ANTENNA

HIGH FREQUENCY LOOP ANTENNA

LOOP ANTENNA PREAMPLIFIER

MINIATURE BROADBAND ANTENNA (3 TO 30 MHz)

OP AMP ANTENNA AMPLIFIER

TUNABLE FM ANTENNA BOOSTER


ACTIVE ANTENNA FOR UHF SCANNERS
ACTIVE ANTENNA FOR UHF SCANNERSFF8-7

This active antenna is a 1/2-wave dipole mounted in a 12" x 12" x 12" 90 degree corner reflector. A built-in active preamp IC1, fed dc through the RF coaxial line, provides 15 dB gain at 900 MHz to offset cable losses. This provides superior reception for scanners covering the 800- to 1000-MHz range. (William Sheets)


ACTIVE ANTENNA I OOKHZ - 3OMHZ -
ACTIVE ANTENNA IOOKHZ - 3OMHZFG26

This circuit uses a FET and bipolar transistor combination to achieve high performance with a short pickup antenna (24 in. or 70 cm). R5 is a gain control and should be set for the minimum gain necessary for good results. Tl is 24 turns of #32 trifilar wire on a Ferroxcube P/N 768Tl 88-3E2A core. J1 is used for DC feed and RF output. A DC block unit can be used at the receiver end. DC power is 12V at 30mA. The pickup wire and preamp should be enclosed in a weatherproof assembly so the antenna can be mounted outdoors in an electrically quiet area. A complete kit of parts, including PC board, is available from North Country Radio, P.O. Box 53,  Wykagyl Station, New Rochelle NY 10804-0053A. (Popular Electronics, August 1997, p. 48)


ANTENNA NOISE BRIDGE DETECTOR
ANTENNA NOISE BRIDGE DETECTORFG22

Parts List:

BT1	9-Volt alkaline battery
Cl	100 pF mica or poly capacitor
C2	140-150 pF variable capaci tor  (see text)
C3	0.1 μF disc capacitor
C4	0.01 μF disc capacitor
D1,D2	Germanium diode: 1N34, 1N60, 1N90, 1N270, etc.
JI	SO-239 UHF female connector (or builder's choice)
Ll	33 turns #26 enam. wire on T50-2 toroid (40-30 meters)
L2	11 turns #26 enam. wire on T50-2 toroid (20 through 10 meters)
M1	100 or 200 μA meter (see text)
Q1	NPN small:signal transistor:  2N2222, 2N3904, 2N4124, etc.
R1,R3	10k 5% 1/4 Watt resistor
R2	1000 Ohm linear taper potentiometer, with switch S2
S1	SPDT toggle or slide switch (Bandswitch)

The circuit is illustrated in figure. The noise output from your antenna noise bridge is applied though a coax jumper cable to J1, an SO-239. This noise, which usually will peak slightly below 1.0 volts, is broadband white noise and is fed though Cl, a 100 pF capacitor, to a pair of small signal diodes connected as a rectifier/voltage doubler. The rectified DC voltage, filtered by C3, an 0.1μF disc capacitor, is then applied to the base of a small signal NPN transistor Ql, which serves as a meter amplifier. Meter Ml is a 200 pA meter. It monitors collector current through Ql. On/Off switch S2 is mounted on the GAIN control which, in series with R3, forms a voltage divider across battery BT1, a 9-volt battery which powers this instrument. The GAIN control is wired so the wiper travels from the end of R3 to ground as the knob is rotated clockwise. This sets the emitter bias and the point at which Ql will go into conduction as rectified noise voltage is applied to Ql base. The current drain from the battery is approximately 8 μA with no input, increasing to slightly over 200 μA with the meter at full scale. With such low current drain, an alkaline battery should last for years, even if you forget to turn the instrument off! This instrument covers the range from below 40 meters to above 10 meters in two bands: 40 and 30 meters; and 20-17-15-12-10 meters. Bandswitch Sl, an SPDT toggle or slide switch, selects the frequency range. The tuning capacitor C2 is a small 150 pF air variable. (73 Amateur Radio Today, May 1996, p. 78)


ANTENNA TUNING INDICATOR
ANTENNA TUNING INDICATORFG24

Parts:

Cl, C2	0-01-μF general-purpose ceramic	R2-R4	51-Ω, 1/2-W, 5%-tolerance carbon- capacitor film resistor
D1	Germanium diode (1N34, 1N601, 1N270 or equivalent)	R5	2.2-kΩ,1/2-W, 5%-tolerance carbon-film resistor
J1-J3	Coaxial jacks	R6	10-kΩ, linear taper potentiometer
Ml	0-50 or 0-1 00 μA dc meter	SlA	Double-throw, double-pole (DPDT)
R1A, R1 B	750Ω, 3-W, 5%-tolerance metal-oxide film resistor; see text		toggle switch (I used one rated for 120-V service)

The Stealth antenna tuning indicator consists of a sensitive reflected-power bridge and indicator (R2-R6 and associated components) and a switch (Sl) that lets you route your transceiver's power into a dummy antenna (TUNE) or your antenna system (OPERATE). One more component, Rl (a resistance consisting of two separate 3-W resistors, R1A and RlB), leaks just enough of your transmitter's power to the bridge and your antenna system to allow low-interference tune-up when Sl is set to TUNE.

(QST Magazine, June 1995, p. 38)


FM AUTO RADIO DIVERSITY ANTENNA
FM AUTO RADIO DIVERSITY ANTENNAFF8-3

A second antenna, installed on your vehicle as far away from the original equipment antenna as practical, provides the second FM signal.

The cables from both antennas are connected to the electronic antenna switch. The 19-kHz pilot signal from the receiver's audio output is passed through a high gain bandpass active filter, which attenuates audio programming that is much stronger than the pilot signal. After amplification, the pilot subcarrier becomes the reference frequency for a phase-locked loop (PLL) circuit. The output of the PLL locks to the 19-kHz pilot signal and functions as a subcarrier detector. When the reference frequency becomes noisy, the PLL will lose "lock" and trigger the flip-flop, whose output switches the state of the electronic antenna switch. This action switches the alternate antenna into the system while disabling the original antenna.

If that second antenna is positioned for better reception, the received signal will clear, and the PLL will again lock to the subcarrier and hold the switch in that state until the pilot signal drops out again. If the second antenna does not restore the pilot signal reception after a 0.1-second delay, the primary antenna is switched back on.

When the radio is receiving AM, the absence of the 19-kHz subcarrier will also reactivate the primary antenna that is tuned to the receiver for the best AM reception.

(Reprinted with permission from Electronics Now, 11/93, (C) Copyright Gernsback Publication, Inc., 1993)


HIGH FREQUENCY LOOP ANTENNA
HIGH FREQUENCY LOOP ANTENNAFG25

Good performance in the 5-to-30-MHz range requires an amplifier with extremely high input impedance and low noise that can drive 75-Ω loads at high signal levels at frequencies over 30 Mhz. Combining dual FET source followers and the new Maxim 436 wideband transconductance amplifier; can produce just such an amplifier. A balanced configuration is used for the tuned loop to preserve the symmetry of the figure-eight polar antenna pattern. As a result of using FET source followers on the amplifiers front end, only the 1-MΩ gate resistors load the tuned circuit, so tuning is very sharp and resistance to off-frequency interference is very high. The FETs drive the differential inputs of the MAS436, which amplifies the balanced signal and converts it to a single-ended output. Voltage gain for this amplifier is switch selectable at either 8 dB or 20 dB into a 75-Ω load. Since the amplifier is designed to work into a 75-Ω load, the device can be connected to the receiver with a length of RG59U cable. Maximum undistorted output is 1500 mV into 75 Ω so overloading is unlikely even at the high-gain setting. (Electronic Design, July 1996, p. 112)


LOOP ANTENNA PREAMPLIFIER
LOOP ANTENNA PREAMPLIFIERFE4-9

This preamplifier has a built-in regeneration control boost gain selectivity. C1 is a single or multi-gang AM broadcast-band tuning capacitor. L1 is a ferrite loop antenna, tapped at about 15 to 25% of total turns. This circuit should prove useful for low-frequency (up to 3 MHz) reception, where a loop would be advantageous to reduce man-made noise pickup. (Reprinted with permission from 73 Amateur Radio Today, 10/92, p. 28)


MINIATURE BROADBAND ANTENNA (3 TO 30 MHz)
MINIATURE BROADBAND ANTENNA (3 TO 30 MHz)FF8-2

A short dipole antenna and impedance converter combined together can be rotated to null out an interfering signal. The converter supplies a tremendous current gain so that the voltage appearing at the dipole's output eventually drives a 75- Ω load. (Reprinted with permission from Electronic Design 2/95, p 107, Copyright 1995 Penton Publishing)


OP AMP ANTENNA AMPLIFIER
OP AMP ANTENNA AMPLIFIERFG23

The impedance of a random-wire antenna at broadcast-band frequencies will be several kilohms, a poor match for the 50-ohm input of a receiver. Also, the inputs of multiple receivers can't be connected directly to a single antenna, or they'll detune each other. The circuit solves both problems. The first op-amp overcomes the impedance mismatch, strengthening the signal greatly even though it has no voltage gain. The rest of the op-amps feed the signals to the separate receivers. No low-pass filter is needed because the gain of these op-amps drops off sharply above 2 or 3 Mhz. (Electronics Now, September 1995, p.7)


TUNABLE FM ANTENNA BOOSTER
TUNABLE FM ANTENNA BOOSTERFF8-4

This two-transistor amplifier circuit with tunable tank circuits boosts the distant FM signals. Coils L1 and L2 are l 1/2 turns #20 AWG bail tinned wire wound around a 3/8 diameter mandrel. (Reprinted with permission from Electronics Now, 5/94, p. 49 (C) Copyright Gernsback Publications, Inc., 1994)


AUDIO EFFECTS CIRCUITS

ANALOG DELAY- LINE (ECHO AND REVERB)

AUDIO DITHERIZING CIRCUIT FOR DIGITAL AUDIO USE

BALANCE AND LOUDNESS AMPLIFIER

DERIVED CENTER-CHANNEL STEREO SYSTEM

VOCAL ELIMINATOR


ANALOG DELAY- LINE (ECHO AND REVERB)
ANALOG DELAY- LINE (ECHO AND REVERB)FD5-6

This circuit uses an SAD 512D (Reticon) chip, which is a 512-stage analog shift register. By varying the clock frequency between 5 and 50 kHz, delay time can be set between 51.2 and 5.12 ms. The clock frequency must be at least twice the highest audio frequency. (Elektor Electronics, 301 Circuits, p. 30- 31.21)


AUDIO DITHERIZING CIRCUIT FOR DIGITAL AUDIO USE
AUDIO DITHERIZING CIRCUIT FOR DIGITAL AUDIO USEFD5-8

By adding a small amount of noise to a signal to be digitized (about 0.7 bit):

VNOISE ~ 0. 7 (VINPUTP-P )

2N

where: n=#of bits  For example, 8 bits and 2 V p-p would be 0. 0055 V.

This circuit uses a transistor (Ql) and an amplifier (Q2 and Ul) to generate the noise signal. Rll controls the noise injection and R12 controls the gain of the system.

(Reprinted with permission from Popular Electronics, 4/90, p. 37-38. (C)Copyright Gernsback Publications, Inc.,1984)


BALANCE AND LOUDNESS AMPLIFIER
BALANCE AND LOUDNESS AMPLIFIERFB6-7

The circuit shows a combination of balance and loudness controls. Due to the non-linearity of the human hearing system, the low frequencies must be boosted at low listening levels. Balance, level, and loudness controls provide all the listening controls to produce the desired music response. (Texas Instruments, Linear and Interface Circuits Applications, Vol. 1, 1985, p. 3-17)


DERIVED CENTER-CHANNEL STEREO SYSTEM
DERIVED CENTER-CHANNEL STEREO SYSTEMFD5-9

A simple method of deriving a center or third channel without the use of an extra transformer or amplifier. (a) 4Ω speakers are connected to 8Ω amplifier taps. 8 and 16-Ω speakers connect to 16-Ω taps. (b) By blending the inputs it is possible to cancel out undesired crosstalk. (Electronics World, 4/66)


VOCAL ELIMINATOR
VOCAL ELIMINATORFD5-4

Otherwise properly mixed sounds often suffer from a predominant solo voice (which might, of course, be the intention). If such a voice needs to be suppressed, the present circuit will do the job admirably.

The circuit is based on the fact that solo voices are invariably situated "at the center" of the stereo recordings that are to be mixed. Thus, voice levels in the left- and right-hand channels are about equal. Arithmetically, therefore, left minus right equals zero; that is, a mono signal without voice.

There is, however, a problem: the sound levels of bass instruments, more particularly the double basses, are also just about the same in the two channels. On the one hand low-frequency sounds are virtually nondirectional and on the other hand, the recording engineers purposely use these frequencies to give a balance between the two channels.

However, the bass instruments can be recovered by adding those appearing in the left + right signal to the left - right signal. The whole procedure is easily followed in the circuit diagram. The incoming stereo signal is buffered by A1 and A2. The buffered signal is then fed to differential amplifier A3 and subsequently to summing amplifier A5. The latter is followed by a low-pass filter formed by A6. You can choose between a first-order and a second-order filter by respectively omitting or fitting C2. Listen to what sounds best.

The low-frequency signal and the difference signal are applied to summing amplifier A4. The balance between the two is set by P1 and P2 to individual taste.

You have noticed that the circuit does not contain input or output capacitors. If you wish, output capacitors can be added without detriment. However, adding input capacitors is not advisable, because the consequent phase shift would adversely affect the circuit operation.

(Elektor Electronics, 7/89 Supplement, p. 5-6)


AUDIO MIXER CIRCUITS

MIXER PREAMPLIFIER WITH TONE CONTROL

PASSIVE MIXER


MIXER PREAMPLIFIER WITH TONE CONTROL
MIXER PREAMPLIFIER WITH TONE CONTROLFA6-5

General-purpose preamplifier/mixer accepts up to four inputs, has a gain of 1600, and provides bass and treble controls that can be varied ±10 dB at 100 Hz and 10 kHz, respectively. IC1 and IC2 are LM301A.


PASSIVE MIXER
PASSIVE MIXERFA6-6

This simple circuit can be used to combine stereo signals to produce a monaural output. Rl and R2 isolate both circuits and R3 controls the level of the combined output signal. (No reference)


AUTOMOTIVE CIRCUITS

AUTO BATTERY CRANKING TESTER

AUTO FUSE MONITOR

AUTO TURN-SIGNAL REMINDER

AUTOMATIC TURN-OFF CONTROL FOR AUTOMOBILES

AUTOMOBILE IGNITION SUBSTITUTE

AUTOMOTIVE ELECTRICAL SYSTEM ANALYZER

BACK-UP BEEPER

BOOSTER AMPLIFIER FOR CAR STEREO USE

BRAKE AND TURN INDICATOR

CAR PRESENCE DETECTOR

CAR-WIPER CONTROL

ELECTRONIC AUTO STETHOSCOPE

FLASHING THIRD BRAKE LIGHT

HEADLIGHT ALARM

IMMOBILIZER

PTC THERMISTOR AUTOMOTIVE TEMPERATURE INDICATOR

THIRD BRAKE LIGHT

TURN SIGNAL ALARM


AUTO BATTERY CRANKING TESTER
AUTO BATTERY CRANKING TESTERFG29

Need to discover if your battery is weak or if your starter windings are shorted? This meter will display how low your battery voltage drops during a start. (Popular Electronics, January 1996, p. 62)


AUTO FUSE MONITOR
AUTO FUSE MONITORFE8-23

This circuit can quickly check a fuse in an automobile circuit. Connect across suspected fuse--either LED glows, fuse is blown. The circuit must be live for this test to work. (William Sheets)


AUTO TURN-SIGNAL REMINDER
AUTO TURN-SIGNAL REMINDERFE8-12

This circuit counts turn signal flashes. At the end of about 70 flashes, a chime sounds to remind the driver to turn off the turn signal. By using various taps on U2, the period can be changed if desired. BZ1 is a buzzer or chime module. (Reprinted with permission from Popular Electronics, 3/93, p.62. (C)Copyright Gernsback Publications, Inc.,1993)


AUTOMATIC TURN-OFF CONTROL FOR AUTOMOBILES
AUTOMATIC TURN-OFF CONTROL FOR AUTOMOBILESFE8-19

When the ignition switch is on, relay K1 is energized continuously, and the headlights can be turned on. Turning off the ignition turns on timer IC1, which keeps IC1 energized for a time determined by R1 and C1. With the values shown, approximately a 1-minute delay will result. The values of R1 and C1 can be changed to vary this delay time. (William Sheets)


AUTOMOBILE IGNITION SUBSTITUTE
AUTOMOBILE IGNITION SUBSTITUTEFC8-1

The ignition substitute provides a constant power source for the ignition coil. Its frequency, 0. 5 - 1.0 kHz, is that used by an 8-cylinder engine with an idling speed of 650 RPM, and the unit provides a rapid spark at a 17% duty cycle, while staying within the power dissipation limits of the components.

The circuit consists of a 555 timer IC configured as an astable free-running multivibrator that is used to drive a high-current npn transistor, such as a 2N6384. The transistor should be heavily heatsinked because it might be drawing several amps over quite a long period of time.

The coil ballast can be from 0.68 to 6.5 Ω, depending on what's available. The 2.5-Ω, 20-W ballast shown works well. All the other resistors can be either 1/4- or 1/2-W devices, and the capacitor, between pins 1 and 5 of the 555, can range from 0.01 to 0.05 μF. Do not omit the 100-V, 0.05-μF capacitor across the transistor; it prevents voltage spikes from damaging the device.

Although designed for an 8-cylinder engine, this device can be used with other types. In addition, a neon bulb can be added to the circuit to verify the presence of a spark.

(Gernsback Publications Inc., 42 New Ideas,1984, p. 9)


AUTOMOTIVE ELECTRICAL SYSTEM ANALYZER
AUTOMOTIVE ELECTRICAL SYSTEM ANALYZERFG27

The automotive electrical diagnostic system is built around a Maxim MAX8214ACPE five-stage voltage comparator, which contains a built-in 1.25-volt precision reference, and on-board logic that allows the outputs of two of the comparators to be inverted. (Popular Electronics, March 1994, p. 67)


BACK-UP BEEPER
BACK-UP BEEPERFC8-14

Put the car in reverse and the circuit provides a loud, audible beep at the rate of about one per second (1 Hz).Half of Ul, a 556 dual oscillator/timer, is used as a slow-pulse oscillator with a rate of about 1 Hz. Components R2, R1, and Cl form the long time constant. You can calculate on time by t=.7 (R1 + R2) Cl or 1.15 seconds. The off time is shorter than the on time, at .77 second. Enabling pin 4 (reset) is held high to keep the oscillator free- running when voltage is applied to pin 14. The output at pin 5 is coupled to pin 10 of Ul enabling oscillator 2. Oscillator 2 of Ul produces an audio output of about 1 kHz, as determined by C2, R3, and R4. Pin 10 (reset) of oscillator 2 is connected to the pin 5 output of oscillator 1. So when pin 5 becomes positive, the oscillator beeps a short pulsed tone of 1 kHz. (TAB Books, 101 Sound, Light, and Power IC Projects, 1986, p. 139)


BOOSTER AMPLIFIER FOR CAR STEREO USE
BOOSTER AMPLIFIER FOR CAR STEREO USEFE8-11

 Only one channel of this circuit is shown. The other is practically a carbon copy.

The input to the circuit, taken from your car radio's speaker output, is divided along two paths; in one path, a high-power divider network (consisting of R8 through R10) provides 4.5-Ω resistance to make the circuit's input impedance compatible with the output impedance of the car radio. In the other path, the signal is fed to the input of Ul through resistor LR7, trimmer potentiometer R21, and capacitor C2. Together, R7 and R21 offer a minimum resistance of 27,000 Ω.

Integrated circuit Ul (a TDA-2004 audio power amplifier) amplifies the signal, which is then output at pins 8 and 10 and fed to the loudspeaker. Note: This amp is designed for use only with car radios whose speaker outputs are referenced to ground: do not use with radios that have balanced outputs.

(Reprinted with permission from PE Hobbyist Handbook, p. 73. Copyright Gernsback Publications, Inc)


BRAKE AND TURN INDICATOR
BRAKE AND TURN INDICATORFE8-17

This might be a quick solution to getting the two wire truck harness to support both turn and braking indications. (Reprinted with permission from Popular Electronics, 3/92, p. 75. (C)Copyright Gernsback Publications, Inc.,1993)


CAR PRESENCE DETECTOR
CAR PRESENCE DETECTORFG28

Here's a circuit that will, if calibrated carefully, detect the presence of a large metal object. Coil L1 is made by winding 50 turns of 26-gauge wire on a 50-inch form. If L1 is buried in the ground, the circuit can be used to detect any car or truck that is driven over the coil. Transistor Ql and its surrounding components make up a Colpitts oscillator, operating at 10 kHz. The output is coupled to a Maxwell bridge through the secondary of Tl, which is a 600-ohm to 600-ohm audio coupling transformer. With Rl, R2 and R3 set properly, the bridge is balanced when no metal is close to L1, producing a near-zero AC signal at the bridge's output (the R5/Ll junction and ground). Should a large-enough ferro-magnetic object pass over L1, the bridge is unbalanced, producing a signal at the junction R5 and Ll. That signal is fed to the base of Q2, part of a common-emitter amplifier stage. Resistor R4 adjusts to the gain of that stage. The signal from the amplifier is fed to the base of Q3, which drives a voltage doubler that supplies current to the relay driver, Q4. The relay, Kl, is a 1 000-ohm, sensitive, 12-volt unit that can drive a normally open or closed alarm circuit to indicate the presence of a vehicle. Use shielded cable to attach Ll to the circuit, and do not bury Ll deeper that 8 inches for best results. Remember to weather-proof all components that will reside outside. (Popular Electronics, January 1996, pp. 63-64)


CAR-WIPER CONTROL
CAR-WIPER CONTROLFB7-17

Ul is configured to operate in the standard astable mode, providing a form of relaxation oscillator. When power is applied, C2 initially charges through Rl, R2 and R3 to two-thirds of the supply voltage. At that point, Ul senses that its threshold voltage at pin 6 has been reached, and triggers the timer, causing its output at pin 3 to go high. That high, applied to the base of Ql, keeps the transistor in the off state. Now C2 begins to discharge through R2 to pin 7 of Ul. When C2 has discharged to about one-third of the supply voltage, U1 is toggled back to its original state. C2 starts to charge again, as pin 3 of Ul goes low. The low at pin 3 causes Ql-which serves as an emitter-follower buffer stage-to turn on, allowing current to flow through the coil of relay Kl. That, in turn, causes Kl's contacts to close, applying power to the wipers. The charge time of capacitor C2 is determined by the setting of potentiometer R3. Capacitor C2 should be a tantalum type, and actually, almost any 12-volt coil relay with sufficiently heavy contacts should serve well. (Hands-On Electronics, 4/87, p. 92)


ELECTRONIC AUTO STETHOSCOPE
ELECTRONIC AUTO STETHOSCOPEFF12-1

 The heart of the Stethoscope is the NE5532 audio op amp, Ul. That component directly drives low impedances and allows the use of headphones without adding another amplifier. (Reprinted with permission from Popular Electronics, 4/95, p.47. (C)Copyright Gernsback Publications, Inc.,1995)


FLASHING THIRD BRAKE LIGHT
FLASHING THIRD BRAKE LIGHTFC8-17

When power is first applied, three things happen: light-driving transistor Ql is switched on due to a low output from U2 pin 3; timer Ul begins its timing cycle, with the output, pin 3, becoming high, inhibiting U2's trigger, pin 2, via D2; and charge current begins to move through R3 and R4 to Cl.

When Ul's output becomes low, the inhibiting bias on U2 pin 2 is removed, so U2 begins to oscillate, flashing the third light via Ql, at a rate determined by R8, R6, and C3. That oscillation continues until the gate-threshold voltage of SCR1 is reached, causing it to fire and pull Ul's trigger, pin 2, low.

With its trigger low, Ul's output is forced high, disabling U2's triggering. With triggering inhibited, U2's output switches to a low state, which makes Ql conduct, turning on I1 until the brakes are released. Of course, removing power from the circuit resets SCR1, but the rc network consisting of R4 and Cl will not discharge immediately and will trigger SCR1 earlier. So, frequent brake use means fewer flashes.

(Popular Electronics/Hands-on Electronics, 3/89, p. 36)


HEADLIGHT ALARM
HEADLIGHT ALARMFE8-24

The base of Q1 is connected to the car's ignition circuit, the easiest point to make that connection is at the ignition switch fuse in the car's fuse panel. Also, one side of the piezoelectric buzzer is connected to the instrument-panel light fuse; when the headlights or parking lights are on, the instrument panel is lit, too. When the headlights are off, no current reaches the buzzer. Therefore, nothing happens. What happens when the head-lights are on depends on the state of the ignition switch. When the ignition switch is on, transistors Ql and Q2 are biased on, effectively removing the buzzer and the LED from the circuit.

When, the ignition switch is turned off, but the headlight switch remains on, transistor Ql is turned off, but transistor Q2 continues to be biased on. The result is that the voltage across the piezoelectric buzzer and the LED is sufficient to cause the buzzer to sound loudly and the LED to light.

(Reprinted with permission from R-E Experimenters Handbook 1989. p. 158)


IMMOBILIZER
IMMOBILIZERFB7-2

A flip of S1 puts the circuit into action. Power for the circuit is picked up from the ignition switch,, and the circuit receives no power until the ignition switch is closed. When' power is turned on, capacitor Cl is not charged and the emitter-follower Darlington pair (formed by Ql and Q2) are cutoff, thus no power is applied to the relay (K1), which serves as Ql's emitter load. The relay's normally-open contacts are connected across the vehicle's points. (At this time, the relay contacts are open and have no effect on the ignition system). Cl charges by way of Rl, causing the voltage at the base of Ql to rise steadily. That creates a similar rise in the voltage at the emitter of Q2. A Darlington pair is used to provide a high input-impedance, buffer stage so that the voltage across C2 is free to rise almost to the full supply potential. Loading effects do not limit the charge potential to just a few volts. Eventually, the voltage applied to the relay becomes sufficient to activate it. The contacts close and short out the points. The ignition system now doesn't act properly and the vehicle is disabled. If the ignition is switched off, power is removed from the circuit and diode D1, which was previously reverse-biased, is now forward biased by the charge on Cl. D1 allows Cl to rapidly discharge through R2 (and any other dc paths across the supply lines). The circuit is ready to operate when the ignition is again turned on. The engine will operate, but not for very long. The values of R1 and Cl provides a delay of about 25 to 30 seconds. Increase Rl's value to provide a longer delay. (Hands On Electronics, 4/87, p.95)


PTC THERMISTOR AUTOMOTIVE TEMPERATURE INDICATOR
PTC THERMISTOR AUTOMOTIVE TEMPERATURE INDICATORFB7-10

The circuit is used to indicate two different water temperature trip points by turning on LEDs when the temperatures are reached. The circuit is constructed around the LM2904 dual operational amplifier powered from the 12 V auto system. The thermistor is in series with a 10 kΩ resistor from ground to the positive 9.1 V point. The top of the thermistor is tied to both non-inverting inputs of the LM2904. The voltage at these inputs will change as the thermistor resistance changes with temperature. Each inverting input on the LM2904 has a reference, or threshold trip point, set by a 10 kΩ resistor and a 2 kΩ potentiometer in series across the 9.1 V regulated voltage. When this threshold is exceeded on the non-inverting input of LM2904, the TIL220 LED lights. The two trip points can be recalibrated or set to trip at different temperatures by adjusting the 2 kΩ potentiometer in each section. In addition to being used as warning lights as shown here, circuits can be added to turn on the fan motor or activate a relay. (Texas Instruments, Linear and Interface Circuits Applications, Vol. 1, 1985, p. 3-5)


THIRD BRAKE LIGHT
THIRD BRAKE LIGHTFD11_4

The circuit is designed to light (via SCR1 and SCR2) only when both the left and right brake lights are activated.  The circuit operates on 12-V negative-ground systems. When the brake pedal is depressed, 12 V is applied to the left and right brake lights.  The gates of the two SCRs are triggered and current flows through the SCRs, which turns on the third brake light.  (Reprinted with permission from Popular Electronics, 9/89, p.22, (c) Copyright Gernsback Publications, Inc., 1989)


TURN SIGNAL ALARM
TURN SIGNAL ALARMFF12-8

This circuit can be used to tell the driver of a vehicle when his or her turn signal has been left on for too long. The circuit consists of IC1, a 555 timer; transistor Q1, and MPS3702 PNP preamp/driver; PBl, a piezoelectric buzzer; along with an assortment of resistors, capacitors, and diodes. The 555 is connected in the monostable mode, requiring only a momentary negative pulse at pin 2 to trigger the timing cycle.

Power for the circuit is picked off the flasher relay and applied to IC1, pin 8, provided by initially discharged capacitor, C2. After the initial triggering, the voltage across C2 rises as it becomes charged through R4, a 10-kΩ resistor. This prevents subsequent interference with the delay function caused by false triggering.

Capacitor C3 and resistor RI determine the delay. With the component values shown, a delay of about one minute will be provided before the intermittent tweet sound generated by the circuit begins. If higher values are used for C2 and Rl, a longer delay time result. The light-emitting diode, LED1, provides a voltage drop to assure complete transistor blocking during the off periods of the flasher. Alternatively, two diodes in series can be used.

(Reprinted with permission from Radio-Electronics, June 1984. (C)Copyright Gernsback Publications, Inc.,1984)


AUTOMOTIVE SECURITY CIRCUITS

AUTO ALARM

AUTO SECURITY SYSTEM TRANSMITTER

AUTO SIGNAL MINDER

AUTOMOTIVE BURGLAR ALARM

BACKUP BEEPER

CAR ALARM WITH HORN AS LOUDSPEAKER


AUTO ALARM
AUTO ALARMFD10-4

Sl is external key switch. The alarm allows a 0- to 45-s delay after Sl is operated before the circuit is armed. During this period, LED1 lights green. After this delay, LED1 lights red, which indicates that the circuit is armed. Then, sensors S2 through S4 -(NO) or S5 through S6 (NO) pull pin 2 of U2 low, which activates Kl and sounds the alarm. The alarm sounds for a duration determined by R4 and C2. After this time, Kl releases and the circuit is again ready. Manual reset is via the key switch, S1. (Reprinted with permission from Popular Electronics, 8/89, p. 24. (C)Copyright Gernsback Publications, Inc.,1989)


AUTO SECURITY SYSTEM TRANSMITTER
AUTO SECURITY SYSTEM TRANSMITTERFF3-2

This transmitter operates at 49 MHz and uses an M145026 programmable digital encoder to generate a unique digital code, depending on the positions of S2 and S3, to control ignition and lights or horn. Ql is the oscillator, Q2 the power amplifier. The antenna is a 36-inch whip or wire antenna. (Reprinted with permission from Popular Electronics, 10/94, p.48. (C) Copyright Gernsback Publications, Inc.,1994)


AUTO SIGNAL MINDER
AUTO SIGNAL MINDERFG30

If the ignition is on and the parking lights are on or off, the non-inverting input of Ul is at 8 volts and the inverting input is either 0 or 4 volts. That causes pin 6 to go high, keeping the buzzer off. If the ignition is off and the parking lights are on, the non-inverting input is at 0 volts and the inverting input is at 4 volts. That brings pin 6 low, activating the buzzer. With the ignition and turn signal on, and the parking lights on or off, the non-inverting input is at 8 volts and the inverting input pulses at 12 volts, causing the buzzer to sound in step with the blinker. (Popular Electronics, June 1994, pp. 22-25)


AUTOMOTIVE BURGLAR ALARM
AUTOMOTIVE BURGLAR ALARMFA1-2

Alarm triggers on after a 13 second delay and stays on for 1-1½ minutes. Then it resets automatically. It can also be turned off and reset by opening and reclosing Sl. (QST, 7/81, p. 28)


BACKUP BEEPER
BACKUP BEEPERFD10-2

When the vehicle's backup lights kick on, or when the manual switch (Sl) is closed, a small current is fed to the base of Ql. Transistor Ql allows current to flow through it and, if the enable switch (S2) is closed, it sends 12 V to Ul, a 555 timer. Timer Ul sends high pulses that last 0.977 13 s and low signals that last 0.488 565 s to the base of Q2. When Ul switches Q2 on, it sends 12 V to BZ1, a piezoelectric buzzer. For best results, the buzzer should be mounted under the vehicle-somewhere where people around the car can hear the warning beeps. (Reprinted with permission from Popular Electronics, 2/90, p. 27. (C) Copyright Gernsback Publications, Inc.,1990)


CAR ALARM WITH HORN AS LOUDSPEAKER
CAR ALARM WITH HORN AS LOUDSPEAKERFD10-6

An auto horn will work as a speaker of limited audio-frequency range. This circuit uses a 555 timer as an oscillator to drive an MJE34 transistor, which in turn drives the horn. Normal horn operation is ensured by blocking diode D4. (Reprinted with permission from Popular Electronics, 1/90. p. 25. (C)Copyright Gernsback Publications, Inc.,1990)


BATTERY CHARGERS

2.5 AMP BATTERY CHARGER IS 96% EFFICIENT

300 MA STEP DOWN BATTERY CHARGER FOR 4 CELL NICAD PACK

90% EFFICIENT CHARGER FOR 4-CELL NICAD PACK

AUTOMATIC SHUTOFF BATTERY CHARGER

BATTERY CHARGER

BATTERY CHARGER SOURCES UP TO 2.5 A

CURRENT-LIMITED 6-V CHARGER

FLOAT CHARGING CIRCUIT USES LIGHT BULBS

LOW-COST TRICKLE CHARGER FOR 12 V STORAGE BATTERY

PRECISION LITHIUM-ION BATTERY CHARGER

SINGLE-CELL LITHIUM BATTERY CHARGER


2.5 AMP BATTERY CHARGER IS 96% EFFICIENT
2.5 AMP BATTERY CHARGER IS 96% EFFICIENTFG40

Battery chargers are usually designed without regard for efficiency, but the heat generated by low-efficiency chargers can present a problem. For those applications, the charger delivers 2.5A with efficiency as high as 96%. It can charge a battery of one to six cells while operating from a battery. IC1 is a buck-mode switching regulator that controls the external power with, Ql, and the synchronous rectifier. IC1 includes a charge pump for generating the positive gate-drive voltage required by Ql. The battery-charging current develops a voltage across the 25mΩ resistor R3 that is amplified by the op amp and presented as positive-voltage feedback to IC1. This feedback enables the chip to maintain the charging current at 2.5A. While charging,, the circuit can also supply current to a separate, load, up to a limit set by the current-sense transformer, Tl, and sense resistor, Rl. It improves efficiency by lowering power dissipation in Rl. The transformer turns ratio (1:70) routes only l/70 of the total battery- plus-load current through Rl, creating a feedback voltage that enables IC1 to limit the overall current to a level compatible with the external components.

(Maxim Engineering Journal, Volume 2, p. 10)


300 MA STEP DOWN BATTERY CHARGER FOR 4 CELL NICAD PACK
300 MA STEP DOWN BATTERY CHARGER FOR 4 CELL NICAD PACKFG32

Low current battery charger circuits are required in hand-held products such as palm-top, pen-based and fingertip computers. The charging circuitry for these applications must use surface mount components and consume minimal board space. The LTC1174 circuit below provides both of these features. The LTC1174 is a current mode, step- down switching regulator with a low loss internal P-channel MOSFET power switch. In this circuit the peak switch current is programmed to 600 mA. The average charging current is determined by the choice of inductor value and the actual battery voltage, according to Equation 1. The voltage feedback resistor network is set for an output voltage of 7V. NiCd cells have a nominal voltage of 1.2V, a discharged voltage of 0.9v, and a fully charged voltage of 1.5V. A 4-cell NiCd pack's voltage will range from 3.6V to 6V, depending upon its state of charge. When it is attached to the charger it will pull the output voltage below 7V and place the LTC1174 into current-limited operation at about 300 mA with the 50μH inductor shown. Diode D2 prevents the batteries from discharging through the divider network when the charger is shutdown by bringing the SHUTDOWN pin low. Less than  l0μA of current is drawn from the supply when shut down. (Linear Technology Power Solutions, 1996, p. 6)


90% EFFICIENT CHARGER FOR 4_CELL NICAD PACK
90% EFFICIENT CHARGER FOR 4-CELL NICAD PACKFG38

An embedded battery charger requires extremely low power dissipation in order to minimize heat build-up in compact portable systems. The schematic below shows a charger that can charge four NiCd cells and is selectable for either 1.3A fast charge or l00 mA trickle charge with up to 90% efficiency. The LTC1148 is a step-down synchronous switching regulator; it controls the charge rate, monitoring the output current via external current-sense resistor R3. Fast charge current is determined by the value of R3 according to the FAST CHARGE equation. In this case it is set to 1.3A. Resistor divider network R4 and R5 sets the output voltage to a nominal 8.1V under no-load conditions, such as when the battery is removed. A 4-cell NiCd pack's voltage will range from 3.6V to 6V depending upon its state of charge. When installed, the battery will pull the output below 8.1V and place the LTC1148 into current-limited operation at 1.3A. This constant current will be delivered until trickle charge is enabled by an external charge termination circuit or the battery is removed. Q3 enables trickle charge operation with charge current set by choice of Rl. Diode D2 prevents the battery from being drained by the feedback resistor network when the LTC1 148 is shut down.

(Linear Technology Power Solutions, 1996, p. 7)


AUTOMATIC SHUTOFF BATTERY CHARGER
AUTOMATIC SHUTOFF BATTERY CHARGERFA11-5

Adjust by setting the 500 ohm resistor while attached to a fully charged battery. (73 Amateur Radio Today, 7/77)


BATTERY CHARGER
BATTERY CHARGERFD13-2

This high-performance charger quickly charges gelled lead-acid batteries, and turns off at full charge. At first, the charge current is held at 2 A, but as battery voltage rises, current decreases. When current falls to 150 mA, the charger automatically switches to a lower float voltage to keep from overcharging. When you hit full charge, transistor Ql lights the LED to indicate that status. (Hands-On Electronics, 11/87, p.92)


BATTERY CHARGER SOURCES UP TO 2.5 A
BATTERY CHARGER SOURCES UP TO 2.5 AFG37

This current-source battery charger can source 2.5 A with up to 96% efficiency. It can operate from an ac adapter or directly from a car battery. By sensing current on the high side of the battery being charged, it presents the low impedance of the automobile's ground-return system. The charger handles battery stacks of five to 15 cells, and its input voltage can range from 28 V down to a level 1.5 V above the terminal voltage of a fully charged battery. Charging current is generated by the current-mode, buck-regulator controller IC1, operating with an external power switch (Ql) and a synchronous rectifier (Q2). Both are n-channel MOSFETS, whose low on-resistance (vs. p-channel types) contributes to high efficiency in the circuit. The IC includes a charge pump for generating the required positive gate voltage for Ql. It also senses the Ql current (via Rl) and shuts down if this current becomes. excessive. The current-sense transformer Tl saves power by diverting a fraction of Ql's current through Rl. Operating on the output's high side is the current-sense amplifier IC2. Its OUT current (1/2000 of the current flowing internally from RS+ to RS-) flows through R2 to produce a feedback signal for IC1. Digital control of the charging current can be introduced by switching among different-switching FET like the 2N7002 ; its 7.5 ohm on-resistance is not a problem because its drain current-no greater than 1.25 ma-introduces an error no greater than 0.5%. Circuit efficiency ranges up to 96%. Efficiency and power output both increase with output voltage since the circuit's power consumption (associated mainly with ICl and the switching MOSFETs) is almost constant. This buck regulator's output cannot. rise about Vin; in most cases, over-voltage protection is not required. Vout, which supplies power to IC2, must not go below 4 V.

(Electronic Design, June 10, 1996, p. 108)


CURRENT-LIMITED 6-V CHARGER
CURRENT-LIMITED 6-V CHARGERFD13-3

An LM317HV regulator is used as a current-limited charger. If current through R4 exceeds 0.6, Ql is biased on, which pulls the ADJ terminal of the LM317 HV to ground and reduces the battery- charging current. (Reprinted with permission from Popular Electronics, Fact Card No. 134. Copyright Gernsback Publications, Inc)


FLOAT CHARGING CIRCUIT USES LIGHT BULBS
FLOAT CHARGING CIRCUIT USES LIGHT BULBSFG36

To float-charge a 12-volt lead-acid battery, all you need is an accurately regulated 13.8- volt power supply. You could connect the power supply directly to the battery, but it is safer to make the connection through a couple of 12-volt, 1-amp automotive light bulbs. The light bulbs serve as current limiters; they guarantee that no matter what happens, the power supply will never have to deliver more than 2 amps. Resistors can also serve as current limiters, but light bulbs are better because their resistance varies with current in a useful way. It's nearly zero at low current, but as the current through each bulb approaches 1 amp, the bulb lights up and the resistance increases. Thus, the bulb limits the current but doesn't waste energy when the current is low. This setup is a good way to power a heavy load that operates intermittently, such as a ham radio transmitter. The battery delivers heavy current when necessary, and the power supply keeps the battery charged up. (Electronics Now, September 1995, p. 8)


LOW-COST TRICKLE CHARGER FOR 12 V STORAGE BATTERY
LOW-COST TRICKLE CHARGER FOR 12 V STORAGE BATTERYFA11-13

Charge rate can be varied and is based on the size of bulb. (William Sheets)


PRECISION LITHIUM-ION BATTERY CHARGER
PRECISION LITHIUM-ION BATTERY CHARGERFG31

An alternative to using expensive 0.25% precision resistors is presented in this battery-charger design, which adds two 1% resistors and two jumpers to the charger. In constant-voltage mode charging, a lithium-ion cell requires 4.1 V ±50 mV. The 1.2% requirement represents a tight tolerance. In a regulation loop where a voltage divider is compared against a reference, the accuracy is typically achieved by selecting a 0.7% reference and a voltage divider with 0.25% tolerance resistors. Unfortunately, 0.25% precision resistors cost three times as much as 1% resistors and have very long lead times. One solution for moderate volume production involves adding two 1% resistors and two jumpers to the charger circuit (see the figure). The jumpers are removed as necessary to bring the constant voltage to the required accuracy of 1.2%. The charger selected for this example is the LT1510. Three lithium-ion cells are in the battery. After selecting a value for R4, the values for Rl, R2, and R3 can be calculated using the equations given. K is the relative change required for a circuit with all of its tolerances in one direction. For example, in the case of a 0.5% reference and two 1% resistors, the total tolerance is 2.5%. To bring it back to 1.2%, the percentage change required is 2.5% - 1.2% = 1.3%, and K = 0.013. The jumpers (J1 and J2) must be opened based on the following:

o If Vout is K/2 below nominal, remove J1.

o If Vout is K/2 above nominal, remove J2.

The following values were calculated: Rl = 4.99k, R2 = 324, R3 = 80.6, and R4 = 20k. The voltage below which jumper Jl should be opened is 12.34 V -1.3%/2 = 12.22 V. The voltage above which jumper J2 should be opened is 12.34 V + 1.3%/2 = 12.42 V.

(Electronic Design, September 3, 1996, p. 102)


SINGLE-CELL LITHIUM BATTERY CHARGER
SINGLE-CELL LITHIUM BATTERY CHARGERFF13-4

An LP2951 regulator was chosen for this single lithium cell-charging circuit for its built-in current-limiting capability. In addition, the regulator's output voltage is extremely stable, which is a prerequisite for lithium battery charging. This figure details an example circuit designed to recharge a single cell. The required output set voltage was specified as 4.200 V (±0.025 V) with a maximum charging current of about 150 mA.

An LP2951 regulator was selected for two reasons. One is that its built-in current limiter holds the maximum current to 160 mA (typical). The other is because the output voltage can be very accurately set to 4.200 V, thanks to the regulator's stable internal bandgap reference.

The 1.23-V reference appears between the feedback pin and ground, which causes a precise current to flow in the output resistive-divider string. The amount of current flowing in these resistors determines (sets) the charger output voltage that appears across the battery terminals. Large-value resistors keep the battery drain below 2 μA when the dc input is removed (a customer requirement). A trimming potentiometer sets the output to 4.200 V. It must be adjusted when the battery isn't connected to the charger output. A blocking diode is required at the LP2951's output to prevent current from flowing out of the battery and back into the output when the dc-input source is removed. Because the diode is in series with the output, the minimum input-output voltage differential required for this circuit to operate is about 1.5 V.

(Reprinted with permission from Electronic Design 6/94, pp. 42-43, Copyright 1994 Penton Publishing)


BATTERY TEST AND MONITOR CIRCUITS

BARGRAPH LED BATTERY TESTER

BATTERY IMPEDANCE MEASUREMENT

INTERNAL RESISTANCE BATTERY TESTER

LEAD/ACID LOW-BATTERY DETECTOR

LITHIUM MEMORY BACKUP BATTERY REPLACEMENT

LOW BATTERY DETECTOR CONTROLS BOOST REGULATOR

LOW-BATTERY INDICATOR

LOW-BATTERY PROTECTOR

NICAD BATTERY CYCLERNI-CAD BATTERY ZAPPER II

NI-CAD BATTERY ZAPPER III

TRI COLOR LED NICAD CHECKER

UNDERVOLTAGE INDICATOR FOR SINGLE CELL


BARGRAPH LED BATTERY TESTER
BARGRAPH LED BATTERY TESTERFE10-11

The LM3914A bargraph LED is used here as a voltmeter for battery testing. The circuit is powered by a 4.5-V battery and compares the battery under test with an internally derived reference, set by R1/R2/Pl. Each LED of the 10 represent 10% of full scale. For best results, the battery (D.U.T) should be loaded with an appropriate resistor. (Reprinted with permission from Elektor Electronics USA, 12/91, p. 36)


BATTERY IMPEDANCE MEASUREMENT
BATTERY IMPEDANCE MEASUREMENTFG43

By applying an ac voltage superimposed on a ten-times larger negative dc voltage (at VFG), the function generator determines the battery current drawn by Ql (see the figure). The generator voltage cause the op-amp (IC2) output to go high and turn Ql on, which allows battery current to flow through the high-side current-sensing amplifier IC1. The output current of IC1, on pin 8, is equal to 1/2000th of this battery current. As a result, IC1, IC2, and Ql form a loop in which the op amp forces a virtual ground at the lCl/IC2 end of R3. The op-amp's extremely low-voltage offset (10 μV maximum) ensures, accuracy. This virtual-ground condition enables the voltage divider (R5, and R3 paralleled with R4) and the function generator to determine the voltage across R3. The resulting current in R3 is: iR3 = RP X VFG/[{RP + R5}R3], where RP is the parallel combination of R3 and R4. Substituting resistor values and noting that battery current (iB) is 2000 times iR3: iB = -VFG/5. To operate the circuit, set the function generator's ac voltage to approximately 10% of its dc component. The equation then gives the resulting ac current in the battery (iB). Using an ac voltmeter, you can measure the ac voltage across the battery (vB) and calculate the average cell impedance as vB/(NiB), where N is the number of cells. The circuit easily accommodates battery voltages of 3 V or more. (Electronic Design Analog Applications, June 24, 1996, pp. 72-74)


INTERNAL RESISTANCE BATTERY TESTER
INTERNAL RESISTANCE BATTERY TESTERFD14-1

A designer often needs to know the value of the internal resistance of a battery. Quite a few testers give a relative indication of the value, but this is seldom in ohms. The present tester can, in principle, provide that information.

The basic idea behind it is to load the battery with a varying current, so as to cause an alternating-voltage drop across the internal resistance that can be measured at the battery terminals. Provided that current variations are regular and constant, the voltage drop is directly proportional to the internal resistance.

Choose the variation of the current carefully to read the value of the internal resistance directly on the scale of an ac voltmeter.

The load current is varied with the aid of a current source, Tl in the diagram, which is switched on and off by square-wave generator IC1. The chosen switching frequency of 50 Hz ensures that the ac component at the battery terminals can be measured by a standard ac voltmeter (universal meter).

The battery is loaded constantly by R8, which has a value of 1.5 Ω for 1.5-V batteries, shunted by the ac voltmeter. The indicated voltage times 10 is the value of the internal resistance of the battery. When the battery under test is flat or if the supply battery is flat, no current flows and the meter will read zero. It would then appear as if the battery under test is an ideal type--without internal resistance.

A flat supply battery is indicated if D1 does not light. You can ascertain that the battery under test is flat by measuring the direct voltage across its terminals. The load must be left connected, of course, otherwise the emf is measured and this may well be 1.5 V-even if the battery is flat.

The tester is calibrated with the aid of the auxiliary circuit (shown at the extreme right in the circuit diagram). The 1.5-V supply and electrolytic capacitor form a virtually ideal voltage source, of which the 3.9Ω resistor forms the internal resistance. With this source connected across the output terminals of the tester, a suitable value should be ascertained for R7. That value is found when the ac voltmeter shows 0.39V. Notice that this procedure is not the same for all measuring instruments: the alternate use of the digital and a moving coil meter, for instance, is not feasible.

The tester is intended for 1.5-V batteries. The load current is fairly high: about 100 mA through R8 and around 170 mA through T1. For 9-V batteries that current is too high: the current should then be reduced by taking greater values for R6 through R8.

(Elektor Electronics, 12/90, p. 519)


LEAD/ACID LOW-BATTERY DETECTOR
LEAD/ACID LOW-BATTERY DETECTORFC9-3

(Linear Technology Corp. Linear Databook, 1986, p. 4-15)


LITHIUM MEMORY BACKUP BATTERY REPLACEMENT
LITHIUM MEMORY BACKUP BATTERY REPLACEMENTFF14-8

Physically very small high-capacitance capacitors are available for memory backup. Here, a 0.1-F (100,000 μF) capacitor and two diodes replace the lithium battery. The lithium battery can be retained as well, providing double backup. (QST, 10/94, p.75)


LOW BATTERY DETECTOR CONTROLS BOOST REGULATOR
LOW BATTERY DETECTOR CONTROLS BOOST REGULATORFG44

Low voltage cutoff is desirable in battery-operated systems to prevent deep discharge damage to the battery. The LT1304 micropower boost regulator contains a low-battery detector which is active even when the regulator is shut down. The output of the detector controls both the LTC1477 and the LT1304 5V boost regulator. In this application the LTC1477 serves to protect against short circuits (850 mA limit selected) and completely disconnects the load under a low-battery condition. In shutdown, the circuit draws less than 25μA from the battery. (Linear Technology Design Note 117)


LOW-BATTERY INDICATOR
LOW-BATTERY INDICATORFD14-8

The sensing circuit consists of a 741 op amp set up as a voltage comparator, using a zener diode as a voltage reference. The op amp is inserted as a bridge between two resistance ladders, one which contains the zener reference, and the other a high-value linear potentiometer. When the voltage at the wiper of the potentiometer drops below the voltage set by the zener, the output of the op amp becomes low; that turns on the LED connected between it and Vcc. The circuit can be adapted to work with battery-powered circuits that require between 6 and 18 V; the only changes needed would be a lower-voltage zener and a smaller current-limiting resistor in the case of voltage below 9 V, and a larger resistor for higher voltages. (42 New Ideas, 1984, p. 14, Gernsback Publications, Inc)


LOW-BATTERY PROTECTOR
LOW-BATTERY PROTECTORFC10-8

To prevent battery damage due to over-discharge, a low-voltage detector and switch should be included in the design of the battery backup circuit. The detector circuit should consume extremely low current. The switch should exhibit a low-voltage drop and be easy to control.

R1 and D2 provide a trickle charge for the battery. Chosen for its low forward voltage drop, Schottky diode D3 prevents forward polarization of the diode incorporated in Ql. When the battery voltage is above approximately 8 V, the output of Ul is low and Ql is turned on. If the battery voltage falls below 8 V, the output of Ul increases and turns off Ql.

(Motorola Inc., Motorola TMOS FET Design Ideas, 1985, p. 6)


NICAD BATTERY CYCLER
NICAD BATTERY CYCLERFG42

The Battery Cycler works with NiCd configurations between three and nine cells. Cell combinations are accommodated by selecting Zl, K1, and R3, based upon the numberof cells in the battery pack. It is basically a voltage comparitor (Ul), voltage reference(Zl) and a switch (Ql and K1). The op-amp (Ul) compares the reference voltage generated by the zener diode (Z1) and the battery. When the battery voltage matches or is less than the reference, the switch is turned off and the battery is allowed to charge. While the battery voltage is above the reference voltage, it is discharged through resistor R3. The resistor has been selected to discharge the battery at a rate between 200 and 300 mA. This rate keeps the power dissipation in R3 below three watts and reduces the risk of opening any fuses in the battery circuitry located in the portable equipment. The push-button switch Sl initiates the discharge process. If the battery voltage is below the reference when Sl is pressed, the unit will not discharge the battery as the lower operating limit of the battery has already been exceeded. If your batteries are in this condition, charge them for 18 hours and measure the voltage. If the batteries are still below the cut-off voltage, there is a problem with one or more cells in the battery pack. (Nuts and Volts Magazine, November 1994, p. 125)


NI-CAD BATTERY ZAPPER II
NI-CAD BATTERY ZAPPER IIFB8-6

This zapper clears internal short in nickel cadmium batteries by burning it away. CAUTION: The negative battery terminal is connected to one side of the ac line. For safety operation use a 1:1 isolation transformer. (William Sheets)


NI-CAD BATTERY ZAPPER III
NI-CAD BATTERY ZAPPER IIIFB8-3

The short in a Ni-Cad battery can be burned off with this zapper. Use of the SCR keeps heavy discharge current from damaging switch contacts. (William Sheets)


TRI COLOR LED NICAD CHECKER
TRI COLOR LED NICAD CHECKERFG41

This circuit uses a window comparator and a bi color LED. VRl and VR2 set the high and low trip points of the comparators, respectively. The LED shows green for highest voltage (good), yellow for intermediate, and red for low voltage (bad). The circuit can be calibrated for other voltages and is generally useful as a voltage indicator. (Everyday Practical Electronics, March 1997, p. 180)


UNDERVOLTAGE INDICATOR FOR SINGLE CELL
UNDERVOLTAGE INDICATOR FOR SINGLE CELLFF14-3

When operating with a single cell, it is necessary to incorporate switching circuitry to develop sufficient voltage to drive the LED. A circuit that accomplishes this is drawn in the figure shown. Basically, it is a voltage-controlled asymmetrical multivibrator with minimum operating threshold given by:

Vth   =    R4(R1+R2)   Vref

        R1(R3+R4)

Above this threshold, flash frequency increases with voltage. This is a far more noticeable indication of a deteriorating battery than merely dimming the LED. In addition, the indicator can be made visible with considerably less power drain. With the values shown, the flash rate is 1.4 sec -1 at 1.2 V with 300-μA drain and 5.5 sec -1 at 1.55 V, with 800-μA drain. Equivalent visibility for continuous operation would require more than 5-mA drain.

(Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 499)


BUFFER CIRCUITS

10 X BUFFER AMPLIFIER

100 X BUFFER AMPLIFIER

HI-Z MICROPHONE BUFFER AMPLIFIER

INVERTING BISTABLE BUFFER

SIMPLE BIDIRECTIONAL BUFFER DESIGN

SIMPLE VIDEO BUFFER

SINGLE-SUPPLY ac BUFFER AMPLIFIER


10 X BUFFER AMPLIFIER
10 X BUFFER AMPLIFIERFA13-8

(Reprinted with permission of National Semiconductor Corporation, Linear Databook 1982, p. 3-324)


100 X BUFFER AMPLIFIER
100 X BUFFER AMPLIFIERFA13-7

(Reprinted with permission of National Semiconductor Corporation, Linear Databook 1982, p. 3-324)


HI-Z MICROPHONE BUFFER AMPLIFIER
HI-Z MICROPHONE BUFFER AMPLIFIERFF16-2

A low impedance output from a high-Z microphone can be obtained with this circuit. No voltage gain is obtained, but a power gain is obtained because the output impedance is much lower (300 ohms), with -6-dB voltage gain. (William Sheets)


INVERTING BISTABLE BUFFER
INVERTING BISTABLE BUFFERFD17-3

This circuit uses a 555 timer as a flip-flop bistable buffer. (Hands On Electronics, Fact Card No. 89)


SIMPLE BIDIRECTIONAL BUFFER DESIGN
SIMPLE BIDIRECTIONAL BUFFER DESIGNFF16-8

This circuit shown in the figure uses two 74LS241s. When both input/output lines are high, IC-1A and IC-2B turn on, and Cl and C2 are charged to high voltage. Meanwhile, IC-1B and IC-2A are off to prevent a logic "1" latch. (Reprinted with permission from Electronic Design 8/94, p 104, Copyright 1994 Penton Publishing)


SIMPLE VIDEO BUFFER
SIMPLE VIDEO BUFFERFE11-6

This simple emitter follower can be used as video buffer. (Reprinted with permission from Electronics Now, 9/92, p. 96. (c) Copyright Gernsback Publications, Inc., 1992)


SINGLE-SUPPLY ac BUFFER AMPLIFIER
SINGLE-SUPPLY AC BUFFER AMPLIFIERFF16-5

This buffer might be used with a single supply without special considerations. The input is dc biased to mid-operating point and is ac coupled. Its input impedance is approximately 500 kΩ at low frequencies. Note that for dc loads referenced to ground, this quiescent current is increased by the load current set at the input dc bias voltage. (Reprinted with permission of National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 542)


BUGGING CIRCUITS

LOW POWER FM TELEPHONE BUG

TELEPHONE BUG


LOW POWER FM TELEPHONE BUG
LOW POWER FM TELEPHONE BUGFG45

Q1 is an oscillator tuned to a quiet spot in the FM broadcast band. Dl through D4 ensure proper polarity. Dc from the line powers the bug. Audio on the line causes incidental FM, which can be heard on an FM receiver tuned to the frequency of the oscillator. WARNING: Use of this device for certain Purposes may violate Federal and/or State laws and subject the violator to prosecution. (Nuts and Volts Magazine, January 1995, p. 111)


TELEPHONE BUG
TELEPHONE BUGFG46

Q1 is an oscillator tuned to a quiet spot in the FM broadcast band, DC from the line powers the bug. Diodes Dl-D4 assure proper polarity. Rl maintains a suitable voltage drop for the bug. Audio on the line causes incidental FM, which can be heard on an FM receiver tuned to the frequency of the oscillator.

WARNING: Use of this device for certain purposes may violate Federal and/or State laws and subject the violator to prosecution. (Nuts and Volts Magazine, January 1995, p. 112)


CARRIER CURRENT CIRCUITS

CARRIER CURRENT TRANSMITTER FOR DATA TRANSMISSION

CARRIER SYSTEM TRANSMITTER

CARRIER-CURRENT RECEIVER FOR DATA TRANSMISSION


CARRIER CURRENT TRANSMITTER FOR DATA TRANSMISSION
CARRIER CURRENT TRANSMITTER FOR DATA TRANSMISSIONFD18-1

f1 =     1

         R3Cl

f2 =f1 + Δf

where:

Δf =    1

          R4Cl

In this circuit, data at input C is amplified by IC2 and then fed to modulator IC1. IC1 generates two frequencies, depending on the values of C5, Rl0, R3, Rll, and R6. The frequency f, is generated if pin 9 of IC1 is low and f2 if pin 9 of IC1 is high. A square wave appears at pin 13 of IC1 and is fed to Ql, an amplifier stage, that is coupled via tuned transformer T, to the ac line via Cl and C2. Notice that, for safety reasons, Cl and C2 must be specifically rated for the ac line voltage.

(Reprinted with permission from R-E Experimenter's Handbook, 1990, p. 158. Copyright Gernsback Publications, Inc., 1990)


CARRIER SYSTEM TRANSMITTER
CARRIER SYSTEM TRANSMITTERFA15-1

The receiver amplifies, limits, and demodulates the received FM signal. It provides audio mute in the absence of carrier and 2.5 W ouput to a speaker. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1982, p. AN146-1)


CARRIER-CURRENT RECEIVER FOR DATA TRANSMISSION
CARRIER-CURRENT RECEIVER FOR DATA TRANSMISSIONFD18-2

Receive frequency:

fo=1/(R27 + R32) C33

This receiver consists of an input network amplifier IC7 FSK PLL detector ICG, and output amplifier/ interface Q2, Q3, IC3A and IC3B, a 1488 Quad RS232 line driver of the carrier-current signal. Tuned amplifier IC7 amplifies this signal and drives PLL detector IC8. The values shown in the circuit are suitable for operation in the 100-kHz range. Recovered data at pins 5, 6, 7 is fed to the output amplifier/interface circuit. This circuit is also used with the carrier-current data transmitter to form a pair.

(Reprinted with permission from R-E Experimenter's Handbook, 1990, p. 162. Copyright Gernsback Publications, Inc., 1990)


CLOCK CIRCUITS

60 Hz CLOCK PULSE GENERATOR

LOW-FREQUENCY CLOCK

SET TIME WINDOWS WITHIN A CLOCK

SIMPLE 5.2 KHZ CLOCK

SINGLE OP AMP CLOCK


60 Hz CLOCK PULSE GENERATOR
60 Hz CLOCK PULSE GENERATORFB14-2

The circuit provides a clean, stable square wave and it will operate on anywhere from 6 to 15 volts. The IC and color-burst crystal are the kind used in TV receivers. The 3.58 MHz output makes a handy marker signal for shortwave bands. (Hands-On Electronics, Nov/Dec 1985, p. 4)


LOW-FREQUENCY CLOCK
LOW-FREQUENCY CLOCKFF17-2

The LM3090 is an LED flasher IC that is designed to oscillate at low frequencies. The clock output of the first circuit can be changed by changing the value of the capacitor, and the second circuit lets you adjust the frequency with the trimmer Bl can be one or two alkaline 1.5-V cells. The LM3909 can supply up to 45-rnA pulses at greater than 2 V. (Reprinted with permission of Electronics Now, 3/95, p. 8, Copyright Gernsback Publications, Inc., 1995)


SET TIME WINDOWS WITHIN A CLOCK
SET TIME WINDOWS WITHIN A CLOCKFF17-1

At times, it is necessary to produce pulses of adjustable width and whose start times might vary with reference to a master clock. The input signal is inverted and buffered by UlA, while UlB and UlC reinvert the signal to produce square, buffered renditions of the input signal. Potentiometers R3 and R4 set references for the comparators.

The input polarity of U2A keeps its output transistor turned on until the voltage at the noninverting input exceeds the reference set bv R4 (the rising edge adjustment). When this reference voltage is exceeded, the output transistor is turned off and the output, signal is pulled up via R6, Meanwhile, the input polarity of U2B keeps its output, transistor off until the voltage at the inverting input exceeds the reference set by R3 (the falling edge adjustment). When this reference voltage is surpassed, the output transistor of U2B is turned on, pulling the output signal low through the wired-OR configuration of U2. The output of U2 is then double inverted and buffered by UlD and UlE. What results is a pulse whose start time (rising edge) can be adjusted by R4, and whose stop time (falling edge) can be adjusted by R3.

The output of the comparators is pulled up to the input waveform through resistor R6 to UlC. This prevents the comparators from switching during the low cycle of the input waveform, regardless of the positions of R3 and R4. This has the effect of "locking out" changes during the low period of the input signal, and would probably require additional logic if it were done strictly in the digital domain. The circuit, with the component values shown, works well between about 50 and 150 kHz.

(Reprinted with permission from Electronic Design 11/94, p 115, Copyright 1994 Penton Publishing Inc)


SIMPLE 5.2 KHZ CLOCK
SIMPLE 5.2 KHZ CLOCKFG47

This circuit will produce a clock signal of 5.2 kHz, using a NE555 timer. (Electronics Now, November 1995, p. 33)


SINGLE OP AMP CLOCK
SINGLE OP AMP CLOCKFC15-3

Capacitor Cl is charged through timing resistor R1 when the clock output is high. When Cl reaches the upper threshold voltage, the output signal decreases, and then Cl discharges through R1 until its voltage reaches the lower threshold point. When this happens, the output increases again and the cycle repeats itself. Using the parts values shown results in a frequency of 1 Hz. The output frequency can be adjusted by trimming the value of R1 slightly. (TAB Books, 44 Electronics Projects for the Darkroom, p. 101)


CODE PRACTICE CIRCUITS

CODE PRACTICE OSCILLATOR

CODE PRACTICE OSCILLATOR USES OPTOISOLATOR

CRYSTAL CONTROLLED CODE PRACTICE TRANSMITTER

MORSE CODE OSCILLATOR

TOUCH OPERATED CODE PRACTICE OSCILLATOR


CODE PRACTICE OSCILLATOR
CODE PRACTICE OSCILLATORFE14-5

 The tone and volume of the sound produced when the telegraph key is depressed can be varied in this code practice oscillator. (William Sheets)


CODE PRACTICE OSCILLATOR USES OPTOISOLATOR
CODE PRACTICE OSCILLATOR USES OPTOISOLATORFE14-1

A slotted pair isolator (A) is effectively an enclosed-pair isolator with a slit that will allow an obstacle to interrupt the light path. That could be useful for building a code key  (B). (Reprinted with permission from 73 Amateur Radio Today, 5/92, p. 20)


CRYSTAL CONTROLLED CODE PRACTICE TRANSMITTER
CRYSTAL CONTROLLED CODE PRACTICE TRANSMITTERFG49

When the CW key is closed, ICl-a's output goes high allowing ICl-b and ICl-c to oscillate. The crystal supplies the feedback path setting the oscillator's operating frequency. The circuit will operate on the 40- and 80-meter bands. Section IC1-d isolates the oscillator from the short antenna, ANT1. A clip lead should do here to get the signal out and about for operation. Tune your ham-band receiver to the crystal's frequency and key down. If the receiver doesn't have a CW mode, turn on the BFO and tune for the desired CW tone. (Popular Electronics, April 1997, pp. 66-67)


MORSE CODE OSCILLATOR
MORSE CODE OSCILLATORFG50

The circuit is built around a 555 oscillator (ICl) and an LM386 audio amplifier (IC2). The 555 circuit is an astable oscillator, with the chip output retriggering the circuit. When the key (S1) is pressed, it activates the circuit. The 555 oscillates at a frequency determined by Rl, R2, and Cl. Potentiometer R2 is used to adjust the tone frequency of the oscillator. Some of the output current of IC1 is coupled to IC2 via a 10 μF capacitor, C2, so that it will be sufficient to drive a loudspeaker. Because the circuit has no gain control, the volume depends on the size and wattage of the speaker. (Popular Electronics, July, 1996, p. 65)


TOUCH OPERATED CODE PRACTICE OSCILLATOR
TOUCH OPERATED CODE PRACTICE OSCILLATORFG48

A touch-operated CPO is shown in the figure. The gates of ICl-a are biased high through the two 22-megohm resistors (Rl and R2) keeping its output in the low state. Gates ICl-b and ICl-c are connected in an audio oscillator circuit that can only operate when pin 5 of ICl-b is high. The last gate of the 4093, ICl-d, adds isolation to the oscillator's circuit and drives the speaker (SPKR1). Touching the key paddle and ground plane lowers ICl-a's input gate voltage to near zero, allowing the output at pin 3 to go high. The tone generator then turns on and sends out an audio note. The touch key paddle and ground plane can be made from a circuit board or any other conductible material. Note that the ground plane should lie flat for a hand rest and the key paddle should be positioned for ease of touch, (Popular Electronics, April 1997, p. 65)


COMPARATOR CIRCUITS

DEMONSTRATION COMPARATOR CIRCUIT

HIGH IMPEDANCE COMPARATOR

LIMIT COMPARATOR

MICROVOLT COMPARATOR WITH HYSTERESIS

VOLTAGE COMPARATOR

VOLTAGE MONITOR/COMPARATOR


DEMONSTRATION COMPARATOR CIRCUIT
DEMONSTRATION COMPARATOR CIRCUITFB15-11

This circuit is an op amp without a feedback resistor. R2 and R3 junction point sets the reference voltage. When the input voltage set by Rl is below the reference voltage, the LED glows. If voltage is above reference, the LED goes off. (Popular Electronics, 3/79, p. 77)


HIGH IMPEDANCE COMPARATOR
HIGH IMPEDANCE COMPARATORFA16-21

(Harris Semiconductor, Linear & Data Acquisition Products, p. 2-46)


LIMIT COMPARATOR
LIMIT COMPARATORFB15-3

(Signetics, 1987 Linear Data Manual Vol. 2: Industrial, 11/86, p. 5-269)


MICROVOLT COMPARATOR WITH HYSTERESIS
MICROVOLT COMPARATOR WITH HYSTERESISFC16-2

Positive feedback to one of the nulling terminals creates approximately 5 μV of hysteresis. The output can sink 16 mA; the input offset voltage is typically changed less than 5 μV because of the feedback. (Linear Technology, 1986 Linear Databook, p. 2-44)


VOLTAGE COMPARATOR
VOLTAGE COMPARATORFG51

The LED turns on when the input voltage at pin 5 of the LM339 falls below the reference voltage pin 4. (Electronics Now, July 1995, p. 8)


VOLTAGE MONITOR/COMPARATOR
VOLTAGE MONITOR/COMPARATORFB15-2

A portion of the monitored voltage (determined by Rl's adjustment) is compared to a fixed voltage obtained from a zener reference network, R2-D1. As long as the monitored voltage remains at or above its present monitor point (determined by Rl's setting), the output indicator, LED1, remains dark. If the voltage drops below this level, the LED goes on. D1 is a 3.3-V zener. A 12 Vdc power supply is suitable for monitoring input voltages of up to 12 volts. (Popular Electronics, 9/77, p. 92)


COMPRESSOR/EXPANDER CIRCUITS

HI-FI EXPANDER WITH DE-EMPHASIS

LOW-VOLTAGE COMPANDER


HI-FL EXPANDER WITH DE-EMPHASIS
HI-FI EXPANDER WITH DE-EMPHASISFC17-4

The expander to complement the compressor is shown. An external op amp is used for high slew rate. Both the compressor and expander have unity gain levels of 0 dB. Trim networks are shown for distortion (THD) and dc shift. The distortion trim should be done first, with an input of 0 dB at 10 kHz. The dc shift should be adjusted for minimum envelope bounce with tone bursts. When applied to consumer tape recorders, the subjective performance of this system is excellent. (Signetics, RF Communications Handbook, 1989, p. 2-17 and 2-18)


LOW-VOLTAGE COMPANDER
LOW-VOLTAGE COMPANDERFC17-1

The NE575 is a dual-gain control circuit designed for low voltage applications. The NE575's channel 1

 is an expander, while channel 2 can be configured either for expander, compressor, or automatic level controller (ALC) applications. (Signetics, 1987 Linear Data Manual Vol., 1, Communications, 2/87, p. 4-373 and 4-375)


COMPUTER CIRCUITS

3 WIRE RS-232 TO RS-485 CONVERTER

5V SUPPLY FROM 3 WIRE RS232 PORT

EEPROM PROGRAMMING DOUBLER CIRCUIT

JOYSTICK CHANGEOVER

PRINTER PORT D/A CONVERTER

RESET PROTECTION FOR COMPUTERS

RS-232-TO-CMOS LINE RECEIVER

RS-422 TO RS-232 CONVERTER

RS232 TEST CIRCUIT

RS232 TO PARALLEL DATA CONVERTER

SERIAL TRANSMITTER CIRCUIT

ULTRA SIMPLE RS232 TESTER

VPP GENERATOR FOR EPROMS

WATCHDOG FOR PCs


3 WIRE RS-232 TO RS-485 CONVERTER
3 WIRE RS-232 TO RS-485 CONVERTERFG56

This circuit needs only a minimal "3-wire" RS232 implementation plus one +10-V to +15-

V supply voltage to provide a transparent link capable of sending data at transmission rates up to tens of kbaud. Circuit operation is as follows: when both 232 and 485 are idle (232 port in MARK state and no 485 device active), the 485 link is held in the "1" state by the 1200-Ω pullup. This causes the top comparator to hold the 232 RCD line negative and therefore in "MARK" state. When a character is transmitted by the 232 port, it begins with a positive-going (SPACE: state) "START" bit on the TXD line, In response the 2N4401 pull  the "-" 485 conductor more positive than the "+" wire, thus transmitting the "START" down the 485 cable. Meanwhile, the bottom comparator holds the "wire-or" (LM393s have open collector outputs ) 232 RCD low, blocking the 232 port from "hearing" its own transmission. The receive side of the 232 port remains idle. The rest of the bits of the character follow along in the same fashion. When a character originates somewhere along the 485 bus. it begins with a 485 transceiver going active and driving the "-" line above "+". This causes the upper half of the LM393 comparator to release RCD and this time the bottom comparator doesn't prevent it from being pulled high. The data bits are thus allowed to arrive at the RS232 port where they appear at standard RS232 bipolar voltage levels, The common mode voltage range and noise rejection capabilities of this circuit are compatible with standard 485 specifications. The converter's speed is mainly limited by loading the comparator outputs due to cable capacitance. (Electronic Design, June 10, 1996, p. 106)


5V SUPPLY FROM 3 WIRE RS232 PORT
5V SUPPLY FROM 3 WIRE RS232 PORTFG60

This circuit produces a semi-regulated 5V output from an RS-232 port. The output current - about 8mA - is sufficient for CMOS microcontrollers and other low-power circuits. IC1 is a switched-capacitor, charge- pump voltage converter that can either invert an input voltage or double it. The connections shown provide a doubler configuration in which the normal input-voltage is reversed: a positive input voltage normally connects between GND and OUT, but this circuit connects a negative input between OUT and GND. The IC then doubles the negative VIN in the positive direction, producing a positive output (at VDD) equal to [VIN]. The zener diode Dl acts as a shunt regulator that "semi-regulates" VIN to -5V (actually to -4.7V). The 33μF capacitor values shown are larger than normal, to support the output voltage during worst-case (all-zero) patterns of transmission. At 9600 baud, for example, an all-zeros character causes an output droop of about 0.2V. For lower baud rates, substitute a proportionally higher value for Cl. (Maxim Engineering Journal, Volume 23, p. 13)


EEPROM PROGRAMMING DOUBLER CIRCUIT
EEPROM PROGRAMMING DOUBLER CIRCUITFF18-8

Even though electrically erasable PROMs offer the convenience of single-byte write and erase operations, the parts require a somewhat nonstandard programming voltage--21 V. A simple circuit that develops the appropriate voltage from a computer systems standard 12-to-15-Vdc supply, remedies the problem nicely. Moreover, it permits the programming voltage to be pulsed under the control of an external CPU.

As shown in the figure, the chip uses its complementary outputs, Ql and Q2 to trigger a bridge rectifier through capacitors C2 and C3. Resistors R2 and R3 and diodes D1 and D2 limit the current and protect IC1 from spikes from C2 and C3. If required, the regulator will deliver up to 150 mA.

Circuit IC3 is an open-collector TTL gate whose output, when low, disables IC2 and causes it to put out 5 Vdc. The regulator delivers the 21-V programming pulse.

(Reprinted with permission from Electronic Design 1/84, p 440, Copyright 1984 Penton Publishing)


JOYSTICK CHANGEOVER
JOYSTICK CHANGEOVERFG59

Many 1/0 cards and sound cards have a standard provision of a 15-way connection for two joysticks. Unfortunately, many programs use the connections for only one joystick. Since often several kinds of joystick are used (especially modern flight simulators have provision for very advanced, specialized joysticks), it is frequently necessary to change over connectors. As the joystick connectors are invariably found at the back of the computer, this can be a tedious operation. Moreover, in the long term, it does not do the connectors any good. The present circuit replaces this changing over of connectors by a simple push on a button. In this way, two joysticks may be connected to the computer in a simple and user-friendly way. An 8-pole switch arranges the interconnection of control X and Y, and fire button 1 and fire button 2. (Elektor Electronics, July-August 1996, p. 69)


PRINTER PORT D/A CONVERTER
PRINTER PORT D/A CONVERTERFG52

Where eight latching outputs are available the Ferranti ZN426e probably represents the simplest means of providing an analog output. Figure 1 shows the circuit diagram for a PC analog output port based on this chip. The full scale output voltage is equal to the reference voltage fed to pin 5. This terminal can be fed from an external reference voltage of up to 3V, but in most cases the built-in 2.55V reference is perfectly adequate. The output voltage from IC1 (in volts) is equal to the value written to the printer port multiplied by 0.001. In most practical applications this output voltage range will have to be modified using an amplifier or an attenuator. In virtually, all cases it will be a small amount of amplification that is required. This is the purpose of IC2, which also provides output buffering. The non-inverting mode amplifier IC2 can have its closed loop voltage gain varied from unity to about 11 times by means of preset VR2. The maximum output voltage of IC2 is about 2V less than its supply potential, or about 3V if its powered from a 5V supply. Therefore, maximum output voltages of more than 3V require IC2 to be powered from a higher supply potential of up to about 30V. This means using a separate supply for IC2, since the converter circuit must be powered from a 5V supply. If preset VRl is included, the best way to find the correct setting is to first write a low value to the port, and adjust VRl for the correct output voltage. Then write a high value to the port and adjust VR2 for the appropriate output voltage. Repeat this process a few times until no further adjustment is needed. If VRl is omitted, write a value of 255 to the port and then adjust VR2 for the required maximum output voltage. Reasonable accuracy should then be obtained over the full range of output voltages. Using GW BASIC it is just a matter of writing the values to the appropriate address using the OUT command. For example, "OUT &H378,123" would write a value of 123 to a digital-to-analog converter connected to printer port LPT1.(Everyday with Practical Electronics, April 1995, p. 316)


RESET PROTECTION FOR COMPUTERS
RESET PROTECTION FOR COMPUTERSFD20-2

This protection circuit is inserted between the reset switch and the motherboard. The earth connection of the computer must be linked to terminal M of the protection circuit. The protection circuit can draw its power from the computer supply.

When the circuit has been fitted, operation of the reset switch will not immediately restart the cornputer. Instead, a buzzer will sound to alert you to the reset operation. The buzzer is actuated for 4 s by monostable IC1A, which is triggered by the reset switch. During these 4 s, the output, pin 5, of IC1A ensures that the reset function, pin 10, of ICIB is disabled. When the reset switch is operated again, monostable IC1B will be triggered and this starts the reset procedure. Transistor T2 is then switched on for 0.5 s and the buzzer is deactuated via Rll and D4.

The circuit around Tl and N4 ensures that IC1A can accept trigger pulses again 10 s after the mono time of lClB has lapsed. This arrangement prevents, for example, children operating the reset switch.

(Elektor Electronics, 6/89, p. S42)


RS-232-TO-CMOS LINE RECEIVER
RS-232-TO-CMOS LINE RECEIVERFC18-8

This RS-232 type line receiver to drive CMOS logic uses a Schmitt-trigger feedback network to give about 1-V input hysteresis for added noise immunity. A possible problem in an interface which connects two pieces of equipment, each plugged into a different ac receptacle, is that the power line voltage might appear at the receiver input when the interface connection is made or broken. The two diodes and a 3-W input resistor will protect the inputs under these conditions. (Harris, Analog Data Product Data Book, 1988, p. 2-106)


RS-422 TO RS-232 CONVERTER
RS-422 TO RS-232 CONVERTERFF18-1

The circuit supplies two LEDs for visual indication of line activity and terminating resistors when needed. The 220-Ω resistors and 5-V zeners at the RS-422 line inputs supply circuit protection.

Switch SW7 allows the circuit monitor both transmitted and received signals when tee-connected into an RS-232 line. One function of this optional feature is the ability to test a software-locking device that connects to the COM1 port on an IBM PC.

(Reprinted with permission from Electronic Design 4/89, p 108, Copyright 1989 Penton Publishing)


RS232 TEST CIRCUIT
RS232 TEST CIRCUITFG55

The tester is basically a window comparator, in which the Low and High levels are set at +3.0V and -3.0V, respectively, by resistors R2, R3, and R4. Resistor Rl, when not driven by an RS-232 output, will have a low voltage across it (approximately 0 V), and the LED D1 at the output of the comparators is turned off. If the unknown wire of the cable that's tested is an RS-232 output, then it will drive the In point to either a voltage between +3 and +12 V or between -3 and -12 V. In both cases, one of the two comparator outputs will be driven low. This turns the LED on, indicating the presence of a wire connected to an RS-232 output. The comparator should be an LM339 type or equivalent (with an open-collector output). The disadvantage of this scheme is that the thresholds are very sensitive to the supply variations. To eliminate that, the thresholds at the inputs of the comparators can be created using the normal forward drop on a simple diode and then be brought to the necessary levels by IC1 (+3 V at its output) and IC2 (a simple inverter). (Electronic Design, July 24,1995, pp.118-120)


RS232 TO PARALLEL DATA CONVERTER
RS232 TO PARALLEL DATA CONVERTERFG53

A simple serial decoder circuit based on a 6402 UART (ICl) is shown in the figure. The RS232C input signal is at signal levels of about plus and minus 12V, and these must be converted to standard 5V logic levels before being applied to the serial input of IC1. A simple common emitter switching stage based on transistor TRl is used to provide the conversion to normal logic levels, and it also gives the necessary inversion of the input signal. Resistor R4 and capacitor Cl provide IC1 with a positive reset pulse at switch-on. The inputs at pins 35 to 39 program the word format and the method of connection shown in the figure provides a format on one start bit, eight data bits, one stop bit, and no parity. Pin 34 is connected to the +5V rail so that the binary pattern on pins 35 to 39 is loaded into ICl's control register. The decoded bytes of parallel data are available at pins 5 to 12, and pin 4 is connected to the 0V rail so that these outputs are permanently enabled. In a stand-alone application, the tristate capability of these outputs is not of great value, but if necessary this facility can be utilized by applying a control signal to pin 4 of IC1. (Everyday Practical Electronics, May 1996, p. 386)


SERIAL TRANSMITTER CIRCUIT
SERIAL TRANSMITTER CIRCUITFG57

 In the figure is shown the circuit diagram for a unit that provides basic parallel-to-serial conversion with the control inputs being connected to provide a word format of one start bit, eight data bits, one stop bit, and no parity. VRl should provide operation at 1200 baud. Adjusting VRl is just a matter of using trial and error to locate a setting that enables the computer to reliably decode the serial data. If a frequency meter is available, adjust VRl for an output frequency of 19.2 kHz at pin 3 of IC2. (Everyday Practical Electronics, June 1996, p. 440)


ULTRA SIMPLE RS232 TESTER
ULTRA SIMPLE RS232 TESTERFG54

 The tester consists of no more than a two-color LED (or a red and a green LED connected anti-parallel) in series with a 1k resistor. The free ends of the resistor and LED should preferably by terminated in 1 mm plugs. One of the free ends should be covered in green sleeving, or used a green 1-mm plug. This is touched on pin 7 (signal ground) of the connector under test. The other end is touched on each pin to be tested, in turn. The LED (or LED pair) is connected so that a positive voltage gives a red glow, and a negative voltage causes a green glow. Sometimes, an RS-232 input will be found that has an internally connected pull-up to drive a particular default RS-232 level when unconnected. Although this will cause the tester to glow as if the pin were an output, it will do so with markedly less brightness. Bearing this in mind, the tester can be used to diagnose most RS-232 problems at the electrical level. (Electronic Design, December 16, 1995, p. 86)


VPP GENERATOR OFR EPROMS
VPP GENERATOR FOR EPROMSFB16-2

(Linear Technology Corp., Linear Databook, 1986, p. 4-15)


WATCHDOG FOR PCS
WATCHDOG FOR PCsFG58

The watchdog is intended to monitor a microprocessor and determine whether this functions correctly or not. It and its software are suitable for use in the background with any PC that runs under DOS or Windows. The hardware is linked to the serial interface, which is then controlled by the software. After the computer has been switched on the data connections at the serial interface are low. The watchdog software is started at the same time as the selected application program. It provides a permanent rectangular signal at pin 20, which results in C2 being charged and T2 conducting. Pin 4 is made high, so that the computer cannot receive a reset signal. This condition is stable as long as the program runs. If the computer fails (crashes), the rectangular signal falls out and C2 is discharged via Rl. This causes T1, to be switched off, whereupon the base of T2 goes high. This transistor is then on and pulls the reset line of the computer to ground. The computer then restarts. Note that the circuit works only if a computer reset also causes the serial interface to be reset, since that is essential for the high level at pin 4 to be removed. It is only when this pin is at ground level that the reset pulse is terminated and the computer can reboot. (Elektor Electronics, July-August 1996, p. 98)


CONTROLLER CIRCUITS

FOUR OUTPUT CONTROLLER

LOW VOLTAGE POWER CONTROLLER

TEN STEP COUNTER FOR CONTROLLERS

TWO FUNCTION CONTROLLER


FOUR OUTPUT CONTROLLER
FOUR OUTPUT CONTROLLERFG63

This controller offers up to four timed outputs that can be used to operate motors, air valves, solenoids, relays, etc. The timer sections are cascaded so that as one timer times out, it triggers the next timer, and so on until the last timer times out. The intended application for the controller required a two-sensor input that would only start when both inputs occur simultaneously. Note, however, that the start-signal logic could be modified to accommodate a combination of any number of input sensors, or even a single switch closure. The controller also includes an inhibit circuit that keeps the sequence from re-starting before a cycle is completed. (Popular Electronics, March 1995, pp. 70-71)


LOW VOLTAGE POWER CONTROLLER
LOW VOLTAGE POWER CONTROLLERFG61

The circuit has a duty-cycle generator that will give an output varying from fully off to fully on and pulses of any duty cycle in between the two extremes. The circuit can be fed from any DC supply source of between 10 and 15 volts. Ul-a and U2-a combine to forma voltage-to-pulse-width converter. The first half of the dual oscillator/timer is configured as an astable oscillator, generating a continuously oscillating ramp voltage. Op-amp U2-a compares the voltage at its non-inverting input to the voltage at its inverting input The op-amp will give a low output if Rl's wiper voltage is higher than the instantaneous voltage present at pins 2 and 6 of Ul-a. The output of U2-a at pin 2 will have an on/off ratio that is proportional to the voltage at Rl's wiper. Since the output of U2-a does not have enough power-handling capacity to drive the MOSFET, its output is fed to Ul-b, which is used to buffer the signal. The low-impedance, pulsed output of U1-b at pin 9 is fed to the gate of MOSFET Ql, driving it hard on or off. Diode Dl is used to suppress the reverse voltage spikes generated by inductive loads during turn off. If the circuit will not be used to drive inductive loads (motors), Dl can be eliminated. Note: This controller can be used only with incandescent lamps and permanent-magnet DC motors. (Popular Electronics, December 1994, pp. 58-59)


TEN STEP COUNTER FOR CONTROLLERS
TEN STEP COUNTER FOR CONTROLLERSFG62

A 4017 divide-by-10 counter IC is the heart of this simple ten-output controller circuit. Two gates of a 4011 quad 2-input NAND gate IC are connected in an astable oscillator circuit o clock the divide-by-10 counter, U1. The step time is set by R5. With the run/reset switch in the run position, Ul takes ten equal steps and then stops. Momentarily switching Sl to reset starts the cycle over. (Popular Electronics, March 1995, p. 72)


TWO FUNCTION CONTROLLER
TWO FUNCTION CONTROLLERFG64

This two function controller operates a motor when started, then energizes a solenoid, relay, etc. when stopped. (Popular Electronics, March 1995, p. 70)


CONVERTER CIRCUITS

1 Hz-TO-10 MHz VOLTAGE-TO FREQUENCY CONVERTER

100 MHz CONVERTER

2-METER CONVERTER

28-Vdc TO 5-Vdc CONVERTER

8 BIT BINARY TO DECIMAL CONVERTER

ACCURATE VOLTAGE-TO-FREQUENCY CONVERTER

AUDIO TO DC CONVERTER CIRCUIT

BUCK/BOOST CONVERTER

CURRENT-TO-FREQUENCY CONVERTER

CURRENT-TO-VOLTAGE CONVERTER

CURRENT-TO-VOLTAGE CONVERTER WITH BOOST TRANSISTOR

HIGH-PERFORMANCE SHORTWAVE CONVERTER

MULTI-SWITCH CHARGE PUMP BOOST CONVERTER

MULTIPLYING D/A CONVERTER

PRECISION FULL-WAVE ac/dc CONVERTER

RATIOMETRIC 20 KHZ V-F CONVERTER

SIMPLE SCANNER CONVERTER

SIMPLE WWV CONVERTER FOR AUTO RADIOS

SINE- TO SQUARE-WAVE CONVERTER

TEMPERATURE TO FREQUENCY CONVERTER CIRCUIT

TEMPERATURE-COMPENSATED ONE-QUADRANT LOGARITHMIC CONVERTER

VLF CONVERTER

WIDE-RANGE VOLTAGE-TO-FREQUENCY CONVERTER


1 Hz-TO-10 MHz VOLTAGE-TO FREQUENCY CONVERTER
1 Hz-TO-10 MHz VOLTAGE-TO FREQUENCY CONVERTERFC123-8

(Linear Technology Corp. Linear Databook, 1986, p. 5-33)


100 MHz CONVERTER
100 MHz CONVERTERFB17-13

The 2N4416 JFET will provide noise figures of less than 3 dB and power gain of greater than 20 dB. The JFET's outstanding low cross modulation and low intermodulation distortion provides an ideal characteristic for an input stage. The output feeds into an LM171 used as a balanced mixer. This configuration greatly reduces local oscillator radiation both into the antenna and into the if strip and also reduces rf signal feedthrough. (National Semiconductor Corp., Transistor Databook, 1982, p. 7-27)


2-METER CONVERTER
2-METER CONVERTERFD77-4

This converter enables a receiver that tunes 28 to 32 MHz to receive the 144- to 148-MHz amateur band. A BF981 dual-gate MOSFET provides RF gain and feeds mixer T2, another BF981. T3 is a 116 MHz crystal oscillator used to provide L. O. injection to T2. Coils are wound on a 6-mm form. L1, L3, and L4 are 8 turns of 1-mm diameter silver-plated copper wire. L2 is 4 turns of 0.2-mm wire through a ferrite lead. L6 has 19 turns on the primary and 3 turns on the secondary. (Elektor Electronics 3/91, p. 37-41)


28-Vdc TO 5-Vdc CONVERTER
28-Vdc TO 5-Vdc CONVERTERFE18-16

The National Semiconductor LM1575-5.0 allows a very simple switching regulator, with >80% efficiency, operating as a 5-V source @ 1A from +28 V bus. (Reprinted with permission from National Semiconductor Corporation, Linear Edge, Spring 1992)


8 BIT BINARY TO DECIMAL CONVERTER
8 BIT BINARY TO DECIMAL CONVERTERFG68

The decimal value of the eight input lines is displayed on three 7-segment displays. Whilst chips exist to perform this function for single displays, none include the possibility of displaying numbers greater than nine. No EPROM is necessary in this design. It operates by using two counters synchronized to one another, one which generates an 8-bit binary output and a second counter which drives the display. If the display is only updated when the binary counter is at the same value as the input, then the display will show the decimal value of the input. IC4 is the binary counter and IC6 to IC8 form the display/counter section. IC5a and IC5b form the astable which clock both counters at some 5kHz. The minimum display refresh rate is therefore 20 times per second. IC1 and IC2 are two 4-bit comparators, ganged to form an 8-bit comparator. This compares the output of the binary counter IC4 with binary input taken from the circuit under test. Resistors Rl to R8 pull down the input lines to prevent them floating when no input is connected. When the comparator inputs are equal, pin 6 of IC2 goes high, triggering the monostable IC3ab which outputs a brief pulse. This latches the value of the display counters IC6 to IC8 to the display. When IC4 reaches a value of 256, the link between pins 11 and 12 reset the chip, and this resets the display counter also. (Everyday Practical Electronics, November 1996, p. 840)


ACCURATE VOLTAGE-TO-FREQUENCY CONVERTER
ACCURATE VOLTAGE-TO-FREQUENCY CONVERTERFC123-11

This linear voltage-to-frequency converter, a, achieves good linearity over 0 to -10 V. Its mirror image, b, provides the same linearity over 0 to + 10 V, but it is not DTL/TTL compatible. (Signetics, 1987 Linear Data Manual Vol. 2: Industrial, 2/87. p. 7-63)


AUDIO TO DC CONVERTER CIRCUIT
AUDIO TO DC CONVERTER CIRCUITFG67

Circuit diagram for the audio input module which produces a DC output voltage relative to the input signal amplitude. (Everyday with Practical Electronics, June 1996, p. 451)


BUCK/BOOST CONVERTER
BUCK/BOOST CONVERTERFC19-4

This converter can accommodate wide input-voltage swings, such as the 8 to 15-V swing typical of a 12-V sealed lead/acid battery. The low battery output indicates when input voltage drops below 8V. Pulling shutdown turns off the circuit. (Maxim, Seminar Applications Book, 1988/89, p.149)


CURRENT-TO-FREQUENCY CONVERTER
CURRENT-TO-FREQUENCY CONVERTERFD21-3

Teledyne Semiconductor's Type TSC9402 IC is eminently suitable as an inexpensive current-to-frequency converter. The maximum input current of the design shown in the diagram is 10 μA (input voltage range is 10 mV to 10 V), while the output frequency range extends from 10 Hz to 10 kHz. The conversion factor is exactly 1 kHz/μA. The factor can be altered by changing the value of Rl--as long as the maximum input current of 10 p-A is not exceeded.

The circuit has two outputs. That at pin 8 is a short-duration pulse, whose rate is directly proportional to the input current; that at pin 10 is a square wave of half the frequency of the pulse at pin 8.

Calibrating the circuit is fairly simple. Connect a frequency meter to pin 8 (preferably one that can read tenths of a hertz) and connect a voltage of exactly 10 mV to the input (check with an accurate milli-voltmeter). Adjust Pl to obtain an output of exactly 10 Hz. Next, connect a signal of exactly 10 V to the input and check that the output signal has a frequency of 10 kHz. If this frequency cannot be attained, shunt Cl with a small trimmer or replace R1 by a resistor of  820 kΩ and a preset of 250 kΩ. The circuit may be adapted to individual requirements with the aid of:

Fout=Iin Ur (Cl + 12 pF)  [Hz]

The reference voltage, Ur here is 5 V.

(Elektor Electronics, 12/90, p. 513-514)


CURRENT-TO-VOLTAGE CONVERTER
CURRENT-TO-VOLTAGE CONVERTERFE18-17

(Reprinted with permission from Popular Electronics, Fact Card 259. (C)Copyright Gernsback Publications, Inc)


CURRENT-TO-VOLTAGE CONVERTER WITH BOOST TRANSISTOR
CURRENT-TO-VOLTAGE CONVERTER WITH BOOST TRANSISTORFF20-14

A transistor such as the MJE200 can be added to an Analog Devices AD830 to produce this current to voltage converter. Loads to 250 mA can be driven. The 5- to 65-pF trimmer is for compensation. (Electronic Design, 3/95, p. 96. Copyright 1995, Penton Publishing, Inc)


HIGH-PERFORMANCE SHORTWAVE CONVERTER
HIGH-PERFORMANCE SHORTWAVE CONVERTERFE18-2

The NE602 chip, Ul, contains oscillator and mixer stages. The, mixer combines the oscillator signal with the input RF signal to produce signals whose frequencies are the sum and difference of the input frequencies .For example, an 8.5-MHz oscillator and a 10-MHz incoming signal will give output signals at 18.5 MHz (10 + 8.5) and 1.5 MHz (10 - 8.5). Recall that 1.5 MHz is 1500 kHz and an ordinary AM radio can tune to it.

The choice of crystal depends on what shortwave band you want to hear. The 9.5- to 10-MHz band is less crowded and includes the time-signal station WWV. For that band, you'll need a crystal of  8.5 to 8.9 MHz. There is no standard microprocessor crystal in that range, but you can use an amateur radio crystal, have a crystal custom-made, or use a CB crystal.

Transformer Tl rejects signals that are outside the band you are interested in. Transformer T1 should pass signals from 9 to 11 MHz and attenuate all others.

The transformer, T1, used in the circuit is a 10.7-MHz IF transformer salvaged from an FM radio. They are fairly easy to obtain new from parts stores and mail-order houses. Most 10.7-MHz IF transformers will tune across the 9.5- to 10-MHz band without modification; all you need to do is turn its tuning slug. To receive the 6.0- to 6.5-MHz shortwave band, you'll have to add a 150 pF capacitor.

Capacitors
C1	150-pF, ceramic disc (see text)
C2	32-pF, ceramic disc
C3, C5	220-pF, ceramic disc
C4	0.04 or 0.05-μF, ceramic disc
Additional Parts and Materials
Ul	NE602N frequency-converter integrated circuit
D1	6.2-V, 0.4 or 1-W Zener diode
R1	10,000-Ω panel-mount potentiometer,
R2	1000-Ω, 5% resistor
J1, J2.	RCA phone jack
S1	DPDT, toggle switch, panel mount
T1	10.7-MHz IF transformer (green color coded)
XTAL1	8.5-MHz crystal or CB channel-5 receiving crystal (see text)
XTAL2	5.0-MHz microprocessor crystal for 6-MHz band

(Reprinted with permission from PE Hobbyist Handbook, 1990, pp. 34-36. (C)Copyright Gernsback Publications, Inc.,1990)


MULTI-SWITCH CHARGE PUMP BOOST CONVERTER
MULTI-SWITCH CHARGE PUMP BOOST CONVERTERFG69

This is useful both in main supplies and in backup supplies. It generates a regulated 5V output for load currents to 20 mA and inputs ranging from l.8V to 3.6V. For input voltages no lower than 3V, the output current can reach 50 mA. The circuit accomplishes regulation without a linear pass element, but its losses are the same as those of an unregulated doubler or tripler feeding into a linear regulator. (Maxim Engineering Journal, Volume 24, p. 4)


MULTIPLYING D/A CONVERTER
MULTIPLYING D/A CONVERTERFC26-5

The circuit performs the function:

VOUT=VIN x    N

                          16

 where N is the binary number from 0 to 15 formed by the digital input. If the analog input is a fixed dc reference, the circuit is a conventional 4-bit D to ac signal, in which case the output is the product of the analog signal and the digital signal. The circuit on the left is a programmable attenuator with weights of 0, 1/4, 1/2, or 3/4. The circuit on the right is a noninverting adder, which adds weights to the first output of 0, 1/16, 1/8, or 3/16. If four quadrant multiplication is required, place a phase selector circuit in series with either the analog input or output. The D0 input of that stage becomes the + or - sign bit of the digital input.

(Harris, Analog Data Product Data Book, 1988, p. 10-17)


PRECISION FULL-WAVE ac/dc CONVERTER
PRECISION FULL-WAVE ac/dc CONVERTERFD21-14

A dc level is produced that corresponds to the ac input rms value (if sine wave). R1/C5 sets the gain of IC2 to 1.11. This factor is the average-to-rms conversion factor. IC1 and IC2 act as a full-wave rectifier circuit, with D1 and D2. (Reprinted with permission from Radio-Electronics, 9/89, p. 60. (C)Copyright Gernsback Publications, Inc.,1989)


RATIOMETRIC 20 KHZ V-F CONVERTER
RATIOMETRIC 20 KHZ V-F CONVERTERFG70

This ratiometric 20-kHz voltage-to-frequency converter (VFC) provides superior performance with strain gauges and other ratio-responding transducers, even with noisy, unregulated excitation voltages (Fig. 1). Feedback isn't used to achieve the excellent 4-Hz linearity, so there's very-low-frequency jitter---period measurements may be used to get several digits of resolution even when operating at a fraction of full scale. An optional synchronizing transistor starts the VFC with zero charge at the beginning of each count cycle, eliminating the characteristic digit-jumping often encountered with VFC designs. Good linearity is attained by making the comparators reference voltage vary with the input voltage, which precisely compensates for the finite capacitor reset time (Fig. 2):

Period = t1 + t2

           =tl + (Vcc - Vref)/AVin

           =(t1 AVin + Vcc - Vref)/AVin

where AVin =ΔV/Δt. If Vref is made to include the amount t1AVin, then the effect of this is eliminated:

Period = [t1AVin + Vcc - (t1AVin + Vref)]/AVin = (Vcc - Vref)/AVin

The MPSA-18 is a remarkably high gain transistor, even at low currents, giving good current-source linearity down to 0 Hz. In addition, bipolar transistors work well with the low collector voltages encountered in this single-supply, 10-V design. Moreover, most single-supply op amps will work in place of the LM10. But the LM10 also has a reference amplifier that could be used to construct a 10-V excitation regulator. The LM311 propagation delay gives a reset Pulse width near 400 ns, which gives the transistor time to discharge the capacitor. Also, the 31l's bias current gives a small, negative offset that ensures a 0-Hz output for 0 V in. (Electronic Design, December 4, 1995, p. 109)


SIMPLE SCANNER CONVERTER
SIMPLE SCANNER CONVERTERFG65

The circuit can be powered from any 9- to 12-volt DC source, including a good alkaline 9-volt battery. Switch Sl either puts the unit into its bypass mode, where a scanner connected to J3 will receive its normal signals, or it applies power to the circuit and down-converts all 800- to 950-MHz signals as follows: At the heart of the circuit is OSC1, a 40-MHz oscillator module. Transistor Ql amplifies the oscillator's output, which is then bandpass filtered four times so that only the tenth harmonic at 400 MHz is presented to the input of Ul, a Mini Circuits MAR1 wideband UHF/VHF amplifier. Signals from an antenna connected to J2 are high-pass filtered by capacitors C4-C7 in conjunction with inductors L2-L4. Those inductors are etched into the tracings on the PC board, making the exact PC board layout a necessary part in order for the circuit to function. Mixer Ul amplifies and mixes the two inputs-signals between 800 and 950 MHz and the 400-MHz local oscillator-and passes the 400- to 550-MHz output to J3. This converter is not suitable for areas where signal strength is low or in areas where there are a large number of strong signals present as no RF stage is used and little input filtering is used before the mixer, making this circuit prone to spurious responses. (Popular Electronics, November 1995, pp. 39-40)


SIMPLE WWV CONVERTER FOR AUTO RADIOS
SIMPLE WWV CONVERTER FOR AUTO RADIOSFE18-4

This simple frequency converter mixes the 15-Mhz WWV/WVH signal with a 16-Mhz signal from the LO to convert it down to 1MHz so that it can be heard on AM band receiver. (William Sheets)


SINE- TO SQUARE-WAVE CONVERTER
SINE- TO SQUARE-WAVE CONVERTERFE18-12

This 555 based Schmitt trigger circuit is useful for creating clock pulses from analog signals since it readily converts sine waves into square waves. (William Sheets).


TEMPERATURE TO FREQUENCY CONVERTER CIRCUIT
TEMPERATURE TO FREQUENCY CONVERTER CIRCUITFG71

The figure shows the schematic. IC1 produces the Fahrenheit-dependent voltage at its output. This is fed into the LM331 VFC through precision resistor Rl. Inside IC2 are a switched current source, an input comparator, and a one-shot timer. The input comparator is designed to produce a trigger pulse if the voltage at pin 7 is greater than the voltage at pin 6. It does this by comparing the two voltages, one of which is generated internally by the switched current source, and the other is obviously the input. The switched current source charges capacitor C3. When the comparator trips and produces its trigger pulse, it activates the monostable multivibrator, outputs a positive pulse that turns on the output transistor. The monostable multivibrator turns on the switched current source for a period of 1.1 times R*C, where R*C is resistor R5 and capacitor C4. C3 charges up to a point where it exceeds the input voltage, and the comparator resets itself, thus the frequency output transistor Ql will be turned off. Resistor R2 discharges C3 in a time interval according to the values of both components. Then, the internal comparator and monstable multivibrator is reset, and another cycle will be implemented, as long as there is sufficient input voltage. Finally, resistors R4 and VRl set the amount of current the constant current source is able to inject into C3. Thus VRl can set the response "span" of the IC by adjusting it. IC3, two gates of a Hex Schmitt Trigger, are used to buffer IC2's output to light a LED and to make available a digital signal. Remember two things about IC3: lts Logic "1" output will be a full 9 volts, not the TTL level of 5 volts, and tie all unused inputs to ground to prevent self-oscillation at RF frequencies and consequent malfunction of the circuit. (Nuts and Volts Magazine, September 1994, p. 97)


TEMPERATURE-COMPENSATED ONE-QUADRANT LOGARITHMIC CONVERTER
TEMPERATURE-COMPENSATED ONE-QUADRANT LOGARITHMIC CONVERTERFE18-18

A logarithmic converter used to produce an output voltage that is proportional to the logarithm of an input current is shown. Rs is the input impedance of the input source. (Reprinted with permission from Popular Electronics Fact Card 257. (C)Copyright Gernsback Publications, Inc)


VLF CONVERTER
VLF CONVERTERFG66

This very simple converter permits reception of the VLF 3-30 kHz band on a shortwave receiver covering the 6 Mhz (49m) shortwave broadcast band. T1 is an audio transformer of about 8 ohms to 1000 ohms. These can be found new or from junked transistor radios. (Popular Electronics, July, 1996, p.63)


WIDE-RANGE VOLTAGE-TO-FREQUENCY CONVERTER
 WIDE-RANGE VOLTAGE-TO-FREQUENCY CONVERTERFC123-5

This circuit uses a programmable op amp such as the HA2730-a two-amplifier monolithic chip with independent programming ports for each amplifier-whose slew rate and other parameters vary linearly with a so-called set current. The converter circuit uses one amplifier, A1, as a slewing amplifier and other, A2, as a comparator function. The control voltage Vc, determines A1's slew rate. And, because A1's output voltage swing is constant, the modulation of its set current results in direct control of the circuit's frequency. A1's internal compensation capacitor acts as the timing component. An internal bipolar current source,. Whose current magnitude is directly proportional to the set current of pin 1, then determines the charge-discharge rate. A conversion nonlinearity of ± 0. 03% of full scale over 3 decades and ± 1.5% of full scale over 4.3 decades of frequency is possible. The frequency range is adjustable by a change in the resistance. (Reprinted with permission from Electronic Design. Copyright 1975, Penton Publishing)


COUNTER CIRCUITS

10-MHZ FREQUENCY COUNTER

100-kHz CRYSTAL CALIBRATOR

100-MHz OVERTONE OSCILLATOR

2-MHz FREQUENCY COUNTER

32.768 KHZ MICROPOWER OSCILLATOR

50-MHz VHF CRYSTAL OSCILLATOR

50-MHz VHF CRYSTAL OSCILLATOR

ANALOG COUNTER CIRCUIT

ATTENDANCE COUNTER

CMOS CRYSTAL OSCILLATOR

COLPITTS OSCILLATOR

COLPITTS OSCILLATOR

LOW POWER, 5 V DRIVEN, TEMPERATURE COMPENSATED CRYSTAL OSCILLATOR (TXCO)

CRYSTAL OSCILLATOR

CRYSTAL OSCILLATOR I

CRYSTAL-CONTROLLED LOCAL OSCILLATOR FOR SSB TRANSMITTER

DIGITAL COUNTER CIRCUIT

ECONOMICAL CRYSTAL TIME BASE

FET QUARTZ CRYSTAL OSCILLATOR

FET VXO CIRCUIT

HEX BUFFER CRYSTAL OSCILLATOR

LOW-FREQUENCY CRYSTAL OSCILLATOR

MARKER GENERATOR

MILLER OSCILLATOR (CRYSTAL CONTROLLED)

NE602 3RD OVERTONE CRYSTAL OSCILLATOR

PIERCE CRYSTAL OSCILLATOR

SIMPLE 25 MHZ COUNTER

TEMPERATURE-COMPENSATED CRYSTAL OSCILLATOR

TWO FREQUENCY COLPITTS OSCILLATOR

UJT 100-kHz CALIBRATION OSCILLATOR

UP/DOWN COUNTER WITH XOR GATES

VERSATILE WIDEBAND CRYSTAL OSCILLATOR

WIDE-RANGE CRYSTAL OSCILLATOR


10-MHZ FREQUENCY COUNTER
10-MHZ FREQUENCY COUNTERFE19-2

The circuit consists of an ICM7208 seven-decade counter (U1), an ICN7207A oscillator controller (U2), and a CA3130 biFET op amp (U3). Integrated circuit U1 counts input signals, decodes them to 7-segment format, and outputs signals that are used to drive a 7-digit display. Integrated circuit U2 provides the timing for Ul, while U3 conditions the input signal to provide a suitable wave- form for input to Ul. The 5.24288-MHz crystal frequency is divided by U2 to produce a 1280-Hz multiplexing signal at pin 12 of U2. That signal is input to Ul at pin 16 and is used to scan the display digits in sequence. The cathodes of each digit are taken to ground several times each second, activating any segments of the digits whose anodes are high as the result of decoding by Ul. The crystal frequency is further divided to produce a short "store" pulse at pin 2 of U2, followed (after about 0.4 ms) by a short "reset" pulse at pin 14 of U2. The frequency of the pulses is determined by the state of U2 pin 11.

When pin 11 of U2 is taken to ground through S1, the pulses occur every 2 seconds and cause U2 pin to go high for one second, which prevents additional input signals from entering Ul. That causes the count latched in Ul's internal counters to be transferred to the display.

Integrated circuit U2 pin 13 then goes low for one second, allowing a new count to be entered into the seven decade counters of Ul. That cycle is repeated, continuously updating the display every two seconds.

When U2 pin 11 is taken to the positive supply rail (+5 V), the "store" and "reset" pulses occur at 0.2-s intervals, resulting in a 0.1-s count-period. Ten input pulses must be counted in order for a " 1 " to appear on the first digit, D1, so that the frequency being measured is obviously 10 times larger than the frequency that is shown on the display. In that mode, the decimal points are driven by M and visually indicate that the 0.1-s count period is being used.

The display must have at least seven 7-segment common-cathode multiplexed LED digits. Any common-cathode seven-segment display can be used; no particular display is specified.

(Reprinted with permission from PE Hobbyists Handbook, 1990, p. 101. (C)Copyright Gernsback Publications, Inc.,1990)


100-kHz CRYSTAL CALIBRATOR
100-kHz CRYSTAL CALIBRATORFD22-5

Using a 12-V supply, this crystal calibrator should prove a useful accessory for a SW receiver. Q1 and Q2 form an oscillator and Q3 is a buffer amp. (Reprinted with permission from Popular Electronics, 7/91, p.58. (C)Copyright Gernsback Publications, Inc.,1991)


100-MHz OVERTONE OSCILLATOR
100-MHz OVERTONE OSCILLATORFD22-6

This oscillator circuit uses a 5th overtone crystal in the 85-to-106 MHz range. Y1 is the crystal . The circuit was originally used to frequency control a microwave oscillator. (73 Amateur Radio, 10/90, p. 65)


2-MHz FREQUENCY COUNTER
2-MHz FREQUENCY COUNTERFE19-1

This is a schematic and block diagram of a 2-MHz frequency counter. It uses and LSI counter/display driver, LCD readout, and a few logic chips for timebase and timing pulse circuitry. Q2 and Q3 form a signal (input) amplifier.

The circuit contains a crystal oscillator built around U3-c and XTAL1, which provides the primary timing-reference signal. That signal is then divided twice to provide two additional timing references, giving the circuitry three selectable timing references. The ICM72241PL is an integrated circuit that consists of the counter and display driver to drive the LCD-004 display.

(Reprinted with permission from Electronics Hobbyist Handbook, 1993, p.47)


32.768 KHZ MICROPOWER OSCILLATOR
32.768 KHZ MICROPOWER OSCILLATORFG77

Using a Linear Device LTC1441 this oscillator pulls 9 microamps at a supply voltage of 2 volts. The circuit has no spurious modes. (Linear Technology Design Note #137)


50-MHz VHF CRYSTAL OSCILLATOR
50-MHz VHF CRYSTAL OSCILLATORFC21-14

The figure shows a 50-MHz oscillator operating on a third harmonic. The collector's load resistor R1 has been increased because the quartz crystal's internal series resistance Rs increases with frequency in the VHF range. The crystal's internal series resistance Rs is 30 Ω, and the transistor's minimum current gain HFE is 100. Using the same technique as for the 20 MHz oscillator, the external series RL CL equivalent load seen by the 50 MHz crystal is 5.6 Ω (RL) and 1000 pF (CL). (RF Design 3/87 p. 31)


ANALOG COUNTER CIRCUIT
ANALOG COUNTER CIRCUITFB18-6

A straightforward circuit using a LM311 for the level detector and a CMOS analog gate to discharge the capacitor is shown. An important property of this type of counter is the ease with which the count can be changed; it is only necessary to change the voltage at which the comparator trips. A low cost A-D converter can also be designed using the same principle since the digital count between reset periods is directly proportional to the analog voltage used as a reference for the comparator. A considerable amount of hysteresis is used in the comparator. This ensures that the capacitor is completely discharged during the reset period. In a more sophisticated circuit, a dual comparator "window detector" could be used, the lower trip point is set close to ground to ensure complete discharge. The upper trip point could then be adjusted independently to determine the pulse count. (Intersil Component Data Catalog 1987, p. 7-96)


ATTENDANCE COUNTER
ATTENDANCE COUNTERFB18-7

The display shows each increment. By using mode 2, external debouncing of the gate switch is unnecessary, provided the switch bounce is less than 35 ms. The 3 V lithium battery can be replaced without disturbing operation if a suitable capacitor is connected in parallel with it. The display should be disconnected, if possible, during the procedure to minimize current drain. The capacitor should be large enough to store charge for the amount of time needed to physically replace the battery (t = VC/1). A 100μF capacitor initially charged to 3 V will supply a current of 1.0 μA for 50 seconds before its voltage drops to 2.5 V, which is the minimum operating voltage for the ICM7249.

Before the battery is removed, the capacitor should be placed in parallel, across the VDD and GND terminals. After the battery is replaced, the capacitor can be removed and the display reconnected.

(Intersil Component Data Catalog 1987, p. 14-121)


CMOS CRYSTAL OSCILLATOR
CMOS CRYSTAL OSCILLATORFG79

This single CMOS 2-input NOR gate crystal oscillator circuit has one major limitation; it lacks high frequency performance, otherwise it is a solid performer. (Popular Electronics, June 1997, p. 64)


COLPITTS OSCILLATOR
COLPITTS OSCILLATORFA19-37

This circuit will operate with fundamental-mode crystals in the range of 1 MHz to 20 MHz. Feedback is controlled by capacitor voltage divider C2/C3. The RF voltage across the emitter resistor provides the basic feedback signal. (The Complete Handbook of Amplifiers, Oscillators & Multivibrators, TAB Book No. 1230, p. 325)


COLPITTS OSCILLATOR
COLPITTS OSCILLATORFF21-11

Here L1 ~ 7 μH/f, C1 ~ C2 ~ C3 ~ 2400 pF/f, where f is in Mhz. In this circuit the oscillator is free-running. (Reprinted with permission from Radio-Electronics Experimenters Handbook, p. 76. (C)Copyright Gernsback Publications, Inc.,1994)


COMPENSATED CRYSTAL OSCILLATOR (TXCO)
LOW POWER, 5 V DRIVEN, TEMPERATURE COMPENSATED CRYSTAL OSCILLATOR (TXCO)FB19-3

(Linear Technology Corp. Linear Databook, 1986, p. 2-104)


CRYSTAL OSCILLATOR
CRYSTAL OSCILLATORFE20-2

The CMOS amplifier is biased into the linear region by resistor RB. The pi-type crystal network (C1 and C2, and XTAL) provides the 180 deg. phase shift at the resonant frequency which causes the circuit to oscillate. (William Sheets)


CRYSTAL OSCILLATOR I
CRYSTAL OSCILLATOR IFF21-2

In this circuit, series resonant crystal XTAL1 is used as a frequency-determining element. XTAL1 is between 0.1 to 10 MHz. (Reprinted with permission from Popular Electronics, 2/94, p.81. (C)Copyright Gernsback Publications, Inc.,1994)


CRYSTAL-CONTROLLED LOCAL OSCILLATOR FOR SSB TRANSMITTER
CRYSTAL-CONTROLLED LOCAL OSCILLATOR FOR SSB TRANSMITTERFB19-4

This oscillator may contain several switched crystals to provide channelized operation. A buffer amplifier may be added, if desired. (QST, 12/85, p.38)


DIGITAL COUNTER CIRCUIT
DIGITAL COUNTER CIRCUITFG74

This circuit shows how a simple digital counter can be implemented. A CD4029B drives a DC4511 decoder and LED driver. A common cathode LED display is used. (Nuts and Volts Magazine, September 1994 p. 97)


ECONOMICAL CRYSTAL TIME BASE
ECONOMICAL CRYSTAL TIME BASEFD22-17

(Elektor Electronics, 302 Circuits, p. 128-129)


FET QUARTZ CRYSTAL OSCILLATOR
FET QUARTZ CRYSTAL OSCILLATORFF21-1

This oscillator uses an MPF102 JFET as an active element. (Reprinted with permission from Popular Electronics, 2/94, p.80. (C)Copyright Gernsback Publications, Inc.,1994)


FET VXO CIRCUIT
FET VXO CIRCUITFF21-3

An MPF 102 is used in a Colpitts-type oscillator in order to pull the crystal frequency slightly. (Reprinted with permission from Popular Electronics, 2/94, p.81. (C)Copyright Gernsback Publications, Inc.,1994)


HEX BUFFER CRYSTAL OSCILLATOR
HEX BUFFER CRYSTAL OSCILLATORFE20-4

A 4049 single section acts as a crystal oscillator, driving another section as a buffer, leaving four sections for other use. Use a 32- or 20-pF parallel resonant fundamental crystal. (Reprinted with permission from Electronics Now, 12/92, p. 12. (C) Copyright Gernsback Publications, Inc., 1992)


LOW-FREQUENCY CRYSTAL OSCILLATOR
LOW-FREQUENCY CRYSTAL OSCILLATORFE20-1

Ql, Q2, and the associated circuitry form a modified astable multivibrator in which the loop gain is automatically adjusted to the threshold of oscillation by means of field effect transistor Q3. Q4 linearly amplifies the signal present at the collector of Q2 and isolates the oscillator section of the circuit from the output. This stage features wideband operation and delivers a clean 2.5-V amplitude sine wave into a resistive load greater than or equal to 20 kΩ. The stage comprising Q5 has a voltage gain of 1 and its sole purpose is to isolate the nonlinear effects of rectifier D1 from the output. (Reprinted with permission from RF Design, 5/92, p. 80).


MARKER GENERATOR
MARKER GENERATORFC21-12

The oscillator section uses three sections of a 7400 quad NAND gate integrated circuit. The 1- MHz signal from the oscillator is fed into a 7490 decade counter configured to divide by ten, providing the 100- kHz signal. To obtain the 50 and 25 kHz outputs, the 100-kHz signal is further  divided by 7473 dual J-K flip-flop. The first half of the 7473 divides the 100-kHz signal by two, yielding the 50 kHz signal. The second half of the 7473 again divides by two, giving the 25 kHz signal. S2 selects the output, a square wave, rich in harmonics. The generator can be powered from any convenient 6 to 12 Vdc source.  A 7805 fixed-voltage regulator supplies the regulated voltage for the oscillator and the divider chips. The generator described here is powered by a 9-V transistor radio battery. (73 Amateur Radio, 1/89, p. 35)


MILLER OSCILLATOR (CRYSTAL CONTROLLED)
MILLER OSCILLATOR (CRYSTAL CONTROLLED)FA19-35

The drain of the JFET Miller oscillator is tuned to the resonant frequency of the crystal by an LC tank circuit. (The Complete Handbook of Amplifiers, Oscillators and Multivibrators, Tab Book No. 1230, p. 324)


NE602 3RD OVERTONE CRYSTAL OSCILLATOR
NE602 3RD OVERTONE CRYSTAL OSCILLATORFG76

This overtone crystal oscillator uses third-overtone crystals and will work from 25 to 50 Mhz. Frequency range is approximately 25 to 50 Mhz. (Popular Electronics, June 1995, p. 84)


PIERCE CRYSTAL OSCILLATOR
PIERCE CRYSTAL OSCILLATORFG75

A simple Pierce crystal-controlled oscillator circuit can be used as a marker generator for receiver alignment use. A single MPF102 FET (field-effect transistor) is the active device supplying sufficient gain for the circuit to oscillate. Feedback is from the FET's drain (d) through crystal to the input gate. Capacitor Cl fine tunes the oscillator. (Popular Electronics, June 1997, pp. 63-64)


SIMPLE 25 MHZ COUNTER
SIMPLE 25 MHZ COUNTERFG72

An Intersil ICM7224 is used to drive a LCD003 4 digit LCD display unit. Three inputs are provided which add signal conditioning, either gain, rectification, or unbuffered input. A Statek PXO-1000 1 Mhz clock is used as a frequency reference. S2 selects gate time and hence range, LED1, 2, and 3 indicating Hz, KHz or MHz respectively. (Electronic Hobbyists Handbook, Fall 1995, pp. 24-26)


TEMPERATURE-COMPENSATED CRYSTAL OSCILLATOR
TEMPERATURE-COMPENSATED CRYSTAL OSCILLATORFA19-23

Two different negative-coefficient capacitors are blended to produce the desired change in capacitance to counteract or compensate for the decrease in frequency of the normal  AT-cut characteristics. (73 Magazine, 8/78, p. 80)


TWO FREQUENCY COLPITTS OSCILLATOR
TWO FREQUENCY COLPITTS OSCILLATORFD22-14

Using switched crystals, This oscillator is intended for receiver alignment purposes. (Reprinted with permission from Popular Electronics, 11/90, p.69. (C) Copyright Gernsback Publications, Inc.,1990)


UJT 100-kHz CALIBRATION OSCILLATOR
UJT 100-kHz CALIBRATION OSCILLATORFF21-4

This unusual 100-KHz oscillator (whose frequency is determined by XTAL1) can be used as a marker generator to calibrate the analog dial of a communication receiver, or its output can be fed to a divider counter to produce a stable lower-frequency output for use as a clock-signal generator. (Reprinted with permission from Popular Electronics, 2/94, p.80. (C) Copyright Gernsback Publications, Inc.,1994)


UP/DOWN COUNTER WITH XOR GATES
UP/DOWN COUNTER WITH XOR GATESFG73

This circuit shows how a regular 4-bit binary counter may be extended with an up/down function just by adding four XOR (exclusive-OR) gates. The principle is simple: the level at the commoned inputs of the XOR gates determines whether the gates invert the counter's QA-QD output levels or not. In this way, the outputs of the XOR gates can be made to cycle from 111 down to 0000 instead of 0000 to 1111. The disadvantage of this circuit over a real up/down counter is the jump which occurs when the level on the U/D control input is changed. The sum of the 'old' stage and the 'new' state is always 15. For example, if the counter is at state '3' in count-up mode, the state becomes 'l2' when the U/D line is made logic high to initiate down counting.( Elektor Electronics, July-August 1996, p. 85)


VERSATILE WIDEBAND CRYSTAL OSCILLATOR
VERSATILE WIDEBAND CRYSTAL OSCILLATORFG78

Crystal oscillator operates from  to 120 Mhz by changing only C2 and L. (RF Design, December 1995, p. 50)


WIDE-RANGE CRYSTAL OSCILLATOR
WIDE-RANGE CRYSTAL OSCILLATORFE20-9

A circuit using one 7400 TTL IC can use crystals of the fundamental type, from 1 to about 13 MHz. Output is rich in harmonics, making this oscillator useful for calibrations and test applications. (Reprinted with permission from 73 Amateur Radio Today, 7/92, p. 60)


CRYSTAL RADIO CIRCUITS

CRYSTAL RADIO USING ANTENNA MATCHING

FULL WAVE DETECTOR CRYSTAL SET

SINGLE COIL CRYSTAL RADIO

THREE COIL CRYSTAL RECEIVER


CRYSTAL RADIO USING ANTENNA MATCHING
CRYSTAL RADIO USING ANTENNA MATCHINGFG82

This receiver uses a tuning circuit that is in some ways similar to an antenna-matching device used by amateur-radio operators to impedance match their receiver/transmitter input/output circuitry to the impedance of the antenna for maximum signal transfer. Inductor L2 gives a DC-signal return path for D1s output. The inductance of L2 is too large to affect the circuit's tuning function. (Popular Electronics, November, 1996, p. 74)


FULL WAVE DETECTOR CRYSTAL SET
FULL WAVE DETECTOR CRYSTAL SETFG80

The 12-turn coil of Ll couples the Rf signal to the large coil, L2. Connect the center tap of L2 to ground, the fourth tap up from the center to the diode Dl, and the fourth tap down from the center to diode D2. The combined audio output drives the headphones (Zl). If you change tap positions, keep the same number of turns on each side of center. That will balance the RF that feeds each detector diode. The circuit's sensitivity and audio output can be increased by placing Ll inside of L2 (the forms specified for the coils should make that possible). For maximum selectivity, Ll should be loose-coupled to L2. (Popular Electronics, November, 1996, p. 77)


SINGLE COIL CRYSTAL RADIO
SINGLE COIL CRYSTAL RADIOFG83

A starting setup for this circuit is as follows: Connect the antenna to the second tap up from the bottom of the coil (that's the end of the coil that's connected to ground). The diode should connect to about the fourth tap up from the bottom, and Cl should be attached to the seventh tap or so up from the bottom. Those tap positions might not be the best starting point for your antenna/ground arrangement. that doesn't matter, however, because to obtain the best results with the receiver at your location, you should experiment with all variables anyway. (Popular Electronics, November, 1996, p. 74)


THREE COIL CRYSTAL RECEIVER
THREE COIL CRYSTAL RECEIVERFG81

This circuit uses three inductors to increase the receiver's selectivity and sensitivity. Components L2 and Cl are used in an antenna impedance-matching circuit, while Ll and C2 operate in a series-tuned low-output impedance circuit that matches the impedance of the diode detector. A 1 - to 2-mH inductor (L3), as in the previous circuit, offers DC continuity to the detector circuit, (Popular Electronics, November, 1996, p. 77)


CRYSTAL TEST CIRCUITS

10- TO 1-Hz TIMEBASE

CRYSTAL ACTIVITY TESTER

CRYSTAL ACTIVITY TESTER

CRYSTAL TESTER


10- TO 1-Hz TIMEBASE
10- TO 1-Hz TIMEBASEFE20-7

This systems uses an MM5369 IC to derive a 60 Hz signal from a TV color burst crystal (3.579 Mhz). U8 and U9 produce a 10-Hz and 1-Hz signal from this 60-Hz signal. Y1 can be any parallel-mode 3.579 Mhz crystal. (Reprinted with permission from 73 Amateur Radio Today, 8/92, p. 48)


CRYSTAL ACTIVITY TESTER
CRYSTAL ACTIVITY TESTERFE20-6

This circuit will check a crystal for activity. Two sections of a 7400 act as an oscillator and its output is rectified and drives an npn transistor that switches an LED (Fig. A). In Fig.B, a meter replaces the LED. (Reprinted with permission from 73 Amateur Radio Today, 5/92, p. 64)


CRYSTAL ACTIVITY TESTER
CRYSTAL ACTIVITY TESTERFG84

U1 is a 74LS00 Quad two-input NAND gate logic chip. The LS version was selected because of its low current requirement. Two of its internal gates are connected as inverters and in conjunction with Rl, R2, and Cl, form a crystal oscillator when a crystal is connected between Jl and J2. The third gate, also connected as an inverter, is used as a buffer to provide RF at the crystal frequency from pin 11, through isolation capacitor C3 and high-pass filter R4 and C6, to J3 so the crystal frequency can be monitored by an external frequency counter. The fourth gate, also connected as an inverter-buffer, provides RF at the crystal frequency from pins 8, 12, and 13 connected in parallel. The RF is fed through isolation capacitor C4 to voltage doubling rectifiers. D2 and D3, and the resulting DC voltage is filtered by C5 and provides a positive bias to the base of Q1, an NPN transistor, which is normally cut off. Ql goes into conduction and its collector current flows through LED diode Dl and R3 in series, both forming the collector load circuit. The greater the activity of the crystal, the higher the positive bias on the base of Ql will be, and the higher its collector current will be. This current illuminates Dl and its relative brightness is indicative of the level of crystal activity. (73 Amateur Radio Today, August 1996, pp. 34 - 36)


CRYSTAL TESTER
CRYSTAL TESTERFB19-18

Transistor Q1, a 2N3563, and its associated components form an oscillator circuit that will oscillate if, and only if, a good crystal is connected to the test clips. The output from the oscillator is then rectified by, the two 1N4148 diodes and filtered by Cl, a .01μF capacitor. The positive voltage developed across the capacitor is applied to the base of Q2, another 2N3563, causing it to conduct. When that happens, current flows through LED1, causing it to glow. Since only a good crystal will oscillate, a glowing LED indicates that the crystal is indeed OK. The circuit is powered by a standard nine-volt transistor-radio battery and the SPST push-button power-switch is included to prolong battery life. (R-E Experimenters Handbook, p. 157)


CURRENT SOURCES AND SINK CIRCUITS

BILATERAL CURRENT SOURCE

MULTIPLE FIXED CURRENT SOURCE

PRECISION NEGATIVE CURRENT SOURCE

PRECISION POSITIVE CURRENT SOURCE

PROGRAMMABLE CURRENT SOURCE

VOLTAGE-CONTROLLED CURRENT SINK

VOLTAGE-CONTROLLED CURRENT SOURCE


BILATERAL CURRENT SOURCE
BILATERAL CURRENT SOURCEFE21-3

Using two op amps, this circuit produces current proportional to Vin. (Reprinted with permission from Popular Electronics, Fact Card 257. (C) Copyright Gernsback Publications, Inc)


PRECISION POSITIVE CURRENT SOURCE
PRECISION POSITIVE CURRENT SOURCEFE21-2

An LM4431 precision 2.5-V reference and an LMC6062 op amp make up a positive current source, from 1 mA to 10 mA. (Reprinted with permission from National Semiconductor Corporation, Linear Edge, Issue #5)


PRECISION NEGATIVE CURRENT SOURCE
PRECISION NEGATIVE CURRENT SOURCEFE21-4

A National Semiconductor LM4431 reference and an LMC6062 op amp make up a negative current source. Current range is 1 μA to 1 mA. (Reprinted with permission from National Semiconductor Corporation, Linear Edge, Issue #5)


PROGRAMMABLE CURRENT SOURCE
PROGRAMMABLE CURRENT SOURCEFG85

Constant-current sources are required in many applications, particularly when it comes to battery charging. In such applications, it's desirable that the output current is accurate, temperature-stable, and adjustable. The controller also can be successfully employed as the control element in a low-cost linear current source. Output current is sensed by resistor R1, with the value selected so that 100mV is full scale. The voltage across Rl is amplified by a factor of 10, and averaged across capacitor C4. An internal transconductance error amplifier compares the voltage on pin 8 against the programming voltage at pin 7. The error-amplifier output is present on pin 2 (Iout), and is level-shifted by Q2 to control the PNP pass transistor. Output current is programmed by adjusting the voltage across R5 (1 V full scale). The LT1121 LDO regulator provides a 5-V, ±1.5% reference voltage, so current can be accurately programmed by simply connecting different values for Rprog. Input voltage may range from +6 V to +28 V, with output current changing less than 0.3%. Proper heat sinking must be provided for Ql, especially when operating with large input-to-output voltage differentials. Transistor Q3 and R4 limit the magnitude of Qls base drive during dropout, preventing excessive dissipation in driver transistor Q2. Using voltage regulator IC2, the constant-current source operates directly from the unregulated input voltage. Pulling IC2's shutdown pin low turns off Vcc to the entire circuit, and limits reverse current drawn from the output to less than 25μA. (Electronic Design, February 3, 1997, p. 158)


VOLTAGE-CONTROLLED CURRENT SINK
VOLTAGE-CONTROLLED CURRENT SINKFF22-3

A voltage-variable current sink is shown in the figure. The output current is 1 mA per volt of Vin (as R5=1 kΩ and the gain is +1). This circuit provides approximately 0 mA output current for Vin = 0V DCL. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 245)


MULTIPLE FIXED CURRENT SOURCE
MULTIPLE FIXED CURRENT SOURCEFF22-4

A multiple fixed current source is provided by the circuit. A reference voltage (1 Vdc) is established across resistor R3 by the resistive divider (R3 and R4). Negative feedback is used to cause the voltage drop across Rl to also be 1 Vdc. This controls the emitter current of transistor Ql and if we neglect the small current diverted into the (-) input via the 1-MΩ input resistor (13.5 μA) and the base current of Ql and Q2 (an additional 2% loss if the β of these transistors is 100), essentially this same current is available out of the collector of Q1.

Larger input resistors can be used to reduce current loss and a Darlington connection can be used to reduce errors caused by the β of Q1.

The resistor, R2, can be used to scale the collector current of Q2 either above or below the 1- mA reference value.

(Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 245)


VOLTAGE-CONTROLLED CURRENT SOURCE
VOLTAGE-CONTROLLED CURRENT SOURCEFF22-2

A voltage-variable current source is shovn in the figure. The transconductance is -(1/R2) as the voltage gain from the input terminal to the emitter of Q1 is - 1. For 0 Vdc, the output current is essentially 0 mA dc. Resistors Rl and R6 guarantee that the amplifier can turn OFF Transistor Ql. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 245)


DECODER CIRCUITS

24% BANDWIDTH TONE DECODER

DTMF DECODER

DTMF DECODER

DTMF DECODER

DUAL-TONE DECODER

FM STEREO DECODER

RTTY TONE DECODER

TONE DECODER WITH RELAY OUTPUT

TYPICAL NE567 TONE DECODER CIRCUIT

VIDEO LINE DECODER II


24% BANDWIDTH TONE DECODER
24% BANDWIDTH TONE DECODERFA23-5

(Signetics Analog Data Manual, 1982, p. 16-28)


DTMF DECODER
DTMF DECODERFF24-1

This DTMF decoder uses a Motorola 68705P3 microcontroller and a 75T202 DTMF receiver (Silicon Systems, Inc). An LCD module is used for the display (MODl). Switch Sl is used to scroll the display, S2 clears the display, and S3 clears the memory. (Reprinted with permission from Electronics Now, 11/93 p. 53. (C) Copyright Gernsback Publications, Inc.,1993)


DTMF DECODER
DTMF DECODERFG86

This decoder uses a G8870 DTMF receiver decoder chip to decode DTMF signals and display them via an LED display driven by a 7448 decoder driver chip. XTAL is a 3.579 MHz TV Burst crystal. Cl = C2 = 0.1 mfd, R1 = R2 = 100K and R3 = 300K. D1 through D4 are small red LEDs. (Nuts and Volts, June 1995, p. 99)


DTMF DECODER
DTMF DECODERFG87

This decoder uses a G8870 DTMF receiver decoder chip to decode DTMF signals and display them in binary via LEDs. XTAL is a 3.579 MHz TV Burst crystal. C1=C2=0. 1 mfd, Rl=R2=100K and R3=300K. Dl through D4 are small red LEDs. (Nuts and Volts, June 1995, p. 98)


DUAL-TONE DECODER
DUAL-TONE DECODERFA23-6

(Signetics Analog Data Manual, 1982, p. 16-28)


FM STEREO DECODER
FM STEREO DECODERFF24-2

Using an LM1800, this circuit takes composite baseband MPX input and recovers L7R audio channels. The VCO is set for 19 kHz (or 15.7 kHz for TV applications) or as needed. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 300)


RTTY TONE DECODER
RTTY TONE DECODERFG88

The full circuit diagram for the RTTY Tone Decoder as shown. The input filter is based on IC1a, and it is a third order (18dB per octave) highpass type having a cut-off frequency at approximately 750 Hz. IC1b is used in the higher frequency bandpass filter. Capacitor C8 couples the output of this filter to a conventional half-wave rectifier and smoothing network based on diodes D1 and D2. The time constant of R7 and C9 is long enough to give a well smoothed output signal, but is short enough to permit the unit to respond rapidly as the input signal alternates between one tone to the other. The second bandpass filter is based on IC2a and is essentially the same as the first, but it has a preset resistor (VR1) as one section of the input attenuator. This enables the center frequency of the filter to be adjusted but in practice it is set 170Hz lower than the center frequency of the other filter. If preferred, preset potentiometer VRl can be set to give a center frequency 170Hz higher than the other filter. It can also be set for shifts of other than 170Hz. The output of IC2a (pinl) feeds into a rectifier and smoothing circuit that is identical to the one used at the output the other filter . The outputs of both the smoothing circuits drive the inputs of IClb, which acts as the voltage comparator. A small amount of DC positive feedback is provided by resistor Rl1, and this helps to avoid problems with "jitter" at the output when only background noise is present at the input. Power is obtained from two of the otherwise unused handshake outputs of the PC's serial port. Diodes D5 to D8 form a bridge rectifier that ensures the circuit is always provided with a supply of the correct polarity. Only a milliamp or two can be drawn from the handshake outputs. Accordingly, IC1 and IC2 must be low supply current operational amplifiers. (Everyday Practical Electronics, October 1995, p. 804)


TONE DECODER WITH RELAY OUTPUT
TONE DECODER WITH RELAY OUTPUTFA23-2

(Reprinted with permission from National Semiconductor Corporation, Data Conversion/Acquisition  Databook 1980, p. 2-5)


TYPICAL NE567 TONE DECODER CIRCUIT
TYPICAL NE567 TONE DECODER CIRCUITFF24-3

This circuit illustrates use of NE567 as a tone decoder. (William Sheets)


VIDEO LINE DECODER 11
VIDEO LINE DECODER IIFF24-5

This circuit will produce pulses useful for gating lines 24 and 257 of a video signal, but by changing the, decoding logic, other lines can be decoded. (Reprinted with permission from Electronics Now, 3/95, p. 86. (C) Copyright Gernsback Publications, Inc.,1995)


DESCRAMBLER AND DECODER CIRCUITS

FREQUENCY DIVISION MULTIPLEX (FDM) STEREO DECODER

SCA DECODER

STEREO TV DECODER

TIME DIVISION MULTIPLEX (TDM) STEREO DECODER


FREQUENCY DIVISION MULTIPLEX (FDM) STEREO DECODER
FREQUENCY DIVISION MULTIPLEX (FDM) STEREO DECODERFB22-8

(Signetics, 1987 Linear Data Manual Vol. 1: Communications, 11/86.p. 7-123)


SCA DECODER
SCA DECODERFB22-4

The circuit uses a Signetics NE565 PLL (Phase-Locked Loop) as a detector to recover the SCA signal.  The input to the SCA decoder circuit is connected to an FM receiver at a point between the FM discriminator and the de-emphasis filter network. The PLL, IC1, is tuned to 67 kHz by R7, a 5 K potentiometer. Tuning need not be exact since the circuit will seek and lock onto the subcarrier. The demodulated signal from the FM receiver is fed to the input of the 565 through a high-pass filter consisting of two 510 pF capacitors (Cl and C2) and a 4.7K resistor (Rl). Its purpose is to serve as a coupling network and to attenuate some of the main channel spill. The demodulated SCA signal at pin 7 passes through a three-stage de-emphasis network as shown. The resulting signal is around 50 mV, with the response extending to around 7 kHz. (Radio-Electronics 6/87, p. 12)


STEREO TV DECODER
STEREO TV DECODERFB22-6

The composite input signal is preamplified by transistor Ql and is then coupled to the high-pass filter composed of C3, C4, R6, and R7. The filtered audio is then passed to IC1, an MC1310P "Coilless Stereo Demodulator." That IC is normally used to demodulate broadcast-band FM signals, but by changing the frequency of its on-board VCO (Voltage Controlled Oscillator) slightly (from 19 kHz to 15.734 kHz), we can use that IC to detect stereo-TV signals. Notice that the components connected to pin 14 control the VCO's frequency, hence the pilot-detect and carrier frequencies. For use in an FM receiver, the VCO would run at four times the 19 kHz pilot frequency (76 kHz), but for our application, it will run at four times the 15.734 kHz pilot frequency of stereo TV, or 62.936 kHz. The MC1310P divides the master VCO signal by two in order to supply the 31.468 kHz carrier that is used to detect the L - R audio signal. The L - R signal undergoes normal FM detection, and at that point we've got two audio signals: L + R and L - R. The decoder block in the IC performs the addition and subtraction to produce the separate left and right signals. R10 and C10 form a de-emphasis network that compensates for the 75 μs pre-emphasis that the left channel underwent; R12 and Cll perform the same function for the right channel. (Radio-Electronics 3/86, p. 51)


TIME DIVISION MULTIPLEX (TDM) STERE0 DECODER
TIME DIVISION MULTIPLEX (TDM) STEREO DECODERFB22-7

(Signetics, 1987 Linear Data Manual Vol. 1: Communications, 11/86. p. 7-123)


DETECTOR, DEMODULATOR AND DISCRIMINATOR CIRCUITS

455-KHZ AM DETECTOR

555 MISSING PULSE DETECTOR

ac NOISE DETECTOR

AIR FLOW DETECTOR

AIR-FLOW DETECTOR

AIR-PRESSURE CHANGE DETECTOR

AM DEMODULATOR

AUDIO DECIBEL LEVEL DETECTOR WITH METER DRIVER

DRAUGHT DETECTOR

DUTY-CYCLE DETECTOR

EDGE DETECTOR

FAST PULSE DETECTOR

FM DEMODULATOR

FREQUENCY LIMIT DETECTOR

FREQUENCY-BOUNDARY DETECTOR

LEVEL DETECTOR

LM556 FREQUENCY DETECTOR

LOW-DRIFT PEAK DETECTOR

LOW-DRIFT PEAK DETECTOR

MISSING PULSE DETECTOR

NEGATIVE PEAK DETECTOR

NEGATIVE PEAK DETECTOR

NOAA WEATHER ALERT DECODER

OP AMP PEAK DETECTOR

POSITIVE PEAK DETECTOR

PULSE WIDTH DISCRIMINATOR

SIMPLE FULL-WAVE ENVELOPE DETECTOR

SINGLE COMPARATOR WINDOW DETECTOR

THERMALLY OPERATED DIRECTION DETECTOR

VIBRATION DETECTOR USES ANALOG METER


455-KHZ AM DETECTOR
455-KHZ AM DETECTORFF26-19

The LTC1278 undersamples the 455-kHz carrier to recover the 5-kHz modulating signal. The application shown uses the LTC1278 to undersample (at 227.5 ksps) a 455-kHz IF amplitude-modulated by a 5-kHz sine wave. Figures A and B show, respectively the 455-kHz IF carrier and the recovered 5-kHz sine wave that results from a 12-bit DAC reconstruction. (Linear Technology Design Note 88)


555 MISSING PULSE DETECTOR
555 MISSING PULSE DETECTORFE24-3

This missing pulse detector can use a LED or relay output. (William Sheets)


ac NOISE DETECTOR
ac NOISE DETECTORFF26-20

This circuit can be added to the glitch detector to trigger on ac noise. (Reprinted with permission from Popular Electronics, 10/94, p.82. (C) Copyright Gernsback Publications, Inc.,1994)


AIR FLOW DETECTOR
AIR FLOW DETECTORFF26-15

(Reprinted with permission from Popular Electronics, Fact Card 270. (C) Copyright Gernsback Publications, Inc)


AIR-FLOW DETECTOR
AIR-FLOW DETECTORFE24-8

Two precision temperature sensors are used to detect a small temperature difference. When air flow occurs, self-heating of the LM335 is reduced, and the output of the two temperature sensors is unequal. This is amplified by Ul. (Reprinted with permission from Popular Electronics, Fact Card, 270. (C) Copyright Gernsback Publications, Inc)


AIR-PRESSURE CHANGE DETECTOR
AIR-PRESSURE CHANGE DETECTORFD24-16

A piezoelectric detector (BZ1) is used in this circuit to detect a change in air pressure. BZI produces a voltage that is amplified by UlA and UlB. Frequency response is limited to low frequencies. The signal is rectified by D1 and D2 and drives Ql, which activates BZ2, a piezoelectric buzzer. (Reprinted with permission from Popular Electronics, 9/91, p.75. (C) Copyright Gernsback Publications, Inc.,1991)


AM DEMODULATOR
AM DEMODULATORFB21-3

Amplifying and limiting of the AM carrier is accomplished by the IF gain block providing 55 dB of gain or higher with a limiting of 40 uV. The limited carrier is then applied to the detector at the carrier ports to provide the desired switching function. The signal is then demodulated by the synchronous AM demodulator (1496) where the carrier frequency is attenuated due to the balanced nature of the device. Care must be taken not to overdrive the signal input so that distortion does not appear in the recorded audio. Maximum conversion gain is reached when the carrier signals are in phase as indicated by the phase-gain relationship. Output filtering is also necessary to remove high frequency sum components of the carrier from the audio signal. (Signetics, 1987 Linear Data Manual Vol. 1: Communications, 2/87. p. 4-66)


AUDIO DECIBEL LEVEL DETECTOR WITH METER DRIVER
AUDIO DECIBEL LEVEL DETECTOR WITH METER DRIVERFC25-5

This circuit draws very little power, less than 5 mA with a single 6-V power supply, making it ideal for portable battery-operated equipment. The small size and low power consumption belie the 90-dB dynamic range and 10.5-,μV sensitivity. Dc output voltage proportional to the log10 of the input signal level. Thus, a standard 0 - 5 voltmeter can be linearly calibrated in decibels over a single 80-dB range. The circuit is within 1.5-dB tolerance over the 80-dB range for audio frequencies from 100 Hz to 10 kHz. Higher audio levels can be measured by placing an attenuator ahead of the input capacitor. (Signetics RF Communications Handbook 1989, p 3-22)


DRAUGHT DETECTOR
DRAUGHT DETECTORFG90

The complete circuit diagram for the Draught Detector is shown. The key components are R2 and R4 - these form a pair of identical positive temperature coefficient (PTC) thermistors. It is essential to use this particular type of thermistor. With switch Sl on, current flows from the nominal 18V supply to the rest of the circuit. The thermistors R2 and R4 are included in a pair of potential dividers. The first comprises fixed resistor Rl in the upper arm and thermistor R2 in the lower one. The second consists of potentiometer VR1, connected in series with fixed resistor R3, in the upper arm and thermistor R4 in the lower one. With room temperature below 60°C, the current in the thermistors will be l50 mA approximately and sufficient for them to self heat. They will then approach the threshold temperature within a few seconds. The thermistors will stabilize when the temperature reaches about 75°C, corresponding to a resistance of some 500 ohms. In the absence of a draught, each thermistor will be surround by a blanket of warm air. However, thermistor R4 is arranged so as not to receive any draught impinging on the detector R2. When a draught is detected, the warm air around R2 is disturbed and this thermistor is cooled slightly. This results in a lower resistance and hence a falling voltage being developed across it. This sounds the alarm. R5 supplies a little hysteresis to the alarm circuit. (Everyday Practical Electronics, September 1996, p. 706)


DUTY-CYCLE DETECTOR
DUTY-CYCLE DETECTORFD24-17

This circuit looks at the time an incoming pulse is high. If the incoming pulse is shorter than the adjusted (VAR1) pulse, the output of U1B is high. Values are shown for a 1-to 2-μs pulse. (Reprinted with permission from Popular Electronics, 9/90, p. 25. (C) Copyright Gernsback Publications, Inc., 1990)


EDGE DETECTOR
EDGE DETECTORFC25-9

The 555 is a monostable that wants a negative-going trigger. If the pulse you're feeding it with is positive-going, you can run it through an inverter made up of either an inverting gate or, if you're tight on space, a single transistor. Both ways are shown. The circuits shown in Fig. b are edge detectors as well, and are usually referred to as half monostables, since they can't be used in every application. The width of the output pulse is determined by the RC value, but there are a few rules governing their use:

o The input pulse has to be wider than the output pulse

o The input pulse can't be glitchy

o The circuit can't be retriggered faster than the RC time

(Radio-Electronics, 3/89, p. 12)


FAST PULSE DETECTOR
FAST PULSE DETECTORFE24-7

A fast pulse detector can be made with this circuit. A very fast input pulse will exceed the amplifier slew rate and cause a long overload recovery time. Some amount of dv/dt limiting on the input can help this overload condition, however this will delay the response. (Reprinted with permission from Linear Technology, Design Note 61)


FM DEMODULATOR
FM DEMODULATORFE24-2

An LM311 comparator converts a small analog signal to a digital level for the DC4046 phase-locked loop, which is configured as a first-order FM demodulator. This demodulator works with a 50-kHz FM modulated input signal. It has applications in FMl light beam receivers or in remote control applications. Pin 1 of IC3 can be used to squelch the receiver if it is lifted from ground; if not desired, leave it grounded. (Reprinted with permission from Electronics Now, 12/92. p.61. (C) Copyright Gernsback Publications, Inc.,1992)


FREQUENCY LIMIT DETECTOR
FREQUENCY LIMIT DETECTORFB23-9

Simple frequency limit detectors providing a GO/NO-GO output for use with varying amplitude input signals may be conveniently implemented with the ICL8211/8212. In the application shown, the first ICL8212 is used as a zero-crossing detector. The output circuit consisting of R3, R4 and C2 results in a slow output positive ramp. The negative range is much faster than the positive range. R5 and R6 provide hysteresis so that under all circumstances the second ICL8212 is turned on for sufficient time to discharge C3. The time constant of R7C3 is much greater than R4C2. Depending upon the desired output polarities for low and high input frequencies, either an ICL8211 or an ICL8212 may be used as the output driver. The circuit is sensitive to supply voltage variations and should be used with a stabilized power supply. At very low frequencies the output will switch at the input frequency. (Intersil, Component Data Catalog, 1987, p. 5-112)


FREQUENCY-BOUNDARY DETECTOR
FREQUENCY-BOUNDARY DETECTORFC25-7

The circuit can be used to tell whether or not an input signal is within a certain frequency range. The device consists of three ICs, a dual monostable multivibrator, and two dual D-type flip-flops. The signal whose frequency is in question is fed to the clock input of one of the flip-flops. The Q output of that flip- flop (ICla) is cross coupled to its data input so that it acts like a divide-by-two counter. The trailing edge of the Q output is used to trigger the one shots formed by IC2. The upper- and lower-frequency boundaries are determined by the two sections of IC2; the dual precision monostable multivibrator and their external rc networks. The upper-frequency boundary, f1, is set by the output of IC2a, and the lower-frequency boundary, f2, is set by the output of IC2b.

The frequency of the input to the circuit can be anywhere from dc to 100 kHz. The states of the outputs of IC2, which determines the upper- and lower-frequency boundaries, are latched by IC3a and IC3b respectively. The output of IC3a will be high only when the input frequency is less than that of the output IC2a, fl. The output of IC3b will be high only when the frequency of the input is greater than that of the output of IC2b, f2.

(Gernsback Publications Inc. 42 New Ideas 1984, p. 6)


LEVEL DETECTOR
LEVEL DETECTORFB23-5

By using the ICL7612 in these applications, the circuits will follow rail to rail inputs. (Intersil, Component Data Catalog, 1987, p. 7-44)


LM556 FREQUENCY DETECTOR
LM556 FREQUENCY DETECTORFF26-10

The circuit (see the figure), is built around an LM556 dual-timer IC. The 556's first timer is wired as a one-shot and is used to stretch the incoming pulses into fixed-length pulses. The second timer, which is similar to an astable multivibrator (pin 13 remains disconnected), functions as follows:

The one-shot's fixed-length pulses, which are output on pin 5, turn on Ql and discharge C2 through R5. If the frequency of the pulses is high enough, the voltage on C2 will fall below 1/3 VCC and the second timer's output, pin 9, will go to a logic 1. Conversely, if the frequency is low enough or is zero, the voltage on C2 will charge through R6 to a level above 2/3 VCC, and the pin 9 output will go to a logic 0.

The idea is to keep the upper and lower peak voltage on C2 below 2/3 VCC and 1/3 VCC, respectively for a logic 1, and above 2/3 VCC and 1/3 VCC, respectively, for a logic 0.

To find the one-shot values, R3 and Cl, select a pulse width (1.1 x R3 x C1) thats greater than the largest input pulse width and less than twice the inverse of the highest input frequency. To find R5, R6, and C2, first determine the duty cycle (Ton/Toff) of the input signal. Next, choose a standard value for C2 and calculate R6:

R6 = (Toff x 0.61)² + Toff

               C2

 Also, R5 = R6 (Ton/Toff). A tweak of resistors R5 and R6 might be needed to get the preferred response. Input signals with low duty cycles work the best. Finally, notice that capacitors C3 and C4 can be any value between 0.01 and 0.1μF.

(Reprinted with permission from Electronic Design 9/94, p 136, Copyright 1994 Penton Publishing)


LOW-DRIFT PEAK DETECTOR
LOW-DRIFT PEAK DETECTORFC25-8

This circuit uses op amp U1 to compensate for the offset in peak detector diode D1. Across CH is the exact peak voltage; U2 is used as a voltage follower to read this voltage. (National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1982, p. 3-97)


LOW-DRIFT PEAK DETECTOR
LOW-DRIFT PEAK DETECTORFE24-10

Leakage of D2 is provided by feedback path through Rf .

Leakage of circuit is essentially Ib (LF155, LF156) plus capacitor leakage of Cp.

Diode D3 clamps Vout (Al) to Vin - VD3 to improve speed and to limit reverse bias of D2.

Maximum input frequency should be <<1/2 π RFCD2, where CD2 is shunt capacitance of D2.

(Reprinted with permission from Popular Electronics, Fact Card, 270, (c) Copyright Gernsback Publications, Inc)


MISSING PULSE DETECTOR
MISSING PULSE DETECTORFA25-18

The timing cycle is continuously reset by the input pulse train. A change in frequency, or a missing pulse, allows completion of the timing cycle which causes a change in the output level. For this application, the time delay should be set to be slightly longer than the normal time between pulses. The graph shows the actual waveforms seen in this mode of operation. (Signetics 555 Timers, 1973, p. 17)


NEGATIVE PEAK DETECTOR
NEGATIVE PEAK DETECTORFF26-17

(Reprinted with permission from Popular Electronics, Fact Card 269. (C) Copyright Gernsback Publications, Inc)


NEGATIVE PEAK DETECTOR
NEGATIVE PEAK DETECTORFE24-9

(Reprinted with permission from Popular Electronics, Fact Card 269. (C) Copyright Gernsback Publications, Inc)


NOAA WEATHER ALERT DECODER
NOAA WEATHER ALERT DECODERFD24-10

This circuit detects the 1050-Hz tone sent by the NOAA (National Oceanic and Atmospheric Administration) Weather radio stations that operate from 162.40 to 162.55 Mhz. This tone lasts for several seconds. Ql is an amplifier that feeds tone detector Ul, an NE567 detects this tone and produces a low on pin 8. This is coupled to a 555 timer (U3), which produces a high on its pin 3, sounds BZ1, triggers SCR1, and lights the LED. S2 is used to reset the circuit. Audio is taken from the receiver that is used with the device. Sl is used to test the device and it will sound the alarm in two seconds if all is OK. (Reprinted with permission from Popular Electronics, 5/91, p. 63. Copyright Gernsback Publications, Inc., 1991)


OP AMP PEAK DETECTOR                                          f4 i
OP AMP PEAK DETECTORFD24-18

The output of this circuit will be a voltage that is equal to the peak of the input. D1 and C1 detect the peak voltage and this is read by the IC2 voltage follower. (Reprinted with Permission from Radio-Electronics, 9/89, p. 59. Copyright Gernsback Publications, Inc., 1989)


POSITIVE PEAK DETECTOR
POSITIVE PEAK DETECTORFF26-18

(Reprinted with permission from Popular Electronics, Fact Card 269. (C) Copyright Gernsback Publications, Inc)


PULSE WIDTH DISCRIMINATOR
PULSE WIDTH DISCRIMINATORFA25-9

(Courtesy of Fairchild Camera & Instrument Corporation, Linear Databook, 1982, p. 5-25)


SIMPLE FULL-WAVE ENVELOPE DETECTOR
SIMPLE FULL-WAVE ENVELOPE DETECTORFE24-4

Simple, yet sensitive, this amplifying full-wave detector circuit has an almost zero rectification threshold. It presents a highly linear RF load to the final IF stage. The gain for the collector output is given (approximately) by rc/re. The emitter output gain is slightly less than unity. (Reprinted with permission from Electronic Design, 5/92, p. 95)


SINGLE COMPARATOR WINDOW DETECTOR
SINGLE COMPARATOR WINDOW DETECTORFF26-11

Simply by adding two steering diodes, a window detector can be built using only a single comparator. The detector performs well for windows of about 1 V or greater, but it isn't suitable where extreme precision is required because the forward drops of the diodes vary.

In the basic circuit, two resistive dividers set threshold voltage levels at both the inverting and noninverting inputs of the comparator by dividing the reference voltage. The input voltage is steered to the appropriate comparator input by diodes CR1 and CR2.

When the input voltage is within the window, neither diode conducts, and the comparator is biased for a high output. When the input goes above the window, CR2 conducts and pulls the inverting input high, causing the comparator output to go low. When the input voltage goes below the window, CR1 conducts, pulling the noninverting input low, again causing the comparator output to go low. The source resistance of Vin must be low compared to the equivalent parallel resistance of each divider.

(Reprinted with permission from Electronic Design 1/95, p 81, Copyright 1995 Penton Publishing)


THERMALLY OPERATED DIRECTION DETECTOR
THERMALLY OPERATED DIRECTION DETECTORFD24-1

A heat-sensitive sensor can be used to construct a direction detector. Such a sensor reacts to all animal heat. The one used in this design has a sensitive surface that has been divided into two. It, therefore, makes a difference, whether the heat approaches from the left or the right. The indication for cold objects, of course, exactly the opposite.

Circuit IC1B forms a symmetric supply. Terminal s of the sensor is its output. The signal at s is amplified in IC1A by a factor of about 70 before it is available at the output of the detector.

To obtain good directivity, it is best to place the sensor behind a single narrow slit, rather than behind the usual raster of a multifaceted mirror. The circuit draws a current of only a few mA from a 5-V supply.

(Elektor Electronics, 12/90, p.520)


VIBRATION DETECTOR USES ANALOG METER
VIBRATION DETECTOR USES ANALOG METERFG89

A D'Arsonval meter movement is used as a vibration detector in this novel application. The meter acts as a generator, producing a voltage when the needle moves. A cheap panel meter can be used, but a high sensitivity movement (50μA) works best. (Popular Electronics, February 1997, p. 73)


DIGITAL TO ANALOG CONVERTER CIRCUITS

9-BIT CMOS D/A CONVERTER

DIGITAL-TO-ANALOG CONVERTER

LINEAR DAC HAS NONLINEAR OUTPUT


9-BIT CMOS D/A CONVERTER
9-BIT CMOS D/A CONVERTERFC26-4

Three CD4007A IC packages perform the switch function using a 10-V logic level. A single 15-V supply provides a positive bus for the follower amplifier and feeds the CA3085 voltage regulator. The scale adjust function is provided by the regulator output control, which is set to a nominal 10 V in this system. The line-voltage regulation (approximately 0.2%) permits 9-bit accuracy to be maintained with a variation of several volts in the supply. System power consumption ranges between 70 and 200 mW, a major portion is dissipated in the load resistor and op amp. The regulated supply provides a maximum current of 440 μA of which 370 μA flows through the scale adjusting. The resistor ladder is composed of 1% tolerance metal-oxide film resistors. The ratio match between resistance values is in the order of 2%. The follower amplifier has the offset adjustment nulled at approximately a 1 V output level. (Intersil, Applications Handbook, 1988, p. 3-183)


DIGITAL-TO-ANALOG CONVERTER
DIGITAL-TO-ANALOG CONVERTERFE18-5

Figure A is an R/2R resistor ladder. Each switch that is closed increases the amount of current at Iout. A simple channel A/D converter is shown in Fig.B. The voltage reference (D2) is common to all channels, but the value of the dropping resistor (R9) varies as the number of DACs installed in the system. IC15 is a DAC0808 A/D converter chip. IC16A is an op amp to interface the output current from the D/A convert to an analog voltage output. (Reprinted with permission from R-E Experimenters Handbook 1992, p. 92)


LINEAR DAC HAS NONLINEAR OUTPUT
LINEAR DAC HAS NONLINEAR OUTPUTFG91

When controlling a nonlinear device such as an incandescent lamp, it is desirable to have fine resolution at the high end, whereas a small change in current may cause a large change in brightness. At the low end, coarser resolution is quite adequate. Using the circuit shown, any desired compression can be produced using just about any multiplying DAC. A negative 10-V reference is fed through R1, to inverting amplifier Al, which has an initial gain set to unity by R2. Al's output supplies a positive variable reference to the DAC. The DAC output provides additional feedback through R3, reducing the amplifiers gain as the DAC data increases. The variable reference is gradually reduced so that each step is progressively smaller than the one before. With the values shown, as the DAC data approaches full scale, the reference approaches 1/4 of its original value. This gives the output four times as much resolution at the high end as the low end. By decreasing the value of R3, greater compression and higher resolution can be achieved. The variable-reference output also may be useful in some applications. (Electronic Design, April 17, 1995, pp.114-116)


 DIGITAL CIRCUITS

7-SEGMENT (LED) DISPLAY DRIVER

7-SEGMENT COMMON-CATHODE LED DISPLAY DRIVER

BAR GRAPH DISPLAY CIRCUIT

BAR-GRAPH LEVEL GAUGE

CASCADED 4026B COUNTER/DISPLAY DRIVER CIRCUIT

CASCADING THREE BARGRAPH DISPLAY DRIVERS

COLOR-SHIFTING LED DISPLAY

ECONOMICAL LED BAR DISPLAY

EL PANEL OPERATES FROM 1.8 TO 8 V

MULTIPLEXED BCD DECODER-DRIVER CIRCUIT

STEREO LEVEL DISPLAY

SURROUND SOUND INDICATOR

USING FLASHING LEDS ON HV SUPPLIES

USING LEDS ON AC - DC SUPPLIES


7-SEGMENT (LED) DISPLAY DRIVER
7-SEGMENT (LED) DISPLAY DRIVERFE26-7

An IC1 like a 7447 drives a 7-segment common anode LED display. Current limiting resistor R should limit the segment current to the rated value at maximum supply voltage. A sample calculation is shown. (William Sheets)


7-SEGMENT COMMON-CATHODE LED DISPLAY DRIVER
7-SEGMENT COMMON-CATHODE LED DISPLAY DRIVERFE26-6

A CD4511 CMOS LED display driver can be used to drive a common cathode LED display. Current limiting resistors limit the segment current to the rated value at maximum supply voltage. A sample calculation is shown. (William Sheets)


BAR GRAPH DISPLAY CIRCUIT
BAR GRAPH DISPLAY CIRCUITFG97

This shows how a LM3914 or LM3915 is connected for 9 to 15V operation. Dl thru D10 are separate LEDs or part of an integral display module. (Everyday with Practical Electronics, June 1996, p. 453)


BAR-GRAPH LEVEL GAUGE
BAR-GRAPH LEVEL GAUGEFF28-5

A quad comparator and divider network form a 4-level comparator that drives 4 LEDs. R1 and R2 can be used to scale the basic sensitivity of 250 mV/LED to higher voltages than the basic 1 volt  (for all 4 LEDs lit). (Maxim, \/OL. III, Data Book, 1994, p. 3-127)


CASCADED 4026B COUNTERIDISPLAY DRIVER CIRCUIT
CASCADED 4026B COUNTER/DISPLAY DRIVER CIRCUITFE26-2

Two or more 4026B counters can be cascaded as shown to give a multiple-digit display. Two, three or more displays can thus be connected. (Reprinted with permission from Radio-Electronics, 5/92. p71. (C) Copyright Gernsback Publications, Inc., 1992)


CASCADING THREE BARGRAPH DISPLAY DRIVERS
CASCADING THREE BARGRAPH DISPLAY DRIVERSFG96

This shows how to cascade three bargraph display drivers. The basic scheme can be extended to four or more drivers if desired. (Everyday Practical Electronics, October 1995, p. 813)


COLOR-SHIFTING LED DISPLAY
COLOR-SHIFTING LED DISPLAYFF28-2

This circuit is used to make a tricolor LED gradually change color from yellow to red to yellow to green, and then back to yellow, where the cycle repeats. It is very simple to make, and the theory of operation is also simple. Both of the timers in the 556 dual oscillator/timer are configured for astable operation with a 50% duty cycle. One timer is set to oscillate much faster than the other. The timing capacitor voltage of each is sent to two comparators, which apply a voltage across the tri-color LED whose polarity, depends on which capacitor voltage is higher. The rapidly changing capacitor's voltage causes the red and green elements of the LED to be alternately lit, thus giving the illusion of yellow light. As the slowly rising and falling voltage from the slower trimming capacitor changes in average value, it shifts the duty cycle to favor one color or the other. That gives the transition between colors a smooth appearance. (Reprinted with permission from Popular Electronics, 1/94, p.24. (C)Copyright Gernsback Publications, Inc.,1994)


ECONOMICAL LED BAR DISPLAY
ECONOMICAL LED BAR DISPLAYFG94

A particular difficulty with LED bar displays is the high current drain. In the diagram, LED driver LM3914 controls a chain of LEDs instead of as usual a number of parallel-connected LEDs. This means that in principle only a single diode current is needed to make several LEDs light. The cost of this, of course, a higher supply voltage, since account must be taken of a number of diode forward voltages. The economizing effect is strengthened if high-efficiency LEDs are used. In the diagram, the current drain of about 15 mA is less than half that of the standard application (32 mA). (Elektor Electronics, July-August 1996, p. 75)


EL PANEL OPERATES FROM 1.8 TO 8 V
EL PANEL OPERATES FROM 1.8 TO 8 VFG98

Electroluminescent (EL) panels offer a viable alternative to LED, incandescent, or CCFL backlighting systems in many portable devices. EL panels are thin, rugged, lightweight, low power, require no diffuser, and emit aesthetically pleasing blue-green light. Capacitive in nature, they typically exhibit about 3000 pF/in.² of panel area and require low frequency (50Hz-lkHz) 120-Vrms ac drive. These problems can be solved by using a setup that includes an LT1303 micropower switching-regulator IC along with a small surface-mount transformer in a flyback topology (Fig. a). The 400-Hz drive signal can be supplied externally or derived from a simple CMOS 555 circuit (Fig. b). When the drive signal is low, flyback transformer Tl charges the panel until the voltage at point A reaches 240 Vdc. C1 removes the dc component from the panel drive, resulting in +120 V dc at the panel. When the input drive signal goes high, the LT1303's feedback (FB) pin is pulled high as well, idling the IC and turning on Ql. Ql's collector pulls point A to ground and the panel to -120 V dc. C2 can be added to limit voltage if the panel is disconnected or open. R1 provides intensity control by varying output voltage. Intensity also can be modulated by varying drive-signal frequency. (Electronic Design, April 17, 1995, p. 95)


MULTIPLEXED BCD DECODER-DRIVER CIRCUIT
MULTIPLEXED BCD DECODER-DRIVER CIRCUITFF28-1

The BCD decoder-driver circuit will interface with any standard BCD output to produce a digital display. (Reprinted with permission from Electronics Now, 3/95. p. 64. (C) Copyright Gernsback Publications, Inc.,1995)


STEREO LEVEL DISPLAY
STEREO LEVEL DISPLAYFF28-3

Two bar graph drivers and LEDs are used in this volume (level) indicator. R3a and R3b set the sensitivity of the circuit. The LEDs can be either bar graph units, or individual LEDs can be used. (Reprinted with permission from Popular Electronics, 1/94. (C) Copyright Gernsback Publications, Inc., 1994)


SURROUND SOUND INDICATOR
SURROUND SOUND INDICATORFG95

The circuit indicates with the aid of two LEDs whether or not the input signal contains surround data. The criterion for this is the phase difference between the two channels: if this is zero, there is no surround data. In the circuit diagram, if there is a phase difference between the two channels, the output levels of comparators IClb and IC1c will differ. These outputs are constantly compared by XOR gate IC2, and, in case of a difference, the output of the gate will go high. Depending on the output state, the red or green half of D1 will be actuated via gate IC2d, which is here connected as an inverter. In case of a pure surround signal, the red half will light brightly; in case of a mono signal, the green half will. If the input is a standard stereo signal, the rapid changes in the output of IC2, will cause the diode to appear yellow-orange. (Elektor Electronics, July-August 1996, p. 88)


USING FLASHING LEDS ON HV SUPPLIES
USING FLASHING LEDS ON HV SUPPLIESFG93

When using FLEDs on a supply voltage higher than the rating of the FLED, precautions should be taken so that the device never sees a voltage above its maximum rating. (Everyday Practical Electronics, October 1996, p. 785)


USING LEDS ON AC - DC SUPPLIES
USING LEDS ON AC - DC SUPPLIESFG92

(a) Series resistor calculation, (b) using an LED on an A.C. supply. (Everyday Practical Electronics, October 1996, p. 784)


DRIVER CIRCUITS

COAX CABLE DRIVER

DRIVER CIRCUITS

ELECTROLUMINESCENT PANEL DRIVER

FIVE-TRANSISTOR AMPLIFIER BOOSTS FAST PULSES INTO 50-OHM COAXIAL CABLE

FLIP-FLOP INDEPENDENT LAMP DRIVER

HIGH-SIDE MOSFET DRIVER

LOW DISTORTION LINE DRIVER

MOSFET GATE DRIVER

TWO-INPUT VIDEO MUX CABLE DRIVER

IMPEDANCE-MATCHED LINE DRIVER WITH 75 OHMS LOAD


COAX CABLE DRIVER
COAX CABLE DRIVERFF29-11

Because of their high-current drive capability, the LH0002, LH0033, and LH0063 buffer amplifiers are suitable for driving terminated or unterminated coaxial cables, and high-current or reactive loads. Current-limiting resistors should be used to protect the device from excessive peak load currents or accidental short circuit. No current limiting is built into the devices other than that imposed by the limited beta of the output transistors. This figure shows a coaxial-cable drive circuit. The 43Ω resistor is included, the output voltage to the load is about half what it would be without the near- end termination. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 541)


DRIVER CIRCUITS
DRIVER CIRCUITSFA30-1

 CMOS drivers for relays, lamps, speakers, etc., offers extremely low standby power. At Vcc = 15 V, power dissipation per package is typically 750 nW when the outputs are not drawing current. Thus, the drivers can be sitting out on line (a telephone line, for example) drawing essentially zero current until activated. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor CMOS Databook 1981, p. 8-44)


ELECTROLUMINESCENT PANEL DRIVER
ELECTROLUMINESCENT PANEL DRIVERFG99

Driving electroluminescent panels, such as those used for backlighting LCD screens in portable devices, is a challenge because they are capacitive loads and require high voltage AC drive signals. Typically, EL panels exhibit about 3nF per sq inch capacitance. The LT1305 circuit below can drive an EL panel with up to l00nF total capacitance. The LT1305 micropower DC/DC converter contains an internal power switch capable of up to 2A switch current. The high power switch drives the primary of flyback transformer Tl. A minimum input voltage of 1.8V ensures operation with 2-cell supplies. The input voltage is boosted to a voltage that ranges from 166VDC to 248VDC, as set by Rl. The AC drive waveform is created by an external square wave control signal turning on and off the NPN transistor, bringing point "A" to ground and inverting the voltage across the panel and then returning to a high positive voltage. By adjusting Rl, the panel AC drive voltage can be set from 83VRMS to 115VRMS to alter the display brightness. The color or hue of the display can also be slightly varied by changing the frequency of the square wave drive signal. This control signal can be from a system microprocessor output pin. (Linear Technology Power Solutions, 1996, p. 22)


PULSES INTO 50-OHM COAXIAL CABLE
FIVE-TRANSISTOR AMPLIFIER BOOSTS FAST PULSES INTO 50-OHM COAXIAL CABLEFB27-2

The circuit works from dc to 50 MHz and will deliver pulses as short as 10 ns. It is driven by a TTL signal through a 740S00 quad Schottky NAND gate, ICA through ICD. Transistor Ql, wired as a common-emitter amplifier, drives transistor Q2, a simple emitter follower. Transistors Q3 and Q4, wired in parallel, also form an emitter follower and drive the output. When Q3 and Q4 are both turned off, transistor Q5 works as low-impedance sink. Schottky diodes D1 and D2 prevent Ql and Q5 from becoming saturated. To adjust the circuit, potentiometer R1 is set to optimize the output pulse's fall time. Inductor L1, a peaking coil, should be adjusted to improve the rise time to within a permissible 5% overshoot. Likewise, capacitor C1 can be varied to control preshooting. Further output pulse shaping is accomplished with the help of capacitor C2. Resistors R2 and R3 ensure a proper 50-ohm impedance at the amplifier's output when the pulse is on or off, respectively. (Electronic Design, 12/87, P. 67)


FLIP-FLOP INDEPENDENT LAMP DRIVER
FLIP-FLOP INDEPENDENT LAMP DRIVERFD27-3

Assume first that SCR1 is on and SCR2 is off so that Cl is fully charged, with its LMP2 end positive. The state of the circuit can be changed by pressing S2. As SCR2 turns on, it turns SCR1 off capacitively via its anode. Capacitor Cl then recharges in the opposite manner (i.e., the left end is now positive). The state of the circuit can be changed again by pressing Sl, thus driving SCR1 on by way of its gate, and driving SCR2 off capacitively via its anode. (Reprinted with permission from Radio-Electronics, 9/87, p. 65, Copyright Gernsback Publications, Inc., 1987)


HIGH-SIDE MOSFET DRIVER
HIGH-SIDE MOSFET DRIVERFF29-7

A Linear Technology LTC1154 is used as a charge pump to drive the gate of a high-side power MOSFET. (73 Amateur Radio Today, 3/95, p. 62)


LOW DISTORTION LINE DRIVER
LOW DISTORTION LINE DRIVERFG100

This low-distortion driver circuit delivers up to ±0.5 A and is suitable for loads of 10Ω and up. Using a low-offset, low-bias-current input stage, the driver can be entirely direct-coupled. Gain is equal to (1 + R2/Rl). (Electronic Design Analog Applications, June 24, 1996, p. 79)


MOSFET GATE DRIVER
MOSFET GATE DRIVERFG101

This ratiometric 20-kHz voltage-to-frequency converter (VFC) provides superior performance with strain gauges and other ratio responding transducers, even with noisy, unregulated excitation voltages. Feedback isn't used to achieve the excellent 4-Hz linearity, so there's very-low-frequency jitter -- period measurements may be used to get several digits of resolution even when operating at a fraction of full scale. An operational synchronizing transistor starts the VFC with zero charge at the beginning of each count cycle, eliminating the characteristic digit-jumping often encountered with VFC designs. Good linearity is attained by making the comparator's reference voltage vary with the input voltage, which precisely compensates for the finite capacitor reset time.

period = tl + t2

           = tl + (Vcc - Vref) / AVin

           = (t1AVin + Vcc - Vref) /ANin

where AVin = DV/Dt. If Vref is made to include the amount t1AVin, then the effect of tl is eliminated:

period = [tlAVin +Vcc - (tlAVin + Vref)] / AVin.

The MPSA-18 is a remarkably high gain transistor, even at low currents, giving good current-source linearity down to 0 Hz. In addition, bipolar transistors work well with the low collector voltages encountered in this single-supply, 10-V design. Moreover, most single-supply op amps will work in place of the LM10. But the LM10 also has a reference amplifier that could be used to construct a 10-V excitation regulator. The LM311 propagation delay gives a reset pulse width near 400 ns, which gives the transistor time to discharge the capacitor. Also, the 31l's bias current gives a small, negative offset that ensures a 0-Hz output for 0 V in.

(Electronic Design, December 4, 1995, pp. 109-110)


TWO-INPUT VIDEO MUX CABLE DRIVER
TWO-INPUT VIDEO MUX CABLE DRIVERFF29-1

(Linear Technology, 2/95)


IMPEDANCE-MATCHED LINE DRIVER WITH 75 OHMS LOAD
IMPEDANCE-MATCHED LINE DRIVER WITH 75 OHMS LOADFF29-2

This circuit has a wideband 75-Ω line driver, for video applications (1 V pp into 75 Ω) (Analog Devices, Analog Dialogue Vol. 26, No. 2, 1992, p. 18)


ELECTRONIC LOCK CIRCUITS

ANALOG ELECTRONIC LOCK

DIGITAL ENTRY LOCK

DIGITAL LOCK CIRCUIT

ELECTRONIC LOCK

KEYLESS LOCK


ANALOG ELECTRONIC LOCK
ANALOG ELECTRONIC LOCKFG103

The system is formed by two separate circuits-a key and a keyhole. The key engages the keyhole by means of a mating pair of connectors. The key is a tone-generator circuit consisting of a 4049 hex inverter CMOS IC (U1), switches (Sl and S2), a resistor (R1), and a capacitor (C1). The value of the tone generated by that circuit in Hz is determined by: 1/(1.4 x R1 C1). The keyhole is a 567 tone-decoder circuit that can be configured to detect any frequency from 0.01 Hz to 500 kHz. The frequency it detects (fo) is set by resistor R2 and capacitor C2, according to: fo = 1.1/(R2C2). When the key is inserted into the lock, and switch Sl is pressed, a tone is supplied to the input of the keyhole circuit. If the tone frequency is close enough to fo, the 567 IC turns on the relay (Kl), which should be connected to the electronic locking device. Components R3 and D1 are used to latch the circuit, so the output stays on even after the input tone is removed. When S2 is pressed, the system is reset. Switch S3 resets the circuit from inside. Note: The accuracy with which the keyhole circuit detects fo can be set by changing the values of three components. First, R2 should be between 2000 and 20,000 ohms. Second, the value in microfarads of capacitor C4 should be: n/fo where n is a value around 1300 (which gives a detection accuracy of up to 14% of fo). Finally, capacitor C3 should have about twice the capacitance of capacitor C4. Battery Bl supplies both circuits.

(Popular Electronics, April 1995, p. 31)


DIGITAL ENTRY LOCK
DIGITAL ENTRY LOCKFD28-1

A keypad enters a four-digit access code, which is programmed via jumpers on a 24-pin plug-in header and socket. Ul is an LS7220, which detects a four-digit sequential data input. When the correct data is entered into the keyboard, pin 13 of Ul goes high, which activates Ql and K1. Kl drives an external electric lock solenoid, etc. (Reprinted with permission from Popular Electronics, 11/90. p. 61-62. (C) Copyright Gernsback Publications, Inc.,1990)


DIGITAL LOCK CIRCUIT
DIGITAL LOCK CIRCUITFG104

This circuit depends on the entry of a correct sequence code. An incorrect number not in the code causes the circuit to reset. When the correct code is entered, Q2 operates relay K1 for a short time depending on C3. (Popular Electronics, October 1995, p. 74)


ELECTRONIC LOCK
ELECTRONIC LOCKFF30-1

 The heart of the circuit is a 4022 octal counter. When first powered up, C2 is charged via R5, so the reset input of the counter is kept high. That causes output Q0 to go high while all other outputs are low. With the switches wired as shown, when S4 is pressed, the BS170 is switched on via de- bouncing network R2/Cl, and Ul receives a clock pulse. Also, C2 is discharged via R4 and Dl, removing the reset signal of the counter, allowing it to advance. The time required for C2 to charge via R5 (i.e., to reset the counter), is the maximum time that can lapse before the next key is pressed. The above cycle is therefore repeated only if S8 (connected to the Ql output) is pressed in time. When all keys have been pressed in time and in the correct order, Q7 goes high for about four seconds to drive the "unlock" circuitry (e.g., a relay driver for an automatic door opener. A builder can change the code by reviewing the switches. The code for the lock shown in the circuit diagram is 4-8-0-1-5-7-0. However, the 4022 octal counter can be replaced by a 4017 divide-by-10 counter. That will make it possible to add two more digits to the combination. (Reprinted with permission from Popular Electronics, 4/95, pp. 29-30. (C) Copyright Gernsback Publications, Inc.,1995)


KEYLESS LOCK
KEYLESS LOCKFD28-2

The circuit uses a four-bit latch (Ul). What makes the circuit sequential is that the set input of the first bit latch is tied to the reset of the second bit latch, and so forth. That ensures that any bit latched will be reset by the previous bit latch. The ECG8314 also has a master reset (pin 9) that is tied to the first bit- latch reset (pin 3), which provides an added measure of security for the lock.

The outputs of Ul are fed to a four-input AND gate (U2), then to Ql (used as switching transistor), which is used to drive relay Kl. The EGC8314 has an enable low (pin) that can be used as a timing circuit, if that is desired.

(Reprinted with permission from Popular Electronics, 12/90, p.24. (C) Copyright Gernsback Publications, Inc., 1990)


FIBER-OPTICS CIRCUITS

DIGITAL FIBER OPTIC RECEIVER

EXPERIMENTAL DATA TRANSMITTER FOR FIBER OPTICS

EXPERIMENTAL FIBER-OPTIC DATA RECEIVER


DIGITAL FIBER OPTIC RECEIVER
DIGITAL FIBER OPTIC RECEIVERFC29-2

This receiver uses the NE5212, the Signetics 10116 ECL line receiver, and the Phillips/Amperex BPF31 pin diode. The circuit is a capacitor-coupled receiver and utilizes positive feedback in the last stage to provide the hysteresis. The amount of hysteresis can be tailored to the individual application by changing the values of the feedback resistors to maintain the desired balance between noise immunity and sensitivity. At room temperature, the circuit operates at 50-M baud with a BER of 10E-10 and over the automotive temperature range at 40-M baud with a BER of 10E-9. Higher speed experimental diodes have been used to operate this circuit at 220-M baud with a BER of 10E-10. (Signetics, Fiber-Optic Communication Data and Applications, 1988, p. 3-63 and 3-64)


EXPERIMENTAL DATA TRANSMITTER FOR FIBER OPTICS
EXPERIMENTAL DATA TRANSMITTER FOR FIBER OPTICSFF31-1

This schematic for an experimental data transmitter uses optical fibers and a laser diode. Transmission frequency of the free-running oscillator is approximately 3 kHz. R5 might have to be varied to suit your laser diode. IC1 is a CD4093. (Laser Cookbook, McGraw-Hill, p.231)


EXPERIMENTAL FIBER-OPTIC DATA RECEIVER
EXPERIMENTAL FIBER-OPTIC DATA RECEIVERFF31-2

An infrared phototransistor acts as the sensor for this receiver. ICla is a section of a CD4093 CMOS NAND gate. (Laser Cookbook, McGraw-Hill, P.231)


FIELD STRENGTH METER CIRCUITS

AMPLIFIED FIELD STRENGTH METER

LOW COST MICROWAVE FIELD STRENGTH METER

SIGNAL-STRENGTH METER

SIMPLE FIELD STRENGTH METER


AMPLIFIED FIELD STRENGTH METER
AMPLIFIED FIELD STRENGTH METERFG105

This field strength meter uses Ql and Q2 to amplify the DC voltage produced by detector Dl. A piezo sound BZl is used as an audible indicator rather than a meter. This circuit may be of use for the visually handicapped. Antenna is a 24-inch whip.(Popular Electronics, November 1995, p. 80)


LOW COST MICROWAVE FIELD STRENGTH METER
LOW COST MICROWAVE FIELD STRENGTH METERFA32-1

When operating, a waveguide directs energy onto a crystal detector. The diode shown is for X-band operation. The wave guide is a 1½ inch piece of plastic tubing with the ends flared. The plastic is coated with in electroless copper solution to provide a conducting surface. The dimensions are not critical. For calibrated readings, the meter is placed in a known field or else compared to a calibrated meter. To operate the meter, point it away from the signal. Switch the meter to the desired range, and adjust the zero control for a 0 reading. Then point the waveguide at the signal, and read field strength directly. (No reference)


SIGNAL-STRENGTH METER
SIGNAL-STRENGTH METERFD29-3

This field-strength meter is useful for antenna testing. It covers 6 to 60 MHz and uses a rugged 0-to-1mA meter. A 9-V battery supplies power. The unit can be mounted in a small plastic or metal case. (Elektor Electronics, 302 Circuits, P. 134)


SIMPLE FIELD STRENGTH METER
SIMPLE FIELD STRENGTH METERFE29-4

Useful for checking transmitters and antennas, this circuit uses a voltage doubling detector D1 and D2 (HP 5082-2800 hot carrier types). D1 and D2 can also be type 1N34 or 1N82. M is a 100 mA meter movement. (Reprinted with permission from 73 Amateur Radio Today, 9/90, p. 9)


FILTER CIRCUITS

600 HZ - 3000 HZ TUNEABLE NOTCH FILTER CIRCUIT

ABSORPTIVE FILTER FOR AMATEUR TRANSMITTERS

ACTIVE BANDPASS FILTER (10 - 1000 HZ)

ACTIVE BANDPASS FILTER CIRCUIT

ACTIVE LOW-PASS FILTER

ACTIVE UNITY-GAIN SECOND-ORDER LOW-PASS FILTER

ADJUSTABLE - Q NOTCH FILTER

ADJUSTABLE Q NOTCH FILTER

CW FILTER FOR SW RECEIVERS

DYNAMIC NOISE FILTER

FIFTH ORDER CHEBYSHEV MULTIPLE FEEDBACK LOW PASS FILTER

FOURTH-ORDER 100 HZ HIGH-PASS FILTER

FOURTH-ORDER HIGH-PASS BUTTERWORTH FILTER

HIGH Q BANDPASS FILTER

HIGH-Q NOTCH FILTER

HIGHPASS - LOWPASS FILTER USES FEW EXTERNAL COMPONENTS

MULTIPLE FEEDBACK BANDPASS ACTIVE FILTER

NOTCH FILTER CIRCUIT

PEAKING FILTER CIRCUIT

PHASE CORRECTION FOR LOW PASS FILTER

SECOND-ORDER BIQUAD BANDPASS FILTER

SHORTWAVE RECEIVER IF FILTER

SUBSONIC FILTER

TUNABLE NOTCH FILTER

TWIN-T NOTCH FILTER

TWO OP-AMP BANDPASS FILTER

TWO-SECTION 300-3000 HZ SPEECH FILTER

UNITY-GAIN SECOND-ORDER HIGH-PASS FILTER

UNITY-GAIN SECOND-ORDER HIGH-PASS FILTER

UNIVERSAL STATE VARIABLE FILTER

VARIABLE HIGH-PASS FILTER

VARIABLE LOW-PASS FILTER

VARIABLE-FREQUENCY AUDIO BP FILTER


600 HZ - 3000 HZ TUNEABLE NOTCH FILTER CIRCUIT
600 HZ - 3000 HZ TUNEABLE NOTCH FILTER CIRCUITFG110

Figure shows a notch filter that will tune roughly from 600 Hz to 3 kHz, and has been used by ham and SWL builders for a number of years. It is used for notching out unwanted CW stations, or for notching out heterodynes in receiver outputs. Insert this filter between the headphone output of the receiver and a power amplifier stage. (73 Amateur Radio Today, November 1995, pp. 67- 68)


ABSORPTIVE FILTER FOR AMATEUR TRANSMITTERS
ABSORPTIVE FILTER FOR AMATEUR TRANSMITTERSFG107

This filter diverts harmonic energy above 30 MHz to a dummy load and dissipates it as heat instead of reflecting it back to the transmitter. The absorptive filter is based on the classic design by Weinreich and Carroll from 1968. The high-pass and low-pass sections are shielded from each other (even though in the same shielded box) to prevent interaction. If you want to try building this filter, wind the coils on high-powered toroids.  Alternatively, you could wind an air-core coil using the nomograms in The ARRL Handbook for Radio Amateurs. (Popular Electronics, February 1997, p. 63)


ACTIVE BANDPASS FILTER (10 - 1000 HZ)
ACTIVE BANDPASS FILTER (10 - 1000 HZ)FB33-10

This filter has a bandpass centered around 1 kHz, for applications such as bridge amplifiers, null detectors, etc.

The circuit uses a μA741 IC and standard 5% tolerance components.

(William Sheets)


ACTIVE BANDPASS FILTER CIRCUIT
ACTIVE BANDPASS FILTER CIRCUITFF32-3

(Amplifiers, Waveform Generators & Other Low-Cost IC Projects, McGraw-Hill, p. 193)


ACTIVE LOW-PASS FILTER
ACTIVE LOW-PASS FILTERFE30-1

(Reprinted with permission from Popular -Electronics, Fact Card 226. (C) Copyright Gernsback Publications, Inc)


ACTIVE UNITY-GAIN SECOND-ORDER LOW-PASS FILTER
ACTIVE UNITY-GAIN SECOND-ORDER LOW-PASS FILTERFE30-29

This second order Butterworth filter cuts off near 10 kHz. The values of C1 and C2 can be changed to alter the frequency, or else calculated from the formula.

Fcutoff  =         1

                2.83πRC

C1= 2C2

  R2=R3=R

(William Sheets)


ADJUSTABLE - Q NOTCH FILTER
ADJUSTABLE - Q NOTCH FILTERFF32-17

This figure shows a circuit where the Q can be varied from 0.3 to 50. A fraction of the output is fed back to R3 and C3 by a second voltage follower, and the notch Q is dependent on the amount of signal fed back. A second follower is necessary to drive the twin "T" from a low-resistance source so that the notch frequency and depth will not change with the potentiometer setting. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 1187)


ADJUSTABLE Q NOTCH FILTER
ADJUSTABLE Q NOTCH FILTERFB63-1

In applications where the rejected signal might deviate slightly from the null on the notch network, it is advantageous to lower the Q of the network. This insures some rejection over a wider range of input frequencies. The figure shows a circuit where the Q may be varied from 0.3 to 50. A fraction of the output is fed back to R3 and C3 by a second voltage follower, and the notch Q is dependent on the amount of signal fedback. A second follower is necessary to drive the twin "T" from a low-resistance source so that the notch frequency and depth will not change with the potentiometer setting. (National Semiconductor Corporation, National Semiconductor Linear Applications Handbook, p. 1096)


CW FILTER FOR SW RECEIVERS
CW FILTER FOR SW RECEIVERSFG106

The CW filter is connected between the headphone or loudspeaker socket or terminal strip of your receiver, and either the headphones or an external loudspeaker. The output of the receiver should have an impedance of 8 ohms or more. As the circuit provides unity gain at pass frequencies and a low impedance output, there should be no problems with a mismatching when the filter is in use. The frequency response of the circuit peaks at approximately 800 Hertz, and the -6-dB bandwidth is about 300 Hertz or so. The -0-dB points occur at about 350 Hertz and 2 kHz. This is sufficient to normally give a substantial reduction in adjacent channel interference, but the response is not so narrow and peaky that using the receiver with the filter in circuit becomes difficult, with the wanted signal tending to drift out of the passband and become lost. (Electronic Experimenters Handbook, 1996, p.57)


DYNAMIC NOISE FILTER
DYNAMIC NOISE FILTERFC31-10

(Popular Electronics Fact Card No. 104)


FIFTH ORDER CHEBYSHEV MULTIPLE FEEDBACK LOW PASS FILTER
FIFTH ORDER CHEBYSHEV MULTIPLE FEEDBACK LOW PASS FILTERFB33-7

The low bias currents permit high resistance and low capacitance values to be used to achieve low frequency cutoff. fc = 10 Hz, Avcl = 4, Passband ripple = 0.1 dB. Note that small capacitors (25-50 pF) may be needed for stability in some cases. (Intersil, Component Data Catalog, 1987, p. 7-45)


FOURTH-ORDER 100 HZ HIGH-PASS FILTER
FOURTH-ORDER 100 HZ HIGH-PASS FILTERFD30-9

This filter using two sections of LM741, can be scaled in frequency, if desired. (Reprinted with permission from Radio-Electronics, 5/89. p. 58. (C) Copyright Gernsback Publications, Inc.,1989.


FOURTH-ORDER HIGH-PASS BUTTERWORTH FILTER
FOURTH-ORDER HIGH-PASS BUTTERWORTH FILTERFE30-5

(Popular Electronics, Fact Card 227)


HIGH Q BANDPASS FILTER
HIGH Q BANDPASS FILTERFE30-7

(Reprinted with permission from Popular Electronics, Fact Card 227. (C) Copyright Gernsback Publications, Inc)


HIGH-Q NOTCH FILTER
HIGH-Q NOTCH FILTERFF32-16

This shows a twin "T" network connected to an LM102 to form a high Q, 60-Hz notch filter. The junction of R3 and C3, which is normally connected to ground, is boot strapped to the output of the follower. Because the output of the follower is a very low impedance, neither the depth nor the frequency of the notch change; however, the Q is raised in proportion to the amount of signal fed back to R3 and C3. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 1187)


HIGHPASS - LOWPASS FILTER USES FEW EXTERNAL COMPONENTS
HIGHPASS - LOWPASS FILTER USES FEW EXTERNAL COMPONENTSFG114

This filter uses a Linear Technology P/N LTC-1560-1 and a LT1360 to implement a HP-LP filter. (Linear Technology Volume VII Number 1, February 1997, p. 12)


MULTIPLE FEEDBACK BANDPASS ACTIVE FILTER
MULTIPLE FEEDBACK BANDPASS ACTIVE FILTERFG109

(73 Amateur Radio Today, November 1995, p. 67)


NOTCH FILTER CIRCUIT
NOTCH FILTER CIRCUITFG113

This circuit is basically a noninverting amplifier with positive feedback. The negative feedback is to unity by a direct connection between the output terminal of the operational amplifier and the inverting input. A frequency selective RC network connects the output to the noninverting input, providing some positive feedback. The center frequency is: Fc = 1/2 π Rl *sqrt(C1 C2) . Where Fc is the center frequency in hertz (Hz), Rl is in ohms, Cl and C2 are in farads. (73 Amateur Radio Today, November 1995, p. 67)


PEAKING FILTER CIRCUIT
PEAKING FILTER CIRCUITFG108

This circuit is basically a noninverting amplifier with positive feedback. The negative feedback path is set to unity by a direct connection between the output terminal of the operation amplifier and the inverting (-) input. A frequency selective RC network connects the output to the noninverting (+) input, providing some positive feedback. The center frequency is:

Fc = 1/2πR1 sqrt(Cl C2)

Where Fc is the center frequency in hertz (Hz), Rl is in ohms, Cl and C2 are in farads.

(73 Amateur Radio Today, May 1996, p. 67}


PHASE CORRECTION FOR LOW PASS FILTER
PHASE CORRECTION FOR LOW PASS FILTERFG112

In some applications it may be desired, or even essential, that the bandwidth of the audio signal is limited, but that the phase relationship with the original signal is retained. A surround-sound encoder is a good example of this. The requirement can be met by combining the low-pass filter with an all-pass section and having the filtered signal compared with the signal corrected by the all-pass network. As it happens, the phase transfer of a 1st order all-pass filter is exactly the same as that of a 2nd order critically damped network. The design of such a combination is shown in the figure. In this, the all-pass network is based on IC1a and the low-pass section on IC1b. The -6dB cut-off point is at exactly 1 kHz, and the -3dB roll-off is at 642 Hz. (Elektor Electronics, July-August 1996, p. 86)


SECOND-ORDER BIQUAD BANDPASS FILTER
SECOND-ORDER BIQUAD BANDPASS FILTERFC31-6

(Intersil, Component Data Catalog, 1987 p. 7-45)


SHORTWAVE RECEIVER IF FILTER
SHORTWAVE RECEIVER IF FILTERFF32-7

An inexpensive filter can be made from microprocessor crystals.  This filter has 700 Hz BW (3 dB) and has a flat response (<l dB) for about 400 to 500 Hz. Although a 3-MHz crystal was used, any frequency from 2 to 15 MHz (using fundamental crystal) should work, with appropriate scaling of components. Crystal resonant frequencies should match within 20% and preferably 10% of expected bandwidth (which is narrower as Cx increases. Impedance is reduced with wider bandwidths. (William Sheets)


SUBSONIC FILTER
SUBSONIC FILTERFG111

The present filter is a 5th order high-pass section that provides 1 dB attenuation at 20 Hz, but below that the response drops off very steeply. The -3 dB point is at 17.3 Hz, and 13.6 Hz, the attenuation is 10 dB. The circuit of the filter is given in the Figure. Note that it is important that Cl-C5 are within 1 percent of one another. Their individual tolerance is not so important, since that merely affects the cut-off point. However, mutual deviation adversely affect the shape of the response, which should be a Butterworth characteristic as specified. All resistors are 1 percent types. (Elektor Electronics, July-August 1996, p. 87)


TUNABLE NOTCH FILTER
TUNABLE NOTCH FILTERFE30-6

(Reprinted with permission from Popular Electronics, Fact Card 227. (C) Copyright Gernsback Publications, Inc)


TWIN-T NOTCH FILTER
TWIN-T NOTCH FILTERFC65-1

This filter is used to reject or block a frequency or band of frequencies. These filters are often designed into audio and instrumentation systems to eliminate a single frequency, such as 60 Hz. Commercial grade components with 5% - 10% tolerance produce a null depth of at least 30 to 40 dB. When a twin-T network is combined with a TL081 op amp in a circuit, an active filter can be implemented. The added resistor capacitor network, R2 and C2, work effectively in parallel with the original twin-T network, on the input of the filter. These networks set the Q of the filter. The op amp is basically connected as a unity-gain voltage follower. The Q is found from:

Q =  R2   =   C1

       2R1        C2

For a 60-Hz notch filter with a Q of 5, it is usually best to pick the Cl capacitor value and calculate the resistor RI. Let Cl = 0.22 μF. Then:

R1 = 12 KΩ

  R2 = 120 KΩ

  C2 = 0.047μF

Standard 5% resistors and 10% capacitors produce a notch depth of about 40 dB, as shown in the frequency response curve.

(Texas Instruments, Linear and Interface Circuits Applications, 1985, Vol 1, p. 3-10 and 3-11)


TWO OP-AMP BANDPASS FILTER
TWO OP-AMP BANDPASS FILTERFF32-14

This circuit uses only two capacitors. The amplifier on the right supplies a controlled amount of positive feedback for improved response characteristics. Resistors R5 and R8 are used to bias the the amplifiers at V+/2. (National Semiconductor, Linear Applications Handbook, 1991, p.229)


TWO-SECTION 300-3000 HZ SPEECH FILTER
TWO-SECTION 300-3000 HZ SPEECH FILTERFD30-7

(Reprinted with permission from Popular Electronics, Fact Card 227. (C) Copyright Gernsback Publications, Inc)


UNITY-GAIN SECOND-ORDER HIGH-PASS FILTER
UNITY-GAIN SECOND-ORDER HIGH-PASS FILTERFE30-28

This filter circuit has a cutoff frequency of 2900 Hz with the values shown:

fcutoff =      1

                     2.83πRC

R = R1

    R2 = 2R1

          C = C1 = C2

(Wiliam Sheets)


UNIVERSAL STATE VARIABLE FILTER
UNIVERSAL STATE VARIABLE FILTERFE30-3

(Reprinted with permission from Popular Electronics, Fact Card 226. (C) Copyright Gernsback Publications, Inc)


VARIABLE HIGH-PASS FILTER
VARIABLE HIGH-PASS FILTERFE30-26

This second-order low-pass filter which should prove useful in audio applications uses an LM1458 or other similar op amp. It is tunable from 30 to 300 Hz cutoff. R2a, b are ganged log-taper potentiometers. (William Sheets)


VARIABLE LOW-PASS FILTER
VARIABLE LOW-PASS FILTERFE30-25

This second-order low-pass filter uses a 741op amp and is tunable from 2.5 kHz to 25 kHz. This circuit is useful in audio and tone control applications. Rl and 2 are ganged potentiometers. (William Sheets)


VARIABLE-FREQUENCY AUDIO BP FILTER
VARIABLE-FREQUENCY AUDIO BP FILTERFE30-24

This variable-frequency, audio bandpass filter is built around two 741 op amps that are connected in cascade. Two 741 op amps are configured as identical RC active filters and are connected in cascade for better selectivity. The filter's tuning range is from 500 Hz to 1500 Hz. The overall voltage gain is slightly greater than 1 and the filter's is about 5. The circuit can handle input signals of 4V peak-to-peak without being overdriven. The circuits input impedance is over 200 kΩ and its output impedance is less than 1 kΩ. (Reprinted with permission from Popular Electronics, 6/92, p. 67. (C) Copyright Gernsback Publications, Inc)


FLASHER AND BLINKER CIRCUITS

ALTERNATING FLASHER

ALTERNATING LED FLASHER

ASTABLE MULTIVIBRATOR

FLASHING CHRISTMAS LED DISPLAY

FLASHING NEON CHRISTMAS LIGHTS

LED FLASHER FOR 2 TO 10 LEDS

LOW VOLTAGE LAMP FLASHER

MINIATURE TRANSISTORIZED LIGHT FLASHER

MULTIPLE LED FLASHER

SEQUENTIAL FLASHER

SINGLE LED FLASHER

SUPER LED FLASHER

XENON FLASHTUBE CIRCUIT


ALTERNATING FLASHER
ALTERNATING FLASHERFB34-3

The LEDs flash alternately. The flash rate is determined by C1 and R4. (Hands-On Electronics, Spring 1986, p. 4)


ALTERNATING LED FLASHER
ALTERNATING LED FLASHERFC32-11

(Texas Instruments, Linear and Interface Circuits Applications, 1985, Vol. 1, p. 7-17)


ASTABLE MULTIVIBRATOR
ASTABLE MULTIVIBRATORFC32-4

The 4047 is configured as a free-running, astable-multivibrator (oscillator) circuit. That configuration, offers three different outputs. The output pulses at the Q and /Q output (pins 10 and 11, respectively) are the same as in the previous two circuits. The third output at pin 13 pulses twice as often as the outputs at 10 and 11. So, the circuit can be used to simultaneously provide both positive- and negative-trigger signals since the Q and /Q output are never in the same state, and a clock frequency. Thus, the 4047 can replace both a simple oscillator (the 555, for instance) and a flip-flop in some applications, (Popular Electronics 9/89, p. 88)


FLASHING CHRISTMAS LED DISPLAY
FLASHING CHRISTMAS LED DISPLAYFF33-3

Using LEDs and 3909 ICs, you can make a flashing-light circuit that will run for months on two AA batteries. (Reprinted with permission from Popular Electronics, 6/95, p.78. (C) Copyright Gernsback Publications, Inc.,1995)


FLASHING NEON CHRISTMAS LIGHTS
FLASHING NEON CHRISTMAS LIGHTSFF33-2

This flashing set of neon Christmas lights will make an attractive decoration for any time of year. B1 is made up of ten 9-V transistor radio batteries in series. The battery life can be measured in months. (Reprinted with permission from Popular Electronics, 6/95, p.7. (C) Copyright Gernsback Publications, Inc.,1995)


LED FLASHER FOR 2 TO 10 LEDS
LED FLASHER FOR 2 TO 10 LEDSFE31-6

This LED flasher has a double-ended output connection. The circuit can be used with 1 to 5 LEDs on each side as indicated. (William Sheets)


LOW VOLTAGE LAMP FLASHER
LOW VOLTAGE LAMP FLASHERFB34-1

The circuit is composed of a relaxation oscillator formed by Ql and an SCR flip-flop formed by Q2 and Q3. With the supply voltage applied to the circuit, the timing capacitor Cl charges to the firing point of the PUT, 2 volts plus a diode drop. The output of thePUT is coupled through two 0.02 μF capacitors to the gate of Q2 and Q3. To clarify operation, assume that Q3 is on and capacitor C4 is charged plus to minus as shown in the figure. The next pulse from the PUT oscillator turns Q2 on. This places the voltage on C4 across Q3 which momentarily reverse biases Q3. This reverse voltage turnsQ3 off. After discharging, C4 then charges with its polarity reversed to that shown. The next pulse from Ql turns Q3 on and Q2 off. Note that C4 is a non-polarized capacitor. For the component values shown, the lamp is on for about 1/2 second and off the sameamount of time. (Motorola: Thyristor Device Data, Series A, 1985, p. 1-6-52)


MINIATURE TRANSISTORIZED LIGHT FLASHER
MINIATURE TRANSISTORIZED LIGHT FLASHERFB34-2

R1 adjusts the flash rate. The lamp should be a No. 122, No. 222 or other similar, miniature incandescent lamp. (Popular Electronics, 3/81 p.100)


MULTIPLE LED FLASHER
MULTIPLE LED FLASHERFG117

Circuit diagram for driving multiple LEDs from a single LM3909 flasher chip. (Everyday with Practical Electronics, October 1995, p. 793)


SEQUENTIAL FLASHER
SEQUENTIAL FLASHERFE31-1

A 555 tinier, IC1, drives a 4017 CMOS decade counter. Each of the 4017's first four outputs drives a CA3079 zero-voltage switch. Pin 9 of the CA3079 is used to inhibit output from pin 4, thereby disabling the string of pulses that the IC normally delivers. Those pulses occur every 8.3 ms, i.e., at a rate of 120 Hz. Each pulse has a width of 120 μs.

Because of the action of the CA3079, the lamps connected to the triacs turn on and off  near the zero crossing of the ac waveform. Switching at that point increases lamp life by reducing an inrush of current that would happen if the lamp were turned on near the high point of the ac waveform. In addition a switching at the zero crossing reduces radio frequency interference (RFI) considerably. Caution: The CA3079s are driven directly from the 117-Vac power line, so use care.

(Reprinted with permission from R-E Experimenters Handbook 1989, p.159)


SINGLE LED FLASHER
SINGLE LED FLASHERFG116

Circuit diagram for LED flasher with low component count. (Everyday with Practical Electronics, October 1995, p. 793)


SUPER LED FLASHER
SUPER LED FLASHERFE31-5

The super LED flasher is actually two complete LED flasher circuits on one circuit board. The first LED flasher is made up of IC1 and LEDs D1 and D2. IC1 is a 555 timer IC configured as an astable (free-running) multivibrator with its output on pin 3.

The frequency of the 555's oscillation is controlled by R2, R3, and C1. Resistor R1 limits the input voltage to a low enough level to prevent damage to the IC. As the 555 IC oscillates, the output of pin 3 goes high (+) then low (-). When the output is high it supplies current to D1, which lights up. When it is low, pin 3 sinks current and D2 lights up. T his happens because LEDs are polarity-sensitive (like all other diodes, they permit current flow in only one direction) and one lead of each LED has been connected to the respective polarity to light that LED.

The second LED flasher, made up of IC2 and LEDs D3 and D4, operates in the same way as the first LED flasher.

 (Reprinted with permission from PE Hobbyists Handbook, 1991, p. 10. (C) Copyright Gernsback Publications, Inc., 1991)


XENON FLASHTUBE CIRCUIT
XENON FLASHTUBE CIRCUITFG115

These are basic circuits for firing Xenon flashtubes. Use the applicable circuit depending on trigger coil polarity. (Electronics Now, May 1996, p. 8)


FREQUENCY MEASURING CIRCUITS

FREQUENCY-RATIO MONITORING CIRCUIT

INEXPENSIVE FREQUENCY COUNTER/TACHOMETER

LINEAR FREQUENCY METER (AUDIO SPECTRUM)

LOW COST FREQUENCY INDICATOR


FREQUENCY-RATIO MONITORING CIRCUIT
FREQUENCY-RATIO MONITORING CIRCUITFD34-8

This circuit produces an output frequency that is linearly proportional to the ratio of the two input frequencies f1/f2. Each pulse of the bias (f1 (or f2) will open G1 for a period T=1/f2 so that fg/f2 pulses pass to the output. (Reprinted with permission from Electronic Design 6/90, p 100, Copyright 1990 Penton Publishing)


INEXPENSIVE FREQUENCY COUNTER/TACHOMETER
INEXPENSIVE FREQUENCY COUNTER/TACHOMETERFA35-1

This circuit uses the low power ICM7555 (CMOS 555) to generate the gating, /STORE and /RESET signals. To provide the gating signal, the timer is configured as an astable multivibrator. The system is calibrated by using a 5M potentiometer for RA as a coarse control and a 1K potentiometer for RB as a fine control. CD40106B's are used as a monostable multivibrator and reset time delay. (Intersil Data Book, 5/83, p. 6-49)


LINEAR FREQUENCY METER (AUDIO SPECTRUM)
LINEAR FREQUENCY METER (AUDIO SPECTRUM)FA35-2

The 555 is used in a monostable multivibrator circuit that puts out a fixed time width pulse, which is triggered by the unknown input frequency. (The Giant Book of Electronic Projects, TAB Book No. 1367, p. 109)


LOW COST FREQUENCY INDICATOR
LOW COST FREQUENCY INDICATORFB37-2

The circuit shows how two tone decoders set up with overlapping detection bands can be used for a go/no go frequency meter. Unit 1 is set 6% above the desired sensing frequency and Unit 2 is set 60% below the desired frequency. Now, if the incoming frequency is within 13% of the desired frequency, either Unit 1 or Unit 2 will give an output. If both units are on, it means that the incoming frequency is within 1% of the desired frequency. Three light bulbs and a transistor allow low cost read-out. The IC is an EXAR 567. (EXAR, Telecommunications Databook, 1986, p. 11-38


FREQUENCY MULTIPLIER AND DIVIDER CIRCUITS

150 TO 300 MHZ DOUBLER

CLOCK INPUT FREQUENCY DIVIDER

DIGITAL FREQUENCY DOUBLER CIRCUIT

DIGITAL LOGIC FREQUENCY DOUBLER

FREQUENCY DOUBLER

LOW-FREQUENCY DOUBLER

NONSELECTIVE FREQUENCY TRIPLER USES TRANSISTOR SATURATION CHARACTERISTICS

SIMPLE FREQUENCY DOUBLER


150 TO 300 MHZ DOUBLER
150 TO 300 MHZ DOUBLERFA36-3

(Courtesy of Motorola Inc., Linear Integrated Circuits, 1979, p. 6-99)


CLOCK INPUT FREQUENCY DIVIDER
CLOCK INPUT FREQUENCY DIVIDERFD26-1

ICA, R1 through R3, and Ql form a current source. The current that charges Cl is given by:

I =     (VD x R1)

     (R1 + R2) x R3

   =                (15 x 3 kΩ)

       (3 kΩ+ 12 kΩ) x 470 kΩ

   = 6.4  μA

The input signal drives ICD. Because ICD's positive input (V+) is slightly offset to +0.l V, its steady-state output will be near + 13 V. This voltage is sent to ICC through D2, setting ICC's output to + 13 V. Therefore, point D is cut off by D1, and C1 is charged by the current source. Assuming the initial voltage on Cl is zero, the maximum voltage (VCmax,) is given by:

TWclk > TPff + dt +TPxr + TWff

The right side of the inequality should be the minimum pulse width (either up time or down time) of the input clock. The circuit, when constructed with standard 74F-type parts, operates without any added delay in the exclusive-OR feedback path and with an input frequency of up to 22.5 Mhz. The circuit's output signal will have the same duty cycle as the input clock.

(Reprinted with permission from Electronic Design 6/91, p 109-114, Copyright 1991 Penton Publishing)


DIGITAL FREQUENCY DOUBLER CIRCUIT
DIGITAL FREQUENCY DOUBLER CIRCUITFG120

The 74LS393 is designed to advance one count on the positive to negative transition of the pulse at the clock input (pins 1 and 13). An inverter in front of the B section of the counter causes the B section to advance one count on the negative to positive transition of the input pulse. Each section of the counter is cleared with a positive-going pulse on the master reset input (pins 2 and 12). Positive-going output pulses from pins 6 and 10 of IC2, reset the respective counters. The duration of the pulses depends upon the propagation delay of the inverters. With the 74LS04 hex inverter, delay will probably be in the vicinity of 20 to 25 nanoseconds. The output pulses are also connected to the remaining inverter gate through switching diodes and a pull-down resistor, which configures the remaining inverter as a NOR gate. The output at pin 8 of IC2 represents the input frequency multiplied by two. (Electronics Now, September, 1996, p. 14)


DIGITAL LOGIC FREQUENCY DOUBLER
DIGITAL LOGIC FREQUENCY DOUBLERFG119

This circuit is usable if very high frequency operation is needed, or if very narrow output pulses can be tolerated.  The output pulse width is determined by the propagation time delay of the exclusive-OR gate, and the input frequency cannot exceed 1/2 (delay). (Electronics Now, April 1997, p. 14)


FREQUENCY DOUBLER
FREQUENCY DOUBLERFA36-2

(Reprinted with permission from National Semiconductor Corporation, Linear Databook 19821, p. 5-9)


LOW-FREQUENCY DOUBLER
LOW-FREQUENCY DOUBLERFA36-4

(Courtesy of Motorola Inc., Linear Integrated Circuits, p. 6-99)


CHARACTERISTICS
NONSELECTIVE FREQUENCY TRIPLER USES TRANSISTOR SATURATION CHARACTERISTICSFB38-1

The turn-on and turnoff characteristics of two complementary transistors can be combined to attain nonselective frequency tripling. The resulting circuit handles any periodic waveform with nonvertical sides. Each input signal peak produces three output signal peaks. The additional peaks occur where the input signal causes saturation of one of the two transistors. The circuit operates over a frequency range from dc to the upper limits of the complementary transistor pair. About the only disadvantage of the circuit is the lack of symmetry of the output signal peaks.(Electronic Design, 8/73, p. 86)


SIMPLE FREQUENCY DOUBLER
SIMPLE FREQUENCY DOUBLERFG118

This circuit uses only a single exclusive-OR gate and a couple of passive components. The width of the output pulses are determined by the time constant of the RC network, and the maximum input frequency cannot exceed (1/2)RC. (Electronics Now, April 1997, p. 14)


 FUNCTION AND SIGNAL GENERATOR CIRCUITS

555 - BASED RAMP GENERATOR

ACCURATE, STABLE FUNCTION GENERATOR

FUNCTION GENERATOR

FUNCTION GENERATOR

LINEAR RAMP GENERATOR

LOW-FREQUENCY FM GENERATORS

NONLINEAR POTENTIOMETER OUTPUTS

PRECISION AUDIO WAVEFORM GENERATOR

PROGRAMMABLE VOLTAGE CONTROLLED FREQUENCY SYNTHESIZER

RANDOM NUMBER GENERATOR

ROOT EXTRACTOR

SIGNAL GENERATOR

TRIANGLE- AND SQUARE-WAVE GENERATOR


555 - BASED RAMP GENERATOR
555 - BASED RAMP GENERATORFE33-6

This circuit is used to generate a ramp voltage for tuning a radio receiver. An N555, running at about 0.1 Hz is used as an astable multivibrator. ( Reprinted with permission from Elektor Electronics, 3/92, p. 58)


ACCURATE, STABLE FUNCTION GENERATOR
ACCURATE, STABLE FUNCTION GENERATORFF36-4

Supply-limited oscillators usually are sensitive to temperature and power-supply changes, are never symmetrical, and don't operate at high frequencies because the amplifier's output is saturated, when it reaches the supply lines.

The circuit shown, a function generator, can alleviate these problems. Its square-wave output boasts a rapid rise time, quick settling time, and an amplitude that's temperature insensitive. Also, its triangular output waveform features a perfectly constant rate of change throughout its range.

Amplifier Al together with A2 generates a stable +10 V. This signal, which is integrated using A3, C2, and R2, makes a negative-going ramp. When the peak output of A3 equals -10 V, the output of Al and A2 change state and the A3's output ramps up. When A3's output equals +10 V, the outputs of Al and A2 change state again and new cycle starts.

(Reprinted with permission from Electronic Design 10/94, p. 110, Copyright 1994 Penton Publishing)


FUNCTION GENERATOR
FUNCTION GENERATORFD34-3

 Using an Intersil ICL8038, this function generator generates frequencies from 1 Hz to over 80 kHz. R1 is the fine frequency control and Sl is the coarse frequency control range switch. S2 selects square-, triangle, or sine-wave output. U2 is a buffer amplifier and R5 sets output level. R2 is adjusted for a symmetrical triangle wave. R3 and R4 are adjusted for minimum sine-wave distortion. Power supply is 12 V at less than 100 mA. (Reprinted with permission front Radio-Electronics, 2/91, p. 23. Copyright Gernsback Publications, Inc., 1991)


FUNCTION GENERATOR
FUNCTION GENERATORFC38-24

This generator will supply sine, triangular, and square waves from 2 Hz to 20 kHz. This complete test  instrument can be plugged into a standard 110 Vac line for power. VOUT will be up to + or - 25V (50 V pk-pk across loads as small as 10 Ohms (about 2.5 A maximum output current). Capacitor working voltages should be greater than 50 Vdc and all resistors should be 1/2 W, unless otherwise indicated. The interconnecting leads from the 741 pins 2 and 3 to their respective resistors should be kept short, less than 2 inches if possible; longer leads might result in oscillation. Full output swing is possible to about 5 kHz; after that the output begins to taper off because of the slew rate of the 741, until at 20 kHz the output swing will be about 20 Vpp + or - 10V. This problem can be remedied by simply using an op amp with a higher slew rate, such as the LF356. (Raytheon, Linear and Integrated Circuits, 1984, p. 12-7)


LINEAR RAMP GENERATOR
LINEAR RAMP GENERATORFB40-15

The linear charging ramp is most useful where linear control of voltage is required. Some possible applications are a long period voltage controlled timer, a voltage to pulse width converter, or a linear pulse width modulator. Ql is the current source transistor, supplying constant current to the timing capacitor Ct. When the timer is triggered, the clamp on Ct is removed and Ct charges linearly toward Vcc by virtue of the constant current supplied by Ql. The threshold at pin 6 is 2/3 Vcc; here, it is termed Vc. When the voltage across C reaches Vc volts, the timing cycle ends. In general, It should be 1 mA value compatible with the NE555. (Texas Instruments, Linear and Interface Circuits Applications, Vol. 1, 1985, p. 7-16)


LOW-FREQUENCY FM GENERATORS
LOW-FREQUENCY FM GENERATORSFC38-11

Here are two FM generators for low frequency, less than 0.5 MHz center frequency, applications. Each uses a 566 function generator as a modulation generator and a second 566 as the carrier generator, Capacitor Cl selects the modulation frequency adjustment range and Cl selects the center frequency. Capacitor C2 is a coupling capacitor which only needs. to be large enough to avoid distorting the modulating -waveform. If a frequency sweep in only one direction is required, the 566 ramp generators given in this section can be used to drive the center generator. (GE/RCA Operational Amplifiers Circuit Ideas, 1987, p. 8)


NONLINEAR POTENTIOMETER OUTPUTS
NONLINEAR POTENTIOMETER OUTPUTSFD34-2

Using these illustrated configurations, various rotation output characteristics can be obtained from potentiometers and one or two resistors. (Reprinted with permission from Electronic Design 5/91, p 95, Copyright 1991 Penton Publishing)


PRECISION AUDIO WAVEFORM GENERATOR
PRECISION AUDIO WAVEFORM GENERATORFC38-13

This circuit generates sinusoidal, square, and triangle waveforms simultaneously. Set the frequency to a particular value or vary it, as shown above. An op amp can be added for extra drive capability and simplified amplitude adjustment. A simple comparator, slicing the triangle waveform, provides continuous duty cycle adjustment at a constant frequency. (Intersil, 1978 Databook)


PROGRAMMABLE VOLTAGE CONTROLLED FREQUENCY SYNTHESIZER
PROGRAMMABLE VOLTAGE CONTROLLED FREQUENCY SYNTHESIZERFB40-6

The μA2240 consists of four basic circuit elements: (1) a time-base oscillator, (2)an eight-bit counter, (3) a control flip-flop, and (4) a voltage regulator. The basic frequency of the time-base oscillator (TBO) is set by the external time constant determined by the values of R1 and Cl (1/R1C1 = 2 kHz). The open-collector output of the TBO is connected to the regulator output via a 20 k ohm pull-up resistor, and drives the input to the eight-bit counter. At power-up, a positive trigger pulse is detected across C2 which starts the TBO and sets all counter outputs to a low state. Once the μA2240 is initially triggered, any further trigger inputs are ignored until it is reset. In this astable operation, the μA2240 will free-run from the time it is triggered until it receives an external reset signal. Up to 255 discrete frequencies can be synthesized by connecting different counter outputs. (Texas Instruments, Linear and Interface Circuits Applications, Vol 1, 1985, p, 7-25)


RANDOM NUMBER GENERATOR
RANDOM NUMBER GENERATORFG122

The 74S74 flip-flops shown in the circuit are arranged to form a four-bit shift register. Binary data enters the Do input on Ul-a and is sequentially shifted to each output (Q0, Ql, Q2, Q3) with each clock pulse. The data input to the shift register comes from the output of U3-a, one gate of a 7486. That exclusive-or gate compares two of the output bits from the shift register. If the two bits are the same, then the output of U3-a is 0 volts(or low). If the two bits are different, then the output of U3 is +5 volts (or high). Therefore, U3-a acts as a type of logical-feedback network that changes the data at D0, which in turn changes the outputs of the flip-flops. The effect of that network is to create a pseudo-random sequence of bits at the outputs of Ul and U2. (Popular Electronics, September 1995, p. 32)


ROOT EXTRACTOR
ROOT EXTRACTORFE33-15

This circuit produces a voltage that is proportional to the root of the input. This gives a logarithmic response log Vinª = a log Vin. (Reprinted with permission from Popular Electronics, Fact Card 258. (C) Copyright Gernsback Publications, Inc)


SIGNAL GENERATOR
SIGNAL GENERATORFE33-8

This simple oscillator is rich in harmonics which make this circuit useful for signal tracing applications. (William Sheets)


TRIANGLE- AND SQUARE-WAVE GENERATOR
TRIANGLE- AND SQUARE-WAVE GENERATORFE33-14

The circuit will generate precision triangle and square waves. The output amplitude of the square wave is set by the output swing of op amp Al, and R1/R21 sets the triangle amplitude. The frequency of oscillation in either case is approximately 1/0.69RC.

The square wave will maintain 50% duty cycle--even if the amplitude of the oscillation is not symmetrical. The use of a fast op amp in this circuit will allow good square waves to be generated to quite high frequencies. Because the amplifier runs open loop, compensation is not necessary. The triangle-generating amplifier should be a compensated type. A dual op amp, such as the MC1458, can be used for most applications.

(William Sheets)


GAME CIRCUITS

COIN TOSS CIRCUIT

ELECTRONIC CRAPS GAME

ELECTRONIC DICE

ELECTRONIC ONE-ARM BANDIT

ELECTRONIC ROULETTE

LIE DETECTOR

LOCK OUT CIRCUIT

MINI ROULETTE

REACTION TIMER

RUN DOWN CLOCK/SOUND GENERATOR

THREE-INPUT FIRST-RESPONSE MONITOR

WHEEL OF FORTUNE


COIN TOSS CIRCUIT
COIN TOSS CIRCUITFG123

Shown is a CMOS coin-toss circuit that works well and can be built with a single 4011 or 4001 CMOS IC. (Note that IC pin numbers in the diagram apply for both the 4001 and 4011) Two gates form a clock, and the others make up a bistable multivibrator. With this circuit, it is necessary to adjust the 10,000-ohm potentiometer (R3) for a 50% duty cycle. If you don't have a scope to do this, simply measure the direct current flowing through each LED while adjusting R3. When the same current level flows through each LED, the clock will be adjusted for a 50% duty cycle. (Popular Electronics, April 1997, pp. 59-61)


ELECTRONIC CRAPS GAME
ELECTRONIC CRAPS GAMEFF37-1

Two gates of a 4093 quad, 2-input NAND, Schmitt trigger CMOS IC are connected in astable-oscillator circuits as clocks. The two 4017 ICs have six LEDs connect to its first six outputs. As the clock pulses enter pin 14 of the 4017s, the ICs count from one, to six over and over as long as the clock pulses are present. When Sl and/or S2 are released, one. of the LEDs  in each circuit will be remain on, indicating a number from one to six.

The circuit is set up so that you can roll the dice together by pressing S1 and S2 at the same time, or roll each die one at a time.

(Reprinted permission from Popular Electronics, 9/94, p. 81. Copyright Gernsback Publications. 1994)


ELECTRONIC DICE
ELECTRONIC DICEFC39-3

The basic dice circuit is given. A 555 timer, IC1, is connected as an astable multivibrator. This feeds clock pulses to divide-by-six counter IC2 the outputs of which are decoded by gates Nl to N6 to drive an array of LEDs in the familiar die pattern. When switch Sl is in position b, the reset input of IC1 decreases and the oscillator is inhibited. Power is fed to the LEDs via S1b so that the display is activated. When the die is rolled by switching S1 to position a, the display is blanked. C4 is connected to positive supply via Sla, producing a short pulse which resets IC2 via N7 and N8. The reset input of IC1 is pulled high via R5, so the multivibrator begins to oscillate and feeds clock pulses to IC2 via N5. When Sl is switched back to position a, the multivibrator is again inhibited. Then, the counter stops and power is applied to the LEDs which display the value of the throw. (Elektor, 6/78, p. 6-18)


ELECTRONIC ONE-ARM BANDIT
ELECTRONIC ONE-ARM BANDITFF37-7

The one-arm bandit circuit is made up of three clock circuits and three counter/readout circuits. A single roll switch, S1, turns on all three clocks at the same time. When S1 is closed, capacitors C4, C5, and C6 are charged through D31, D32, and D33 to about 8 V. After S1 is released, the three clocks run, taking energy from the three charged capacitors. As the capacitors discharge, the three clocks begin to slow down, producing the effect of the drums in a mechanical bandit slowing to a stop.

The 4017's 10-output LEDs can be numbered or designated -,is apples, cherries, bells, wild cards, or anything you like to make the game more interesting. Additional logic circuitry can be added to the 4017 outputs to sound an alert or turn on a light when any three numbers or output items match.

Three potentiometers, R12, R13, and R14, can be varied for each roll to change the clock's frequency and the roll rate.

(Reprinted permission from Popular Electronics. Copyright Gernsback Publications. 1994)


ELECTRONIC ROULETTE
ELECTRONIC ROULETTEFB41-1

Ul (a 4046 PLL containing a voltage controlled oscillator or VCO, two phase comparators, a source follower, and a Zener diode) is used to produce a low frequency, pulsed output of about 40 Hz. The VCO's frequency range is determined by R6 and C2, which can be altered by varying the voltage at pin 9. The rising voltage causes the frequency to rise from zero to threshold and remain at that frequency as long as Sl is closed. When Sl is opened, Cl discharges slowly through Rl to ground and the voltage falls toward zero. That produces a decreasing pulse rate. The output of Ul at pin 4 is connected to the clock input of U2 (a 4017 decade decoder/driver) at pin 14 via C3. U2 sequentially advances through each of its ten outputs (0 to 9)-pins 1 to 7, and 9 to 11-with each input pulse. As each output goes high, its associated LED is lighted, and extinguished when it returns to the low state. Only eight outputs are used in the circuit, giving two numbers to the spinner of the house. The circuit can be set up so that the LED's lights sequence or you can use some staggered combination; the LEDs grouped in a straight line or a circle. (Tab Books, Inc., 101 Sound, Light, and Power IC Projects)


LIE DETECTOR
LIE DETECTORFB41-2

The two probes shown are held in the hands and the skin resistance applies bias to the transistor. The 5 k ohm pot is set for zero deflection on the meter. When the "subject" is embarrassed or lies sweating on the hands takes place, increasing the bias to the transistor and upsetting the bridge balance. (William Sheets)


LOCK OUT CIRCUIT
LOCK OUT CIRCUITFG125

This circuit is used in contests, games, etc. When a contestant presses one of the buttons, an SCR triggers, lighting the associated LED and preventing anyone else from actuating the system. U2 and U3 form a warble tone generator while U4 and U5 provide time delay. (Popular Electronics, September, 1996, p. 68)


MINI ROULETTE
MINI ROULETTEFG124

A circuit diagram for a mini battery-powered version of Roulette is shown. This circuit uses a 4017 decade counter (IC2) driving 10 LEDs. Since only one LED is ever illuminated at any one time, a common limiting resistor R4 is used. They may also be placed in alternating red/green order for added effect. The counter IC2 is clocked by IC1, a classic 555 timer connected as an astable. When the "spin" button is pressed and then released, full speed is achieved and then the display gradually slows down until it stops on a single number. Capacitor C2 governs the oscillator speed and resistor R3 prevents instability when the LED rotation stops. The piezo disc transducer, Xl, is placed on the output of the oscillator to provide a sound effect. (Everyday Practical Electronics, August,1996, p. 643)


REACTION TIMER
REACTION TIMERFD35-1

This circuit uses a timer to generate pulses at a 5-ms clock rate. The pulses are shifted into the shift register, one at a time, lighting an LED. An auxiliary timer that generates one pulse per second is used to generate timing to activate the "go" LED and start the 5 ms pulses clocking into the registers. At the GO signal each player presses his buttons (S3 or S4). The delay (reaction time) is read out on LED4 to LED17; after six seconds, the sequence repeats. (Reprinted  with permission from Radio-Electronics 4/90, p. 33-36. Copyright Gernsback, Publications, Inc., 1990)


RUN DOWN CLOCK/SOUND GENERATOR
RUN DOWN CLOCK/SOUND GENERATORFD35-3

Used in electronic roulette or dice games, this circuit produces a clock signal that initially is several tens of kHz (depending on C2) and gradually decreases to zero in about 15 seconds, as C1 discharges through R4. (Reprinted with permission from Radio-Electronics, 12/89, p.57. (C) Copyright Gernsback Publications, Inc.,1989)


THREE-INPUT FIRST-RESPONSE MONITOR
THREE-INPUT FIRST-RESPONSE MONITORFF37-5

(Reprinted with permission from Popular Electronics, 4/94, p.80. (C) Copyright Gernsback Publications, Inc.,1994)


WHEEL OF FORTUNE
WHEEL OF FORTUNEFD35-4

This circuit is a 10-LED spinning wheel that "clicks" as the wheel passes each point. The rotation starts fast, then gradually slows down to a random stop (with a click at each position). After the rotation ceases, the selected LED stays lit for about 10 seconds, then goes out. The cycle restarts by depressing the push button switch. (Reprinted with permission from Popular Electronics, 10/77, p.82. (C) Copyright Gernsback Publications, Inc.,1977)


GAS AND SMOKE DETECTOR CIRCUIT

COMBUSTIBLE GAS DETECTOR

EXPLOSIVE GAS DETECTOR


COMUSTIBLE GAS DETECTOR
COMBUSTIBLE GAS DETECTORFE35-2

The circuit shown is useful for the detection of dangerous levels of combustible fumes or gases. It uses a comparator circuit to trigger an alarm buzzer.  The sensor's resistant element is connected in series with resistor Rl to form a voltage-divider circuit; Rl is specifically matched to each gas sensor by the manufacturer. (Reprinted with permission from Electronics Now, 7/93, p.33. (C) Copyright Gernsback Publications, Inc.,1993)


EXPLOSIVE GAS DETECTOR
EXPLOSIVE GAS DETECTORFE35-1

A gas sensor (TGS823 from Allegro Electronics, Cornwall Bridge, CT 06754) conducts in the presence of explosive gases. U5 is a voltage-to-frequency converter that produces a frequency proportional to the sensor conductance. The output frequency ranges from 100 Hz in clean air to 8 kHz in a contaminated atmosphere. The dc voltage from the sensor also drives bar graph LED U7 and comparators U4-b and U4-c to sense present caution and danger levels.  Ul drives an ac load up to 100 mA (relay, indicator, alarm, etc). (Reprinted with permission from Popular Electronics, 11/93, p. 33. (C) Copyright Gernsback Publications, Inc.,1993)


HALL EFFECT CIRCUITS

DOOR OPEN ALARM

SECURITY DOOR AJAR ALARM


DOOR OPEN ALARM
DOOR OPEN ALARMFB43-2

Door open alarms are used chiefly in automotive, industrial, and appliance applications. This type of circuit can sense the opening of a refrigerator door. When the door opens, a triac could be activated to control the inside light. The figure shows a door position alarm. When the door is opened, an LED turns on and the piezo alarm sounds for approximately 5 seconds. This circuit uses a TL3019 Hall-effect device for the door sensor. This normally open switch is located in the door frame. The magnet is mounted in the door. When the door is in the closed position, the TL3019 output goes to logic low, and remains low until the door is opened. This design consists of a TLC555 monostable timer circuit. The 1 μF capacitor and 5.1 M ohm resistor on pins 6 and 7 set the monostable RC time constant. These values allow the LED and piezo alarm to remain on about 5 seconds when triggered. One unusual aspect of this circuit is the method of triggering. Usually a 555 timer circuit is triggered by taking the trigger, pin 2, low which produces a high at the output, pin 3. In this configuration with the door in the closed position, the TL3019 output is held low. The trigger, pin 2, is connected to 1/2 the supply voltage Vcc. When the door opens, a positive high pulse is applied to control pin 5 through a 0.1 μF capacitor and also to reset pin 4. This starts the timing cycle. Both the piezo alarm and the LED visual indicator are activated. (Texas Instruments, Linear and Interface circuits Applications, 1987, P. 12-10)


SECURITY DOOR AJAR ALARM
SECURITY DOOR AJAR ALARMFC41-2

In operation, the TL3019 device will activate, or become low, when a south pole of a magnet comes near the chip face of the device. The example shows five doors. Each door has a magnet embedded in its edge with the south pole facing the outer surface. At the point where the magnet is positioned with the door closed, a TL3019 sensor is placed in the door jamb. With the door closed, the Hall devices will be in a logic low state. This design has five doors and uses five TL3019 devices. Each TL3019 has a 4-KΩ resistor in series and all door sensor and resistor sets are in parallel and connected to the inverting input of an LM393 comparator. With all doors closed, the effective resistance will be about 800 Ω and produce 2.2 V at the inverting input. The noninverting input goes to a voltage divider network which sets the reference voltage. The 1.5-KΩ potentiometer is adjusted so the indicator goes out with all doors closed. This will cause 2.35 V to appear at the noninverting input of the comparator. When a door opens, the voltage at the inverting input will go to 2.5 V which is greater than VREF, and the LED will light. A large number of doors and windows can be monitored with this type of circuit. Also, it could be expanded to add an audible alarm in addition to the visual LED. (Texas Instruments, Linear and Interface Circuits Applications, 1987, p. 12-9)


INDICATOR CIRCUITS

ac CIRCUIT LED POWER INDICATOR

BALANCE INDICATOR

RECEIVER SIGNAL-STRENGTH INDICATOR

RF-ACTUATED RELAY

STEREO INDICATOR


ac CIRCUIT LED POWER INDICATOR
AC CIRCUIT LED POWER INDICATORFD37-5

 Many electronic circuits need an indication that they are under power; for most ac circuits, a neon lamp is the device of choice. A bidirectional tricolor LED can be used if a capacitor is connected in series with the LED to limit the current through the LED. A 1 μF, 250-WVdc capacitor, which has a reactance of 2650 ohms at 60 Hz, is used in series with an LED to limit the current through the unit to 43 mA. The impedance of the LED is low compared to the reactance of the capacitor, so nearly all the impedance will be caused by the capacitor with the added advantage of no energy loss caused by the capacitor.

The power of the LED is 1.175 V x 0.043 A = 50 mW compared to an NE-2H at 250 mW. For 230 V, use a 0.47 -μF, 400-WVdc capacitor.

(Reprinted with permission from Popular Electronics, 3/91, p.25. (C) Copyright Gernsback Publications, Inc.,1991)


BALANCE INDICATOR
BALANCE INDICATORFD37-7

 If your amplifier is fitted with two level controls, it actually offers you a balance control and a level control. A drawback of this is that it is quite difficult to set the balance properly. T his can be obviated, however, by replacing the two monopotentiometers with stereo versions Pl and P2 in the diagram.

One half of the pair, PlA and P2A, assumes the tasks of the removed components. The other half is connected in a bridge circuit. The voltage between wipers of the potentiometers is then a measure of the balance between the two channels. The lower the potential, the better the balance. If you are interested in knowing the degree of unbalance, connect a center-zero moving coil meter with a bias resistor between A and B. With this arrangement, zener diodes Dl and D2 can be omitted: they are necessary only with the LED indicator shown in the diagram to prevent the input voltage of the op amp from getting too close to the level of the supply voltage.

The circuit around IC1 is a classical differential amplifier. Resistors R5 and R6 provide a virtual earth for the LEDs, which is necessary to ensure that, in spite of the asymmetrical supply voltage, a positive and a negative output is obtained.

Because the LEDs have been included in the feedback loop of the indicator, the circuit is pretty sensitive. At only 40 mV, that is, just 1/400 of the supply voltage, one of the LEDs begins to light. The maximum current drawn by the LEDs is determined by the values of R5 and R6.

(Elektor-Electronics, 7/8/91, S44)


RECEIVER SIGNAL-STRENGTH INDICATOR
RECEIVER SIGNAL-STRENGTH INDICATORFF39-3

Using an AD606 log amplifier, this indicator gives a logarithmic output of +0.3 V at -80-dBm input to +3.5 V at 10-dBm input. Frequency range is to 50 Mhz for this IC device. (Analog Devices, Analog Dialogue, Vol. 27. No. 1 (1993), p. 21)


RF-ACTUATED RELAY
RF-ACTUATED RELAYFC44-4

Automatic antenna switching or rf power indication can be achieved with this circuit. Relay will key with less than 150 mW on 2 m. (73 Amateur Radio Today, 10/83, p. 53)


STEREO INDICATOR
STEREO INDICATORFC44-1

On most FM tuners, the stereo indicator lights upon detection of the 19-kHz pilot tone. However, this doesnt mean that the program is actually stereophonic, since the pilot tone is often transmitted with mono programs also. A similar situation exists on stereo amplifiers, where the stereo LED is simply controlled from the mono/stereo switch.

The LED -based stereo indicator described here lights only when a true stereo signal is fed to the inputs. Differential amplifier A1 raises the difference between the L and R input signals. When these are equal, the output of A1 remains at the same potential as the output of A2, which forms a virtual ground rail at half the supply voltage. When A1 detects a difference between the L and R input signals, it supplies a positive or negative voltage with respect to the virtual ground rail, and so causes C3 to be charged via D1 should not be less than 100 mV to compensate for the drop across D1 or D2. The sensitivity of the stereo indicator is adjustable with P1.

(Elektor Electronics, 7-8/87 Supplement, p. 36)


INFRARED CIRCUITS

AUDIO-MODULATED IR TRANSMITTER

CORDLESS HEADPHONES

DTMF INFRARED TRANSMITTER

FM INFRARED RECEIVER FOR AUDIO RECEPTION

INFRARED ALARM TRANSMITTER

INFRARED DATA RECEIVER

INFRARED TRANSMITTER

IR ILLUMINATOR FOR NIGHT-VISION TV CAMERAS AND SCOPES

IR RECEIVER

IR TRANSMITTER

LOW-POWER INFRARED DATA-LINK RECEIVER

PHOTOTRANSISTOR IR RECEIVER

REMOTE-CONTROL TESTER

VERY SIMPLE IR REMOTE-CONTROL CIRCUIT

WIRELESS IR HEADPHONE RECEIVER

WIRELESS IR HEADPHONE TRANSMITTER


AUDIO-MODULATED IR TRANSMITTER
AUDIO-MODULATED IR TRANSMITTERFF40-1

This circuit produces an effect similar to frequency modulation (FM) by varying the voltage at pin 6 of the PLL using an audio signal. The FM IR signal can be picked up by a receiver with an FM detector suitably tuned . (Reprinted with permission from Popular Electronics, 4/90, p.102. (C)Copyright Gernsback Publications, Inc.,1990)


CORDLESS HEADPHONES
CORDLESS HEADPHONESFG128A

Although no hi-fi, it is possible to use headphones with no direct connection to the audio source. Figure illustrates a simple transmitter circuit suitable for connecting to an audio source. Diodes Dl to D3 are three infra-red LEDs in series, driven by TR2 an n-channel MOSFET transistor with a drain current rating of 500 mA maximum. The illumination of the LEDs is modulated by the audio signal applied, with TRl current-limiting and shunting the bias of TR2 to ground when TR2 source current exceeds roughly 100 MA. Potentiometer Vrl should be adjusted for best results. A 9V power supply is best used in this circuit due to the sustained level of current consumption The transmitter range is about one to two meters but this can be extended by using reflectors behind the diodes. A suggested receiver circuit, using an infra-red photodiode, D4, to detect the IR light, is shown in Fig. b. The received signal is AC coupled to TR3, another MOSFET. The output is taken from the drain terminal via capacitor C5. Bias can be adjusted with pot. VR2, and this circuit will run from a PP3 size battery. The circuit could be adapted for other applications. (Everyday Practical Electronics, May 1996, p. 389)


DTMF INFRARED TRANSMITTER
DTMF INFRARED TRANSMITTERFG126

This transmitter uses a 5089 DTMF generator chip and a keypad to generate DTMF signals and modulate these on an IR light beam from an IR LED. XTAL  is a 3.579 Mhz Burst crystal. (Nuts and Volts, June 1995, p. 98)


FM INFRARED RECEIVER FOR AUDIO RECEPTION
FM INFRARED RECEIVER FOR AUDIO RECEPTIONFF40-11

Modulated IR energy strikes Q2, a phototransistor. Q1 is a tuned amplifier and feeds PLL detector U1. U2 is an audio amplifier that drives a speaker. (Reprinted with permission from Popular Electronics, 4/90, p.103. (C) Copyright Gernsback Publications, Inc.,1990)


INFRARED ALARM TRANSMITTER
INFRARED ALARM TRANSMITTERFG129

The oscillator uses IC1 in relaxation oscillator. Capacitor C2 and resistor R4 are the timing components and they are connected between the output of ICl and its inverting input (pin 2). A roughly squarewave signal is generated at pin 6, the output of IC1. This signal is used to drive the infra-red LED Dl, via the emitter follower buffer stage transistor TR1, and current limiter resistor R5. The specified value for R5 sets the LED current at nearly-100 milliamps, but as the LED is switched off for about 50 per cent of the time, the average LED current is a little under 50 milliamps. This is the maximum acceptable drive current for most normal infra-red LEDs. (Everyday with Practical Electronics, October 1995, p. 787)


INFRARED DATA RECEIVER
INFRARED DATA RECEIVERFG128

The LT1328 circuit operates ever the full 1 cm to 1 meter range of the IRDA standard at the stipulated light levels. For IRDA data rates of 115kbs and below, a 1.6 μs pulse width is used for a zero and no pulse for a one. Light levels are 40 mW/sr (milliwatts per steradian) to 500 mW/sr. Figure shows a scope photo for a transmitter input (top trace) and the LTI328 output (bottom trace). Note that the input to the transmitter is inverted; that is, transmitted light producers a high at the input, which results in a zero at the output of the transmitter. The Mode pin (pin 7) should be high for these data rates. (Linear Technology, Volume VII, Number 1, February 1997, p. 6)


INFRARED TRANSMITTER
INFRARED TRANSMITTERFB45-2

The ultra simple one transistor, IR transmitter shown is designed to transmit the sound from any 8 or 16 ohm audio source, such as a TV radio, or tape recorder on an infrared beam of light. (Hands-On Electronics, Jul/Aug 1986, p. 86)


IR ILLUMINATOR FOR NIGHT-VISION TV CAMERAS AND SCOPES
IR ILLUMINATOR FOR NIGHT-VISION TV CAMERAS AND SCOPESFF40-6

This source uses LEDs and an astable oscillator to control the switch, duty-cycle, and effective IR illumination output. (Reprinted with permission from Popular Electronics, 4/94, p.34. (C) Copyright Gernsback Publications, Inc.,1994)


IR RECEIVER
IR RECEIVERFC45-3

Infrared emissions detected by Ql are fed through Ula to Ulb, which amplifies the signal by a factor of 100. The amplified output of Ulb is fed to Ulc through R9, C2, and R6. Potentiometer R9 serves as a volume control. With R9 set to pass the maximum signal, Ulc provides a gain of 100, for a total system gain of 10,000 dB. The output of Ulc is connected to voltage follower circuit Uld to better match and drive headphones that can be plugged into J1. (Popular Electronics/Hands-On Electronics, 4/89, p. 83)


IR TRANSMITTER
IR TRANSMITTERFD38-10

Using an NE567 as a tone oscillator, this circuit produces an IR signal from the LED, which is modulated with a square wave. LED1 is an IR emitting LED. The modulation helps improve performance under high ambient light conditions. (Reprinted with permission from Popular Electronics, 4/90, p.90-91. (C) Copyright Gernsback Publications, Inc.,1990)


LOW-POWER INFRARED DATA-LINK RECEIVER
LOW-POWER INFRARED DATA-LINK RECEIVERFF40-7

The Maxim MAX403 in this circuit consumes only 1 mA and is capable of speeds over 1 MBPS. (Maxim, Vol. III, New Releases Data Book, 1994, p. 3-100)


PHOTOTRANSISTOR IR RECEIVER
PHOTOTRANSISTOR IR RECEIVERFG127

This receiver uses an op amp and a phototransistor as a receiver for IR signals. Q1 is a photransistor. The op amp is a CMOS or FET type such as a TL081, etc. R1 and R2 depend on the phototransistor but are typically 2.2K and 330 ohms respectively. R3=R4=10K, R5=100K and C1 is 0.1 mfd or larger. (Nuts and Volts, June 1995, p. 99)


REMOTE-CONTROL TESTER
REMOTE-CONTROL TESTERFE39-13

The IR tester circuit lets you know if the button you press on a remote control is working. Q1 is a photo transistor that is activated by IR energy. (Reprinted with permission from Electronics Now, 3/93, p. 83. (C) Copyright Gernsback Publications, Inc.,1993)


VERY SIMPLE IR REMOTE-CONTROL CIRCUIT
VERY SIMPLE IR REMOTE-CONTROL CIRCUITFE39-11

(Reprinted with permission from Popular Electronics 3/93, p. 43. (C) Copyright Gernsback Publications, Inc.,1993)


WIRELESS IR HEADPHONE RECEIVER
WIRELESS IR HEADPHONE RECEIVERFF40-13

A photodiode D1 feeds high gain IR remote control preamp IC, a CA3237E. U2 is a PLL FM detector tuned to around 100 kHz. The detector output is amplified by U3 and it can drive a speaker or set of headphones. (Reprinted with permission from Popular Electronics, 12/93, p.32. (C) Copyright Gernsback Publications, Inc.,1993)


WIRELESS IR HEADPHONE TRANSMITTER
WIRELESS IR HEADPHONE TRANSMITTERFF40-3

Audio input from PL1 frequency modulates the VCO section of a 4046 PLL chip. The VCO output drives Q1, a switching transistor. Q1 drives two IR LEDs. The signal produced is around 100kHz, FM carrier VCO sensitivity is around 5.5 kHz/V. (Reprinted with permission from Popular Electronics, 12/93, p.31. (C) Copyright Gernsback Publications, Inc.,1993)


INTERCOM CIRCUITS

TWO-WIRE INTERCOM

VERY SIMPLE TELEPHONE INTERCOM CIRCUIT


TWO-WIRE INTERCOM
TWO-WIRE INTERCOMFD40-1

The design consists of an amplifier, a double-pole changeover switch and two loudspeakers: one for the master station and one for the slave. More than one slave unit can be used, but each requires an additional changeover switch.

The power amplifier is a Type LM384, which can provide almost 2 W output at a supply voltage of 15V. Pins 3, 4, 5, 10, 11, and 12 are connected to ground and at the same time afford some cooling of the device. Because of that, the IC should not be fitted in a socket, but be soldered direct to the circuit board.

The LM384 processes signals with respect to earth so that an asymmetric supply is sufficient. The amplification has been set internally to x 50 (34 dB). The IC's supply fine is decoupled by C9.

To ensure adequate input sensitivity, a preamplifier, IC1, is provided, which has an amplification of 11 (21 dB). Because this stage is intended for speech only, its bandwidth is limited to 160 Hz to 10 kHz. Divider R2/R3 at the input of the op amp is decoupled by C3.

Special loudspeakers that can also serve as microphones are readily available: in the prototype, MS-55 units from Monacor were used, but a number of other makes will do just as well. The bandwidth of the MS-55 (used as loudspeaker) extends from 150 Hz to 20 kHz and (used as a microphone) from 20 Hz to 20kHz. The MS-55 can handle up to 5-W output. To ensure satisfactory operation, particularly as a microphone, the loudspeaker must be fitted in a closed box.

Although it is advantageous for the "microphone" to have a low internal resistance, it is necessary for a transformer to be used at the input of the circuit. This has, however, the advantage that long cables can be used. The present circuit uses a standard mains transformer instead of a special microphone transformer. For this purpose, the secondary (6 V) winding is connected to the "microphone." The microphone impedance is thereby magnified from about 8Ω to around 10 kΩ. The power handling of the transformer is quite light to ensure that signal losses in the primary winding are kept at a minmum. Capacitor Cl suppresses HF interference.

If the mains transformer and the "microphone transformer" are housed in the same enclosure, some trial and error and screening are necessary to eliminate hum. The "microphone transformer" itself might cause hum in the remainder of the circuit. In that case, the preamp stage must also be screened. In the prototype, the speech bandwidth was limited from 400 Hz to 4 kHz and this proved perfectly acceptable for good speech transfer. Most of the current drawn by the circuit flows through the power amplifier. At worst, this is 210 mA (680 mA peak), when the amplifier delivers 1.8-W output. The LM384 can deliver a power of up to 5 W. The supply voltage should then be raised to 22 V and a heatsink for the device will be necessary.

(Elektor Electronics, 12/90, p. 515-516)


VERY SIMPLE TELEPHONE INTERCOM CIRCUIT
VERY SIMPLE TELEPHONE INTERCOM CIRCUITFE43-2

Two telephones can be used as an intercom by using this circuit. Older style rotary phones that are nonelectronic might work best in this application. Also, handsets only might be powered this way. (Reprinted with permission from Popular Electronics, 8/91, p.75. (C) Copyright Gernsback Publications, Inc.,1991)


INTERFACE CIRCUITS

MICROCOMPUTER-TO-TRIAC INTERFACE

PROCESS-CONTROL INTERFACE

RECEIVER-INTERFACE CIRCUIT FOR PREAMPS


MICROCOMPUTER-TO-TRIAC INTERFACE
MICROCOMPUTER-TO-TRIAC INTERFACEFE44-5

A microcomputer-to-triac interface uses a phototriac optoisolator to let safety-isolated logic signals directly control high-power loads. Depending on the input waveforms and the load, this circuit can be used in either an on/off switch or a proportional phase control. A low input powers the lamp. (Reprinted with permission from Radio-Electronics, 7/90, p. 64. (c) Copyright Gernsback Publications, Inc., 1990)


PROCESS-CONTROL INTERFACE
PROCESS-CONTROL INTERFACEFE44-2

This circuit can be used to interface a 2-wire transmitter/sensor combination to an external device or measurement setup. (Reprinted with permission from Popular Electronics, Fact Card 2657. (C) Copyright Gernsback Publications, Inc)


RECEIVER-INTERFACE CIRCUIT FOR PREAMPS
RECEIVER-INTERFACE CIRCUIT FOR PREAMPSFE44-4

The purpose of the receiver/interface circuit is to pass RF to the receiver through capacitor C9, while adding dc power to the feedline through R2 and RF choke L7. (Reprinted with permission from Popular Electronics, 6/93 p. 55. (C) Copyright Gernsback Publications, Inc.,1993)


ION GENERATOR AND DETECTOR CIRCUITS

ION-SENSING ELECTROSCOPE

ION DETECTOR

NEGATIVE ION GENERATOR

NEGATIVE ION GENERATOR II


ION -SENSING ELECTROSCOPE
ION-SENSING ELECTROSCOPEFF45-2

Negative ions are sensed by a plate antenna. A negative charge induced on the plate cuts off a vacuum tube, causing the neon indicator to go out. (73 Amateur Radio Today)


ION DETECTOR
ION DETECTORFF45-4

This circuit detects static charges and free ions in the air. It can be used to indicate the presence of ion emissions, high-voltage leakage, static electricity, electrostatic fields, etc. The ground connection is made by either an earth ground or by touching the aluminum foil electrode with your hand. M1 is a 100-μA meter. R3 is a sensitivity control. (Spring 1994 Electronic Hobbyists Handbook)


NEGATIVE ION GENERATOR
NEGATIVE ION GENERATORFF45-1

An NE555 drives a Darlington connected pair of transistors. T1 is a small high-voltage transformer or auto ignition coil, B/W TV flyback, etc. C3, C4 and D1 must be rated for 10 to 15 kV. The fan blows air across the discharge point. (Fantastic Electronics, McGraw-Hill)


NEGATIVE ION GENERATOR II
NEGATIVE ION GENERATOR IIFF45-3

In this circuit, air is circulated past a pointed electrode that has a high negative voltage applied to it. The transformer is a small 4- to 6-kV output type with a filament winding. A good source of parts is a discarded bug catcher. (73 Amateur Radio Today)


LASER CIRCUITS

2,000-V LOW-CURRENT POWER SUPPLY

LASER BEAM ACTIVATED RELAY

LASER DIODE TRANSMITTER

LASER MODULATION

LASER POWER SUPPLY

LASER POWER SUPPLY

LOW COST LASER DIODE DRIVER


2,000-V LOW-CURRENT POWER SUPPLY
2,000-V LOW-CURRENT POWER SUPPLYFD99-8

In this circuit Ql, Q2, Rl, and Cl form a multivibrator. The square wave that results from the oscillation of this circuit (20 to 30 Vpp) is stepped up by Tl (an audio transformer of the type used in radios or small Tvs). An 8- to 1,200-Ω impedance ratio equates to a turn ratio of 12:1. The ac from the secondary of Tl is applied to the multiplier circuit (Dl to D8 and C2 to C9). NEl/R2 are used as an operating indicator. The circuit will supply about 2,000 V. C2 to C9 should have a 400-V or higher voltage rating. (Reprinted with permission from R-E Experimenters Handbook 1990. p. 45. (C) Copyright Gernsback Publications, Inc., 1990)


LASER BEAM ACTIVATED RELAY
LASER BEAM ACTIVATED RELAYFG132

Two-transistor relay circuit will activate whenever the phototransistor is illuminated by the laser beam. (Electronics Now, September 1996, p. 77)


LASER DIODE TRANSMITTER
LASER DIODE TRANSMITTERFF46-4

(Laser Cookbook, McGraw-Hill, p.201)


LASER MODULATION
LASER MODULATIONFG134

Electronics modulation of a laser beam can be handled in this fashion. Obviously, the transformer you use must be able to handle the high voltage from the laser power supply without breaking down. (Electronics Now, May 1996, p. 52)


LASER POWER SUPPLY
LASER POWER SUPPLYFD99-7

IC1 is a 555 timer running at about 16 kHz. This IC drives Ql, a TIP146, which produces a 12 V square wave across Tl primary. This produces between 800 and 2,000 V across the secondary, which is doubled to 3 to 5 kV. When the load (laser) on the power supply increases, current Q2 is turned on, which energizes RY1. This changes the duty cycle of the 555 timer. To adjust this supply, set R12 and R13 at the center. Adjust R12 until the laser tube triggers, and make sure that the relay pulls in. If the relay chatters, adjust R12. If the full-clockwise adjustment of R12 fails to ignite the tube, adjust R13. (Reprinted with permission from Radio-Electronics, 3/89, p. 33-37. (C) Copyright Gernsback Publications, Inc.,1989)


LASER POWER SUPPLY
LASER POWER SUPPLYFE47-6

This supply generates an initial high voltage for ignition purposes. After ignition, the supply generates about 1300 to 1500 V. If a higher ignition voltage (than the 6000 V supplied) is necessary, more multiplier stages can be added to D5 and D8. (Reprinted with permission from Popular Electronics, 6/93. p.78 (C) Copyright Gernsback Publications, Inc., 1993.)


LOW COST LASER DIODE DRIVER
LOW COST LASER DIODE DRIVERFG131

The circuit presented is a low-cost laser-diode driver with current limiting and a lasing monitor for safe operation of the laser. The driver provides temperature stabilization using a built-in thermoelectric-cooler (TEC) controller. This circuit is designed around a QLM5S876 1.55-μm laser-diode module with a built-in monitor photodiode, TEC, and thermistor. The laser is driven by the constant current source Q2 and Ql. The drive current is stabilized against supply changes by Z1, limited by R2, and adjusted by R3 to the desired operating point. When the current is small, the laser doesn't lase and the monitor photodiode detects no optical power. As a result, comparator UlC goes below its trip point and LED1 turns off. When the current is adjusted and passes the laser threshold, sufficient optical power is generated by the laser, causing photo current to flow through the photodiode and the comparator to drive the lasing monitor indicator LED1 to on. The TEC controller circuit is a feedback system. If the temperature is higher than the set point, the comparator output is high and driving the TEC element through R15, Q3, and Q4. The TEC drive current is limited by Z2. When the TEC is driven on, it cools the laser. This increases the voltage of the inverting output until it passes the comparator's upper trip point and turns off the TEC's drive current. The temperature set point can be adjusted by R16. (Electronic Design, July 22, 1996, p. 114)


LIGHT BEAM COMMUNICATION CIRCUITS

FM LIGHT BEAM RECEIVER

FM LIGHT-BEAM TRANSCEIVER

LIGHT-WAVE VOICE-COMMUNICATION TRANSMITTER

MODULATED LIGHT RECEIVER

MODULATED LIGHT TRANSMITTER


FM LIGHT BEAM RECEIVER
FM LIGHT BEAM RECEIVERFE49-3

This receiver will pick up IR or light beams that are frequency modulated on a 50-kHz carrier. Q2/Q1/Q3/Q4 form an active filter and amplifier and differential amp Q5/Q6 provide more gain (Reprinted with permission from Electronics Now, 12/92. p. 60. (C) Copyright Gernsback Publications, Inc.,1982)


FM LIGHT-BEAM TRANSCEIVER
FM LIGHT-BEAM TRANSCEIVERFE49-4

This transmitter uses two stage amplifier Q1/Q2 to frequency modulate an NE555 (configured as a VCO) operating at about 50 kHz. The resultant FM-modulated pulse train is converted to light pulses via LED1 through LED4, driven by Q3 and Q4.(Reprinted with permission from Electronics Now, 12/92. p. 59. (C) Copyright Gernsback Publications, Inc.,1982)


LIGHT-WAVE VOICE-COMMUNICATION TRANSMITTER
LIGHT-WAVE VOICE-COMMUNICATION TRANSMITTERFE49-5

This transmitter uses a 741 op amp as a high-gain audio amplifier which is driven by a microphone. The output of the 741 is coupled to Ql, which serves as the driver for a LED. Potentiometer R1 is the amplifier's gain control. Miniature trimmer resistor R6 permits adjustment of the base bias of Ql for best transmitter performance. Gain control R1 can be eliminated if Cl and R2 are connected directly to pin 2 of the 741. For maximum sensitivity, increase the value of R2 from 1 to 10 MΩ and use a crystal microphone with a large diaphragm.. (William Sheets)


MODULATED LIGHT RECEIVER
MODULATED LIGHT RECEIVERFE49-2

Using a phototransistor, this receiver will detect and demodulate a modulated light beam. R6 affects sensitivity. (Reprinted with permission from Popular Electronics, Application Circuit 215. Copyright Gernsback Publications, Inc)


MODULATED LIGHT TRANSMITTER
MODULATED LIGHT TRANSMITTERFE49-1

A light-bulb filament can be modulated with audio as a method of optical transmission. Amplifier  Q1/Q2/Q3 drives emitter-follower TR4. Ad just R10 for the Q point (light bulb) giving best results. It should have a filament with low thermal inertia for best audio responses. (Reprinted with permission from Popular Electronics, Application Circuit 215. Copyright Gernsback Publications, Inc)


LIGHT CONTROL CIRCUITS

CHRISTMAS LIGHT DIMMER

HALOGEN LAMP DIMMER

HOLIDAY LIGHT SEQUENCER

LIGHT SEQUENCER

PHASE-CONTROLLED DIMMER

TRIAC ZERO-POINT SWITCH


CHRISTMAS LIGHT DIMMER
CHRISTMAS LIGHT DIMMERFG135

It is based on a standard diac/triac dimmer configuration which has been optimized for this application. Resistor R2 is, however, optional and was only included to help discharge the capacitors quickly. All capacitors are 260V AC X2 rated (this is very important) all resistors are 500V working voltage, and the triac CSR1 was chosen for its low holding current so that it would function with small loads. Note that Vrl is fitted with a double-pole mains switch for complete isolation. Even with only one 20-lamp string plugged in (22 watts) control is very smooth with barely any trace of hysteresis .It can be built safely on a piece of matrix board, wired point-to-point, provided it is mounted in a completely insulated plastic case and that no external components (i.e. Sl and VR1) are metal. (Do not build this circuit if you do not understand the safety requirements). (Everyday with Practical Electronics, December 1996, p. 931)


HALOGEN LAMP DIMMER
HALOGEN LAMP DIMMERFC50-1

This circuit is suitable for fitting into slide projectors without a dimmer facility as with 24-Vac fed halogen lamps. With a few small alterations, it can also be used for dimming 12-V halogen lamps, but not those in a car, because these are fed from a dc source. The circuit shown in figure a is intended for operation from a 24-Vac supply, and can handle a lamp load of up to 150 W. For loads up to 250 W, the TIC236 should be replaced by a TIC246.

Figure b shows detail of the connection of a potentiometer to the intensity control input of the TCA280A. Voltage divider R10-Pl-R11 is fitted externally and can be fed from the stabilized voltage available at pin 11 of IC1. The minimum and maximum intensities of the lamp are determined by R10 and R11, respectively.

(Elektor Electronics, 7-8/87 Supplement, p. 56)


HOLIDAY LIGHT SEQUENCER
HOLIDAY LIGHT SEQUENCERFE50-2

Integrated circuit Ul (a 555 oscillator/timer) is wired as a conventional pulse generator. The frequency of the pulse generator is controlled by potentiometer R11. Resistor R2 puts a reasonable limit on the highest speed attainable.

The output of the pulse generator is fed to the common clock input of U2, a 74C175 quad D-type flip-flop. Each flip-flop is configured so that its Q output is coupled to the D input of the subsequent flip-flop.

Information on the D input of each flip-flop is transferred to the Q (and /Q) outputs on the leading edge of each clock pulse. Switch S2 allows you to invert the information on the D input of the first flip-flop at any time during the cycle. This allows you to create a number of different sequences, which are determined by the state of the CQ output at the time of the switching. Some of the possible sequences are:

 1 through 4 on, 1 through 4 off;

 1 of 4 on sequence;

 1 of 4 off sequence;

 2 of 4 on sequence;

 1 and 3 on to 2 and 4 off;

 and other instances when the sequence of events is difficult to determine.

However, if S2 is switched to position B while all outputs are high or all are low (which seldom occurs), the sequence stops and the outputs remain either all on or all off. If that happens, you only need to switch back to position A for at least one pulse duration, then back to position B again.

Likewise, S2 should be in position A (pin 4 connected to pin 14) each time the power is turned on. This is because the data on pin 4 must be a logic 1 in order to start a sequence; otherwise all outputs remain at logic 0, regardless of the clock pulses.

Each output of the sequencing circuit is connected to an MOC3010 optoisolator/coupler (U3 through U6), which contains an infrared-emitting diode with an infrared-sensitive diac (triac driver or trigger) in close proximity. The diac triggers the triac, which carries the 117-volts ac.

Each time that the infrared-emitting diode receives a logic 1, it turns on and causes the diac to conduct. With the optoisolator/coupler's internal diac conducting, the triac turns on, and power is supplied to whatever load is plugged into the corresponding ac socket. So, the sequencing circuit and the 117-V ac outputs are "optically coupled" and are effectively isolated from each other.

Power for the sequencing circuit is provided by a 6.3-V miniature transformer. The output of the transformer is rectified by a four-diode bridge circuit, the output of which is filtered by Cl (1000-μF electrolytic capacitor). Capacitor C3 is added at the supply pin of' U2 to suppress transients.

(Reprinted with permission from PE Hobbyist Handbook, 1990, pp. 45-47. (C) Copyright Gernsback Publications, Inc)


LIGHT SEQUENCER
LIGHT SEQUENCERFE50-1

The light sequencer uses two ICs and 10 SCRs to create an ac sequencer. The first IC, a 555 timer, is used to provide clock pulses for IC2. The IC is configured as an astable multivibrator, and its output is on pin 3.

Capacitors Cl and C4, along with resistor R2 and potentiometer P1, control the frequency of the pulses. IC2 is a 4017 Johnson counter, which shifts a high-signal level to each one of its 10 output pins in sequence. Each output pin is resistively coupled to the gate lead on an SCR. When the respective output pin on the 4017 is high and the positive half of the ac cycle is on the anode lead of the SCR, it turns on. The lamp that is connected to its anode lights.

Power is brought into the PC board by the line cord, then the circuit is fuse-protected. Diode LD1 changes the ac to pulsating, which is smoothed by C2 and C3. R23 limits the current, and zener diode D2 limits the de voltage to 6 Vdc.

C1, C4	0.1-μF Capacitor	R2, R4, R6,
C2	100-μF Capacitor	R8, Rl0, Rl2,
C3	47-μF, 350-V Electrolytic Capacitor	R14, Rl6, R18
D1	lN4007 Diode	R20, R22	100-kΩ Resistor
D2	6-V Zener (M747814)	R3, R5, R7
IC1	555 Timer IC	R9, R11, R13
IC2	4017 CMOS IC	R15,Rl7,Rl9
P1	500-kΩ Potentiometer	R21	2.2-kΩ Resistor
Ql-Ql0	106 SCR	R23	15-kΩ  7-W Resistor
R1	560-Ω Resistor
(Reprinted with permission from PE Hobbyists Handbook 1991. pp. 79-80. (C) Copyright Gernsback Publications, Inc., 1991)


PHASE-CONTROLLED DIMMER
PHASE-CONTROLLED DIMMERFE50-6

A phase-controlled dimmer delays the triac turn-on to a selected point in each successive ac half cycle. Use this circuit only for incandescent lamps, heaters, soldering irons, or "universal" motors,  that have brushes.


TRIAC ZERO-POINT SWITCH
TRIAC ZERO-POINT SWITCHFB49-9

On the initial part of the positive half cycle, the voltage is changing rapidly from zero causing a large current to flow into capacitor C2. The current through C2 flows through R4, D3, and D4 into the gate of the TRIAC Q2 causing it to turn on very close to zero voltage. Once Q2 turns on, capacitor C3 charges to the peak of the line voltage through D5. When the line voltage passes through the peak, D5 becomes reverse-biased and C3 begins to discharge through D4 and the gate of Q2. At this time the voltage on C3 lags the line voltage. When the fine voltage goes through zero there is still some charge on C3 so that when the he voltage starts negative C3 is still discharging into the gate of Q2. Thus Q2 is also turned on near zero on the negative half cycle. This operation continues for each cycle until switch S1 is closed, at which time SCR Ql is turned on. Ql shunts the gate current away from Q2 during each positive half cycle keeping Q2 from turning on. Q2 cannot turn on during the negative cycle because C3 cannot charge unless Q2 is on during the positive half cycle. (Motorola, Thyristor Device Data, Series A, 1985, p. 1-6-60)


LIGHT CONTROLLED CIRCUITS

DARK-ACTIVATED RELAY WITH HYSTERESIS

ELECTRONIC WAKE-UP CALL

HIGH-OUTPUT PULSED-TONE/LIGHT-ACTIVATED ALARM

LIGHT ACTIVATED SWITCHLIGHT CONTROLLED MONOSTABLE

PRECISION DARK-ACTIVATED SWITCH WITH HYSTERESIS

PRECISION LIGHT ALARM WITH HYSTERESIS

PROGRAMMABLE CONTROLLER LIGHT SENSOR INTERFACE

SELF-LATCHING LIGHT-ACTIVATED SWITCH

TRAFFIC LIGHT CONTROLLER


DARK-ACTIVATED RELAY WITH HYSTERESIS
DARK-ACTIVATED RELAY WITH HYSTERESISFE51-6

The hysteresis of a 555 IC can be used to advantage for sensing a drop in light. An LDR or CDS cell with about 2 to 8 k resistance at desired light level should be used. (William Sheets)


ELECTRONIC WAKE-UP CALL
ELECTRONIC WAKE-UP CALLFB51-8

A cadmium sulfide photocell (LDR1, which is a light-dependent resistor) is connected to the base and collector of an npn transistor, Ql. When light hits LDR1, the internal resistance goes from a very high (dark) value to a low (light) value, supplying base current to Ql, turning it on. The voltage across R1 produces a bias that turns Q2 on, which in turn, supplies the positive voltage to Ul at pin 8 (the positive-supply input) and pin 4 (the reset input), to operate the 555 audio oscillator circuit. The circuit's sensitivity to light can be set via R6 (a 50,000 ohm potentiometer). R7 sets the audio tone to the most desirable sound. The square wave audio tone is fed from Ul pin 3 to a small speaker through coupling capacitor C4 and current limiting resistor R4. (Hands-On Electronics, 10/87, p. 92)


HIGH-OUTPUT PULSED-TONE/LIGHT-ACTIVATED ALARM
HIGH-OUTPUT PULSED-TONE/LIGHT-ACTIVATED ALARMFE1-22

This circuit can produce up to 1 W of audio power to drive a speaker or horn. When the CDS cell is struck by light, it resistance decreases thus activating NOR gate (a) thereby causing (a) and (b) to produce a low frequency (10-Hz) square wave. This pulses the 1-kHz oscillator (c) and (d) causing it to generate a pulsed 1-kHz tone at a 10-Hz rate. Q1 and Q2 amplify this signal. Q2 (2N3055) drives the speaker. (William Sheets)


LIGHT ACTIVATED SWITCH
LIGHT ACTIVATED SWITCHFG136

When even a little light hits the light-dependent resistor, R5, transistor Ql is turned off because the base has less resistance to the ground than to the positive rail. In that situation, the base is at a negative potential. when the sun sets, R5 is no longer illuminated, giving the transistor's base a high resistance to ground - higher than 100,000 ohms. With less resistance to positive potential, the base is biased, turning on Ql. Relay RY1 is then energized and pulls in, connecting the SCR1's anode to positive potential. The 555 timer, ICl, powers up, and its output goes high to approximately 10.67 volts, which is sufficient to energize RY2. Relay RY2 then pulls in, keeping the AC bulb on the whole night, and turning it off again at sunrise. (Popular Electronics, October 1996, pp. 64)


LIGHT-CONTROLLED MONOSTABLE
LIGHT-CONTROLLED MONOSTABLEFF47-9

The light-controlled monostable was produced by combining a 555 monostable multivibrator  with a pair of light-controllled comparators. The circuit can be used to enable the operation of the  load device, depending on the time of day. During the daylight hours, the timer U2, is disabled, and  so produces no output. However, during the nighttime hours, U2 is enabled by the output of U1-b so  that pressing S1 initiates a timing cycle, which activates LED1 for a time determined by R8 and C1.


PRECISION DARK-ACTIVATED SWITCH WITH HYSTERESIS
PRECISION DARK-ACTIVATED SWITCH WITH HYSTERESISFE51-3

A CdS cell is one leg of a bridge circuit. Potentiometer R6 in another leg sets the trip point. Potentiometer R5 provides hysteresis adjustment to prevent chattering or hunting of the relay. The light level has to increase noticeably before the 2N3904 turns off and the circuit deactivates.(William Sheets)


PRECISION LIGHT ALARM WITH HYSTERESIS
PRECISION LIGHT ALARM WITH HYSTERESISFE1-21

 The TL081 is used as a comparator in a Wheatstone bridge circuit. When the CDS cell resistance decreases due to exposure to light, the output from IC2 cause the low-frequency oscillator (a) and (b) to generate a 10-Hz square wave, getting the 1000 Hz oscillator (c) and (d) on and off. This signal drives an amplifier. R3 controls hysteresis, which reduces on-off-trigging near the threshold set by R4. (William Sheets)


PROGRAMMABLE CONTROLLER LIGHT SENSOR INTERFACE
PROGRAMMABLE CONTROLLER LIGHT SENSOR INTERFACEFG137

As long as an object remains between LED1 and Q1, no output occurs. But as soon as the object moves out from between the LED and phototransitor, IC1 (again a 555-timer) is triggered, producing a timed output pulse. This circuit may be used to indicate when a part has moved away from a location. (Popular Electronics, January 1997, p. 71)


SELF-LATCHING LIGHT-ACTIVATED SWITCH
SELF-LATCHING LIGHT-ACTIVATED SWITCHFE51-11

When light strikes the CDS cell it turns on the transistors which activates the relay which latches. Depressing S1 grounds the base of the 2N3565 and the relay resets. The 250 K potentiometer adjusts the sensitivity of the circuit. (William Sheets)


TRAFFIG LIGHT CONTROLLER
TRAFFIC LIGHT CONTROLLERFF47-12

Oscillator U5A-B drives a 4017 divide-by-10 counter. The first output of Ul appears at pin 3, which supplies a positive voltage to U2, a MOC 3010 optocoupler/triac-driver IC, turning it and triac TRl on. That lights I1, the red lamp. The second output appears at pin 2 and passes through D1 to the second MOC3010, U3, thereby lighting the yellow lamp, I2. The third output at pin 4 turns on UJ4 and the green lamp, I3. The fourth output at pin 7 travels through D2 and into U3 to light the yellow lamp, I2, again.

If you would like the traffic-light system to follow the normal sequence of green, yellow, and red, make the following circuit changes: Disconnect pins 10 and 15 of U1 from each other. Remove D1 and D2 and connect pin 2 of Ul to pin 1 of U3. Then connect pins 7 and pins 15 of Ul together .Use U2 to drive I3 (the green light) and U4 for I1 (the red light).

(Reprinted with permission from Popular Electronics, 5/94, p.45. (C) Copyright Gernsback Publications, Inc.,1994)


LIMITER CIRCUITS

NOISE LIMITER

OUTPUT LIMITER


NOISE LIMITER
NOISE LIMITERFC53-1

This circuit is fed from the earphone jack of your receiver and goes to limiter control R6 and is then amplified by Ql: a common-emitter stage that has a voltage gain of only about 10, because of the negative feedback introduced by R3. The output of Ql is fed to a simple clipping circuit, consisting of diodes D1 through D4. The diodes, connected in pairs, act like Zeners with an avalanche rating of about 1 V. The two pairs are connected opposite in polarity to each other, so that the audio signal is clipped at about 1 V. The signal is then coupled to the output socket through an emitter-follower buffer stage built around Q2 and an output attenuator control R7. (Hands-On Electronics, 9/87, p. 96)


OUTPUT LIMITER
OUTPUT LIMITERFC53-3

HA-5190 is rated for ± 5 V output swing, and saturates at ± 7 V. As with most op amps, recovery from output saturation is slow compared to the amplifier's normal response time, Some form of limiting, either of the input signal or in the feedback path, is desirable if saturation might occur. The circuit illustrates a feedback limiter, where gain is reduced if the output exceeds  ± (Vz + 2 Vf). A 5-V zener with a sharp knee characteristic is recommended. (Harris Analog Product Data Book, 1988, p. 10-54)


LIQUID LEVEL DETECTOR CIRCUITS

FLUID LEVEL CONTROLER

FULL-CUP DETECTOR FOR THE BLIND

HIGH LEVEL WARNING DEVICE

LOW-LEVEL WARNING WITH AUDIO OUTPUT

WATER DETECTOR

WATER-LEVEL CONTROL

WATER-LEVEL MEASUREMENT CIRCtIlT

WATER-LEVEL SENSOR AND CONTROL


FLUID LEVEL CONTROLER
FLUID LEVEL CONTROLLERFA47-2

This circuit can be used to maintain fluid between two levels. Variations on this control circuit can be made to keep something that moves within certain boundary conditions. (Courtesy of Texas Instrument Incorporated, Optoelectronics Databook, 1983-84, p. 15-9)


FULL_CUP DETECTOR FOR THE BLIND
FULL-CUP DETECTOR FOR THE BLINDFD32-8

At the heart of the Full-Cup Detector is a 555-oscillator/timer configured to produce a 15-Hz clock, until its probe contacts are bridged, at which time its output frequency goes to about 500 Hz.

This circuit can be used by the visually handicapped to determine when a cup or bowl is full of liquid (coffee, soup, etc). Ul, an NE555, produces ticks at 15 Hz. A set of probes (wire, etc) is placed in the container at the desired level. When the liquid level contacts the probes, the frequency of clicks increases to several hundred hertz, depending on its conductivity.

(Reprinted with permission from Popular Electronics, 3/90, p. 25, Copyright Gernsback Publications, Inc., 1990)


HIGH LEVEL WARNING DEVICE
HIGH LEVEL WARNING DEVICEFA47-3

(Reprinted with permission from National Semiconductor Corporation, Linear Databook 1982, p. 9-93)


LOW-LEVEL WARNING WITH AUDIO OUTPUT
LOW-LEVEL WARNING WITH AUDIO OUTPUTFA47-10

(Reprinted with permission from National Semiconductor Corporation, Linear Databook 1982, p. 9-93)


WATER DETECTOR
WATER DETECTORFG138

The heart of the circuit is the LM1830 fluid detector. It contains all the circuitry needed to sense fluid levels and activate an external device (relay, etc). The IC generates an AC signal that is passed through two probes in the fluid. The IC's detector circuit senses the presence or absence of fluid by comparing the resistance between the probes with its internal reference resistance. When the probes detect the presence of water, the LM1830 will trigger Ql, and that in turn will trigger IC2 (an LM555), which starts a timing period. The output from pin 3 of IC2 closes the relay and the bilge pump is activated for the duration of the timing period. The timing period is adjustable, using R6, a 1-megohm potentiometer. For the values shown, and depending on the setting of R6, the timing period is about 5-120 seconds. Components R4, Dl, and C7 are tied to pin 4 of IC2 to hold the timer at reset when power is first applied. (Popular Electronics, February 1996, p. 68)


WATER-LEVEL CONTROL
WATER-LEVEL CONTROLFD32-1

 This circuit will power up a water pump when the water reaches a predetermined level. Then it turns itself off when the water recedes to another predetermined point.

Gates U1A through UlC each have their two inputs tied together, and serve as probes. The probes are then placed at various levels to trigger a particular function at a predetermined time. The ground side of the circuit is placed below the minimum water level. The inputs to each gate are tied high through a 100-kΩ resistor connected to the + 12.5-V bus.

As the water level slowly rises to probe 1, the input to UlA is pulled low by the conduction of current through the water to the ground probe. That turns Ql off and Q2 on. With Q2 turned on, the circuit is placed in the standby mode, ready to activate the pump when conditions are right.

Probe 2 is placed at the maximum water level. If the water level reaches probe 2, the input of UlB is brought low, turning Q3 on, which, in turn, causes current to be applied to the gate of SCR1, turning it on. The circuit through K1, Q2, and SCR1 is now complete to ground, and the water pump is now turned on, which causes the water level to recede, When the water level falls below probe 2, UlB goes back to logic high. However, because of the latching nature of SCR1, the pump continues to run until the water level falls below probe 1. At that point, the ground circuit opens and de-energizes Kl, which turns the pump off. The pump will not turn on again until the water level again rises above probe 2.

Probe 3 was added as a warning. If the water level reaches probe 3, LED2 indicates that the pump is not working. Switch S2 is a manual over-ride and S1 powers the sensing circuit. LED3 indicates that power has been applied to the pump. LED1 indicates that power has been applied to the sensor.

(Reprinted with permission from Popular Electronics, 3/91, p.24. (C) Copyright Gernsback Publications, Inc.,1991)


WATER-LEVEL MEASUREMENT CIRCtIlT
WATER-LEVEL MEASUREMENT CIRCUlTFD32-11

Using a capacitor sensor to detect a water level is a simple method of sensing. This circuit uses C5, which is 10" to 20" of #22 enameled wire as one electrode. This shifts the oscillator, an NE556 timer, in frequency. The frequency shift depends on the capacitance charge, which in turn varies with water level. A meter connected to pin 9 of the 556 is used as an indicator. C5 can be made larger or smaller to suit the intended application. (Reprinted with permission from Popular Electronics, 1/90, p.24. (C) Copyright Gernsback Publications, Inc.,1990)


WATER-LEVEL SENSOR AND CONTROL
WATER-LEVEL SENSOR AND CONTROLFC34-3

(Radio Electronics, 6/88, p. 49)


LOGIC CIRCUITS

AND GATE

LOGIC STATE CHANGE INDICATOR

RELAY "AND" CIRCUIT

RELAY "OR" CIRCUIT


AND GATE
AND GATEFE36-1

A left over section of a quad op amp can be used to save cost and eliminate an extra logic chip for this AND gate. (Reprinted with permission from Popular Electronics, Fact Card 268. (C) Copyright Gernsback Publications, Inc)


LOGIC STATE CHANGE INDICATOR
LOGIC STATE CHANGE INDICATORFF48-1

A circuit consisting of a one-shot multivibrator IC, a pair of diodes, and some resistors and capacitors delivers an output pulse when the logic state at its input terminal changes-either from high to low or from low to high. Thus, this circuit can serve as a state-change indicator or as a frequency doubler for a square-wave input.

Any monostable can be used; the arrangement in the figure achieves low power dissipation (80 milliwatts) by using half of a Fairchild 96L02 transistor-transistor-logic dual multivibrator. The 96L02 is triggered when pins 3 and 5 are high and pin 4 changes state from low to high. It also triggers if pin 3 is high, pin 4 is low. The circuit shown here allows these conditions to be satisfied with a single input terminal, plus the fixed bias on pin 3; the arrangement of resistors, capacitors, and diodes automatically biases pin 5 high when transmitting a rising transition to pin 4 and biases pin 4 low when applying a falling transition to pin 5.

For example, if the input terminal has been low and then goes high, Cl charges through a forward-biased diode that shunts its 100-Ω resistor; therefore pin 5 goes high immediately. C2 changes through 100 Ω; however, because its diode is back-biased, The rising level is not applied to pin 4 until 5 is already high. Therefore, the conditions for triggering an output pulse are satisfied.

The output pulse duration, t, is set by the value of time constant RxCx.

(NASA TECH BRIEFS Spring 1977)


RELAY "AND" CIRCUIT
RELAY "AND" CIRCUITFF48-4

All switches S1 through Sn must be closed to operate the relay. If one opens, the relay drops out. Use this circuit for burglar alarms etc.  (William Sheets)


RELAY "OR" CIRCUIT
RELAY "OR" CIRCUITFF48-5

Closing any switch S1, S2, S3, or Sn will actuate the relay (n=any number). Use this circuit for burglar alarms, etc. (William Sheets)


MEASURING AND TEST CIRCUITS - CABLE

CABLE SHORT DETECTOR

CABLE TESTER

CABLE TESTER RECEIVER

CABLE TESTER TRANSMITTER


CABLE SHORT DETECTOR
CABLE SHORT DETECTORFG141

A five-input short detector circuit can be used to check out long runs of a two- to five- wire cable for shorts between any of the wires. An LM741 op-amp IC, Ul, is connected in a comparator circuit, The inverting input (pin 2) of Ul is connected to a +9-volt source and a series of 6 resistors, while the noninverting input (pin 3) of the op-amp is connected to an adjustable voltage-divider circuit. To use the circuit, potentiometer Rl0 should be used to set the voltage at pin 3 to slightly more negative voltage than that at pin 2; Ul's output will swing low, lighting LED1. Make that adjustment slowly until LED1 just barely turns on. Then connect one end of a cable to points A-E. When any of resistors R2-R6 are shorted out, the voltage at pin 2 will go negative in respect to pin 3. That will make the op-amp's output go positive, which will light LED2, indicating a short in the cable. (Popular Electronics, September 1995, pp. 74-75)


CABLE TESTER
CABLE TESTERFE55-9

At the heart of the cable tester are two op amps which are used is a window comparator to indicate a short or open-circuit condition. A third op amp comparator is used to indicate a good circuit (i.e., neither open nor shorted). Colored LEDs are used to show the condition of individual conductors within the cable under test; a red one to indicate a short between conductors, a yellow one to identify an open conductor, and a green one to signify that the conductor is okay. Individual LEDs of a bar-graph display are used to show which conductor in a cable is being tested. (Reprinted with permission from Popular Electronics, 4/92, p. 53. (C) Copyright Gernsback Publications, Inc.,1992)


CABLE TESTER RECEIVER
CABLE TESTER RECEIVERFG140

The four inputs are connected to four input contacts of a quad bilateral switch, IC5, with the output contacts tied together and connected to the inputs of the 567 decoders through R9 and C16. The bilateral switch's four control inputs are operated by IC6, a 4017 decade counter IC, which is driven by a low-frequency oscillator made up of two gates of IC7, a quad two-input NAND gate. Four LED'S, LED5 through LED8, are connected to IC6's four outputs and indicate which input is being checked, just as in manual mode. When LED5 is on, input 1 is switched through to the four decoder circuits. The decoder that responds, by lighting its LED, indicates which output, 700 Hz, 775 Hz, 880 Hz, or 950 Hz, is connected to that input. Resistor R14 sets the input-stepping rate, which should be slow enough for recording. (Popular Electronics, April 1996, p. 66)


CABLE TESTER TRANSMITTER
CABLE TESTER TRANSMITTERFG139

Four 567 tone-decoder ICs, ICl-IC4, are used to generate four different audio frequencies between 700 Hz and 950 Hz. The capacitor from pin 6 of each 567 to circuit ground, along with the resistor between pins 5 and 6, set the operating frequency. A 2N3904 NPN transmitter is connected in an emitter follower circuit to isolate the ICs from output loading. Each output supplies a different audio tone to four wires in a cable. (Popular Electronics, April 1996, p. 65)


MEASURING AND TEST CIRCUITS - CAPACITANCE

CAPACITANCE METER ADAPTER FOR DVMS

CAPACITOR ESR MEASURER

HIGH RESOLUTION BRIDGE MEASURES SMALL CAPACITORS


CAPACITANCE METER ADAPTER FOR DVMS
CAPACITANCE METER ADAPTER FOR DVMSFG143

Schematic for the Capacitance Meter Adapter. The circuit outputs one-millivolt per picofarad in the Low range setting of S2, and one-volt per microfarad in the HIGH range. When power-switch Sl is in the ON position, a LM7805 regulator (IC2) provides a 5-volt source to the circuit. Switch S2 is used to select between the high and low capacitance ranges. The circuit measures from 0 to 2200 pF in its low range and from 0 to 2.2 μF in its high range. The Adapter outputs one millivolt per picofarad in the lower range and one volt per microfarad in the higher range. Those are the voltages that would be displayed on a DMM, and which would have to be read as capacitance values. Gate ICl-d is configured as a free-running oscillator whose frequency is determined by the setting of potentiometer Rl. The output of IC1-d, pin 11, is a square-wave voltage that's fed to the other two gates configured as inverters (IC1-a and lCl-c). A capacitor with an unknown value (Cx) is connected across input-terminals Jl and J2. Note that the positive lead of a polarized capacitor must be connected to Jl. The capacitor under test charges through diode Dl on positive half-cycles and discharges through R5 on negative half-cycles in the low range, or through R3, R4 and R5 in the high range. In the high range, the square-wave output from ICl-d is fed directly to the inputs of the other two gates. With no capacitor connected to Jl and J2, the outputs of ICl-a and ICl-c are identical, inverted versions of the input signal. The average voltage across the outputs of the gates at pins 3 and 8 in this case is zero. With Cx in place, and depending on its value, the input voltage to IC1-c, pin 9, stays higher longer than the input to ICl-a, pin 2. The output pulses from ICl-a and ICl-c are filtered and smoothed by R8, R9, C2, and C5. The average DC voltage across the outputs is then proportional to the value of Cx. The circuit is a bit different in the low range, because compensation must be made for stray capacitance. In the low range, the output from ICl-d is fed to pin 1 of ICl -a through diode D2, which also charges Cl. Capacitor Cl charges quickly and discharges slowly through potentiometer R6. The charge on Cl holds the input to ICl-a higher for slightly longer than it normally would be. That causes its inverted output to be low for slightly longer and conversely high for slightly shorter. Stray capacitance across input terminals J 1 and J2 does the same thing to IC1-c, holding its input higher for slightly longer than it would if there were none. Potentiometer R6 is adjusted so that the discharge time for Cl matches that of the stray capacitance is canceled out. In the low range an offset voltage is applied to the negative output terminal via D3, R7, and R8 to prevent the gates from locking together with such close trigger points. (Popular Electronics, November, 1996, pp. 47-49)


CAPACITOR ESR MEASURER
CAPACITOR ESR MEASURERFD46-22

The equivalent series resistance (ESR) of a capacitor can be measured using this circuit and an ac voltmeter. Ul functions as a 50-kHz square-wave generator. It drives a current waveform of about ± 180mA in the capacitor-under-test, through R1 and R2. When R3 is adjusted to the proper value, the voltage drop across the equivalent series resistor is precisely nulled by the inverting amplifier (U2). Thus, Vo is the pure capacitor voltage which is the minimum voltage that can be produced at Vo.

To make an ac voltage measurement, adjust R3 until Vo is minimized. Then, note the position of the potentiometer and multiply it by the value of R2, 1 Ω in this case. That product equals the capacitor's ESR. The capacitor is biased at about 7.5 V. Lower-voltage capacitors won't work with this circuit. By changing the value of R2, other ranges of ESR can be measured. However, for small R2 values, the current level should be increased to keep a reasonable voltage across R2. This requires some sort of buffer. The circuit is intended for capacitors greater than 100 μF. The ripple voltage gets large for smaller values and accuracy decreases. (Reprinted with permission from Electronic Design, 6/91, p. 101. Copyright 1991, Penton Publishing)


HIGH RESOLUTION BRIDGE MEASURES SMALL CAPACITORS
HIGH RESOLUTION BRIDGE MEASURES SMALL CAPACITORSFG142

A JFET-input op amp (LT1462) amplifies the signal before demodulation for good noise performance, and the integrator's output is attenuated by Rl and R2 to increase the sensitivity of the circuit. If ACx<<Cx, and CREF  CX, then VOUT - VREF = VREF(ΔCX/CREF)[(Rl +R2)/R2]. With CREF = 50 pF, the circuit has a gain of 5V/pF and can resolve 2 pF. Supply current is 1 mA. The synchronous detection makes this circuit insensitive to external noise sources and, in this respect, shielding isn't terribly important. However, to achieve high resolution and stability, care should be taken to shield the capacitors being measured. Bridge circuits are particularly suited for differential measurements. When CX and CREF are replaced with two sensing capacitors, these circuits measure differential capacitance changes, but reject common-mode changes. CMRR for the circuit in this figure exceeds 70 dB. In this case, however, the output is linear only for small relative capacitance changes. (Electronic Design, Nov. 4, 1996, pp. 110 - 112)


MEASURING AND TEST CIRCUITS - CURRENT

AMMETER

AMMETER WITH SIX DECADE RANGE

CURRENT MONITOR AND ALARM

NANO AMMETER


AMMETER
AMMETERFA20-1

Current meter ranges from 100 pA to 3 mA full scale. Voltage across input is 100 μV at lower ranges rising to 3 mV at 3 mA. The buffers on the op amp are to remove ambiguity with high-current overload. The output can also drive a DVM or a DPM. (Reprinted with permission from National Semiconductor Corporation, Linear Databook 1982, p. 3-123)


AMMETER WITH SIX DECADE RANGE
AMMETER WITH SIX DECADE RANGEFB20-6

The Ammeter measures currents from 100 pA to 100 μA without the use of expensive high value resistors. Accuracy at 100 μA is limited by the offset voltage between Ql and Q2 and, at 100 pA, by the inverting bias current of the LT1008. (Linear Technology Corp. Linear Databook, 1986, p. 2-85)


CURRENT MONITOR AND ALARM
CURRENT MONITOR AND ALARMFC56-11

The circuit in Fig. a lights the signal lamp upon detecting a line current consumption of more than 5 mA, and handles currents of several amperes with appropriate diodes fitted in the Dl and D2 positions. Transistor T1 is switched on when the drop across D1/D2 exceeds a certain level. Diodes from the well-known 1N400x series can be used for currents of up to 1 A, while lN540x types are rated for up to 3 A. Fuse Fl should suit the particular application.

The circuit in Fig. b is a current-triggered alarm. Rectifier bridge D4 through D7 can only provide the coil voltage for Rel when the current through Dl/D2 exceeds a certain level, because then series capacitor Cl passes the alternating main current. Capacitor Cl needs to suit the sensitivity of the relay coil. This is readily effected by connecting capacitors in parallel until the coil voltage is high enough for the relay to operate reliably. (Elektor Electronics, 7-8/87 Supplement, p. 23)


NANO AMMETER
NANO AMMETERFA20-3

Resistance Values for

DC Nano and Micro Ammeter

1 FULLSCALE	Rf (Ω)	Rf ' (Ω)
100 nA	1.5M	l.5M
500 nA	300k	300k
lμA	300k	0
5μA	60k	0
l0μA	30k	0
50μA	6k	0
100μA	3k	0
The complete meter amplifier is a differential current-to-voltage converter with input protection, zeroing and full scale adjust provisions, and input resistor balancing for minimum offset voltage. ( Reprinted with permission from National Semiconductor Corporation, Application Note AN71, p. 5)


MEASURING AND TEST CIRCUITS - FREQUENCY

555 ASTABLE FREQUENCY METER

ANALOG FREQUENCY METER

AUDIO FREQUENCY METER

FREQUENCY METER


555 ASTABLE FREQUENCY METER
555 ASTABLE FREQUENCY METERFG145

The circuit shown in the figure is a simple digital frequency meter which indicates, the frequency in Hertz of an astable 555 timer. It could perhaps be adapted for other uses. An npn transistor, TR2, is connected to the 555 astable to be measured, as shown inset, and the output signal obtained is "hooked" to the main circuit via transistor TRl collector (c). Two CMOS 7555 timers, IC3 and IC4, are wired as monostables and these will trigger via R6/Cl when the Display switch Sl is closed. The period of IC3 is adjustable using VR1 whilst IC4 times for a fraction of a second. Upon closing Sl, IC4 sends a reset signal to IC1 and IC2, which are two decade counters each driving a 7-segment common cathode LED display directly. IC3 then drives transistor TR1, which allows pulses generated by the 555 "under test" to be fed into pin 1 (Clock) of IC2, the first decade counter. Monostable IC3 needs to be trimmed such that it triggers for approximately l00ms. Pressing switch Sl then allows "100ms "worth" of pulses to clock up on the display and simply multiplying the result by ten will yield the value in Hertz. It would be feasible to cascade several counters to show a higher range of frequencies. (Everyday Practical Electronics, September 1996, p. 712)


ANALOG FREQUENCY METER
ANALOG FREQUENCY METERFE55-21

This 1-kHz linear-scale frequency meter circuit uses the 555 as a pulse counter. Frequency is read on M1, (or 1 mA meter) which can be calibrated to read 0 to 1 kHz. (William Sheets)


AUDIO FREQUENCY METER
AUDIO FREQUENCY METERFF50-11

A pulse shaper is used in a tachometer circuit to drive a meter. (Reprinted with permission from Elektor Electronics, 12/91, p. 87)


FREQUENCY METER
FREQUENCY METERFD46-28

Using an LM2917N, this F/V converter based circuit indicates the frequency on a meter. S1 selects full-scale range ( up to 100 Khz). R8 is recommended to obtain the battery source. (Reprinted with permission from Popular Electronics, 10/90, p.23-24. (C) Copyright Gernsback Publications, Inc.,1990)


MEASURING AND TEST CIRCUITS (HIGH FREQUENCY AND RF)

LED SWR INDICATOR CIRCUIT

LITTLE DIPPER

RF SIGNAL STRENGTH INDICATOR

SIMPLE SWR BRIDGE


LED SWR INDICATOR CIRCUIT
LED SWR INDICATOR CIRCUITFG146

Dl and D2 act as half-wave diode detectors for the forward and reverse voltages. In traditional SWR-meter circuits, the output of these detectors feeds a panel meter via a forward/reflected switch and a scaling resistor, which typically provides the detector diodes with a load on the order of 25kΩ. This relatively low load impedance limits the diodes' performance at low power levels because it causes their forward voltage drop to be higher than the sampled RF voltages to be detected. To use LEDs (DS1 and DS2) as indicators, some sort of dc amplifier was needed. Operational amplifiers were used because their high input impedance lets us load the, diodes so lightly that their detection range can extend down to about 50mV. UlA and UlB, halves of a TL072 dual JFET- input op amp (see figure), do the dc amplification. The dc voltage developed by each detector is presented to its op amp across a 5.6-MΩ resistor. Each op amp operates a voltage gain of 1 (unity), but provides enough current gain to drive an LED and to cause a matching voltage to appear across R3. To provide each half of Ul with split (positive and negative) power supplies in environments in which only single-polarity, negative-ground supplies are typical, it was necessary to provide an artificial ground. U2 provides a stiffly regulated dc voltage between ground and the positive supply. (Note that the bridge circuit's dc reference is also set to +5V because the RF-grounded end of Ll, which is connected to dc ground in traditional directional-watt-meter circuits, is also connected to the +5V supply provided by U2). The overall sensitivity of the circuit can be adjusted to match the power level expected by changing the values of R3 and R4 to drive the LEDs with an appropriate current level. If you use different LEDs or want to use the bridge at a different power level, you may want to adjust these resistor values according to the formula R3 and R4 (ohms) = Po x 50/30 x If(LED) where Po is the transmitter power watts, 50 is the system impedance in ohms, 30 is Tl's turns ratio, and If (LED) is the current level (in amperes) that produces the LED brightness you need. With the resistor values chosen to light the FED Led (DS2) brightly, the REV LED (DS1) will be easily visible at SWRs around 2:1, allowing no-guess SWR dipping with tuner adjustment. (QST Magazine, June 1995, pp. 40-42)


LITTLE DIPPER
LITTLE DIPPERFB25-1

The circuit consists of two basic circuits, the oscillator and the detector. The oscillator uses an FET in a Colpitts configuration. The energy circulating in the oscillator tank is coupled through C4 to the detector circuit where a small diode (D2) rectifies it, feeding a dc voltage to the Darlington pair (Q2, A3) controlled by the sensitivity control (R3). Any small variations in the bias of the amplifier will cause large variations of current through the LED indicator in the DIP mode; however, in the PEAK mode the current produces a corresponding voltage drop through R5 and the action of the LED is reversed. The circuit shown will work practically on any frequency from LF to VHF if the appropriate components are used.(CQ, 1/87, p. 36)


RF SIGNAL STRENGTH INDICATOR
RF SIGNAL STRENGTH INDICATORFG147

This circuit is useful for test purposes as it gives an output that varies logarithmically with RF input level. A Motorola MC3356 IC is used for its received signal strength output (pin 14), the other functions remaining unused. An attenuator is placed at the input of the circuit to increase useable range. For best results, the circuit should be enclosed in a metal shielding box (Popular Electronics, February 1997, pp. 76-77)


SIMPLE SWR BRIDGE
SIMPLE SWR BRIDGEFG148

This circuit can be used to measure SWR. It uses a coupler made from a 6.5 inch piece of RG58/U coax. First remove, the outer plastic jacket, then open up the braid a little bit. Next, thread two lengths of #22 tinned bus wire into Teflon spaghetti. Then thread the insulated wires inside the braid, trying to keep them on opposite sides of the center conductor. Be careful to keep the leads to the 1N67A diodes and the 150 ohm resistors very short. If you can't find 1N67A diodes, use 1N34. The RG-58 A/U braid should, of course, be grounded at both ends. If carefully constructed, the result should be a perfectly balanced VSWR meter. It should need no adjustment. (73 Amateur Radio Today, February 1997, p. 22)


MEASURING AND TEST CIRCUITS - MISCELLANEOUS

AUDIBLE CONTINUITY TESTER

DEVIATION METER

ENERGY CONSUMPTION MONITOR

LIGHT METER

SHORT-CIRCUIT BEEPER

SIGNAL TRACER

WATCH TICK TIMER


AUDIBLE CONTINUITY TESTER
AUDIBLE CONTINUITY TESTERFE55-42

This 555 oscillator sounds a tone when continuity exists between the probes. Oscillator frequency is determined by the values of R1 and C1. (William Sheets)


DEVIATION METER
DEVIATION METERFD48-11

You can use this circuit in most FM VHF receivers; the hookup is off the FM discriminator. Because every signal transmitted has its own deviation signature, this can be a real plus in hunting jammers. (73 Amateur Radio, 3/89, p. 66)


ENERGY CONSUMPTION MONITOR
ENERGY CONSUMPTION MONITORFE55-1

The ECM circuit consists of four sections, as shown in the block diagram. A power converter generates a voltage that is proportional to the true of real power consumed by the load. That voltage feeds both a bargraph and a voltage-to-pulse converter. The bargraph gives an approximate indication of the amount of power used, and the voltage-to-pulse converter produces a pulse whose frequency is proportional to the power. The pulse triggers the counter module, which displays the cost of powering the monitored load. (Reprinted with permission from Radio-Electronics, 12/91, pp. 31-36. Copyright Gernsback Publications, Inc., 1991)


LIGHT METER
LIGHT METERFE55-13

The outputs from the comparators will swing, in sequence, from high to low as the input voltage rises above the reference voltage applied to each comparator. The output LEDs will then switch on in sequence as the voltage rises.

The inverting inputs of the comparators are connected in common to the collector of photo-transistor Ql. When Ql is illuminated, its collector-emitter junction conducts, thereby placing all the inverting inputs within a few millivolts of ground. For most settings of R1, each of the four reference voltages exceeds the value. Therefore, when Ql is illuminated, the output from each comparator is high and its respective indicator LED is off.

(William Sheets)


SHORT-CIRCUIT BEEPER
SHORT-CIRCUIT BEEPERFF19-1

This design offers a way to trace resistance in the milliohm range, right to a short between bridged traces beneath a solder mask. It simply translates resistance into an audible tone, which increases in pitch as the measured value approaches zero.

In the classic op-amp multivibrator (shown in the inset), oscillation frequency is determined not only by the Rl/Cl time constant, but also by the hysteresis set by the R2/R3 resistance ratio. Al in the main figure, with current boosters Ql and Q2, is this same configuration.

Assuming a virtual ground at the output of A2, free-run frequency is about 1 kHz---quite audible- through a tiny 8-Ω speaker. Ql and Q2 deliver a ± 10-V squarewave to R4, dumping a ±100 mA through a short circuit placed across the probe tips. R5 ensures that open circuit voltage never exceeds ±0.1V.

A2 monitors the voltage between the probes. The differential input must have its own separate path to the probe tips to eliminate test lead resistance from the measurement. Miniature "zip-cord" sold as loudspeaker wire makes a tidy two-conductor test lead.

When the probes are open, A2's gain equals the R4/R5 divider loss, and the output of both amplifiers is identical. This has two effects: first, hysteresis is greatly increased and the frequency falls to a low growl; second, the loudspeaker that bridges the two in-phase outputs is effectively silenced.

The dead short across the probe tips will return nothing to A2 and the circuit will squeal at its nominal 1-kHz rate. Anything less than a perfect short produces some output from A2, increasing multivibrator hysteresis and lowering the pitch. The circuit has so much "leverage," and the ear is so sensitive to pitch changes in this range, that it's easy to resolve minute resistance differences. Any general-purpose op amp will suffice in this circuit---a couple of 741s or an equivalent dual.

(Reprinted from Electronic Design, 3/95)


SIGNAL TRACER
SIGNAL TRACERFG149

The Sig-Tracer has good sensitivity so that it can be used for any normal type of audio signal tracing. The circuit provides AM demodulation, and the Sig-Tracer can therefore be used for IF and RF testing on AM radios provided a suitably strong antenna signal is available. The unit has an integral loudspeaker, and although the maximum output power is only a few tens of milliwatts, the volume level obtained is more than adequate for this application. If preferred though, the loudspeaker could be replaced by an earpiece or headphones. Low, medium and high impedance headphones are all suitable for use with the unit. (Electronic Experimenters Handbook, 1996, p.56)


WATCH TICK TIMER
WATCH TICK TIMERFE55-3

This circuit adapts a frequency counter to measure intervals. It was originally used as a shutter speed checker for a photo application. The watch ticks are clipped and shaped and formed into a square wave. This square wave is used to gate an accurately known clock (1-MHz TTL XTAL OSC) and an external counter is used to directly count the clock pulses during the interval to be measured. A 1-MHz clock can be used to measure to a resolution of 1 μsec. Accuracy = ± time base ± 1 μs count LSB. (William Sheets)


MEASURING AND TEST CIRCUITS - POWER

NOVEL RF POWER METER

SIMPLE WATTMETER


NOVEL RF POWER METER
NOVEL RF POWER METERFF50-28

The circuit matches the diode with a voltage variable attenuator that has a logmarithic response. By varying the attenuation until the diode output is zero, the resulting attenuation value then corresponds to the input power level. Because the voltage-variable attenuators output is logarithmic, diode nonlinearities become negligible. (RF Design, August 1994, p. 78)


SIMPLE WATTMETER
SIMPLE WATTMETERFG150

A current transformer T1 is used to derive a larger AC voltage which is rectified by D1 and D2 to produce a DC voltage proportional to AC line current. B1, R2 and D3 and D4 are used to linearize the circuit. (73 Amateur Radio Today. November 1995, pp. 20-21)


MEASURING AND TEST CIRCUITS - RESISTANCE

5-RANGE LINEAR-SCALE OHMMETER

MILLIOHM DMM ADAPTER

OHMMETER

WHEATSONE RESISTANCE BRIDGE


5-RANGE LINEAR-SCALE OHMMETER
5-RANGE LINEAR-SCALE OHMMETERFD47-10

Rx is inserted in the feedback  path of IC1. A known reference current is selected from reference voltage generator Q1, D1, and R5 through R9. A meter reading will be produced:

       I = Rx x 1 mA

R5

where R5=R5 through R9 is selected. This corresponds linearly to the value of Rx.

(Reprinted with permission from Radio-Electronics, 9/89. p. 62. (C) Copyright Gernsback Publications, Inc.,1989)


MILLIOHM DMM ADAPTER
MILLIOHM DMM ADAPTERFG151

The circuit provides a 1.000-ampere constant-current pulse of 100-μS duration, at a 100-Hz repetition rate, to the unknown (Rx) resistance, and provides an output voltage to your DMM of 1.000-volt per ohm of input resistance. Accuracy is better than ±l % up to 5.00 ohms, and the resolution using a 3 1/2-digit DMM is 100 micro-ohms. Extremely low resistance readings are only limited by the quality of the mechanical connections to Rx and the accuracy of the NULL setting. ICl (a TLC555) provides the pulse timing to a TIP125 transistor, Ql, which is configured as a capacitive discharge-current source. Capacitor C2 provides the current through R2, a stable metal-film or wire-wound resistor. Two red LEDs, LED1 and LED2, are selected to have a forward voltage drop of about 1.75 volts each (3.50 volts total) at a current range of 4 to 15 mA, as provided in the circuit. Transistor Ql has a dynamic Vbe of about 1.50 volts, so the LEDs provide a 2.00-volt reference across R2 with some temperature compensation. Integrated-circuit IC3 (a TLC272) is configured as a peak detector. The 78Ll2, provides a regulated 12 volts to the circuit. The Rx terminals, BPl and BP2, rnust be heavy-duty binding posts; do not uses test leads as that will introduce errors greater than the value of Rx. Resistor R5, the 0.005-ohm trimmer potentiometer, is simply a 2 1/2-inch length of tinned, 24-gauge bus-bar wire, with the lead from pin 3 of IC3 terminated in a clip that will slide on the bus-bar. To calibrate the circuit, first use a heavy shorting-bar between the input terminals, push Sl (TEST), and adjust R5 (NULL) for an output of 1.00 mV, or whatever value is convenient. You'll have to subtract that "null" value from your actual readings. Next, replace the shorting-bar with an accurate resistance, such as two 10.00-ohm, 1 % resistors in parallel, and adjust R3 for the proper output (5.000 volts). (Popular Electronics, March 1996, p. 67)


OHMMETER
OHMMETERFA72-2

This circuit has a linear reading scale, requires no calibration, and requires no zero adjustment. It may be made multirange by switching in different standard resistors. (CQ, 6/78, p.32)


Wheatsone Resistance Bridge
WHEATSONE RESISTANCE BRIDGEFG152*

R7 is a calibrated potentiometer. At null, Rx equals Rn * (R7/R6) where Rn = R1, R2, R3, R4, or R5 as selected by switch S1. (Popular Electronics, March 1994, p. 83)


MEASURING AND TEST CIRCUITS - SEMICONDUCTOR

DIODE MATCHING CIRCUIT

DIODE MATCHING CIRCUIT II

DIODE TESTING

SCR TESTER

SIMPLE CURVE TRACER


DIODE MATCHING CIRCUIT
DIODE MATCHING CIRCUITFG153

A 2N2222 transistor is connected in an emitter-follower circuit that's powered by a 12-volt DC source. Potentiometer R4 sets the voltage feeding the diodes under test. Two 1000-ohm, 1 % resistors, Rl and R2, make up two legs of a four-element bridge circuit. The diodes you want to test make up the other two legs. Potentiometer R3 is a fine-balance control. Meter Ml is a 100-0-100-μA, center-zero unit. Connect jumpers in place of the test diodes, set R3 to mid-position, and set R4 to its maximum-voltage position (minimum resistance). Apply power and adjust R3 for a zero meter reading. Disconnect the power and set R4 to its minimum voltage, position (maximum resistance) and connect two diodes in the rest positions. Slowly increase the bridge voltage with R4 and watch the meter for any change. The diodes are perfectly matched if the meter remains at zero as the voltage is increased. (Popular Electronics, May 1996, p. 65)


DIODE MATCHING CIRCUIT II
DIODE MATCHING CIRCUIT IIFG154

To match diode pairs with this circuit, simply insert diodes of equal rating in the D1 and D2 positions. When the DVM reading drops to zero, you have found a set. D1, D2 are diodes under test. S1A, B selects currents of 8 mA, 800 μA or 250 μA. (Popular Electronics, October 1994, p. 84)


DIODE TESTING
DIODE TESTINGFB54-5

The circuit will display curves on a scope, contingent on the state of the diode. To calibrate, substitutes a 1000-ohm resistor for the diode and adjust the scope gains for a 45-degree line. The drawings show some expected results. (Popular Electronics, 1/82, p. 76)


SCR TESTER
SCR TESTERFC56-22

The DUT's (Device Under Test) cathode, anode, and gate are connected to the unit's K, A, and G terminals, respectively. Pressing switch Sl feeds a gate current to the DUT, which triggers it on. Resistor R1 limits the gate current to the appropriate level. Resistor R3 limits the current through the LED to about 20 mA, which, with the current through R2, results in a latching current of about 110 mA. The LED is used to monitor the latching current. If the DUT is good, once the gate is triggered with S1, the LED will remain lit, indicating that the device is conducting. To end the test, turn off the device by interrupting the latching current flow using switch S2. The LED should turn off and remain off. The preceding procedure will work with SCRs and triacs. To check LEDs and other diodes, connect the anode and cathode leads to the anode and cathode of the diode; LED1 should light. When the leads are reversed, the LED should remain off. (Siliconix, Integrated Circuits Data Book, 3/85, p. 10-137)


SIMPLE CURVE TRACER
SIMPLE CURVE TRACERFE55-10

Useful for checking diodes, transistors, triacs, SCRs, resistors, and LEDs, this curve tracer should prove useful in the experimenters lab. It displays the volt-ampere characteristic of a two terminal device on an oscilloscope. (Reprinted with permission from Popular Electronics, 12/91, p.26. (C) Copyright Gernsback Publications, Inc.,1991)


MEASURING AND TEST CIRCUITS (SOUND)

SOUND LEVEL METER

SOUND-LEVEL METER

HV STATIC DETECTOR

STEREO AUDIO-LEVEL METER

STEREO POWER METER


SOUND LEVEL METER
SOUND LEVEL METERFG155

Power for the circuit is provided by Bl, a 9-volt battery. Total battery current is 14.5 mA, so an alkaline battery should last about 250 hours. Audio signals are picked up by microphone MIC1. The output of MIC1 is buffered by Ql to maintain the 3000-ohm load of resistor R2. The input impedance at pin 16 of the NE614 (Ul) is 1600 ohms of resistance to reduce the gain on the high end and preserve the RSSI linearity. The RSSI signal is a current source that flows through R6 to establish a voltage at pin 5 of Ul; the RSSI output voltage is a function of the input SPL. Capacitor C10 removes high-frequency components. The slope of the RSSI line is nominally 0.084Vcc/10 dB. Op-amp U2-b is configured as a non-inverting voltage buffer with a gain of 1.2; multiplied by the RSSI slope, produces a slope of 0.lVcc/10 dB. The display, DISP1, is a ten-bar LED that is used to indicate sound level in 10-dB increments from 30 to 120 dB(A). The display is driven by an LM3914 linear bar-graph driver, U5. The internal voltage regulator of U5 functions by establishing a constant current through Rl5, because the voltage between pins 7 and 8 is maintained at 1.25 volts. The resulting voltage at the emitter of Q2 is about 5 volts, which powers Ul, U3, and the internal voltage-divider string of U5 at pin 6. Each segment of the display will increase by 10 dB, independent of the exact magnitude of Vcc. While the slopes of the display driver and the RSSI signal are the same, they might not have the same offset. For that reason, an LM334, U4 is used to source a constant 1 0-microamp current through Rl7 to generate a fixed offset voltage on top of the composite RSSI voltage at the output of U2-a. By adjusting the value of the potentiometer Rl7, differences in microphone sensitivity can be accommodated so that the display reads properly from 30 to 120 dB(A). the proper readout of the display is also ensured by an ICM7555 timer, U4, which is configured as a self-excited, square-wave oscillator; the resulting peak-to-peak, 1-kHz signal of the timer is almost one step size of DISP1. (Popular Electronics, November 1995, p. 57)


SOUND-LEVEL METER
SOUND-LEVEL METERFD49-1

An electret microphone feeds an audio amplifier/rectifier combination. The amplifier has switchable gain. The rectifier output drives and LM3914 bar-graph generator. R14 provides fine gain control. (Reprinted with permission from Popular Electronics, 10/89, p. 84. (C) Copyright Gernsback Publications, Inc.,1989)


STATIC DETECTOR
HV STATIC DETECTORFG156

One leg of Wheatstone bridge is replaced by an MPF102 N-channel JFET. The JFET's high gate-input impedance turns the simple bridge circuit into a very sensitive high-voltage static detector. The JFET's gate is tied to ground through four 22-megohm resistors. A 1- to 2-inch piece of solid copper wire is connected directly to the JFET's gate and serves as the input sensor. With the sensor clear, adjust RB for a zero meter reading. Run a comb through your hair and move it toward the sensor. The meter should go off the scale. Place the static sensor next to your computer or any static sensitive equipment and take special notice when the meter moves. (Popular Electronics, March 1994, p. 90)


STEREO AUDIO-LEVEL METER
STEREO AUDIO-LEVEL METERFD49-6

A Samsung KAA2281 and a few LEDs make up a simple stereo indicator. Levels displayed are -16, -11, -6, -3 and 0 dB. Input sensitivity is 1 mV. LEDs can be any suitable types or a bar-graph display. (Reprinted with permission from Radio-Electronics, 1/91. p 71. (C) Copyright Gernsback Publications, Inc.,1991)


STEREO POWER METER
STEREO POWER METERFC56-3

The Stereo Power Meter is made up of two identical circuits and a power supply. Each circuit contains two LM3914 display chips which contain 10 voltage comparators, a 10-step voltage divider, a reference- voltage source, and a mode-select circuit that selects a bar or dot display via a logic input at pin 9. The brightness of the LEDs is controlled by the 1900-Ω resistors and the reference voltage is controlled by the 3900-Ω resistors. The 10-step voltage divider within the chips is connected between the reference voltage and ground. Since each step of the voltage divider is separated by a 1-K Ω resistor, each comparator senses a voltage 10% greater than the preceding comparator. The signal is applied to pin 5, which is buffered through a resistor-diode network and then amplified as it passes to each of the 10 comparators. Each LED is grounded through the comparators as the input signal voltage matches the reference voltage. That results in one to 10 LEDs illuminating as the signal voltage increases. (Hands On Electronics, Winter 1985,  p.31)


MEASURING AND TEST CIRCUITS - VOLTAGE

AUDIBLE VOLTMETER

DC MILLIVOLTMETER

ELECTROSCOPE CIRCUIT

GROUND TESTER

MOTOR HOUR METER

TONAL VOLTMETER

VOLTAGE MONITOR


AUDIBLE VOLTMETER
AUDIBLE VOLTMETERFG158

The Audible Voltmeter can be used to test for AC or DC voltages in a circuit. With Sl closed, the circuit can be used to test for voltages between 4 and 24 volts, and when Sl is open, it can be used to check for the presence of voltages of up to 200 volts. (Popular Electronics, May 1994, p. 79)


DC MILLIVOLTMETER
DC MILLIVOLTMETERFD47-19

An LF356 op amp is used as a gain amplifier with the output taken across R5. When a full-scale current of 1 mA is flowing through the meter, exactly 1 V appears across R5 (should be 1% tolerance or better). This is fed back to R2 to the summing junction of IC1 (a full-scale produces l μA). This offsets the current through Rl. Rl has a value of 1 MΩ/V which is used to zero the meter. R4 provides some overcurrent protection for the meter. (Reprinted with permission from Radio-Electronics, 9/89 p.61. (C) Copyright Gernsback Publications, Inc.,1989)


ELECTROSCOPE CIRCUIT
ELECTROSCOPE CIRCUITFG159

This circuit detects a charged object at a respectable distance and display the polarity (positive, negative, or earth grounded) and relative-intensity. In operation, Cl reduces AC noise but lowers the sensitivity a bit. The MPF102 and Rl form a voltage divider. When the FET's gate is earth-grounded, the divider's output will be about 4.5 volts giving a half-scale reading on Ml, a 200-microamp meter. A positively charged object (like cotton-rubbed glass) will give a positive deflection from half-scale, and a negatively charged object (a plastic comb, for example) will give a negative meter deflection. The whole circuit (including the 9-volt supply) should be in a metal enclosure. (Popular Electronics, November, 1994, p. 91)


GROUND TESTER
GROUND TESTERFB54-7

This circuit is simple and foolproof if wired correctly. Under normal conditions, only lamps 1 and 3 should be lit. If lamp 2 comes on, the cold lead is 117 volts above ground. (Popular Electronics, 8/69, p. 71)


MOTOR HOUR METER
MOTOR HOUR METERFC56-16

In this application, the ICM7249 is configured as an hours-in-use meter and shows how many whole hours of line voltage have been applied. The 20-MΩ resistor and high-pass filtering allow ac line activation of the S/S input. This configuration, which is powered by a 3-V lithium cell, will operate continuously for 2 ½ years. Without the display, which only needs to be connected when a reading is required, the span of operation is extended to 10 years. (Intersil, Component Data Catalog, 1987, p. 14-121)


TONAL VOLTMETER
TONAL VOLTMETERFG157

The frequency of the VCO contained within IC1 is determined by the voltage at pin 9, Cl, Rl, and R2. The circuit is based on a CD4046B phase-locked loop (PLL) IC with a built-in voltage-controlled oscillator (VCO). The frequency of the VCO is determined by the voltage at pin 9, capacitor Cl between pins 6 and 7, potentiometer R2 at pin 12, which sets the TVM's minimum frequency. The VCO output, which appears at pin 4, is normally fedback into the comparator input at pin 3. However, in this circuit, the VCO output drives a speaker directly. The VCO operates while the inhibit line (INH) at pin 5 is held logic low, and it turns off when INH is logic high. A touch switch consisting of two Schmitt-trigger inverters (IC2-a and -b) turns the circuit on and off to conserve power when the TVM is not being used. The touch switch can be replaced with a standard SPST switch, if so desired. This is recommended if you don't have a Schmitt-trigger inverter and don't want to purchase one. The TVM emits a low tone when reading a logic low. As voltage input increases, the tone pitch increases until the input voltage reaches a logic high. As the voltage input decreases, the pitch decreases. (Electronics Now, September 1996, pp. 61, 79)


VOLTAGE MONITOR
VOLTAGE MONITORFE55-38

If the DC voltage is less than the voltage at pin 5 of U1-B, then LED1 will light. If the voltage is over 5V, LED2 will light. If the voltage is within the window set by R4 and R5, neither LED will light. This circuit is useful as an under-or-over voltage monitor. (Reprinted with permission from Popular Electronics, 9/92, p.72. (C) Copyright Gernsback Publications, Inc.,1992)


MEDICAL ELECTRONICS CIRCUITS

BIOLOGICAL SIGNAL WAVEFORM GENERATOR

DRINK AID FOR THE BLIND

HEART SOUND SIMULATOR

HEARTBEAT TRANSDUCER

ISOLATION AMPLIFIER FOR MEDICAL TELEMETRY


BIOLOGICAL SIGNAL WAVEFORM GENERATOR
BIOLOGICAL SIGNAL WAVEFORM GENERATORFG160

The circuit operates as follows: U1A and UlB form a triangle waveform generator using R6 to offset the output so that it's a positive-going signal. The amplitude is set by R2 and R3, and the ramp's rate of rise is set by Rl and Cl. Using the values shown, the output has an amplitude of ±lV with rise and fall times of 0.5 ms giving a total Zeta duration of 1 ms. U1C provides an inverted output of U1B. When the reset pin on U3 is triggered, its Ql output goes low and the short across Cl by one half of the analog switch (U4) is removed. At this time, the output of UlA will be negative and the output of U1B will start to ramp up. During this time, the output of the circuit is taken via the other half of the analog switch from U1B. When the ramp reaches its positive voltage threshold, the output of UlA goes positive and UlB will start to ramp down. The output of UlA is taken via U2A and U2B (both inverting Schmitt triggers with special input circuitry that protects the input from negative voltages and allows them to level shift) to the clock input of U3. It's also taken to the analog switch, which now takes the output of the circuit from UlC (which has an output ramping up from the negative maximum to 0V). At 0 V, the output of UlA will go negative, resulting in the Ql output of U3 going high and again shorting Cl. This produces 0 V output until the next trigger input resets U3 and the cycle is repeated. (Electronic Design, May 1, 1997, p. 172)


DRINK AID FOR THE BLIND
DRINK AID FOR THE BLINDFG161

The circuit is an audio oscillator based around IC1, a 555 astable which drives a piezo disc directly. Transistor TRl acts as a switch, which will enable the audio oscillator when the two probes detect liquid. By using two sets of probes formed at different lengths (see inset diagram), the audio alarm will activate when enough milk then water, has been added. The circuit is powered by a small 12V battery (e.g. MN21 type) which should give many years continuous service as the quiescent current is virtually nil. The device were housed in a small circular plastic box, approximately 4cm in diameter. The probes were formed from sheathed, thick solid-core copper wires protruding from either side, so that the container could clip onto the side of the cup. (Everyday Practical Electronics, October 1996, P. 801


HEART SOUND SIMULTOR
HEART SOUND SIMULATORFG162

This oscillator circuit imitates the sound of a heartbeat. Use a 4-inch or larger speaker to get good bass response. (Electronics Now, January 1997, p.13)


HEARTBEAT TRANSDUCER
HEARTBEAT TRANSDUCERFF52-27

A simple heart-beat transducer can be made from an infrared LED and an infrared phototransistor. It works because skin acts as a reflective surface for infrared light. The IR  reflectivity of ones skin depends on the intensity of blood in it. Blood density rises and falls with the pumping action of the heart. So the intensity of infrared reflected by the skin (and thus  transmitted to the phototransistor) rises and falls with each heartbeat. (Reprinted with permission from Popular Electronics, 4/94, p.52. (C) Copyright Gernsback Publications, Inc.,1994)


ISOLATION AMPLIFIER FOR MEDICAL TELEMETRY
ISOLATION AMPLIFIER FOR MEDICAL TELEMETRYFA43-13

(Reprinted with permission from National Semiconductor Corporation, Hybrid Products Databook 1982, p. 3-7)


METAL DETECTOR CIRCUITS

LOW-COST METAL DETECTOR FOR EXPERIMENTERS

METAL DETECTOR

METAL DETECTOR II


LOW-COST METAL DETECTOR FOR EXPERIMENTERS
LOW-COST METAL DETECTOR FOR EXPERIMENTERSFE56-2

This circuit is an oscillator with L1 being a 4 diameter coil of 35 turns of #26 magnet wire. Metal in proximity to L1 will cause the oscillator to shift frequency. An AM transistor radio is used to detect the frequency shift. (Reprinted with permission from Popular Electronics, 3/89, p.69. (C) Copyright Gernsback Publications, Inc.,1989)


METAL DETECTOR
METAL DETECTORFD24-3

An NE602 acts as a heterodyne detector and Ql as a sense oscillator. When Ll is brought near metal, it causes a charge in loop inductance, shifting the resonant frequency of Ll C6/C7. Ll is 5 turns #20 wire on a 9" diameter wood or plastic form. (Reprinted with permission from Popular Electronics, 8/91, p, 73. Copyright Gernsback Publications, Inc., 1991)


METAL DETECTOR II
METAL DETECTOR IIFD24-4

Using an oscillator running at 455 kHz, the metal-detector circuit produces an indication on the meter M1. When the oscillator frequency changes because of metal in the field of Ll, the change will show as an increase or decrease in frequency, which produces a charge in the meter reading. The ceramic filter FILT1 produces a selective bandpass that yields this effect. L1 can be a 4" diameter coil wound on a suitable plastic form. About 10 turns of #26 wire are required. Use a frequency counter to adjust Ll and verify that Ql is operating on or near 455 kHz. (Reprinted with permission from Popular Electronics, 3/91, p, 92. Copyright Gernsback Publications, Inc., 1991)


METRONOME CIRCUITS

AUDIBLE METRONOME

LOW-POWER METRONOME

METRONOME II

NOVEL METRONOME


AUDIBLE METRONOME
AUDIBLE METRONOMEFF51-1

IC1 generates an audible frequency while a variable very low frequency is generated by IC2. R1 sets the metronome rate. The two signals are combined in IC3. (Sound, Light and Music, Delton T. Horn, McGraw-Hill, p. 123)


LOW-POWER METRONOME
LOW-POWER METRONOMEFD50-1

Using only 0.25 mA, this metronome is ideal for battery operation. The tempo range is 34 to 246 beats per minute. Use a CMOS timer, such as an LM555 CN or TLC55CP. (Reprinted with permission from Electronic Design 11/88, p 144, Copyright 1988 Penton Publishing)


METRONOME II
METRONOME IIFD50-4

This electronic metronome, using a 555 oscillator/timer, provides 10 to 40 beats per minute. The frequency is controlled by R3. (Reprinted with permission from Popular Electronics/Hands-On Electronics, 12/88, p.103. (C) Copyright Gernsback Publications, Inc.,1988)


NOVEL METRONOME
NOVEL METRONOMEFD50-5

The LM3909 is configured so that the frequency of oscillation is dependent on a single RC timing circuit, which consists of Cl and R2. LED1 discharges capacitor Cl and the resultant pulse is directed into pin 3 as well as pin 1 of the LM386 audio amplifier to externally control that unit, thereby providing adequate volume. The circuit, as it is configured, provides frequency ranges from 57 to 204 beats per minutes and plenty of volume. (Reprinted with permission from Popular Electronics, 7/89, P. 26. Copyright Gernsback Publications, Inc., 1989)


MISCELLANEOUS TREASURES

BAR-CODE SCANNER

BUG DETECTOR

CHARGE PUMP GENERATES GATE DRIVE

GAME FEEDER CONTROLLER

GYRATOR CIRCUIT

PRECISION FULL-WAVE RECTIFIER

SIGNAL AVERAGER CIRCUIT

VARIABLE-VOLTAGE REFERENCE SOURCE

VOCAL STRIPPER

VOCAL-STRIPPER POWER SUPPLY

ZENER DIODE SIMULATOR CIRCUIT


BAR-CODE SCANNER
BAR-CODE SCANNERFC59-13

The circuit illustrates a method of interfacing a HEDS-1000 emitter-detector pair with a HA-5144 for

use as a bar-code scanner circuit. The HA-5144 is used as an amplifier system which converts the bar and space widths of the printed bar code into a pulse-width modulated digital signal. Amplifier Al is used to amplify the current output of the detector. The output of Al is passed to two precision peak-detector circuits which detect the positive and negative peaks of the received signal. Amplifier A4 is used as a comparator whose reference is maintained at the midpoint of the peak-to-peak signal by resistors R5 and R6. This provides a more accurate edge detection and less ambiguity in bar width. Amplifier A5 is used as an optional noise gate which only allows data to pass through the gate when the peak-to-peak modulation signal is larger than one diode drop. This circuit is operated by a single supply voltage with low-power consumption which makes it ideal for battery-operated data entry systems. (Harris, Analog Product Data Book, 1988, p 10-109)


BUG DETECTOR
BUG DETECTORFC59-16

This RF detector can locate low-power transmitters (bugs) that are hidden from sight. It can sense the presence of a 1-mW transmitter at 20 feet, which is sensitive enough to detect the tiniest bug. As you bring the RF detector closer to the bug, more and more segments of its LED bar-graph display light, which aids in direction finding.

The front end has a two-stage wideband RF amplifiers and a forward-biased hot-carrier diode for a detector. After detection, the signal is filtered and fed to IC1, an LM3915N bar-graph driver having a logarithmic output. Each successive LED segment represents a 3-dB step.

(Radio Electronics, 6/89, p. 42)


CHARGE PUMP GENERATES GATE DRIVE
CHARGE PUMP GENERATES GATE DRIVEFG166

A charge pump built as a voltage trippler can provide just the right amount of voltage needed for gate drive in a 5-V system. (Electronic Design, September 18, 1995, p. 97)


GAME FEEDER CONTROLLER
GAME FEEDER CONTROLLERFB58-5

The circuit is built around an LM339 quad comparator, Ul, which forms the basis of a Schmitt trigger, timer circuit, and a window comparator. One comparator within the LM339 (pins 1, 7, 6), plus LDR1, R4, R5, R6 and R8, is used as a Schmitt trigger. The timer circuit (which receives its input from the Schmitt trigger consists of R9, R10, R11, R13. The last two -fourth's of Ul (pins 8, 9, 10, 11, 13 and 14) are wired as a window comparator. The two inputs to the window comparator are derived from the charge on capacitor C1 which is fed to pins 9 and 10 of U1. The other inputs are picked from two points along a voltage-divider network, consisting of R1, R2, and R3. Diode D1 is used as a blocking diode, forcing capacitor Cl to discharge through R10 and R13. The window comparator looks for any voltage falling between one-third and two-thirds of the supply voltage V; when the voltage falls between those two points, the output of the window comparator (pins 13/14) goes high. Transistors Ql and Q2 are turned on, when the pins 13/14 junction goes high, energizing the relay, Kl. The energized relay provides a dc path to ground, activating the motor, Ml, which reloads the feeder. The timer circuit also provides immunity from triggering, due to lightning. The on-time of relay Kl is determined by the charge cycle of Cl, R11, and R9 or the discharge cycle of Cl, R10, and R13. Changing the value of either a resistor or the capacitor, changes the timing cycle.

(Hands-On Electronics, 9/87, p. 71)


GYRATOR CIRCUIT
GYRATOR CIRCUITFG163

The gyrator circuit has been around for a number of years. This active circuit can be used in place of an inductor. With two operational amplifiers (two sections of a dual or quad op amp are preferred), the value of the inductance simulated by this circuit is: L= Rl R3 R5/(R2/C4) or, in the case where R2 = R3, L= Rl R5 C4. (73 Amateur Radio Today, November 1995, p. 68)


PRECISION FULL-WAVE RECTIFIER
PRECISION FULL-WAVE RECTIFIERFD52-13

Using two op amps, this circuit produces a full-wave rectified version of the input signal. Op amp IC1inverts the negative-going signal, but because of D2, it stays near zero. IC2 produces a positive-going signal. For positive-going signals, IC1 produces a negative output through Dl to IC2, where it is combined with positive VIN from R4/R5. At the summing junction of IC2, the negative output of IC1 is doubled and inverted via IC2, R3, and R5 to produce + VOUT. This is summed with negative output of IC1 to produce + VOUT. (Reprinted with permission from Radio-Electronics, 9/89, p. 60. (C) Copyright Gernsback Publications, Inc., 1989)


SIGNAL AVERAGER CIRCUIT
SIGNAL AVERAGER CIRCUITFG165

The first operational amplifier, ICl-a, is an inverting amplifier whose gain can be adjusted up to 5. Adjustable feedback resistor, R2, sets the circuit gain. The second amplifier, ICl-b, forms a half-wave rectifier and signal averager that clips the brief peaks and displays them over a longer period of time. (Electronics Now, January 1996, pp. 29-31)


VARIABLE-VOLTAGE RE
VARIABLE-VOLTAGE REFERENCE SOURCEFD52-10

The noninverting terminal of the op amp is grounded, and the circuit uses the voltage at the inverting terminal as a reference. Its voltage gain is determined by the R2/R1 ratio. When R2 is set at zero, the circuit has unity gain and a 0.55-V output. When R2 is set to the maximum value, the circuit has a gain of 50 and an output of about 25 V. The circuit provides good regulation and can supply output currents of several milliamps. The output voltage however, is not temperature compensated. (Reprinted with permission from Radio-Electronics, 12/88, p. 72. (C)Copyright Gernsback Publications, Inc.,1988)


VOCAL STRIPPER
VOCAL STRIPPERFF52-6

The schematic of the lead vocal filter is shown in the figure. The left and right channel signals are coupled through Cl and C2 to buffer amps IC4-a and IC4-b. From the buffer amps, the left and right channel signals pass through active crossovers IC5-a and IC5-b, sending all low frequencies to a final mixer IC6-c, and all middle and high frequencies to analog delay lines IC1 and IC2, RD5106 256-sample bucket-brigades. Integrated circuit IC2 delays the left-channel signal by 2.4 ms, set by the fixed- frequency clock generated by 1/2 IC3, R47, and C24. The right channel signal is delayed by IC1 with a variable-frequency clock generated by 1/2 IC3, R48, R49, and C23. Potentiometer R49 is used for phase adjustment.

The output of each delay line from IC1 and IC2 passes through low-pass filters IC6-a and -d, and their associated parts, to filter out high-frequency sample-steps produced by IC1 and IC2. Balance control R36 is adjusted for equal amplitude of the left and right channels. IC6-b is a difference amplifier that cancels all lead vocals that are common to both channels. The resulting signal from IC6-b is remixed with low frequencies by IC6-c and is then sent to the output via buffers IC4-c and IC4-d. (Reprinted with permission from Radio-Electronics Experimenter's Handbook, pp. 98-99. (C)Copyright Gernsback Publications, Inc.,1994)


VOCAL-STRIPPER POWER SUPPLY
VOCAL-STRIPPER POWER SUPPLYFF52-7

The power supply schematic for the lead vocal filter circuit. (Reprinted with permission from Radio-Electronics, Experimenter's Handbook, p. 99. (C) Copyright Gernsback Publications, Inc.,1994)


ZENER DIODE SIMULATOR CIRCUIT
ZENER DIODE SIMULATOR CIRCUITFG167

Conventional Zener diodes, unless specially compensated, all exhibit a similar problem-as the Zener bias current increases, the temperature coefficient also increases in a positive direction. Also, the temperature compensation can be negative or positive, depending on the Zener voltage and the particular bias current used-even for a single diode over its characteristic curve! Also, Zener diodes available for less than approximately 5.0-volt values also exhibit very weak "knees," where the Zener impedance causes a large voltage change over the full bias-current range. This circuit is an attempt to reduce those problems. The bias current range is 1 to 20 mA, which can be extended by using a higher-power transistor for Q2. This circuit has an adjustable "Zener" voltage of from 1.5 to 6.5 volts. That voltage (Vz) can be determined using:

Vz = 1.5 = (5R2/10000)

For any setting of R2, the voltage varies less than 1% over the 2- to 20 mA bias current.The base-emitter voltage of Ql provides the reference voltage that is temperature D1, a 1N34A germanium diode. A stable voltage of about 375 mV is then present across Rl, and a constant current of 0.5mA flows through the resistor divider. The net temperature coefficient is complex, but remains below -2mV/ºC, due to the interaction of the diode and transistors. Darlington-pair Q2 handles all the bias current except for the 600 pA needed to bias the reference. (Popular Electronics, March 1996, pp. 68-75)


MIXER AND MULTIPLEXER CIRCUITS

32-CHANNEL ANALOG MULTIPLEXER

ANALOG MULTIPLEXER WITH BUFFERED INPUT AND OUTPUT

AUDIO MIXER USING LM3900

FET OP AMP MICROPHONE MIXER

INPUT-BUFFERED MIXER

LOW-COST FOUR-CHANNEL MULTIPLEXER

SIMPLE MIXER

SIMPLE UTILITY MIXER

TWO CHANNEL MIXER FOR AUDIO

WIDE BAND DIFFERENTIAL MULTIPLEXER


32-CHANNEL ANALOG MULTIPLEXER
32-CHANNEL ANALOG MULTIPLEXERFE64-1

Using two Siliconix DG506 multiplexer chips, this 32-channel analog multiplexer selects 1 of 32 channels, depending on data inputs A0-A4 (William Sheets)


ANALOG MULTIPLEXER WITH BUFFERED INPUT AND OUTPUT
ANALOG MULTIPLEXER WITH BUFFERED INPUT AND OUTPUTFC63-7

This circuit is used for analog signal selection or time division multiplexing. As shown, the feedback signal places the selected amplifier channel in a voltage follower (noninverting unity gain) configuration, and provides very high input impedance and low output impedance. The single package replaces four input buffer amplifiers, four analog switches with decoding, and one output buffer amplifier. For low-level input signals, gain can be added to one or more channels by connecting the (-) inputs to a voltage divider between output and ground. The bandwidth is approximately 8 MHz, and the output will slew from one level to another at about 15.0 V per μs.

Expansion to multiplex 5 to 12 channels can be accomplished by connecting the compensation pins of two or three devices together, and using the output of only one of the devices. The enable input on the unselected devices must be low.

Expansion to 16 or more channels is accomplished easily by connecting outputs of four 4-channel multiplexers to the inputs of another 4-channel multiplexer. Differential signals can be handled by two identical multiplexers addressed in parallel. Inverting amplifier configurations can also be used, but the feedback resistors might cause crosstalk from the output to unselected inputs.

(Harris Analog Product Data Book, 1988, p. 10-12)


AUDIO MIXER USING LM3900
AUDIO MIXER USING LM3900FG169

An audio mixer is a handy circuit that will combine two or more audio signal sources into one signal channel. The figure shows an audio mixer that is built around the LM3900 CDA. The crux of this circuit is the three input networks, principally R3, R4, and R5. These resistors are connected to different input sources (labeled VIN1, VIN2, and VIN3). Those three resistors all connect to the inverting input of the CDA. The gain is approximately:

Av = R2/Rx,

where the Rx is the value of any one input resistor. The output voltage is:

Vo = R2 ((VINl/R) + (VIN2/R4) + (VIN3/R5))

If resistor R2 is made variable, then the potentiometer used for R2 will serve as a master gain control for the audio mixer. (Popular Electronics, July 1996, p. 52)


FET OP AMP MICROPHONE MIXER
FET OP AMP MICROPHONE MIXERFE58-5

(Reprinted with permission from Popular Electronics, Fact Card 264. (C) Copyright Gernsback Publications, Inc)


INPUT-BUFFERED MIXER
INPUT-BUFFERED MIXERFC60-3

A high signal-to-noise ratio is important in signal construction and combination. The HA-5147 aids in lowering overall system noise and thereby raises system sensitivity. The signal combination circuit incorporates input buffering with several other features to form a relatively efficient mixer stage with a minimum of channel crosstalk. The potentiometer used for each channel allows for both variable input levels and a constant impedance for the driving source. The buffers serve mainly to prevent reverse crosstalk back through the resistor network. This buffering allows for the combination of varying strength signals without reverse contamination. The gain of the final stage is set at a minimum of 10 and can be adjusted to as much as 20. This allows a great amount of flexibility when combining a vast array of input signals.

(Harris Analog Product Data Book, 1988, p. 10-170)


LOW-COST FOUR-CHANNEL MULTIPLEXER
LOW-COST FOUR-CHANNEL MULTIPLEXERFC63-3

(Intersil, Applications Handbook, 1988, p. 5-6)


SIMPLE MIXER
SIMPLE MIXERFC60-2

This mixer is built around a TL072 dual BIFET op amp with a JFET input stage, and can be powered from a single-ended 9- to 18-V power supply. The microphone input is capacitively coupled to the noninverting input of Ula. Resistors Rl and R3 set the voltage gain at about 26 dB and serve as a negative feedback network for Ula. Capacitors Cl through C3 are dc-blocking capacitors. Most high-impedance microphones have outputs of a few mV. Often, a preamp stage just isn't enough, so the microphone signal is given a boost of about 20 db in the mixer. The noninverting input of Ulb is biased to half the supply voltage by R6, R7, and C6. Resistors R5 and R8 make up the negative-feedback network and set the voltage gain of Ulb at unity. Capacitor C5 is for dc blocking at this input. (Popular Electronics, 7/89, p. 23)


SIMPLE UTILITY MIXER
SIMPLE UTILITY MIXERFD53-8

Here's an interesting mixer circuit. With it you can effectively combine signals from audio to high-frequency RF. Also, as a special bonus, this circuit will provide some gain at a low noise figure. The inputs can be of almost any level or impedance, and the output (low-Z) will drive most tuned circuits or transistors. Basically, the device consists of two similar FET amplifier stages with a common load resistor (R2). Each FET develops a signal across this resistor, a form of cancellation occurs, and a difference signal results. If you want less gain, try reducing R2 to 2200-Ω. This modification will not affect the mixing ability. (Reprinted with permission from Radio Electronics, 4/70, p. 29- Copyright Gernsback Publications, Inc., 1970)


TWO CHANNEL MIXER FOR AUDIO
TWO CHANNEL MIXER FOR AUDIOFG168

Basic 2-channel op amp mixer circuit. Gain is equal to R5/R1 or R5/R2 for channels 1 or 2 respectively. Typically R1, R2 are 2.2K to 22K and R5 is 10 to 100K, and the op amp is any suitable type such as a 741 or its numerous variations. (Everyday with Practical Electronics, June 1996, p. 452)


WIDE BAND DIFFERENTIAL MULTIPLEXER
WIDE BAND DIFFERENTIAL MULTIPLEXERFA53-7

This design allows high frequency signal handling and high toggle rates simultaneously. Toggle rates up to 1 Mhz, and Mhz signals are possible with this circuit. (Reprinted with permission from National Semiconductor Corporation, Transistor Databook 1982, p. 11-34)


MODEL AND HOBBY CIRCUITS

GRAND PRIX STARTING LIGHTS

MODEL AIRCRAFT LED FLASHER

MODEL CAR DERBY WINNER INDICATORMODEL FIRE ENGINE FLASHER CIRCUIT

MODEL TRAIN AND SLOT-CAR CONTROLLER

MODEL TRAIN SOUNDER

MODEL TRAIN TRACK CONTROL SIGNAL

PWM MODEL RAILROAD CONTROLLER


GRAND PRIX STARTING LIGHTS
GRAND PRIX STARTING LIGHTSFG174

Figure shows a circuit design for a "starting gantry" with three red and three green starting lights. It can be powered from the racing set's mains operated power supply unit. A 12V regulator (ICl) provides a stabilized supply for the circuit, and diode Dl prevents accidental reverse connection by the young motor enthusiast. The circuit uses a system of relays to start and stop the sequence. When Start switch Sl is pressed, relay contacts RLA1 close and this applies + 1 2V to the sequencer and also latches the relay. Contacts RLA2, across capacitor C3, open. Three comparators are used (IC2a, IC2b, IC2c) and their non-inverting (+) terminals each have a reference voltage set by a potential divider at about +2.10V, +2.75V and +4.75V respectively. Either an LM339 quad comparator or an LM324 quad op-amp can be used. When capacitor C3 charges in excess of +1.75V, transistor TRl conducts and the red LEDs D4 to D6 illuminate. At +2.75V, TR2 conducts and the green LEDs D7 to D9 light. IC2a also swings high, via resistor R6 so the red lamps extinguish. When capacitor Cl reaches +4.75V, transistor TR3 conducts and completes the circuit to relay RLB. Contacts RLB1 (normally closed) now open and disconnect relay RLA. Also, contacts RLA2 then close which discharges the timing capacitor Cl, ready for next time. (Everyday Practical Electronics, August 1996, p. 643)


MODEL AIRCRAFT LED FLASHER
MODEL AIRCRAFT LED FLASHERFG170

This circuit was used to simulate machine gun firing on a model aircraft, but can also be used for other applications. (Everyday with Practical Electronics, October 1995, p. 794)


MODEL CAR DERBY WINNER INDICATOR
MODEL CAR DERBY WINNER INDICATORFF39-1

This derby winner indicator uses infrared emitters and sensors to detect a car crossing the finish line. The first car to finish locks out the data from the second car, and the system can be reset by pressing S1. (Reprinted with permission from Popular Electronics, 6/93, p.74. (C)Copyright Gernsback Publications, Inc.,1993).


MODEL FIRE ENGINE FLASHER CIRCUIT
MODEL FIRE ENGINE FLASHER CIRCUITFG175

This circuit was designed to add both a blue flashing light sequence plus a two-tone  siren effect, to a model fire engine. IC1 is a Quad NAND Schmitt trigger and IC1a  provides a low-frequency waveform which is inverted by IC1b. Complementary outputs  are obtained which drive transistors TR1 and TR2. These driver transistors operate D1  and D2 which are two blue l.e.d.s. The model had a blue translucent moulding on its  roof and yielded a surprising realistic effect. The outputs from IC1a and IC1b are also  used to control gated astables IC1c and IC1d, which are se to oscillate at different  frequencies to simulate a typical British two-tone siren sounded by WD1, a piezo disc. (Everyday Practical Electronics, September 1996, p. 725)


MODEL TRAIN AND SLOT-CAR CONTROLLER
MODEL TRAIN AND SLOT-CAR CONTROLLERFD54-1

As shown, a 555 timer (Ul) is configured as an astable multivibrator (oscillator) with a 400:1 duty cycle and a frequency of 40 Hz.

When power is applied to the circuit, capacitor Cl (connected to pin 6 of Ul) is discharged and the output of the 555 (which is used to sink current) is low. Capacitor Cl begins to charge via RI and R2 toward the positive supply rail. When the charge on Cl reaches about 66% of +V, the output of Ul at pin 3 goes high.

At that point, Cl begins to discharge through R2. When the charge on Cl decreases to about 33% of the supply voltage, the output of Ul returns to the low state, and the cycle is repeated until power is removed from the circuit.

When the output of Ul is low, C3 is discharged into Ul via transistor Q2. When Ul pin 3 goes high, C3 charges through a current source that consists of D1, D2, R3, R4, and Ql. The charge/discharge cycling of C3 produces a stream of pulses that are fed to the inverting inputs of U2A and U2B (an LM358 dual op amp). Two voltage-divider networks (R7, R8, R9, and R10, R11, R12) set the reference voltage that is applied to the noninverting inputs of U1A and U1B at pins 3 and 5.

Potentiometers R9 and R12 set the low-level duty cycle (5 to 10%) of UlA and UlB. They are adjusted so that the train head-lights glow, but the motor hums only slightly. Potentiometer R3 adjusts the ramp rate of C3 for 100% duty cycle at the full throttle setting. A double-pole, single-throw switch (S1A and S1B) is used to place R3/C4 and R4/C5 in the circuit.

The R5/C4 and R6/C5 combinations cause the reference voltages presented to the noninverting inputs to U2A and U2B to change very slowly when the throttle is turned up and down. When the ACL/DCL switch is turned off, the resistance of the throttle-divider networks are much smaller than those of R5 and R6, so the reference voltages on C4/C5 change "instantly" to the new throttle setting,

The output drivers consist of resistors R13 and R15, and transistors Q3 and Q4 for output "A"; and resistors R17 to R20, and transistors Q5 and Q6 for output "B." Components R13/R16/Q3 and R17/R20/Q5 limit the output drive currents of Q4 and Q6 to about 3 A each. Resistors R14/R15 and R18/R19 turn on Q4 and Q5, respectively,-- before the breakover voltage is reached to prevent damage to the output drivers and dissipate the energy that is stored in an inductive field (such as in a motor).

The power supply delivers 18 V to the track. Voltage regulator U3 (a 78L09 9-V, 100-mA voltage regulator) supplies power to the control circuits.

(Reprinted with permission from Popular Electronics, 12/90, p.22. (C) Copyright Gernsback Publications, Inc.,1990)


MODEL TRAIN SOUNDER
MODEL TRAIN SOUNDERFG173

This circuit can fit inside a model-train car and output any sound you record in the ISD1000A. Imagine a cattle car that moos! The circuit can be used in model railroading to sound an electronic diesel horn when the train approaches a railroad crossing. It is mounted on the bottom of the car. When the "sound car" approaches the crossing, Sl is momentarily closed by a magnet that must be installed under the track, thus starting the timing cycle and sounding the horn. Before you can use U2, the ISD1000A record and playback IC, you must first program it by breadboarding the circuit found in the applications data included with the IC. To record sound on U2, you'll need a sample of the sound that you want the IC to play. The phone jack which is mounted on the bottom of the car, serves two purposes. It serves as a means of charging B1, the 7.2-volt NiCd battery, and also provides a way to turn the circuit off. (Popular Electronics, March 1995, p. 29)


MODEL TRAIN TRACK CONTROL SIGNAL
MODEL TRAIN TRACK CONTROL SIGNALFG171

The circuit is based on a 555 timer IC, Ul, and operates on 5-volts DC to make it usable with digital logic. The operating power of the circuit can be converted to 12 volts by increasing the values of R2 and R3. Train detection is accomplished by photocell PC1, which should be mounted between the rails, flush with or slightly below the ties. A small light must be mounted directly above PCl when used in any dark area. Resistor R4 is adjusted so that when a train covers PCl the circuit triggers. Resistor Rl reduces the current to Ul if R4 is set for minimum resistance. Variable resistor R4 can also be adjusted so that each individual car in a train will change the colors of LED1, a bi-color unit, back and forth indicating train movement. That can be handy if 2 circuits are used, one at each end of the track block. It will indicate that the train has begun to move. Mount LED1 on the control panel. The circuit is designed to indicate a green when no train is present. When a train covers PC1, Ul switches LED1 to red, indicating the train is in position. (Popular Electronics, March 1995, p. 30)


PWM MODEL RAILROAD CONTROLLER
PWM MODEL RAILROAD CONTROLLERFG172

A PWM Model Train Controller shown offers far superior results than a traditional rheostat-type model train controller and provides better fine control of train speeds. A 555 timer chip (ICl) is configured as a free running oscillator operating at some 80 kHz. The exponential ramp waveform generated across capacitor C3 feeds a comparator(IC2) whose threshold reference is set by a logarithmic potentiometer VR1. Comparator IC2 output is inverted by IC3a and IC3b and drives the output stage comprising transistors TRl and TR2; the latter can handle some 2A and dissipate 1W, more than adequate for a saturated switch operation. Diode D2 protects against back e.m.f. in the train motor. Short circuit protection is provided with a 0.5 ohm series sense resistor (R8/R9). Transistor TR3 switches on when the current flowing, reaches approximately 1.2A. This sets the output of an S-R flip-flop (IC3c/IC3d) low. LED D3 illuminates to indicate a fault, and TRl is disabled by the inverters. Capacitor C4 introduces a short time period across TR3 to prevent the cutout triggering falsely. Push-switch Sl is a "kick" button. Pressing this causes a short, higher voltage burst to be applied to reluctant motors. (Everyday Practical Electronics, August 1996, p. 642)


MODULATOR CIRCUITS

FM MODULATOR

PULSE-WIDTH MODULATOR

PULSE-WIDTH MODULATOR

VARACTORLESS HF MODULATOR

VIDEO MODULATOR

VIDEO MODULATOR CIRCUIT


FM MODULATOR
FM MODULATORFE59-1

The FM modulator is built with a Motorola MC1648P oscillator. Two varactors, Motorola MV209, are used to frequency modulate the oscillator. The 5000-Ω potentiometer is used to bias the varactors for best linearity. The output frequency of approximately 100 MHz can be adjusted by changing the value of the inductor. The output frequency can vary as much as 10 MHz on each side. The output level of the modulator is -5 dBm. In this prototype, the varactor bias was 7.5 V for best linearity-, but this could be different ,with other varactors. (Reprinted with permission from RF Design, 3/93, pp. 92-93)


PULSE-WIDTH MODULATOR
PULSE-WIDTH MODULATORFA55-4

If the timer is triggered with a continuous pulse train in the monostable mode of operation, the charge time of the capacitor can be varied by changing the control voltage at pin 3. In this manner, the output pulse width can be modulated by applying a modulating signal that controls the threshold voltage. (Courtesy of Motorola Inc., Linear Integrated Circuits, 1979, p. 6-137)


PULSE-WIDTH MODULATOR
PULSE-WIDTH MODULATORFF55-5

(Reprinted with permission from Popular Electronics, Fact Card No. 249. (C) Copyright Gernsback Publications, Inc)


VARACTORLESS HF MODULATOR
VARACTORLESS HF MODULATORFF55-1

Traditionally, high-frequency oscillators are frequency-modulated using a varactor. However, varactors usually require a large voltage change to achieve a reasonable capacitance change-a problem in many battery-powered systems.

Such a problem can be overcome by employing base-charging capacitance modulation. Resistor R1 establishes Ql's current, and R2 allows control of the collector bias current by Vmod. The transmission line (Tl) in the negative resistance-type oscillator determines the frequency of oscillations. Tl is a high-quality, low-loss, ceramic coaxial shorted quarter wave transmission line. Under proper terminal impedances, a negative resistance is "seen" at Q1's base. T1 reacts with this negative resistance to produce sustained oscillations.

Frequency modulation is accomplished by changing Ql's collector bias current and thus changing  Ql's base-charging capacitance. This effect is "seen" at Q1's base and causes a frequency shift in the resonators quarter-wave node.

(Reprinted with permission from Electronic Design 10/94, pp 94-96, Copyright 1994 Penton Publishing)


VIDEO MODULATOR
VIDEO MODULATORFB59-4

This circuit permits direct connection of composite video signals from video games and microcomputers to the antenna terminals of TV sets. The output signals level is controlled by the modulation input. (Radio Electronics, 8/77, p. 33)


VIDEO MODULATOR CIRCUIT
VIDEO MODULATOR CIRCUITFB59-3

These are modulator circuits for modulation of video signals on a VHF/UHF carrier. The circuits require a 5 V power supply and few external components for the negative modulation mode. For positive modulation an external clamp circuit is required. The circuits can be used as general-purpose modulators without additional external components. The IC is TDA6800. (Signetics, Linear Data Manual Vol. 3: Video, p. 11-3)


MOISTURE AND FLUID DETECTOR CIRCUITS

AC OPERATED WATERING CONTROL SYSTEM

AUTOMATIC WATERING SYSTEM CONTROLLER

FLOOD ALARM

LATCHING WATER SENSOR

SOIL MOISTURE MONITOR


AC OPERATED WATERING CONTROL SYSTEM
AC OPERATED WATERING CONTROL SYSTEMFG178

AC operation of the circuit reduces the possible electrolysis effects over time. Two probes are inserted into the soil. When the soil is wet it is more conductive and Q1 conducts cutting Q2 off. As the soil dries, Q1 loses bias, allowing Q2 to turn on, actuating the relay RY1. RY1 closes, operating the watering system control valve. When the soil is sufficiently moist, Q1 turns on, cutting off RY1, and the water valve, R2 sets trip level. (Popular Electronics, July 1996, p. 70)


AUTOMATIC WATERING SYSTEM CONTROLLER
AUTOMATIC WATERING SYSTEM CONTROLLERFG177

Two probes are inserted into the soil. When the soil is wet, it is more conductive and Q1 is forward biased, cutting Q2 off. As the soil dries, Q1 loses bias, allowing Q2 to turn on, actuating the relay RY1. RY1 closes, operating the watering system control valve. When the soil is sufficiently moist, Q1 turns on, cutting off Q2 RY1, and the water valve. (Popular Electronics, July 1996, p. 70)


FLOOD ALARM
FLOOD ALARMFD32-6

Using a few bipolar transistors, this circuit acts as a flood alarm. When liquid touches the probes, leakage current biases Q1, Q2, Q3 (a dc coupled amplifier) into conduction which activates the relay. The contacts can be hooked into the alarm system. (Reprinted with permission from Radio-Electronics, 7/90. p. 59. (C) Copyright Gernsback Publications, Inc.,1990)


LATCHING WATER SENSOR
LATCHING WATER SENSORFD32-9

A balanced Wheatstone bridge controls a JK flip-flop that uses an op amp as an interface. This in turn drives a relay circuit. R1 through R4 can be made larger for increased sensitivity. (Reprinted with permission from Popular Electronics, 11/90, p.22. (C) Copyright Gernsback Publications, Inc.,1990)


SOIL MOISTURE MONITOR
SOIL MOISTURE MONITORFG176

In the circuit, when the value of R6 equals the value of the resistance of the soil between the two probes, the bridge circuit is in balance. To set up the circuit, bring the soil you wish to monitor to the proper moisture level and insert the two probes into that soil. Then adjust R6 until the two LEDs are both off, or at least dim to the same level. The two LEDs serve as a null indicator. That is, LED2 is on when the ground resistance is higher than the preset resistance value of R6, and LED1 is on when the ground resistance is lower than the preset value. When both LEDs go dark or dim to the same brilliance, the bridge circuit is in balance. At balance, the setting of R6 equals the ground resistance. The probes are two 6-inch by 1/16-inch, round, stainless-steel rods mounted about 1-inch apart in an insulated handle. (Popular Electronics, July, 1996, p. 69)


MOTION AND PROXIMITY DETECTOR CIRCUITS

MICROWAVE MOTION DETECTOR

PROXIMITY DETECTOR

SENSITIVE LOW-CURRENT-DRAIN MOTION DETECTOR

UHF MOTION DETECTOR


MICROWAVE MOTION DETECTOR
MICROWAVE MOTION DETECTORFE62-1

Operating at around 1.1 GHz, the detector senses field disturbance in the neighborhood of the antenna. The Doppler signal from detector D1 is amplified and drives a power MOSFET switch. The antenna is a short (2 to 3) length of wire. (Reprinted with permission from Popular Electronics, 10/93, p.31. (C) Copyright Gernsback Publications, Inc.,1993)


PROXIMITY DETECTOR
PROXIMITY DETECTORFD55-6

In this proximity detector an NE567 tone decoder provides a signal of about 100 kHz that is fed to one sensor. The sensors are copper or aluminum wires or plates, or any other suitable conductive material. When another object is near the sensors, it causes an increase in capacitance between the sensors. Ql and Q2 amplify the signal and feed it to Ul. Notice that C8 and R4 phase shift the VCO signal from the NE567 so that Ul can detect its own output signal. (Reprinted with permission from Popular Electronics, 5/91, p.76. (C) Copyright Gernsback Publications, Inc.,1991)


SENSITIVE LOW-CURRENT-DRAIN MOTION DETECTOR
 SENSITIVE LOW-CURRENT-DRAIN MOTION DETECTORFD55-1

This highly sensitive movement detector is designed from bipolar transistors and draws a current of only 0.3 mA during quiescent operation. It is intended primarily as a protection device, but it can also be used in certain games.

The principle is simple: a magnet is suspended by a thin thread 20 to 30 mm long, and a few millimeters above the coil of a relay (whose contacts are not used). Even a minute movement of the protected object will disturb the magnet. The resulting changes in the magnetic field above the relay coil will induce a tiny varying voltage across the coil.

The first stage consists of a common emitter design with automatic regulation. The collector resistors and the resistors in the regulation bridge have unusually high values.

Feedback from the bridge ensures stability of operation for Tl. Each increase in collector voltage will be opposed by an increase in base-emitter current. Conversely, each reduction in collector voltage will be opposed by a decrease in base-emitter current. Consequently, the collector voltage will stabilize at a value that corresponds to a base voltage of about 0.6 V. Capacitor Cl delays the immediate effect of the feed-back when the collector voltage changes rapidly.

The small varying voltage induced in the relay coil is magnified appreciably by T1 because Cl prevents automatic regulation. The output impedance of the first stage is very high, which is, of course, the price to be paid for low consumption. It would not make sense to follow this stage by one with a low output impedance, because this would adversely affect the overall amplification. Because of that, T1 is followed by an emitter-follower, T2, which provides the coupling between T1 and T3. Resistor R5 allows a partial discharge of C2 if T2 is switched off by a reduction in the output of T1. Because this resistor, as a result of the low-consumption requirement, has a high value, the circuit will attain its maximum sensitivity 10 seconds after the last movement detection. This is the time that is required for the charge on capacitor C2 to stabilize.

The detection proper is carried out by T4, which switches on when the voltage variations in the amplifier passed on by C4, reach a level of 0.6 V. Saturating T4 leads to the instant charging of C5. This capacitor will discharge partly via R10 and R11 to the base of T5 when T4 switches off again. When C5 discharges, T5 is on, which will make T6 conduct. This in turn will actuate a load, for instance, a buzzer, in the collector circuit of T6.

The sensitivity of the detector depends to a large extent on the distance between the magnet and relay and the length of the "pendulum." If the circuit is powered by a battery, there is a little problem: batteries have large internal resistances. Thus, a supply voltage can vary by some tenths of a volt if a sudden, large current is drawn. If the buzzer has stopped after a detection, such a situation can retrigger the circuit and cause undesired oscillations. To prevent this happening, the supply of the amplifier stage is decoupled by R3 and C6.

(Elektor Electronics, 12/90, p.54)


UHF MOTION DETECTOR
UHF MOTION DETECTORFD55-3

The UHF motion detector operates on the Doppler radar principle. Ql is an oscillator that creates a radiated signal. An object in the radiated field reflects some of this energy back to the detector. If the object is moving, the reflected signal will have a different frequency because of Doppler shift. Ql is an oscillator coupled to a small (8-cm) antenna. This antenna also receives the reflected signal. Dl acts as a mixer and produces a beat note of frequency that is equal to the difference in reflected and radiated signal. Q2 amplifies this signal and couples it to comparator/detector IC1A and IClB. The output can continue on to an alarm, relay, lamp, etc. (RF Design, 7/88, P. 43)


MOTOR CONTROL CIRCUITS

CONSTANT-SPEED MOTOR DRIVER

LONG TIME-DELAY MOTOR-CONTROL CIRCUIT

MOTOR DIRECTION CONTROL USING DISCRETE TRANSISTORS

MOTOR/TACHOMETER SPEED CONTROL

PM DC MOTOR SPEED CONTROL

PWM MOTOR CONTROLLER

SOLID STATE DRILL SPEED CONTROL

SPEED-CONTROL SWITCH

SPEED-CONTROLLED REVERSIBLE DC MOTOR DRIVE

TACHLESS MOTOR-SPEED CONTROLLER


CONSTANT-SPEED MOTOR DRIVER
CONSTANT-SPEED MOTOR DRIVERFC62-10

When the torque load on the motor increases, its current increases. This current increase is sensed across Rs, and positive feedback is applied to the noninverting terminal of the LH0101, thereby increasing the motor voltage to compensate for the increased torque load. With the proper amount of positive feedback, the motor-speed variation can be kept below 1% from no load to full load. (Maxim, Maxim Advantage, p. 47)


LONG TIME-DELAY MOTOR-CONTROL CIRCUIT
LONG TIME-DELAY MOTOR-CONTROL CIRCUITFF57-4

Circuit controls forward and reverse motors. Every hour, one motor runs for 10 seconds. (Electronics Now, 5/95, p. 8)


MOTOR DIRECTION CONTROL USING DISCRETE TRANSISTORS
MOTOR DIRECTION CONTROL USING DISCRETE TRANSISTORSFF57-3

For best operation mount the transistors on heat sinks. The transistors specified are fine for small hobby motors, or up to 6 volts dc and between 800 and 1000 mA. M1 is a small hobby motor. (Gordon McCombs Gadgeteerss Goldmine, McGraw-Hill, p. 355)


MOTOR/TACHOMETER SPEED CONTROL
MOTOR/TACHOMETER SPEED CONTROLFB60-16

The tachometer, on the same shaft as the dc motor, is simply a generator. It gives a dc output voltage proportional to the speed of the motor. A summing amplifier, Al, controls its output so that the tachometer voltage equals the input voltage, but of opposite sign. With current drive to the motor, phase lag to the tachometer is 90°, before the second order effects come in. Compensation on Al is designed to give less than 90 deg. phase shift over the range of frequencies where the servo loop goes through unity gain. Should response time be of less concern, a power op amp could be substituted for Al to drive the motor directly. Lowering break frequencies of the compensation would, of course, be necessary. The circuit could also be used as a position servo. All that is needed is a voltage indicating the sense and magnitude of the motor shaft displacement from a desired position. This error signal is connected to the input, and the servo works to make it zero. The tachometer is still required to develop a phase-correcting rate signal because the error signal lags the motor drive by 180°. (Reprinted with permission from National Semiconductor Corporation, Linear Applications Handbook, p. 1066)


PM DC MOTOR SPEED CONTROL
PM DC MOTOR SPEED CONTROLFG180

Speed control of permanent-magnet (PM) dc motors with the aid of optical or dc tachometers is generally inconvenient and difficult, particularly on motors with integral gearboxes. The high-speed shaft of the motor that drives the gearbox isn't always accessible and the speed of the geared-down shaft often is too low for tachometers. Described here is a single-supply regulating speed-control circuit that doesn't require a tachometer. It keeps the motor torque high under load by using positive feedback to compensate for the drop due to armature resistance. In unregulated variable-speed PM dc motor systems, the drop in speed under load in particularly pronounced at low motor supply voltages. The positive-feedback generates a negative resistance that compensates for the nonlinear effects caused by armature resistance and thereby ensures that the speed-control input voltage (Vi) linearly controls the speed of the motor. Armature resistance compensation is achieved if:

Rs = RA / [Gain(R3)/(R3 + R4)] - 1

The divider action of R3 and R4 together with the Gain reduce the value required for Rs to minimize the power dissipation. Cl and R4 damp the positive-feedback signal's response time, but they also form a low-pass filter and attenuate the motor current noise fed to the A2 input. The maximum output voltage swing from A2 is approximately Vcc - 2V, and there is a 1.2-V Vbe loss by T1. This implies that the supply voltage Vcc should be about 5 V above the maximum desired motor voltage in order to allow for extra output drive to the motor under heavy load conditions. A reasonable choice for Rs is approximately RA/10 and the gain of A2 should be trimmed with RV2 to ensure the motor's speed does not drop when loaded. (Electronic Design, November 18, 1996, pp. 115-116)


PWM MOTOR CONTROLLER
PWM MOTOR CONTROLLERFC62-14

The PWM controller uses complementary half-H peripheral drivers SN75603 and SN75604, with totem-pole outputs rated at 40 V and 2.0 A. These drivers effectively place the motor in a full-bridge configuration, which has the ability to provide bidirectional control.

Timer Ul operates in the astable mode at a frequency of 80 Hz. The 100-Ω discharge resistor results in an 8-µs trigger pulse which is coupled to the trigger input of timer U2. Timer U2 serves as the PWM generator. Capacitor Cl is charged linearly with a constant current of 1 mA from the lN5297, which is an FET current-regulator diode.

Motor speed is controlled by feeding a dc voltage of 0 to 10 V to control input pin 5 of U2. As the control voltage increases, the width of the output pulse pin 3 also increases. These pulses control the on/off time of the two motor drivers. The trigger pulse width of timer Ul limits the minimum possible duty cycle from U2.

(Texas Instruments, Linear and Interface Circuits Applications, Vol. 1, 1985, p. 7-22)


SOLID STATE DRILL SPEED CONTROL
SOLID STATE DRILL SPEED CONTROLFG179

Add this circuit to a single-speed drill to make it a variable-speed one. The bridge rectifier (BR1) provides the full-wave pulsing direct current for the SCR switch (SCR1); BR1 should be rated at 200 PIV and have a current rating of 10A, while SCR1 should have a PIV of 300V and a current rating of 25A. Diode Dl is used to counter the back voltage developed by the drill motor; Dl can be rated at 2A. The speed of the drill is varied by Rl. (Popular Electronics, April 1997, pp. 58-59)


SPEED-CONTROL SWITCH
SPEED-CONTROL SWITCHFE63-6

The speed control switch offers reasonably good control and stability to both ends of its operating range. This circuit uses two SCR devices in a full wave configuration to control the dc power to a motor. A center-tapped transformer is used to supply the SCRs. (Reprinted with permission from Popular Electronics, 6/93, p.73. (C) Copyright Gernsback Publications, Inc.,1993)


SPEED-CONTROLIED REVERSIBLE DC MOTOR DRIVE
SPEED-CONTROLLED REVERSIBLE DC MOTOR DRIVEFC62-13

The figure illustrates a reversible dc motor drive application with adjustable speed control. The D inputs for these drivers are complementary and can be tied together and driven from the same logic control for bidirectional motor drive. The enables are tied together and driven by a pulse-width-modulated generator, providing on duty cycles of 10 to 90% for speed control. A separate enable control is provided through an SN7409 logic gate. See the truth table for this motor controller application.

Definitions for the terms used in the truth table are as follows:

EN	Enable

DC 	Direction control

SP.C	Speed control

A	Direction of current-right to left

B	Direction of current-left to right

H	Logic I voltage level

L	Logic 0 voltage level

N	Speed control set for narrow pulse width

W	Speed control set for wide pulse width

W	Irrelevant

Truth Table for Motor Control Circuit

EN	DC	SP.C	MOTOR DIRECTION	MOTOR SPEED
L	X	X	OFF	OFF
H	L	N	A	SLOW
H	L	W	A	FAST
H	H	N	B	SLOW
H	H	W	B	FAST
(Texas Instruments, Linear and Interface Circuits Applications, Vol. 1, 1985, p. 10-22)


TACHLESS MOTOR-SPEED CONTROLLER
TACHLESS MOTOR-SPEED CONTROLLERFC62-9

This circuit is particularly applicable to digitally-controlled systems in robotic and X-Y positioning applications. By functioning from the 5-V logic supply, it eliminates additional motor-drive supplies. The tachless feedback saves additional space and cost. The circuit senses the motor's back EMF to determine its speed. The difference between the speed and a set point is used to close a sampled loop around the motor. Al generates a pulse train. When Al's output is high, Ql is biased, and Q3 drives the motor's ungrounded terminal. When Al decreases, Q3 turns off and the motor's back EMF appears after the inductive flyback ceases. During this period, S1's input is turned on, and the 0.047-μF capacitor acquires the back EMF's value. A2 compares this value with the set point and the amplified difference (trace D) changes Al's duty cycle, controlling the motor speed.

(Linear Technology Corp. Linear Applications Handbook, 1987, p. AN11-7)


MULTIVIBRATOR CIRCUITS

ASTABLE MULTIVIBRATOR II

ASTABLE MULTIVIBRATOR WITH STARTING NETWORK

ASTABLE WITH VARIABLE PULSE WIDTH

BASIC 555 ASTABLE MULTIVIBRATOR

BISTABLE MULTIVIBRATOR

FREE-RUNNING MULTIVIBRATOR USING OP AMP

MONOSTABLE MULTIVIBRATOR

MONOSTABLE MULTIVIBRATOR

ONE-SHOT MULTIVIBRATOR

ONE-SHOT MULTIVIBRATOR II


ASTABLE MULTIVIBRATOR II
ASTABLE MULTIVIBRATOR IIFE65-7

An astable multivibrator based on the 555 is shown. Freq. is approximately 975 Hz as determined by the values of RB and C. (William Sheets)


ASTABLE MULTIVIBRATOR WITH STARTING NETWORK
ASTABLE MULTIVIBRATOR WITH STARTING NETWORKFF58-1

This circuit will start  with a slowly rising supply voltage waveform. (William Sheets)


ASTABLE WITH VARIABLE PULSE WIDTH
ASTABLE WITH VARIABLE PULSE WIDTHFF58-4

This produces a positive variable width pulse and has a symmetry control. R1 and R2 control the pulse width and symmetry. (Reprinted with permission from Popular Electronics, 1/94, p.73. (C) Copyright Gernsback Publications, Inc.,1994)


BASIC 555 ASTABLE MULTIVIBRATOR
BASIC 555 ASTABLE MULTIVIBRATORFF58-6

F=1.44

(R1=2R2)C1

(Amplifiers, Waveform Generators & Other Low-Cost IC Projects, McGraw-Hill, p. 24)


BISTABLE MULTIVIBRATOR
BISTABLE MULTIVIBRATORFF58-2

Positive feedback is provided by a resistor R4, which causes the latching. A positive pulse at the set input causes the output to go high and a reset positive pulse will return the output to essentially 0 Vdc. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 240)


FREE-RUNNING MULTIVIBRATOR USING OP AMP
FREE-RUNNING MULTIVIBRATOR USING OP AMPFE65-10

(Reprinted with permission from Popular Electronics, Fact Card 268. (C) Copyright Gernsback Publications, Inc)


MONOSTABLE MULTIVIBRATOR
MONOSTABLE MULTIVIBRATORFE65-3

(William Sheets)


MONOSTABLE MULTIVIBRATOR
MONOSTABLE MULTIVIBRATORFC38-14

The circuit illustrates the usefulness of the HA5151 as a battery-powered monostable. In this circuit, the ratio is set to .632, which allows the time constant equation to be reduced to:

T = RtCt

D2 is used to force the output to a defined state by clamping the negative input at + 0.6 V. Triggering is set by Cl, R3, and D2. An applied trigger pulls the positive input below the clamp voltage, + 0.6 V, which causes the output to change state. This state is held because the negative input cannot follow the change because of Rt * Ct. This particular circuit has an output pulse width set at approximately 100 μs. Use of potentiometers for Rt and variable capacitors for Ct will allow for a wide variation in T.

(Harris Analog Data Product Data Book, 1988, p. 10-109)


ONE-SHOT MULTIVIBRATOR
ONE-SHOT MULTIVIBRATORFE65-8

A section of a quad LM139 is used here as a one-shot pulse former. (Reprinted with permission from Popular Electronics, Fact Card 259. (C)Copyright Gernsback Publications, Inc)


ONE-SHOT MULTIVIBRATOR II
ONE-SHOT MULTIVIBRATOR IIFF58-5

An LM139 section can be used as a one shot. (Reprinted with permission from Popular Electronics, Fact Card 268. (C) Copyright Gernsback Publications, Inc)


MUSICAL CIRCUITS

MELODY CIRCUIT

MUSICAL INSTRUMENT DIGITAL

MUSICAL INSTRUMENT DIGITAL INTERFACE (MIDI) TRANSMITTER

ONE CHIP THEREMIN CIRCUIT

PRECISION AUDIO GENERATOR FOR MUSICAL INSTRUMENT TUNE-UP

TOP OCTAVE GENERATOR


MELODY CIRCUIT
MELODY CIRCUITFE66-6

A high quality melody circuit. The slow decay waveform produced will create chime-like notes. Pitch, tempo, and duration are all adjustable. (Reprinted with permission from Radio-Electronics, 7/90. p. 60. (C) Copyright Gernsback Publications, Inc.,1990)


MUSICAL INSTRUMENT DIGITAL
MUSICAL INSTRUMENT DIGITAL INTERFACE (MIDI) RECEIVER FE66-3

Receiver photodiode SFH250 is used to convert optical data pulses at 32.5 Kb to electrical signals. Buffer T2 feeds the signals to cascade amplifier T3-T4, then to op amp IC4, and buffers IC5-f and IC5-e. IC6 supplies 9 V for the circuit. (Reprinted with permission from Elektor Electronics, 3/92, p. 15)


MUSICAL INSTRUMENT DIGITAL INTERFACE (MIDI) TRANSMITTER
MUSICAL INSTRUMENT DIGITAL INTERFACE (MIDI) TRANSMITTERFE66-5

Used for digital control of musical instruments, this transmitter converts the digital data signals to equivalent optical signals for fiber optic cable interface. Optocoupler IC1 provides isolation, and drives IC2-a and -b and T1 and finally provides a cable driver LED (SFH750). (Reprinted with permission from Elektor Electronics, 3/92, p. 14)


ONE CHIP THEREMIN CIRCUIT
ONE CHIP THEREMIN CIRCUITFG181

Typically, a Theremin uses two separate Colpitts LC oscillators, one of which can be slightly varied in frequency. The two frequencies are mixed together, and demodulated to reveal a beat frequency. If the two oscillators are at the same frequency, there's no beat or audio, but if they're off due to the proximity of your hand, a difference or beat-frequency results, which is the audio output of the Theremin. A 4011 quad gate, IC1, is the heart of this Theremin. Two gates are used for each of the two required oscillators running at 250 kHz. For the aerial, use a metal toilet-tank float. It provides much better sensitivity than a length of wire. The two RF signals are mixed, then amplified by IC2, an LM741 op-amp. Audio is detected by Dl, a 1N34 diode. Another LM741, IC3, is setup as an adjustable band-pass filter, another LM741, IC4, further amplifies the audio for IC5, an LM386 audio amp. (Popular Electronics, August 1996, pp. 66 - 67)


PRECISION AUDIO GENERATOR FOR MUSICAL INSTRUMENT TUNE-UP
PRECISION AUDIO GENERATOR FOR MUSICAL INSTRUMENT TUNE-UPFE66-1

One section of the precision audio frequency generator uses an electret microphone element to pick up audio from the piano. That signal is then processed and sent to one channel of a dual-trace oscilloscope. The other section of the circuit is used to produce a variable-frequency signal that is fed to a digital frequency counter. After conditioning, the audio signal is presented to the second channel of the scope and output to a set of stereo headphones. (Reprinted with permission from Electronics Hobbyist Handbook, 1993, p.17)


TOP OCTAVE GENERATOR
TOP OCTAVE GENERATORFE66-7

Using an MK50240, this circuit produces 12 top octave tones. The input and output lines can be divided using a binary divider IC to obtain the lower notes. (Reprinted with permission from Radio-Electronics, 3/92, p. 77. (C) Copyright Gernsback Publications, Inc.,1992)


NOISE GENERATOR CIRCUITS

NOISE GENERATOR

PINK NOISE GENERATOR

SIMPLE WIDEBAND NOISE GENERATOR

WHITE-NOISE GENERATOR

WIDEBAND NOISE GENERATOR

ZENER-DIODE WHITE-NOISE GENERATOR


NOISE GENERATOR
NOISE GENERATORFD49-4

This noise generator provides constant noise energy over its bandwidth, which results from the non-linear behavior of its switching components, more particularly T4. It is very useful for measurements where limited noise bands are required. Varying the ratio R6:R7 and the clock frequency enables the generated noise to be adapted to specific requirements.

Transistors T2 and T3 are current sources. The current through T2 is about 10 times the level of that through T3. Assuming that T4 is on and that the clock input is low, T1 is off, and C2 discharges. The capacitor is pulled to about half of the supply voltage by the two current sources. When that state is reached, stability ensues because the potential then present at the gate of T4 keeps the FET switched on.

When the clock goes high, T1 is switched on so that C2 is connected between the gate of T4 and the earth. Because C2 is only partly charged, the FET is switched off. Transistor T1 is kept switched on by OR gate Dl/D2 so that the clock pulses are blocked. Capacitor C2 then charges via T3 until the potential across it becomes high enough to switch on T4. Transistor Tl is then switched off and the circuit is ready to receive another clock pulse (or rather a leading edge of one).

Because it is not known when the clock pulse arrives, it is not known to what potential C2 will be discharged by T2 (and countered by T3). It is therefore also not known when the next clock pulse will arrive. In other words, the pulse width of the output signal is varying constantly, which is characteristic of a noise signal.

(Elektor Electronics, 7/89, p. S32)


PINK NOISE GENERATOR
PINK NOISE GENERATORFA59-2

A reverse-biased pn junction of a 2N2712 transistor is used as a noise generator. The second 2N2712 is an audio amplifier. The 0.005 μF capacitor across the amplifier output removes some high-frequency components to simulate pink noise more closely. The audio output may be connected to high-impedance earphones or to a driver amplifier for speaker listening. (Popular Electronics, 4/75, p. 87)


SIMPLE WIDEBAND NOISE GENERATOR
SIMPLE WIDEBAND NOISE GENERATORFG182

This relatively simple op-amp noise generator amplifies the input voltage noise of a wideband, decompensated op amp. By selecting a device with a single gain stage, the output noise will be spectrally flat up to the closed loop bandwidth. Op amp is by Analog Devices Inc. (Electronic Design, October 1, 1996, p. 102)


WHITE-NOISE GENERATOR
WHITE-NOISE GENERATORFF104-2

Here, a 2N3904 E-B junction is used as a noise generator, reversed bias. C is chosen to pass the lowest desired frequency components of the noise. (William Sheets)


WIDEBAND NOISE GENERATOR
WIDEBAND NOISE GENERATORFA59-4

This circuit will produce wideband RF noise. It uses a reverse bias diode and has a low-impedance output. Can be used to align receivers for optimum performance. (Popular Electronics, 12/76, p. 28)


ZENER-DIODE WHITE-NOISE GENERATOR
ZENER-DIODE WHITE-NOISE GENERATORFF104-1

This circuit uses a Zener diode as a noise source. C is chosen to pass the lowest desired frequency components of the noise. (William Sheets)


NOISE REDUCTION CIRCUIT

ADJUSTABLE NOISE CLIPPER

AUDIO DYNAMIC NOISE-REDUCTION SYSTEM

DOLBY NOISE-REDUCTION CIRCUIT

SIMPLE NOISE LIMITER


ADJUSTABLE NOISE CLIPPER
ADJUSTABLE NOISE CLIPPERFF59-4

This circuit uses two diodes and is a peak-to-peak limiter. The capacitors charge up to a dc level  determined by the peak-to-peak audio signal and the clipping control.  A positive or negative peak or  spike is clipped if it exceeds this level plus the diode drops.  The circuit should be operated at several  volts level for best results. (William Sheets)


AUDIO DYNAMIC NOISE-REDUCTION SYSTEM
AUDIO DYNAMIC NOISE-REDUCTION SYSTEMFE68-1

U1 is a dedicated IC (National Semiconductor) that achieves up tp 10 dB noise reduction by an adaptive bandwidth scheme and a psycho acoustic masking technique. (Reprinted with permission from Popular Electronics, Fact Card 242. (C) Copyright Gernsback Publications, Inc)


DOLBY NOISE-REDUCTION CIRCUIT
DOLBY NOISE-REDUCTION CIRCUITFF59-2

(Reprinted with permission from National Semiconductor Corporation, National Semiconductor NSLAH 1991, p. 998)


SIMPLE NOISE LIMITER
SIMPLE NOISE LIMITERFF59-5

This circuit uses a symmetrical limiter obtained by biasing a transistor to a Q point that is half of the supply voltage and driving it into saturation and cutoff.  An input of 1 to 2 V RMS is sufficient.  This output will be approximately 4 V p-p into a high-impedance load. (William Sheets)


OPTICAL CIRCUITS

OPTICAL COMMUNICATION SYSTEM

OPTICAL SAFETY CIRCUIT SWITCHES

VARIABLE-SENSITIVITY PHOTOTRANSISTOR CIRCUIT


OPTICAL COMMUNICATION SYSTEM
OPTICAL COMMUNICATION SYSTEMFB65-13

The circuit will modulate the light from the LED using a crystal microphone or a loudspeaker output. To obtain the maximum range, the optical system must be efficient (see example). Either a convex lens or a concave mirror can be used to convert the LED output into a parallel beam. The received light is concentrated onto a sensitive photodarlington transistor. At short range the signal across the load resistor is adequate to drive a crystal earpiece, for longer range an amplifier and a loudspeaker are needed. (William Sheets)


OPTICAL SAFETY CIRCUIT SWITCHES
OPTICAL SAFETY CIRCUIT SWITCHESFE70-6

Use of two LDR devices replaces the two pushbuttons used in safety switches. The lamps provide light sources for the LDR devices. (Reprinted with permission from Popular Electronics, 9/93, p.76. (C) Copyright Gernsback Publications, Inc.,1993)


VARIABLE-SENSITIVITY PHOTOTRANSISTOR CIRCUIT
VARIABLE-SENSITIVITY PHOTOTRANSISTOR CIRCUITFE70-8

A variable resistor will work well with just about any phototransistor. Phototransistors are more light sensitive than photodiodes, but they generally have poorer frequency response. (William Sheets)


OSCILLATOR (AUDIO)

BASIC LM3909 AUDIO OSCILLATOR

LOW-FREQUENCY OSCILLATOR

ONE-TANSISTOR PHASE-SHIFT OSCILLATOR

QUAD TONE OSCILLATOR

QUADRATURE OSCILLATOR

THREE TONE OSCILLATOR

WIEN BRIDGE OSCILLATOR


BASIC LM3909 AUDIO OSCILLATOR
BASIC LM3909 AUDIO OSCILLATORFF61-4

The LM3903s oscillator frequency can be fine tuned by adding a resistor to a basic circuit. (Amplifiers, Waveform Generators & Other Low-Cost IC Projects, McGraw-Hill, p. 17)


LOW-FREQUENCY OSCILLATOR
LOW-FREQUENCY OSCILLATORFC68-13

This simple RC oscillator uses a medium-speed comparator with hysteresis and feedback through Rl and Cl as timing elements. The frequency of oscillation is, at least theoretically, independent from the power supply voltage. If the comparator swings to the supply rails, if the pull-up resistor is much smaller than the resistor Rh, and if the propagation delay is negligible compared to the RC time constant, the oscillation frequency is:

fosc =   0.72

          R1C1

(Linear Technology Corp. Linear Applications Handbook, 1987, p. AN20-11)


ONE-TANSISTOR PHASE-SHIFT OSCILLATOR
ONE-TRANSISTOR PHASE-SHIFT OSCILLATORFF61-3

A single transistor is used as an active element in an RC phase shifter oscillator (William Sheets)


QUAD TONE OSCILLATOR
QUAD TONE OSCILLATORFF61-2

A quad op amp (TL084, etc) can be used to produce four audio tone generators for use in a test setup. The circuit uses a 12-V supply. (William Sheets)


QUADRATURE OSCILLATOR
QUADRATURE OSCILLATORFC68-14

(Fairchild Camera and Instrument, Linear Databook, 1982, p. 4-71)


THREE TONE OSCILLATOR
THREE TONE OSCILLATORFG183

This TTL tone oscillator can generate one of three tones. The tone generation depends on the status of the two input control line. The design consists of two standard TTL audio tone oscillators merged together using one 7400 TTL chip. Two input lines control the output status. With both inputs low, RC output is generated. When input "A" is high, the high-tone oscillator is gated on. When input "B" is high, the low-tone oscillator is gated on. With both "A" and "B" high, both oscillators are gated on the output tone generated is midway between the high and low tones. The 1N914 diode in series with a 1-k resistor imposes a 50% duty cycle on the waveform. A low-pass filter on the output removes harmonics and "mellows" the output tone. (Electronic Design, May 15, 1995, pp. 136-138)


WIEN BRIDGE OSCILLATOR
WIEN BRIDGE OSCILLATORFA7-1

Field effect transistor, Q1, operates in the linear resistive region to provide automatic gain control. Because the attenuation of the RC network is one-third at the zero phase-shift oscillation frequency, the amplifier gain determined by resistor R2 and equivalent resistor R1 must be just equal to three to make up the unity gain positive feedback requirement needed for stable oscillation Resistors R3 and R4 are set to approximately 1000 ohm less than the required R1 resistance. The FET dynamically provides the trimming resistance needed to make R1 one-half of the resistance of R2. The circuit composed of R5, D1, and C1 isolates, rectifies, and filters the output sinewave, converting it into dc potential to control the gate of the FET. For the low drain-to-source voltages used, the FET provides a symmetrical linear resistance for a given gate-to-source voltage. (Courtesy of Fairchild Camera & Instrument Corporation, Application Note 300)


OSCILLATORS (MISCELLANEOUS)

4093 CMOS ASTABLE OSCILLATOR

50% DUTY-CYCLE 555 CIRCUITASTABLE OSCILLATOR

ASTABLE OSCILLATOR II

CD4047 CMOS OSCILLATOR

LOGIC-GATE SINE-WAVE OSCILLATOR

PRECISION GATED OSCILLATOR

TTL RING OSCILLATOR

VARIABLE DUTY CYCLE FROM ASTABLE

VARIABLE DUTY-CYCLE OSCILLATOR

VARIABLE-FREQUENCY ASTABLE

VARIABLE-FREQUENCY ASTABLE II

VARIED REP RATE, DUTY CYCLE WITH 555


4093 CMOS ASTABLE OSCILLATOR
4093 CMOS ASTABLE OSCILLATORFE71-20

Two gates of the Quad 4093 are used to make an oscillator. Rx can be from about 5 kΩ to around 10Ω, Cx can be from about 10 pF to many μF, the limit being set by the leakage of the capacitor, Frequency is approximately 2.8/RxCx (R MΩ, C mfd). (Reprinted with permission from Popular Electronics, 12/93, p.68. (C) Copyright Gernsback Publications, Inc.,1993)


50% DUTY-CYCLE 555 CIRCUIT
50% DUTY-CYCLE 555 CIRCUITFF62-8

Using an external charge transistor and diode enables a 50% duty cycle and easy frequency control.  When the 555's discharge transistor is cut off, the 2N2222 acts as an emitter follower. When the discharge transistor turns on, the 2N2222 turns off and Cl discharges through (R1 + R2) at the same rate. The 1N4148 provides temperature compensation. ( Reprinted with permission from Electronics Now, 12/93. p. 16. (C) Copyright Gernsback Publications, Inc.,1993)


ASTABLE OSCILLATOR
ASTABLE OSCILLATORFF62-3

By using transistor switch Q1/R2/R3, the frequency of an astable oscillator can be changed with a dc voltage or logic level. (Reprinted with permission from Popular Electronics, 12/93, p.71. (C) Copyright Gernsback Publications, Inc.,1993)


ASTABLE OSCILLATOR II
ASTABLE OSCILLATOR IIFF62-2

In this circuit, two gates from the quad 4093 package are used to form a simple astable square-wave oscillator.

The values for R. and C. are approximately as follows:

Cx	Rx	fo
0.001 μF	1 MΩ	3 kHz
0.1 μF	1 MΩ	30 Hz
1 μF	10 MΩ	0.03 Hz

These values can be scaled for other frequencies.

(Reprinted with permission from Popular Electronics, 12/93, p.68. (C) Copyright Gernsback Publications, Inc.,1993)


CD4047 CMOS OSCILLATOR
CD4047 CMOS OSCILLATORFG239

CMOS square-wave is based on the 4047 multivibrator circuit, which can be used for  either monostable ("one-shot") or astable applications. In the configuration shown, the  4047 is an astable multivibrator. There are Three outputs from 4047. The first is the  oscillator (OSC) output, which is connected directly to the internal oscilllator circuit. The  other two outputs, Q and Q, are complmentary to each other and operate at one-half the  frequency of the internal oscillator. The output frequency is set by timing components  R1 and C1.

fo = 1/(4.4R1C1)

The value of R1 should be between 10,000 ohms and 1 megohm, while the value of C1  should be 100 pF or more (the maximum capacitance is not limited theoretically, but a  practical limit exists when the leakage resistance of C1 is of the same order of   magnitude as R1).  )Electronics Hobbyists Handbook, Fall 1995, p.99)


LOGIC-GATE SINE-WAVE OSCILLATOR
LOGIC-GATE SINE-WAVE OSCILLATORFF61-12

An inductor and capacitor are used here as frequency-determining elements in an LC oscillator. (Reprinted with permission from Popular Electronics, 12/93, p.71. (C) Copyright Gernsback Publications, Inc.,1993)


PRECISION GATED OSCILLATOR
PRECISION GATED OSCILLATORFE71-16

A 1 kHz gated oscillator with no long turn on cycle is shown. R2, R3, and D1 preset the voltage on tuning capacitor C1 to 1/3 of the supply voltage. (William Sheets)


TTL RING OSCILLATOR
TTL RING OSCILLATORFG184

A TTL ring oscillator circuit uses an odd number of inverters in an astable configuration. (Electronic Hobbyists Handbook, Fall 1995, p. 98)


VARIABLE DUTY CYCLE FROM ASTABLE
VARIABLE DUTY CYCLE FROM ASTABLEFF61-8

IF R=R1=R2 and C=C1=C2

If potentiometer R3 is set at N% of rotation then

Ttotal ~ 0.7[(R+NR3)C + (R + (1-N)R3)C]

Ttotal ~ 1.4(R+R3/2)C

(William Sheets)


VARIABLE DUTY-CYCLE OSCILLATOR
VARIABLE DUTY-CYCLE OSCILLATORFE71-18

Using a potentiometer and steering diodes, this 1.2 kHz oscillator will provide 1 to 99% duty cycle. Vary C1 to change frequency. (William Sheets)


VARIABLE-FREQUENCY ASTABLE
VARIABLE-FREQUENCY ASTABLEFF62-4

This circuit uses a single potentiometer and switched capacitors to cover 2 Hz to 30 kHz. (Reprinted with permission from Popular Electronics, 12/93, p.70. (C) Copyright Gernsback Publications, Inc.,1993)


VARIABLE-FREQUENCY ASTABLE II
VARIABLE-FREQUENCY ASTABLE IIFF62-1

This circuit is a variable frequency oscillator using a trimmer capacitor or a three gauge AM broadcast capacitor salvaged from an old AM radio. The three sections must be paralleled. (Reprinted with permission from Popular Electronics, 12/93, p.70. (C) Copyright Gernsback Publications, Inc.,1993)


VARIED REP RATE, DUTY CYCLE WITH 555
VARIED REP RATE, DUTY CYCLE WITH 555FF62-9

To independently vary RPM and dwell, or duty cycle, a 555 timer is used to produce a ramp waveform, which is compared to an adjustable reference (Reprinted with permission from Electronic Design 7/94, p 94, Copyright 1994 Penton Publishing)


OSCILLATORS (RF)

AM OSCILLATOR FOR WIRELESS MICROPHONES

BEAT-FREQUENCY OSCILLATOR FOR AM/SW RADIOS

CLAPP JFET VFO

CRYSTAL OSCILLATOR WITH FM CAPABILITY

FM HF OSCILLATOR WITH NO VARACTOR

HARLEY OSCILLATOR

HARTLEY OSCILLATOR

HARTLEY VFO WITH BUFFER AMPLIFIER

HF VFO CIRCUIT

TUNABLE UHF OSCILLATOR

VLF LC OSCILLATOR


AM OSCILLATOR FOR WIRELESS MICROPHONES
AM OSCILLATOR FOR WIRELESS MICROPHONESFF63-3

This circuit will generate an AM-modulated signal in the AM broadcast band that can be picked up on a receiver. About 2 V of audio input will produce about 30% modulation of the oscillator signal. An old AM broadcast oscillator coil or other two-winding coil with about 10:1 turn ratio and about 50 to 150 μH inductance can be used for T1. (William Sheets)


BEAT-FREQUENCY OSCILLATOR FOR AM/SW RADIOS
BEAT-FREQUENCY OSCILLATOR FOR AM/SW RADIOSFF63-6

This BFO can be added to inexpensive AM/SW receivers to enable reception of CW signals. Output couples to base of last IF stage. T1 is any 455-kHz IF transformer. The BFO switch should be a DPDT type (as needed), and the radio AGC circuit will probably have to be disabled for CW reception. (William Sheets)


CLAPP JFET VFO
CLAPP JFET VFOFG186

The JFET VFO circuit shown here can be identified as a Clapp oscillator by its series tuned LC network. This circuit as shown can be used from 0.5 to 7 Mhz. (Popular Electronics, October 1994, p. 44)


CRYSTAL OSCILLATOR WITH FM CAPABILITY
CRYSTAL OSCILLATOR WITH FM CAPABILITYFF21_5

This crystal oscillator produces a good FM signal that can be tripled to 146 MHz and produces a clean 5-kHz deviation signal for FM voice. The bias control is adjusted for cleanest audio while the 1-to 5-uH coil is adjusted to set the oscillator frequency to the exact setting required.


FM HF OSCILLATOR WITH NO VARACTOR
FM HF OSCILLATOR WITH NO VARACTORFF63-14

Instead of using a varacter to frequency modulate a high frequency oscillator, this circuit uses base-charging capacitance modulation. Consequently, the large voltage change required by a varacter, which can be a major problem in battery-powered systems with limited supply voltages is eliminated. T1 is a ceramic coaxial quarter-wave resonator. (Reprinted with permission from Electronic Design 10/94, p 96, Copyright 1994 Penton Publishing)


HARLEY OSCILLATOR
HARTLEY OSCILLATORFG187

A Hartley transistor oscillator circuit is shown. The oscillator's operating frequency is determined by the values of Ll and C3. The feed-back level is determined by the location of the tap on Ll, which normally will be about 1/5 th to 1/4 th of the total turns. As an example, the Hartley oscillator will operate in the 5-MHz range with the following L/C values. Ll is 20 turns of number 18 enamel, copper wire close wound on a 1-inch plastic form with a tap up five turns from the bottom. Capacitor C3 may be any small variable capacitor with a maximum capacitance value of 100 pF. With the proper L/C values, the Hartley oscillator can operate from audio to UHF. (Popular Electronics, June 1997, p. 63)


HARTLEY OSCILLATOR
HARTLEY OSCILLATORFF63-21

This circuit uses a tapped inductor in a Hartley oscillator circuit. The tap is generally at 25 to 35% total turns in most instances. (William Sheets)


HARTLEY VFO WITH BUFFER AMPLIFIER
HARTLEY VFO WITH BUFFER AMPLIFIERFG185

A Hartley oscillator with buffer amplifier. This circuit can be tuned via C1, or if C1 is removed and the varactor network is connected to point A, a tuning voltage can be used instead. For best stability, L1 can be replaced with an air core unit. Frequency range is 2 to 5 Mhz but the circuit can operate 1 to 10 Mhz with suitable values of L1, C2, C3, C4 and C5. (Popular Electronics, October 1994, p. 43)


HF VFO CIRCUIT
HF VFO CIRCUITFF63-12

This typical HF VFO circuit has several stability enhancing features including well chosen capacitor types. The frequency of the VFO is approximately 2π(C1 + C2 + C3). L1 should be aircore type coil, rigidly mounted with high (>200 value) value of Q. (Reprinted with permission from Popular Electronics, 11/94, p.42. (C) Copyright Gernsback Publications, Inc.,1994)


TUNABLE UHF OSCILLATOR
TUNABLE UHF OSCILLATORFF63-15

This oscillator is typical for 350- to 500-Mhz operation. The microstrip inductor is a PC board trace. The tap is typically 15% from then bottom end. The output power is 55 to 100 mW into 50 Ω, with the frequency stability typically 0.1% over 0 to 50 ºC. (William Sheets)


VLF LC OSCILLATOR
VLF LC OSCILLATORFF63-10

The VLF oscillator uses a large toroid coil as the frequency-determining component and a 2N5485 FET as the active device. R3 is used as a feedback control and also by running the circuit with slightly less feedback than needed for oscillation, can serve as a regenerative amplifier or detector. (Reprinted with permission from Popular Electronics, 2/94, p. 53. (C) Copyright Gernsback Publications, Inc., 1994)


OSCILLATOR (SINE WAVE) CIRCUITS

EASILY TUNED SINE-WAVE OSCILLATOR

LOW-DISTORTION SINE-WAVE OSCILLATOR

LOW-DISTORTION SINE-WAVE OSCILLATOR

PURE SINE-WAVE GENERATOR

SIMPLE AUDIO SINE-WAVE OSCILLATOR

SIMPLE SINE-WAVE GENERATOR

SINE WAVE OSCILLATOR

SINEWAVE DOUBLER

SUPER-LOW-DISTORTION VARIABLE SINE-WAVE OSCILLATOR

THREE-DECADE 15-HZ TO 15-KHZ WIEN-BRIDGE OSCILLATOR

WIEN-BRIDGE SINE-WAVE OSCILLATOR


EASILY TUNED SINE-WAVE OSCILLATOR
EASILY TUNED SINE-WAVE OSCILLATORFF61-1

The circuit will provide both a sine- and square-wave output for frequencies from below 20 Hz to above 20 kHz. The frequency of oscillation is easily tuned by varying a single resistor. This is a considerable advantage over Wien bridge circuits, where two elements must be tuned simultaneously to change frequency. Also, the output amplitude is relatively stable when the frequency is changed.  An operational amplifier is used as a tuned circuit, driven by square wave from a voltage comparator. Frequency is controlled by Rl, R2, Cl, C2, and R3, with R3 used for tuning. Tuning the filter does not affect its gain or bandwidth, so the output amplitude does not change with frequency. A comparator is fed with the sine-wave output to obtain a square wave. The square wave is then fed back to the input of the tuned circuit to cause oscillation. Zener diode, Dl, stabilizes the amplitude of the square wave fed back to the filter input. Starting is ensured by R6 and C5, which provide de negative feedback around the comparator. This keeps the comparator in the active region. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 1209)


LOW-DISTORTION SINE-WAVE OSCILLATOR
LOW-DISTORTION SINE-WAVE OSCILLATORFB88-2

(Linear Technology Corp. Linear Databook, 1986, p. 2-113)


LOW-DISTORTION SINE-WAVE OSCILLATOR
LOW-DISTORTION SINE-WAVE OSCILLATORFF61-5

Cl, C2	Min. Frequency	Max. Frequency
0.47 μF	18 Hz	80 Hz
0.1 μF	80 Hz	380 Hz
0.022 μF	380 Hz	1.7 kHz
0.0047 μF	1.7 kHz	8 kHz
0.002 μF	4.4 kHz	20 kHz

(Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 1210)


PURE SINE-WAVE GENERATOR
PURE SINE-WAVE GENERATORFE91-9

 A TTL counter, an 8-channel analog multiplexer, and a fourth-order low-pass filter can generate 10- to 25-kHz sine waves with a THD better than -80 dB. The circuit cascades the two second-order, continuous-time Sallen-Key filters within IC3 to implement the fourth-order low-pass filter.

To operate the circuit, choose the filter's cutoff frequency, fc by tying IC3's D0 through D6 inputs to 5 V or ground. The cutoff frequency can be at 128 possible levels between 1 and 25 kHz, depending on those seven digital input levels. Because the circuit ties D0 through D6 to ground, fc equals 1 kHz. The 100-kΩ potentiometer adjusts the output level between VDD - 1.5 V and VSS+ 1.5 V. (Reprinted with permission from Maxim Engineering Journal, Vol. 4, p. 15)


SIMPLE AUDIO SINE-WAVE OSCILLATOR
SIMPLE AUDIO SINE-WAVE OSCILLATORFB88-4

UlA, an op amp, oscillates at the frequency at which the phase shift in the Wien bridge network is exactly zero degrees. Changing bridge component values changes the oscillator frequency. In this circuit, we need change only the two resistors to do this. SlA chooses a value among Rl through R6, and SlB similarly selects a value from R7 through R12. UlA must provide enough gain to overcome losses in the bridge, but not so much gain that oscillation builds up to the point of overload and distortion. U2 and Cl automatically regulate circuit gain to maintain oscillation. U2 places Dl across R13 with the proper polarity on both positive and negative alterations of the signal at pin 1 of Ul. As the voltage at pin 1 of Ul approaches its peak value, Dl enters its Zener breakdown region, effectively shunting R13 with a resistive load. This increases the amount of negative feedback around Ul, reducing its gain. R15, WAVEFORM ADJ, allows you to optimize circuit operation for lowest distortion. UlB provides isolation between oscillator and load. With the values shown for R17 and R18, UlB operates at unity gain. (QST, 4/87, p. 48)


SIMPLE SINE-WAVE GENERATOR
SIMPLE SINE-WAVE GENERATORFE91-6

A 555 timer operating in the astable mode generates the driving pulses and two 4518 dual BCD (binary coded decimal) counters provide the square waves. A TL081 op amp serves as an output buffer-amplifier, and potentiometers R1 and R2 are used in order to control the pulse's frequency and amplitude, respectively.

The output-frequency range can be varied by changing Cx. For example, a value of 0.1 mF gives a range from about 0.1 to 30 Hz, and a value of' 470 pF gives a range from about 10 Hz to 1.5 kHz. The maximum output frequency is 30 kHz.

(Reprinted with permission from R-E Experimenters Handbook 1992)


SINE WAVE OSCILLATOR
SINE WAVE OSCILLATORFA7-6

(Reprinted with permission from National Semiconductor Corporation, Linear Applications Handbook 1982, p. AN29-9)


SINEWAVE DOUBLER
SINEWAVE DOUBLERFG188

This circuit uses a four quadrant multiplier by Analog Devices to perform frequency doubling on a sine wave input signal. By applying a sine wave to both x and y inputs, the multiplier multiplies the sine wave by itself, resulting in a sine squared waveform. This waveform is equivalent to a DC level and a cosine component at twice the frequency and half the amplitude i.e. (SIN^2)X=(1-COS 2X)/2 --3B bandwidth is typically 30 MHz. (Electronic Experimenters Handbook, 1996, pp. 32-35)


SUPER-LOW-DISTORTION VARIABLE SINE-WAVE OSCILLATOR
 SUPER-LOW-DISTORTION VARIABLE SINE-WAVE OSCILLATORFC89-3

(Linear Technology Corp. Linear Applications Handbook, 1988, p. S2-S4)


THREE-DECADE 15-HZ TO 15-KHZ WIEN-BRIDGE OSCILLATOR
THREE-DECADE 15-HZ TO 15-KHZ WIEN-BRIDGE OSCILLATORFD79-9

In this circuit, an LM741 op amp drives a Wien-bridge network using two zener diodes as an amplitude limiter. Range selection is done by switch selecting the capacitors (C1 through C6) and tuning is done via a ganged pot. The output is about 8 Vpp max., depending on the setting of S2 and R6. R4 is set for maximum distortion consistent with stable output. (Reprinted with permission from Radio-Electronics, 7/89, p.52. (C) Copyright Gernsback Publications, Inc.,1989)


WIEN-BRIDGE SINE-WAVE OSCILLATOR
WIEN-BRIDGE SINE-WAVE OSCILLATORFE91-3

This Wien-bridge sine-wave oscillator uses a 2N3819 as an amplitude stabilizer. The 2N3819 acts as a variable-resistance element in the Wien bridge. (Reprinted with permission from Popular Electronics, Fact Card 256. (C) Copyright Gernsback Publications, Inc)


OSCILLATORS (VOLTAGE-CONTROLLED)

10-HZ TO 10-KHZ 3-DECADE VCO

1700 MHZ VCO CIRCUIT WITH TRANSMISSION LINE RESONATOR

GATED WIDE-RANGE VCO

THREE-DECADE VCO

VCO CIRCUIT USING TRANSMISSION LINE RESONATOR

VOLTAGE-CONTROLLED CRSYTAL OSCILLATOR

VOLTAGE-TUNED CLAPP OSCILLATOR

VOLTAGE-TUNED VHF OSCILLATOR


10-HZ TO 10-KHZ 3-DECADE VCO
10-HZ TO 10-KHZ 3-DECADE VCOFE109-3

(Reprinted with permission from Popular Electronics, Fact Card 269. (C) Copyright Gernsback Publications, Inc)


1700 MHZ VCO CIRCUIT WITH TRANSMISSION LINE RESONATOR
1700 MHZ VCO CIRCUIT WITH TRANSMISSION LINE RESONATORFG191

This VCO circuit is for 1700 Mhz and uses a ceramic coaxial resonator. (RF Design, Nov. 1995, p. 55)


GATED WIDE-RANGE VCO
GATED WIDE-RANGE VCOFD98-2

A CD4046 can be gated either with a switch or electronically, as shown in the figure. Frequency range of this circuit is to 1.5 kHz; use another C1 for higher frequencies. (Reprinted with permission from Radio-Electronics, 12/98. p. 56. (C) Copyright Gernsback Publications, Inc.,1989)


THREE-DECADE VCO
THREE-DECADE VCOFE100-1

Using an AMI chip P/N S2561, this telephone ringer can be powered directly off the telephone line. Audio output is about is about 50 mW when powered from a 10 V source. (Reprinted with permission from Radio-Electronics, 7/90, p.8)


VCO CIRCUIT USING TRANSMISSION LINE RESONATOR
VCO CIRCUIT USING TRANSMISSION LINE RESONATORFG190

A typical VCO circuit using a transmission line resonator and varactor tuning. This circuit is for 855-890 Mhz. (RF Design, Nov. 1995, p. 52)


VOLTAGE-CONTROLLED CRYSTAL OSCILLATOR
VOLTAGE-CONTROLLED CRYSTAL OSCILLATORFC21-7

A voltage-variable capacitance tuning diode is placed in series with the crystal feedback  path. Changing the voltage on VR varies the tuning diode capacitance and tunes the oscillator. The  510-KOHM resistor, R1, establishes a reference voltage for VR-ground is used in this example. A 100-KOHM resistor, R2, isolates the tuning voltage from the feedback loop and 0.1-uF capacitor C2  provides ac coupling to the tuning diode. The circuit operates over a tuning range of 0 to 25 V. It is possible to change the tuning range from 0 to 25 V by reversing the tuning diode D1. Center  frequency is set with the 2-60 pf trimmer capacitor. Deviation on either side of center is a function of the crystal frequency. the table in the figure shows measured deviation in parts per million  for several tested crystals.


VOLTAGE-TUNED CLAPP OSCILLATOR
VOLTAGE-TUNED CLAPP OSCILLATORFG189

This voltage tuned Clapp oscillator uses a varactor diode to set its operating frequency. D1 is a NTE614. L1 is about 7/f Mhz microhenries. With the circuit shown, the frequency range is about 6 to 15 MHZ. (Popular Electronics, October 1994, pp. 44)


VOLTAGE-TUNED VHF OSCILLATOR
VOLTAGE-TUNED VHF OSCILLATORFD98-6

This VHF VCO circuit is suitable for 30 to 200 Mhz. Q1 can be replaced by a 2N3565 for operation above 100 Mhz. L1 is chosen to resonate the desired frequency with the varactor capacitance of 40 pF. Other varactors can be used for better linearity, depending on the application. (Reprinted with permission from Popular Electronics, 11/90, p.102. (C) Copyright Gernsback Publications, Inc.,1990)


OSCILLOSCOPE CIRCUITS

ANALOG MULTIPLEXER CONVERTS SINGLE-TRACE SCOPE TO FOUR-TRACE

EIGHT-CHANNEL VOLTAGE DISPLAY

OSCILLOSCOPE-TRIGGERED SWEEP

PORTABLE SCOPE CALIBRATOR

SCOPE VOLTAGE CURSOR ADAPTER

VARIABLE GAIN AMPLIFIER


ANALOG MULTIPLEXER CONVERTS SINGLE-TRACE SCOPE TO FOUR-TRACE
ANALOG MULTIPLEXER CONVERTS SINGLE-TRACE SCOPE TO FOUR-TRACEFB67-1

This adapter circuit, based on a dual four-channel analog multiplexer handles digital signals to at least 1 MHz, and analog signals at least through the audio range. The dual multiplexer's upper half selects one input for display. The lower half generates a staircase to offset the baselines of each channel, keeping them separate on the screen. The emitter-follower buffers the staircase, which is then summed with the selected signal. A two-bit binary counter addresses the CMOS 4052 multiplexer. (Electronic Design, 5/79, p. 102)


EIGHT-CHANNEL VOLTAGE DISPLAY
EIGHT-CHANNEL VOLTAGE DISPLAYFC69-2

This circuit turns a common oscilloscope into a versatile eight-channel display for direct voltages. The trend of each of the eight input levels is readily observed, albeit that the attainable resolution is not very high.

The circuit diagram shows the use of an eight-channel analog multiplexer IC1, which is the electronic version of an eight-way rotary switch with contacts X0 through X7 and pole Y. The relevant channel is selected by applying a binary code to the A-B-C inputs. For example, binary code 011 (A-B-C) enables channel 7 (X6 Y). The A-B-C inputs of IC1 are driven from three successive outputs of binary counter IC2, which is set to oscillate at about 50 kHz with the aid of Pl. Since the counter is not reset, the binary state of outputs Q5, Q6, and Q7 steps from 0 to 7 in a cyclic manner. Each of the direct voltages at input terminals 1 to 8 is therefore briefly connected to the Y input of the oscilloscope. All eight input levels can be seen simultaneously by setting the timebase of the scope, in accordance with the time it takes the counter to output states 0 through 7, on outputs Q5, Q6, and Q7.

The timebase on the scope should be set to 0.5 ms/div, and triggering should occur on the positive edge of the external signal. Set the vertical sensitivity to 1 V/div. The input range of this circuit is from - 4 V to +4 V; connected channels are terminated in about 100 KΩ.

(Elektor Electronics 7-8/87 Supplement, p. 50)


OSCILLOSCOPE-TRIGGERED SWEEP
OSCILLOSCOPE-TRIGGERED SWEEPFC69-8

The circuits input op amp triggers the timer, sets its flip flop and cuts off its discharge transistor so that capacitor C can charge. When capacitor voltage reaches the timers control voltage of 0.33 VCC, the flip-flop resets and the transistor conducts, discharging the capacitor. Greater linearity can be achieved by substituting a constant-current source for frequency adjust resistor R. (Signetics , 1987 Linear Data Manual Vol. 2: Industrial, 2/87, p. 7-62.


PORTABLE SCOPE CALIBRATOR
PORTABLE SCOPE CALIBRATORFG192

This simple circuit can be used for calibrating scopes or other equipment. (Popular Electronics, April 1997, p. 59)


SCOPE VOLTAGE CURSOR ADAPTER
SCOPE VOLTAGE CURSOR ADAPTERFF64-1

The voltage cursor adapter superimposes horizontal cursor lines on the top and bottom of the waveform--a kind of electronic calipers--to permit direct readout of the voltage value. The cursor lines extend across the entire screen. The MC78LI2 voltage regulator (ICl) supplies regulated 12- Vdc to the rest of the circuit. The ICM7555 timer (IC2) drives the CD4066B, a CMOS bilateral switch (IC3). This drive frequency can either be a normal frequency (NORM) of 100 Hz or a low-frequency (LO-F) of 10 kHz, depending on the setting of switch S. Set S1 to LO-F for inputs below 500 Hz.

The dc reference voltage supplied to pin 3 of IC3 is set by R3, a 10-turn, 5000-Ω precision potentiometer. The voltage can be read directly from a turns counter dial coupled directly to the potentiometer's wiper. The accuracy of this reading can be 1% or better. Trimmer potentiometer R1 permits the voltage to R3 to be calibrated to precisely 10 V.

The circuit is calibrated by setting the digital reading on the turns counter of R3 to the full clockwise position and adjusting R1 for a reading of 10 V at the wiper of R3 with a digital voltmeter.

Bilateral switch IC3 converts the dc reference to a square wave with exactly the same wiper amplitude. The square wave output appears on common pins 4, 9, and 10 of IC3 and coaxial plug PL1.

(Reprinted with permission from Radio-Electronics, 5/95. (C) Copyright Gernsback Publications, Inc.,1995)


VARIABLE GAIN AMPLIFIER
VARIABLE GAIN AMPLIFIERFE72-5

This circuit uses 1/4 of an LM3900 to build a simple variable-gain front end for an oscilloscope. R7 is the gain control Also shown is a simple preamp if you need more than 10X of gain. (Reprinted with permission from Electronics Now, 7/92. p. 88. (C) Copyright Gernsback Publications, Inc.,1992)


PHASE SEQUENCE AND PHASE SHIFT CIRCUITS

LONG-TAILED PAIR PHASE-SPLITTER

PHASE INDICATOR

PHASE SELECTOR/PHASE DETECTOR/SYNCHRONOUS RECTIFIER/BALANCED MODULATOR


LONG-TAILED PAIR PHASE-SPLITTER
LONG-TAILED PAIR PHASE-SPLITTERFE74-1

The single-phase input produces out-of phase outputs at the outputs at the collectors of Q1 and Q2. (William Sheets)


PHASE INDICATOR
PHASE INDICATORFB69-2

 The circuit provides a simple means of determining the succession of phases of a 3-phase 120 V source used in synchro work. Terminals A, B, and C are connected to the three terminals of the source to be checked. If the neon bulb lights, interchange any two leads; the light then extinguishes and A, B, and C indicate the correct sequence. If power on any one be is lost, the neon bulb will light. This feature may be useful for monitoring purposes. (William Sheets)


MODULATOR
PHASE SELECTOR/PHASE DETECTOR/SYNCHRONOUS RECTIFIER/BALANCED MODULATORFC70-1

This circuit passes the input signal at unity gain, either unchanged or inverted, depending on the digital control input. A buffered input is shown, since low-source impedance is essential. Gain can be added by modifications to the feedback networks. Signals up to 100 kHz can be handled with 20.0-V pk-pk, output. The circuit becomes a phase detector when driving the digital control input with a reference phase at the same frequency as the input signal; the average dc output is proportional to the phase difference, with 0 Vat + 90°. By connecting the output to a comparator, which in turn drives the digital control, a synchronous full-wave rectifier is formed. With a low-frequency input signal and a high-frequency digital control signal, a balanced (suppressed carrier) modulator is formed.

(Harris, Analog Product Data Book, 1988, p. 10-14)


PHOTOGRAPHY RELATED CIRCUITS

CAMERA TRIP CIRCUIT

DARKROOM TIMER

ENLARGER EXPOSURE METER

PHOTO FLASH SLAVE UNIT

SCR SLAVE FLASH

SLIDE STEPPER


CAMERA TRIP CIRCUIT
CAMERA TRIP CIRCUITFD61-4

This circuit was used to trip a camera shutter.  Grounding pin 2 of Ul makes pin 4 of Ul go high. This triggers both timers of dual timer Ul. One output holds reset (pin 4) of Ul low to keep Ul from accepting another trigger, depending on the time constant of R7 and C3. This prevents camera film waste. The other timer is used to generate a 1/2-second pulse to drive U4 and Ql, the relay driver. Kl triggers the camera. (Reprinted with permission from Popular Electronics, 1/91, p.28-29. (C) Copyright Gernsback Publications, Inc.,1991)


DARKROOM TIMER
DARKROOM TIMERFE75-5

 The electronic darkroom timer is built around a 555 oscillator/timer, a pair of general purpose transistors, a buzzer, and an LED. The 555 (Ul) is configured as an astable multivibrator (free-running oscillator). The frequency of the oscillator is determined by the values R1 through R3 and C1 through C4.

Switch S1 is used to divide the capacitor network to vary the time interval between beeps; when S1 is closed, the circuit beeps at intervals of 30 seconds. With S1 closed, it beeps at 15-second intervals.

When power is applied to the circuit (by closing switch S2), the output of U1 at pin 3 is initially high. That high is applied to the base of transistor Ql (an MPS2907 general-purpose pnp device), keeping it turned off. That high is also applied to the anode of LED1 (which is used as a power on indicator) through resistor R7, turning it on.

Timing capacitors Cl through C5 begin to charge through timing resistors R1 through R3. dc voltage is applied to BZ1's driver input through R5 and to its feedback terminal (through R4), which is also connected to Q2's base terminal. The V+ voltage that applied to Q2's base causes it to turn on, tying BZ1's common terminal high.

When the timing capacitors are sufficiently charged, a trigger pulse is applied to pin 2 (the trigger input) of U2, causing Ul's output to momentarily go low. This causes LED1 to go out and transistor Ql to turn on. That, in turn, grounds the common lead of buzzer BZ1, causing BZ1 to sound. Afterward, the output of Ul returns to the high state, turning off Ql, and turning on LED1, until another time interval has elapsed and the process is repeated.

The circuit is powered by a 9-Vac adapter, which plugs into 117-V household outlet. Because the circuit draws only about 10 to 15 mA, a 9-V alkaline transistor-radio-battery can also be used to power the circuit.

(Reprinted with permission from PE Hobbyists Handbook 1991, p. 38. (C) Copyright Gernsback Publications, Inc.,1991)


ENLARGER EXPOSURE METER
ENLARGER EXPOSURE METERFE75-8

Two gates of a 4011 are used as a comparator. When the resistance of R4 decreases the voltage at pin 1 and 2 increases, produces a logic zero at pin 3, causing pin 4 to go high and activating the LED. R3 is calibrated in light units, or seconds exposure time. To calibrate, set pot R3 so as to just be on the LED ON/OFF threshold. With a light level that is suitable to correctly expose a photographic print, use a known enlarger and a known negative. (Reprinted with permission from Popular Electronics, Fact Card 198. (C) Copyright Gernsback Publications, Inc)


PHOTO FLASH SLAVE UNIT
PHOTO FLASH SLAVE UNITFE75-2

Phototransistor Q1 receives a light pulse from a photoflash unit. The pulse is ac-coupled to amplifier Q2. It then triggers SCR1, which triggers a flash unit that is connected to J1 (Reprinted with permission from Popular Electronics, Fact Card 198. (C) Copyright Gernsback Publications, Inc)


SCR SLAVE FLASH
SCR SLAVE FLASHFD61-2

Using a light -activated SCR, this circuit can trigger a slave flash unit. (Reprinted with permission from Popular Electronics, Fact Card 65. (C) Copyright Gernsback Publications, Inc)


SLIDE STEPPER
SLIDE STEPPERFF65-2

This stepper circuit replaces remote controls and will automatically advance slides in a projector. The time delay is variable with R4. The cable connections are for a Kodak carousel slide projector. (Reprinted with permission from Electronics Now, 5/95. p. 91. (C) Copyright Gernsback Publications, Inc.,1995)


PIEZO CIRCUITS

CMOS PIEZO DRIVER

CMOS PIEZO DRIVER USING 4049

PIEZO DRIVER

PIEZO MICROPOSITIONER DRIVER


CMOS PIEZO DRIVER
CMOS PIEZO DRIVERFE76-1

A CMOS gate and transistor buffer can be used as an effective driver for a piezoelectric transducer. (Reprinted with permission from Popular Electronics, 5/92, p.60. (C) Copyright Gernsback Publications, Inc.,1992)


CMOS PIEZO DRIVER USING 4049
CMOS PIEZO DRIVER USING 4049FE76-2

This circuit uses a 4049 IC to drive a 2N2222 switching transistor. The transistor drives crystal 1 a piezo transducer. (Reprinted with permission from Popular Electronics, 5/92, p.60. (C) Copyright Gernsback Publications, Inc.,1992)


PIEZO DRIVER
PIEZO DRIVERFE76-3

Using a PA41 from Apex Microtechnology, this monolithic amplifier is capable of 350-V operation and delivers 660 V p-p in a bridge circuit. (Reprinted with permission from Apex Microtechnology Corporation)


PIEZO MICROPOSITIONER DRIVER
PIEZO MICROPOSITIONER DRIVERFE76-4

The PA41 from Apex Microtechnology is used here to drive a piezoelectric micropositioner. The drive voltage is less than 20 V p-p at input. (Reprinted with permission from Apex Microtechnology Corporation)


POWER SUPPLY CIRCUITS - DC-DC

±20 VOLT CHARGE PUMP BOOST CONVERTER

+5 V/+3.6 V FROM 4 AA CELLS

1 VOLT 600 KHZ SWITCHING SUPPLY DELIVERS UP TO 40MA AT 5V

500 KHZ 3.3V TO 12V DC CONVERTER

DC-DC CONVERTER FOR DIGITAL PANEL METERS

DC-TO-DC CONVERTER

DC-TO-DC SMPS VARIABLE 18 V TO 30 V OUT AT 0.2 A

LOW NOISE DC-DC CONVERTER

NEGATIVE BUCK REGULATOR USES STEP UP CONTROLLER

NEGATIVE VOLTAGE FROM A POSITIVE SUPPLY

ONE CELL CONVERTER

STEP UP SUPPLY CHARGES BATTERY WHILE SERVING LOAD


±20 VOLT CHARGE PUMP BOOST CONVERTER
±20 VOLT CHARGE PUMP BOOST CONVERTERFG199

A low-power converter of 5V to ±20V can be made surprisingly small by enhancing a dual-output charge pump IC with an extra boost stage composed of discrete diodes. Such supplies are useful for CCD power supplies, LCD bias and varactor tuners. The MAX864 on its own can generate ±10V (minus load proportional losses) from a 5V input. or ±6.6V from a 3.3V input. Using additional diode-capacitor stages, these outputs can be doubled again to approximately ±4Vin or multiplied by 1.5 to approximately ±3Vin. Note that the external diode/capacitor network connects to C1 for ±15V outputs, or to C2 for ±20V outputs. (Maxim Engineering Journal, Volume 24, pp. 7-9)


+5 V/+3.6 V FROM 4 AA CELLS
+5 V/+3.6 V FROM 4 AA CELLSFE78-3

With this unique logic-power-converter design (see the figure), a switchable 3.6 or 5 V at 200 mA can be attained by using four AA cells. The supply incorporates a MOSFET switch that can switch to a lithium backup battery, providing a 3.4-V output when the main battery is dead or removed. The supply consumes only 380 mA under no-load conditions.

The circuit operates in a somewhat novel mode as a step-up/step-down converter. When the cells are fresh (from about 6 V to about 5.2), the LT1173's gain block drives the p-channel MOSFET, which turns the circuit into a linear voltage regulator. This might seem inefficient, but the batteries are quick to drop from 6 V to 5 V. with a 5-V input, the efficiency, (for the 3.6-V output) is 3.6/5 or 72%, which is reasonable. As the battery-pack drops in voltage, efficiency increases, reaching greater than 90% with a 4.2-V input.

At a point below a 4-V input, the circuit switches to step-up mode. This mode squeezes the batteries for all of their available energy. In this case, efficiency, runs between 83% at approximately a 4-V input to 73% at a 2.5-V input.

The supply can deliver 200 mA over its entire operational range. In its linear mode of operation, the supply has no current spikes that, because of the fairly high internal resistance of the alkaline cells, can reduce battery life. The topology delivers over 9.3 hours of 3.6-V 200-mA output power, compared to just 7 hours using the traditional flyback topology that is used in other designs.

(Reprinted with permission from Electronic Design, 2/93, p.71)


1 VOLT 600 KHZ SWITCHING SUPPLY DELIVERS UP TO 40MA AT 5V
1 VOLT 600 KHZ SWITCHING SUPPLY DELIVERS UP TO 40MA AT 5VFG196

The LT1037 chip will produce 5V at 40 mA or 3.3V at 75 mA from a single AA cell power source. It operates at 600 kHz and uses 60 μA standby current, and has a low battery detector. (Linear Technology LT1307 Advertisement)


500 KHZ 3.3V TO 12V DC CONVERTER
500 KHZ 3.3V TO 12V DC CONVERTERFG197

The LT1309 500kHz micropower DC/DC converter circuit provides a compact 12V supply. High frequency operation permits the use of low inductance and low capacitance values for surface mount parts. The LT1309 provides 60 mA of output current at 12V required for 8-bit wide flash memory chips. In addition, when the flash memory card is removed the LT1309 can be shut down by the system reducing current draw to 6μA. A Soft Start feature allows the output voltage to ramp up to 12V over a period of time, minimizing in-rush current needed from the 3.3V supply to charge the PCMCIA input capacitance. An active-low VPP Valid output signals the system that the 12V supply is within regulation after being switched on. (Linear Technology Power Solutions, 1996, p. 29)


DC-DC CONVERTER FOR DIGITAL PANEL METERS
DC-DC CONVERTER FOR DIGITAL PANEL METERSFG200

Often a digital panel meter is used in an application where the meter is on the hot side of a circuit. This supply will provide the 9 to 12 V DC floating supply for the meter. (Popular Electronics, October, 1996, pp. 39-44)


DC-TO-DC CONVERTER
DC-TO-DC CONVERTERFF23-2

This converter should be useful where a few milliamperes of dc at a higher voltage than available supplies can deliver is needed. T1 is typically a 1 kΩ CT:10-KΩ transistor audio transformer. Depending on T1, about 50 to 150 Vdc can be obtained at a few millamperes. (William Sheets)


DC-TO-DC SMPS VARIABLE 18 V TO 30 V OUT AT 0.2 A
DC-TO-DC SMPS VARIABLE 18 V TO 30 V OUT AT 0.2 AFB72-20

(Signetics, Analog Data Manual 1983. p. 12-27)


LOW NOISE DC-DC CONVERTER
LOW NOISE DC-DC CONVERTERFG195

Low noise is achieved by this inexpensive and versatile 5-V to +12-V dc-dc converter. Wideband output noise appears to be well under 500 μV p-p. The converter accepts external clocks from 80 kHz to 120 kHz. The converter operates much like a TV horizontal deflection circuit. Q3 is a logic level power MOSFET driven by an external clock. When Q3 is switched on, current ramps up through Tl's primary. When Q3 is switched off, Q3's drain flies back to 25 V as C4 resonates with Tl's primary, transferring energy to the secondary. As the flyback voltage falls and attempts to go below ground, the intrinsic diode of the power MOSFET clamps it. In addition, the excess resonate energy flows backward through Tl's primary, recharging Cl. When reaching this point, Q3 is again switched on and the cycle repeats. Q3's gate (trace 2) is switched on and off when Q3's drain is near ground. Q3's gate driver power requirements are modest enough to be handled by any 74HC logic gate. Regulation is achieved by the error amplifier (LT1013). Despite the fact that Ql acts as a linear pass transistor, converter efficiency can exceed 75% if the voltage drop across Q 1 is minimized. This can be accomplished by either adjusting the clock frequency or tuning C4 to adjust the flyback voltage. (Electronic Design, October 24, 1995, p. 102)


NEGATIVE BUCK REGULATOR USES STEP UP CONTROLLER
NEGATIVE BUCK REGULATOR USES STEP UP CONTROLLERFG194

This circuit adopts a step-up (boost) dc-dc controller for use in a negative buck-regulator application. The supply voltage must be negative, and it must deliver l60mA to 750mA. Although the boost-regulator IC operates as a buck-regulator circuit, its standard connections enable proper control of Ql. The output voltage, however, must be inverted by an op amp for proper voltage feedback the load is referred to the most positive supply rail instead of IC l's ground terminal so the controller must increase its duty cycle as VOUT (referred to that terminal) increases. The op amp therefore inverts the feedback signal and shifts it to match the 1.5V threshold internal to IC1. IC1 is configured in its non-bootstrapped mode, which provides an adequate gate-drive signal (ground to - 5.2V) for the external MOSFET Ql. With VOUT set to -3V and the output current ranging from l60mA to above 700mA, the circuit's conversion efficiency ranges from 84% to as high as 87.5%. (Maxim Engineering Journal, Volume 23, p. 12)


NEGATIVE VOLTAGE FROM A POSITVE SUPPLY
NEGATIVE VOLTAGE FROM A POSITIVE SUPPLYFD63-10

By using a 555 timer to generate a square wave and voltage-doubling the output, a negative voltage that is almost equal to the positive supply can be obtained. The current available is up to 20 to 30 mA or so, depending on the regulation and voltage needed. (Reprinted with permission from Radio-Electronics, 10/90, p14. (C) Copyright Gernsback Publications, Inc.,1990)


ONE CELL CONVERTER
ONE CELL CONVERTERFG201

The regulator generates a 5-V output from a single lithium-ion cell. Initially, the lithium- ion cell is at 4.2 V, which is greater than the 3.75-V undervoltage-lockout (UVL) limit of the LM2587 Simple Switcher. Once it starts up, the boost circuit will continue to regulate even when the battery voltage drops lower than the UVL limit. The level that the input voltage can drop to depends on the maximum load current desired. Of course, the source can be any type of battery-three alkaline, four NiCd, or even two lithium batteries. When power is applied to the circuit, the 10-kΩ resistor charges up the 47-μF input capacitor and supplies the startup current to the LM2587. After startup, the LM2587 input and the input capacitor draw current from the switch node through the 1N914B bootstrap diode. When that happens, the IC input pin gets charged up to the output voltage minus a diode drop. In the circuit, with a 5-V output, the IC input voltage is 4.5 V after startup. It stays at 4.5 V even when the input voltage drops to below 3.75 V. The input voltage can drop to 1.25 V when the regulator is supplying 250 mA. At 2.4V, the regulator is 84% efficient if the 1N914B bootstrap diode is replaced with a lN5817 Schottky diode. (Electronic Design, December 16,1995, pp. 88-90)


STEP UP SUPPLY CHARGES BATTERY WHILE SERVING LOAD
STEP UP SUPPLY CHARGES BATTERY WHILE SERVING LOADFG39

IC1 is a step-up switching regulator that boosts VIN (nominally 5V) as necessary to supply the combination of charging current and load current. The 5V source must include short-circuit protection IC2 is a high-side current-sense amplifier that monitors the charging current. Commands from the processor include CHARGE ON/OFF and FAST/TRICKLE CHARGE. IC2 produces an output current (OUT) equal to 1/10,000 of the current through sense resistor R9. Q3 and Q4 are on during a fast-charge operation, so this output current flows through the parallel combination of R11 and (approximately) R4. The resulting feedback to IC1 (pin 3) maintains the fast-charge current through R9 at 50 mA. This feedback also enables the regulator to supply as much as 500 mA of load current in addition to the fixed 500 mA of charging current. Q2 limits the battery voltage to 10V (2V/cell). During the fast charge, an external processor and multi-channel A/D converter (ADC) must monitor the batterys terminal voltage. When the ADC senses a change of slope in this voltage, the processor terminates the fast charge by asserting a high on FAST/TRICKLE CHARGE.  Q3 turns off, causing a rise in the feedback (FB) that lowers the charging current to the trickle-charge rate (approximately 60 mA).  If IC1 shuts down, or if load current plus charging current exceeds the capability of IC1, the R9 current reverses as current flows out of the battery.  IC2 indicates the reversal by allowing R13 to pull its open-collector SIGN output high, turning off Q4 and turning on Q5. Current through R12 then produces a voltage proportional to the battery's discharge current (5A through R9 produces a full-scale response of 3V across R12). By integrating this voltage over time (sampling at fixed intervals and multiplying by the time interval), the A/D-processor system can monitor energy removed from the battery. Based on this measurement and the terminal-voltage measurement, the processor can then re-initiate a fast charge (by asserting FAST/TRICKLE CHARGE low) before the battery reaches its end of life. (Maxim Engineering Journal, Volume 23, pp. 14-15)


POWER SUPPLY CIRCUITS (FIXED)

AC-TO-DC CONVERTER

ANTIQUE RADIO POWER SUPPLY

SERIES REGULATED LINEAR POWER SUPPLY

SIMPLE 12-V POWER SUPPLY


AC-TO-DC CONVERTER
AC-TO-DC CONVERTERFD63-5

By coupling two back-to-back diodes in series with an ac power circuit, a voltage of about 1.4 Vpp can be obtained. This voltage is useful for exciting the primary coil of a small transformer. The voltage induced in the secondary coil can then be rectified and used to power solid-state control circuits. The forward-voltage drop of the diodes is inherently constant and stable over a wide range of ac-circuit power variations. The resulting voltage developed across the transformer windings is also free from variation that might be caused by changes in the circuit's current or voltage.

In the circuit, a lamp (LMP-1) is connected to the primary ac input line (Ll and L2) through a pair of inverse-parallel-connected power diodes (D1 and D2). As power flows to the lamp, a drop of about 0.7 V is alternatively developed across each of the diodes. This voltage feeds the primary of a small transformer (Tl). Tl can be a small 8Ω to 500Ω transistor radio output, etc. This will deliver about 11 Vpp across its secondary winding. LMP1 can be a small 120-V lamp of 5 to 25 W, etc.

(Reprinted with permission from Electronic Design 11/90, p 136, Copyright 1990 Penton Publishing)


ANTIQUE RADIO POWER SUPPLY
ANTIQUE RADIO POWER SUPPLYFG202

This supply was intended for powering an antique radio using 01A triodes needing DC filament voltage. It is a straight forward Zener regulator and pass transistor,. The large values of capacitance used for reducing 120 Hz hum to minimum. (Popular Electronics, January 1997, p. 60)


SERIES REGULATED LINEAR POWER SUPPLY
SERIES REGULATED LINEAR POWER SUPPLYFG203

The AC line is isolated from the power supply by transformer Tl. Full-wave diode bridge BR1 delivers unregulated DC with ripple on it to the filter capacitor Cl. The filtered DC is delivered to pass transistor Ql, shown here in series with the load. The series-pass regulator with a transistor pass element regulates the voltage to assure that a constant output level is maintained despite variations in the power line voltage or circuit loading. The basic linear series regulator consists of transistor Q1, reference resistor Rl, sensing resistors R2 and R3, a voltage reference Zener diode D1, and an operation amplifier IC1, organized as an error amplifier. The zener diode Dl provides a fixed reference voltage at the positive input to the amplifier-IC1. The output voltage of the supply establishes the emitter voltage and provides a feedback voltage for the negative terminal of the amplifier IC1. The equation for the regulated output voltage is:

VREG = VREF(1 + R1/R2).

(Electronics Now, December 1994, pp. 69-70)


SIMPLE 12-V POWER SUPPLY
SIMPLE 12-V POWER SUPPLYFF68-23

This 12-V power supply is easy to build, and it produces a smooth output. D1 is a 14-V, 1/2-W Zener diode. The voltage can be varied by a few volts up or down to change the output voltage. (Reprinted with permission from Popular Electronics, 6/95, p.78. (C) Copyright Gernsback Publications, Inc.,1995)


POWER SUPPLY CIRCUITS - HIGH VOLTAGE

 -100-VDC SUPPLY

AC-OPERATED HE-NE POWER SUPPLY

FLUORESCENT TUBE POWER SUPPLY

HELIUM-NEON LASER POWER SUPPLY WITH HV PULSE IGNITION

HIGH VOLTAGE POWER SUPPLY FOR NEON TUBES

HIGH-VOLTAGE DC GENERATOR

NEON LAMP DRIVER FOR 5- TO 15- V SUPPLIES

VACUUM TUBE EXPERIMENTERS SUPPLY


-100-VDC SUPPLY
-100-VDC SUPPLYFF69-5

The combination Hartley oscillator/step-up transformer shown in A can generate significant negative high voltage---especially if the voltage output of the transformer is multiplied by the circuit in Figure B. T1 is a small low voltage filament transformer of around 4- to 10-Vac output, 120-V primary. (Reprinted with permission from Popular Electronics, 6/93, p.77. (C) Copyright Gernsback Publications, Inc.,1993)


AC-OPERATED HE-NE POWER SUPPLY
AC-OPERATED HE-NE POWER SUPPLYFF69-6

T1 is a 120-V to 1000-V step-up 60-Hz transformer. C1, C2, C3, C4, and D2 through D5 form a voltage quadrupler. The initial voltage is  4 to 5 kV, which drops when the laser tube fires. (Laser Cookbook, McGraw-Hill, p. 163)


FLUORESCENT TUBE POWER SUPPLY
FLUORESCENT TUBE POWER SUPPLYFE77-2

A 2N3055 oscillator (Q1) drives a homemade transformer, wound on a 5/16 x 1 7/8 ferrite rod. S2 is used as a filament switch and it can be eliminated, if desired. A 20 W fluorescent tube is recommended. The supply is 12V. (Reprinted with permission from Popular Electronics, 6/93, p.77. (C) Copyright Gernsback Publications, Inc.,1993)


HELIUM-NEON LASER POWER SUPPLY WITH HV PULSE IGNITION
HELIUM-NEON LASER POWER SUPPLY WITH HV PULSE IGNITIONFG206

The HeNe laser requires two voltages, a voltage in the range of 10 kV that starts the laser and then turns off once the discharge begins, and a lower voltage power supply to sustain the discharge. The circuit diagram illustrates one method of generating the laser ignition voltage. A fraction of the main supply voltage is used to charge up a capacitor. When triggered, it's discharged through a high-voltage ignition transformer in series with the main power supply output. When the supply is first turned on, a delay circuit allows the main supply to stabilize at full voltage and charge up the capacitor. A nonlatching relay operates to discharge the capacitor on a one-shot basis into the ignition coil after the timing delay. The HV diode in series with the ignition coil and the capacitor across the supply rectifies the damped oscillatory waveform out of the ignition coil, producing a single positive pulse across the laser tube ionizing the gas in the laser. Once the laser is ignited by the HV pulse, the main power supply maintains the discharge. (Communications Quarterly, Winter 1996, pp. 10-11)


HIGH VOLTAGE POWER SUPPLY FOR NEON TUBES
HIGH VOLTAGE POWER SUPPLY FOR NEON TUBESFG205

Power for the circuit is supplied by a step-down transformer, T2, and fullwave bridge rectifier, BR1, which convert 117-volts AC to 12-volts DC. Capacitor C3 acts as a filter. The heart of the circuit is a Schmitt trigger hex invert, Ul. Capacitor Cl, resistor Rl, and potentiometer R2 are connected to one section of the inverter, U1-a, to form an oscillator that runs at approximately 15 kHz (because U1 is a Schmitt trigger, the output squarewave is very clean). Adjusting R2 varies the frequency. The output of the oscillator is fed into the remaining five inverters (Ul-b through Ul-f), which are connected in parallel to create a buffer that is capable of increasing the drive current of the oscillator. The squarewave output is used to drive the switching transistor, Ql, which in turn switches the primary windings of the ferrite-core transformer, T1. Approximately 500-volts AC at 15 kHz are output from the secondary of the transformer. Tl is made from a Ferrite Pot Core. Wind 500 turns of #30 gauge wire for the secondary. Coat with insulating varnish, and add a layer of insulating tape over which a 20 turn winding of #22 gauge wire is wound to form the primary winding. (Popular Electronics Magazine, July, 1996, pp. 47-48)


HIGH-VOLTAGE DC GENERATOR
HIGH-VOLTAGE DC GENERATORFE77-1

In the miniature high-voltage dc generator, the input to the circuit, taken from a 12-Vdc power supply, is magnified to provide a 10,000-Vdc output causing a pulsating signal, of opposite polarity, to be induced in Tl's secondary winding.

The pulsating dc output at the secondary winding of T1 (ranging from 800 to 1000 V) is applied to a 10-stage voltage-multiplier circuit, which consists of Dl through D10, and C3 through C12. The multiplier circuit increased the voltage 10 times, producing an output of up to 10,000 Vdc. The multiplier accomplishes its task by charging the capacitors (C3 through C12); the output is a series addition of the voltages on all the capacitors in the multiplier.

In order for the circuit to operate efficiently, the frequency of the square wave, and therefore the signal applied to the multiplier, must be considered. The output frequency of the oscillator (U1-a) is set by the combined values of R1, R5, and C1, (which with the values specified is approximately 15 kHz). Potentiometer R5 is used to fine tune the output frequency of the oscillator. The higher the frequency of the oscillator, the lower the capacitive reactance in the multiplier.

Light-emitting diode LED1 serves as an input-power indicator, and neon lamp NEl indicates an output at the secondary of T1. A good way to get the maximum output at the multiplier is to connect an oscilloscope to the high-voltage output of the multiplier, via a high-voltage probe, and adjust potentiometer R5 for the maximum voltage output.

(Reprinted with permission from PE Hobbyist Handbook, 1990, p. 92. (C) Copyright Gernsback Publications, Inc.,1990)


NEON LAMP DRIVER FOR 5- TO 15- V SUPPLIES
NEON LAMP DRIVER FOR 5- TO 15- V SUPPLIESFE78-14

This neon lamp driver is based on the 555. T1 can be wound on an old TV flyback transformer core (William Sheets)


VACUUM TUBE EXPERIMENTERS SUPPLY
VACUUM TUBE EXPERIMENTERS SUPPLYFG204

This supply furnishes +250V at about 60 mA and 2.5V AC at 4.5 A and has a balance pot for filament (B-return) center tap. T1 is a power transformer with 350-0-350V AC Center Tapped, 5V AC at 3A, T2 is 2.5V AC at 4.5 A. (Popular Electronics, February 1996, p. 40)


POWER SUPPLY CIRCUITS - MULTIPLE OUTPUT

 ± 35-V SUPPLY FOR AUDIO AMPLIFIERS

5- AND ± 12-V AC-POWERED SWITCHING SUPPLY

BRIDGE RECTIFIER

DUAL OUTPUT 500KHZ ± 15V DC/DC CONVERTER

DUAL SUPPLY FROM SINGLE SOURCE

SIMPLE DUAL VOLTAGE POWER SUPPLY

SUBWOOFER AMPLIFIER POWER SUPPLY

SWITCHABLE LINEAR VOLTAGE REGULATOR


+/- 35-V SUPPLY FOR AUDIO AMPLIFIERS
± 35-V SUPPLY FOR AUDIO AMPLIFIERSFD63-12

This supply will be found useful for operating various transistor AF power amplifiers in the 50-to 100-W output range. T1 = 120 V: 70 V CT at 5 A.

(Reprinted with permission from Radio-Electronics, 3/89, p. 53. Copyright Gernsback Publications, Inc., 1989)


5- AND +/- 12-V AC-POWERED SWITCHING SUPPLY
5- AND ± 12-V AC-POWERED SWITCHING SUPPLYFD63-23

This supply uses an SGS-Thomson UC3842 IC in an off-line flyback regulator, providing + 5 V at 4 A and ±12 V at 300 mA. This enables a small high-frequency (50 kHz) transformer, to handle large amounts of power that are normally handled by a 60-Hz transformer. Ql is a 5-A 500-V MOSFET, and the diodes are fast-recovery types. Tl has a 45-turn primary winding of #26 wire. The 12-V windings are each 9 turns of #30 wire, bifilar wound. The 5-V winding is 4 turns of four bifilar #26 wires. The control (feed back) winding is two bifilar, parallel 10-turn, #30 windings. The core is Ferroxcube EC35-3C8 with a 3/8" center leg. (Radio Electronics 5/91, pp. 49-55)


BRIDGE RECTIFIER
BRIDGE RECTIFIERFD63-11

This bridge circuit is intended for those cases where two unequal supply voltages are required. The lower voltage is obtained with the aid of a transformer with symmetric windings and half-wave rectification of the potential across one winding.

For the higher voltage, the potential across both windings is rectified. To that end, the output of the transformer is linked to the bridge rectifier via two electrolytic capacitors that provide isolation of the two direct voltages.

A bonus with this type of circuit is that although the two supplies can be loaded unequally, the currents through the two transformer windings are the same. Thus, the transformer is loaded symmetrically so that its full capacity can be used. Moreover, no unnecessary dissipation is in the voltage regulators. The load on the lower voltage supply depends primarily on the rating of the transformer.

The load on the higher voltage supply is limited by the reactance of C, and C2 (= 1/2 π 50 C) and the required minimum output voltage.

(Elektor Electronics, 12/90 Supplement, p. 536)


DUAL OUTPUT 5OOKHZ +/- 15V DC/DC CONVERTER
DUAL OUTPUT 500KHZ ± 15V DC/DC CONVERTERFG210

The LT1371 dual output flyback converter circuit generates ±l5V at 200 mA each from a 5V supply. The LT1371 is a 500 kHz high efficiency switching regulator with 3A power switch, yet uses only 4mA typical quiescent current. The high operating frequency allows a small surface mount, dual-output winding flyback transformer to be used. Each output is monitored by separate positive and negative feedback inputs on the LT1371 to make sure that neither output rises above its set point. This removes a common problem in dual-output designs using a single controller where the voltage of the least loaded output will tend to fly high. Output voltage regulation is best when both outputs are evenly loaded. (Linear Technology Power Solutions, 1996, p. 38)


DUAL SUPPLY FROM SINGLE SOURCE
DUAL SUPPLY FROM SINGLE SOURCEFG209

The key idea is that in a dual-supply powered circuit, "ground" is midway between the positive and negative supply voltages. Unfortunately, ordinary voltage regulators can't do the job. The reason is that they can only source current, not sink it. However, the ground terminal in a dual supply may have to either source or sink current, depending on which half of the load is drawing more current at the time. In the circuit, Rl and R2 divide the input voltage in half. Opamp Ul reproduces that voltage at the "ground" output terminal by making either Ql or Q2 conduct as much as necessary. Capacitors Cl and C2 hold the output voltage steady when the load changes suddenly. Diode Dl is present to protect the circuit's input from reversed polarity by blowing the fuse of the main power supply. If your power supply has no fuse, place Dl in series with the circuit. That will afford the same protection with only slightly reduced regulation and voltage output. (Popular Electronics, June 1994, pp. 47 - 48)


SIMPLE DUAL VOLTAGE POWER SUPPLY
SIMPLE DUAL VOLTAGE POWER SUPPLYFG207

This circuit can be used to power op amp circuits or other applications requiring dual plus and minus supplies. This is a most basic circuit and is not regulated. T1 is a 120 /12V Transformer of 100 mA or more capacity. (Popular Electronics, October 1996, p. 68)


SUBWOOFER AMPLIFIER POWER SUPPLY
SUBWOOFER AMPLIFIER POWER SUPPLYFE78-23

Although intended to power a 100 W low frequency amplifier, this power supply should handle many stereo amplifiers in the medium power range that require ± 30 to 35 V. (Reprinted with permission from Popular Electronics, 1/92, p.37. (C) Copyright Gernsback Publications, Inc.,1992)


SWITCHABLE LINEAR VOLTAGE REGULATOR
SWITCHABLE LINEAR VOLTAGE REGULATORFG208

This three voltage regulated supply can be added to for more voltage ranges. (Popular Electronics, February 1997, p. 76)


POWER SUPPLIES (VARIABLE)

ADJUSTABLE 0- TO 5-V SUPPLY

ADJUSTABLE POWER SUPPLY

EXPERIMENTERS POWER SUPPLY

SWITCH-SELECTED FIXED-VOLTAGE POWER SUPPLY

TRACKING POWER SUPPLY

VARIABLE VOLTAGE REGULATOR WITH CURRENT CROWBAR LIMITING

VARIABLE VOLTAGE SOURCE USES LM3900


ADJUSTABLE 0- TO 5-V SUPPLY
ADJUSTABLE 0- TO 5-V SUPPLYFF71-2

Although linear-regulator ICs are frequently used in variable power-supply applications, they might not always be the best choice. At low output voltages, power losses in these regulators can cause headaches for designers. For example, if an output current of 1.25 A is required at 1.25 V from an input of 8 V, a regulator (such as the LT317) dissipates more than 10 W.

The figure depicts a dc-dc converter that functionally replaces a linear regulator in the just described application. The converter not only eliminates the problem of power loss, but it can be adjusted for output voltages (as low as 25 mV) while delivering an output current of 1.5 A.

The circuit uses a basic positive-buck topology with one exception. A control voltage is applied through R4 to the feedback summing node at pin 1 of the LT1076 regulator IC, making it possible to adjust the output from 0 V to approximately 6 V. This range encompasses the 3.3-V and 5-V logic supply voltages for portable and desktop equipment, as well as battery-pack combinations of one to four cells.

As R4 is driven from 0 to 5 V by the buffer (U1), more or less current is required from R2 to satisfy the loop's desire to hold the feedback summing point at 2.37 V. This forces the converter's output to swing over the range of 0 to 6 V. The LT1076 is capable of 1.75-A guaranteed output current in this application, and 2 A is typical. If more current is required, the LT1074 can be substituted for the LT1076.

(Reprinted with permission from Electronic Design, 6/94, p. Copyright 1994, Penton Publishing, Inc)


ADJUSTABLE POWER SUPPLY
ADJUSTABLE POWER SUPPLYFF71-4

Using an LM317, this supply delivers 1.25 to 22 Vdc for various purposes. The LM317 should be heatsinked. This supply will deliver 200-mA output current. (William Sheets)


EXPERIMENTERS POWER SUPPLY
EXPERIMENTERS POWER SUPPLYFG212

The power supply circuit has an output that can be varied linearly by potentiometer R2 or switched to specific levels by rotary-switch S3. (Popular Electronics, May 1996, p. 57)


SWITCH-SELECTED FIXED-VOLTAGE POWER SUPPLY
SWITCH-SELECTED FIXED-VOLTAGE POWER SUPPLYFD65-5

This supply can serve as a battery eliminator for various devices (such as tape recorders, small radios, clocks, etc).

Sl selects a resistance that is predetermined to provide a preselected output voltage. In this circuit, various commonly used supply voltages produced by batteries were chosen, but any voltages up to the rating of Tl (approximately) can be produced by choosing an appropriate resistor. The resistor value is given by:

Rx=Rl  (VOUT -  1)

       1.25

R1 =220 Ω

Remember to provide adequate heatsinking for Ul.

(Reprinted with permission from Popular Electronics, 9/90, p.27. (C) Copyright Gernsback Publications, Inc.,1990)


TRACKING POWER SUPPLY
TRACKING POWER SUPPLYFF68-13

Two op amps are used in this basic op-amp regulator circuit. The outputs can be fed to current amplifier stages or emitter followers, if needed.( Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 30).


VARIABLE VOLTAGE REGULATOR WITH CURRENT CROWBAR LIMITING
VARIABLE VOLTAGE REGULATOR WITH CURRENT CROWBAR LIMITINGFF71-1

The variable voltage regulator with current-crowbar limiting, shown in figure A overcomes the disadvantage of constant and foldback limiting. As you can see in the graph (Figure B), the current crowbar quickly shuts down the supplied power when a preset current is exceeded. It also has excellent load regulation over its operating range. (Reprinted with permission from Popular Electronics, 4/95, p. 96. (C) Copyright Gernsback Publications, Inc.,1995)


VARIABLE VOLTAGE SOURCE USES LM3900
VARIABLE VOLTAGE SOURCE USES LM3900FG211

The figure shows the circuit or a variable voltage source that produces outputs of 0.6 to 20 volts, depending on the setting of potentiometer R1. That circuit can also be used as a fixed-voltage source by replacing the potentiometer with a fixed resistor of appropriate value. Like the other circuits discussed thus far, it is based on the LM3900. The maximum voltage that is produced depending on the Zener voltage of the Zener reference diode (D1). In the case shown here, the Zener is a 22-volt unit, so the maximum output voltage will be something between 20 and 22 volts. Lower values of maximum output voltage can be accommodated by using a diode with a lower Zener voltage for D1. (Popular Electronics, July 1996, p. 52)


POWER SUPPLY MONITOR CIRCUITS

ACTIVE RF DETECTOR PROBE

LOGIC PROBE

LOGIC PROBE CIRCUIT


ACTIVE RF DETECTOR PROBE
ACTIVE RF DETECTOR PROBEFD67-5

An MFP102 FET is used as a wideband amplifier. L1 can be 100 μH for 40 to 100 Mhz or 1000 μH for 2 to 30 Mhz. For LF, (less than 3 Mhz), use a 2.5 μH RF choke. This probe will work as a relative indicator device, but it can be calibrated over a frequency range, if needed. (Reprinted with permission from Popular Electronics, 7/91, p.57. (C) Copyright Gernsback Publications, Inc.,1991)


LOGIC PROBE
LOGIC PROBEFG214

The figure shows the schematic for a versatile logic probe. The Zener diode clamps the input signal just above the TTL inverter's 2.2-volt trigger voltage. Zener-diode Dl can be left out if the probe is going to be used on only TTL circuits, The logic probe is based mainly on inverters IC1 -a and IC1 -b, which are sections of a 7404 integrated circuit. Depending on whether the input is high or low, the inverters enable AND gate IC2-a or IC2-b, which are sections of a 4081. Each AND gate is connected to an oscillator, one low-frequency the other high. When an AND gate is made high, it passes the frequency of its oscillator to the Piezo buzzer (BZ1). Whenever there's a high at the input, the buzzer will produce the high tone, whenever there's a low at the input, the buzzer will sound the low tone. With switch S2 in the "pulse" position, if there are pulses present at the input, a yellow LED will light and the buzzer will sound at the frequency of the pulses. The CMOS/TTL switch selects the voltage from the circuit under test or the voltage from the 78L05 regulator. Note that when this switch is in the TTL position, it can work only with 5-volts DC, but when the switch is in the CMOS position, it can work from 7.5- to 35-volts DC. (Popular Electronics, 5/97, pp. 69-70)


LOGIC PROBE CIRCUIT
LOGIC PROBE CIRCUITFG213

In this logic probe circuit, the red LED indicates logic high and the green indicates logic low. The optional use of a LED seven segment readout is also shown. (Electronic Experimenters Handbook, 1996, p. 26)


PROTECTION CIRCUITS

DELAYED ACTION MOBILE RADIO PROTECTION CIRCUIT

DIODE RELAY DRIVER PROTECTION

ELECTRONIC FUSE

MOV SURGE PROTECTION CIRCUIT

POWER SUPPLY PROTECTION CIRCUIT


DELAYED ACTION MOBILE RADIO PROTECTION CIRCUIT
DELAYED ACTION MOBILE RADIO PROTECTION CIRCUITFG217

This circuit uses an SCR and an RC circuit to delay application of power to a mobile radio or other equipment. This is to provide protection form starting motor and alternator induced transients. (Nuts and Volts, June 1996, p. 83)


DIODE RELAY DRIVER PROTECTION
DIODE RELAY DRIVER PROTECTIONFG215

Diode protects switching transistor from voltage spike caused by the relay coil. (Electronics Now, December 1995, p. 10)


ELECTRONIC FUSE
ELECTRONIC FUSEFE80-2

Basically this circuit is an adjustable electronic circuit breaker, containing a toroidal transformer that senses 60 Hz load current. T1 has a two-turn winding for primary and 100 turns of #30 gauge wire for the secondary. A high-low range select switch selects 0.1 to 6A or 1 to 12 A. The primary winding of T1 carries the full load current and voltage; should be suitably insulated as should be RY1. (Reprinted with permission from Radio-Electronics, 12/91, p. 63. (C) Copyright Gernsback Publications, Inc.,1991)


MOV SURGE PROTECTION CIRCUIT
MOV SURGE PROTECTION CIRCUITFG216

Three MOV devices connected as shown provide superior protection against line surges as all three legs are protected against excessive potential differences. (Popular Electronics, May 1996, p. 73)


POWER SUPPLY PROTECTION CIRCUIT
POWER SUPPLY PROTECTION CIRCUITFB74-5

When using a regulated supply to reduce a supply voltage there is always the danger of component failure in the supply and consequent damage to the equipment. A fuse will protect when excess current is drawn, but might be too slow to cope with overvoltage conditions. The values shown are for a 12 V supply being dropped to 5 V. The trip voltage is set to 5.7 V to protect the equipment in the event of a regulator fault. The 330 ohm resistor and the 500 ohm potentiometer form a potential divider which samples the output voltage as set by adjustment of the potentiometer. The SCR is selected to carry at least twice the fuse rating. The full supply voltage is connected to the input of the regulator. The 2N2906 is held bias off by the 10 k resistor and the SCR so that the LED is held off. If the output voltage rises above a set trip value then the SCR will conduct, the fuse will blow, and the 2N3906 will be supplied with base current via the 10 k resistor, and the LED will light up. (William Sheets)


PROXIMITY SENSOR CIRCUITS

FIELD DISTURBANCE SENSOR/ALARM

PROXIMITY ALARM

PROXIMITY SWITCH

SCR PROXIMITY ALARM

UHF MOVEMENT DETECTOR


FIELD DISTRURBANCE SENSOR/ALARM
FIELD DISTURBANCE SENSOR/ALARMFB76-2

The change in ambient light triggers the alarm by changing resistance of LDR1 and LDR2.

Q1=Radio Shack 276-2024

A1=Mallory SC628P Sonalert

LDR1,LDR2=Cadmium sulfide photocell, Radio Shack 276-116

(Popular Electronics, 12/75, p. 15)


PROXIMITY ALARM
PROXIMITY ALARMFE81-2

A CMOS logic gate is used to make up this circuit. When an object is near the antenna, the change in oscillator output is detected by D1 and D2 and amplified by U1C, which drives sounding alarm BZ1. (Reprinted with permission from Popular Electronics, Fact Card 270. (C) Copyright Gernsback Publications, Inc)


PROXIMITY SWITCH
PROXIMITY SWITCHFC80-3

A 3- x -3-inch piece of circuit board, or similar size metal object which functions as the pick-up sensor, is connected to the gate of Ql. A 100-MΩ resistor, R2, isolates Ql's gate from Rl, allowing the input impedance to remain very high. If a 100-MΩ resistor cannot be located, just tie five 22-MΩ resistors in series and use that combination for R2. In fact, R2 can be made even higher in value for added sensitivity.

Potentiometer RI is adjusted to where the piezo buzzer just begins to sound off and then carefully backs off to where the sound ceases. Experimenting with the setting of Rl will help in obtaining the best sensitivity adjustment for the circuit. Resistor R1 can be set to where the pick-up must be contacted to set off the alarm sounder. A relay or other current-hungry component can take the place of the piezo sounder to control most any external circuit.

(Popular Electronics/Hands-On Electronics, 5/89, p.85)


SCR PROXIMITY ALARM
SCR PROXIMITY ALARMFC80-4

(Hands-On Electronics, Fact Card No. 57)


UHF MOVEMENT DETECTOR
UHF MOVEMENT DETECTORFC80-2

The oscillator is a standard UHF design which delivers about 10 mW at 1.2 Ghz. Rl and R2 bias the base of Ql to 1.2 V via L2. Collector current is set by R3 to about 30 mA. C2 couples the base of Ql to the stripline circuit. Tuning is provided by CV1, and Cl plus Cla decouple the collector. R2 and R3 are not decoupled, since this could cause instability.

Q2 is a simple one-transistor amplifier. C4 and C7 reduce gain below 1.5 and above 100 Hz; the remaining band of frequencies is amplified and passed on to the level detector. Two comparators of IC1 provide level detection. The trigger voltage is set by R7, Rvl, R8, and R9; it is adjustable from 8 to 60 mV by Rvl.

Positive voltage swings above the trigger level cause the IC1A output to become low, while negative swings cause IClb to become low. C8 decouples IC1 from the power supply, and R10 is a pullup resistor for the open collector output of IC1.

(RF Design, 12/86, P. 41)


RADAR DETECTOR CIRCUITS

2.6-GHZ OSCILLATOR FOR RADAR SPEED GUN

DISPLAY BOARD FOR RADAR GUN

RADAR DETECTOR


2.6-GHZ OSCILLATOR FOR RADAR SPEED GUN
2.6-GHZ OSCILLATOR FOR RADAR SPEED GUNFF74-2

This circuit consists of a 2.6-Ghz oscillator Q2, a coupling microstripline to ANT1, a 1.1 1/4-wave probe, detector D2, and audio amp Q1. The oscillator feeds power to the antenna, which radiates the signal. The reflected signal from a moving target mixes with the oscillator signal in D2. The resultant beat note (doppler shift) is amplified by Q1 and fed to jack J1, which is used to feed the circuit 12 Vdc. (Reprinted with permission from Popular Electronics, 6/95, p.38. (C) Copyright Gernsback Publications, Inc.,1995)


DISPLAY BOARD FOR RADAR GUN
DISPLAY BOARD FOR RADAR GUNFF74-1

This circuit takes signal (doppler) from a radar gun, amplifies and limits it, and feeds the frequency into a counter (U4) and display circuit (DISP1, DISP2, U5, U6). Counter calibration is set by clock circuit U2B. Calibration is obtained via R21 and R22. R21 can be changed if kilometers/hour readout is desired. (Reprinted with permission from Popular Electronics, 6/95, p.38. (C) Copyright Gernsback Publications, Inc.,1995)


RADAR DETECTOR
RADAR DETECTORFD69-1

A simple detector of radar signals uses the junctions of the input transistors of an LM1458 op amp as RF detectors. The leads of C1 act as an antenna and should be about 0.4 long measured from the IC package. Detected audio components are further amplified by IC1A and IC1B and drive a piezo transducer. Mount the circuit so that incident RF energy will not be blocked. (Reprinted with permission from R-E Experimenters Handbook 1987. p. 122. (C) Copyright Gernsback Publications, Inc., 1987)


RADIATION DETECTOR CIRCUITS

GEIGER COUNTER

ION DETECTOR


GEIGER COUNTER
GEIGER COUNTERFF75-1

An HV generator (IC2, C2, Q1, T1, and associated components) power a G-M tube. A pulse from the GM tube is interface through Q2 and IC1 to pulse generator IC3, which drives a speaker. (Fantastic Electronics, McGraw-Hill, pp. 67-73)


ION DETECTOR
ION DETECTORFF75-5

ANT1 is a short whip antenna from a junked radio or other device. R3 is adjusted to bring the meter on scale. This device should be grounded to operate properly. A length of aluminum or copper foil tape attached to the instrument case makes contact with the hand, and the body serves as a ground via hand contact with this tape. (Reprinted with permission from Popular Electronics, 5/93, p.40. (C) Copyright Gernsback Publications, Inc.,1993)


RECEIVING CIRCUITS

3.5- TO 10-MHz SIMPLE SUPERHETERODYNE RECEIVER

ONE-TUBE AM RECEIVER

SCA RECEIVER DEMODULATES ADDITIONAL SUBCARRIERS


3.5- TO 10-MHz S.IMPLE SUPERHETERODYNE RECEIVER
3.5- TO 10-MHz SIMPLE SUPERHETERODYNE RECEIVERFD71-2

 SupeRX Parts List

Part	Value	Type
C1	47 pF	silver-mica or polystyrene
C2	100 pF	silver-mica or polystyrene
C3	0.0l pF	polystyrene or monolithic
C4	27 pF	silver-mica or polystyrene
C5	0.1l pF	ceramic disc or monolithic
C6	0.l pF	polystyrene or monolithic
C7	0.022 μF	polystyrene or monolithic
C8	0.1 μF	polystyrene or monolithic
C9	0.047 μF	monolithic
C10	0.22 μF	monolithic
	0.15 μF	(alternate)
C11	0.22 μF	monolithic
	0.15 μF	(alternate)
C12	0.047 μF	monolithic
C13, C14	0.1 μF	ceramic disc or monolithic
C15	l0 μF	electrolytic, 16V
C16	l00 μF	electrolytic, 16V
C17	47 μF	electrolytic, 16V
C18	5-20 pF	panel mounted tuning capacitor
C19, C20	220μF	electrolytic, 16V
Dl, D2	1N34A	germanium diode or equivalent
Rl,R2,R3,R8	100 ohm,	1/4W carbon composition
R4, R5	2.2 k, 1/4 W	carbon composition.
	1.5k	(alternate)
R6, R7	10k, 1/4W	carbon composition
R9	10k	potentiometer
Tl, T2	10.7 MHz	microminiature (7mm) Mouser PN 42IF223 IF transformer, green core
T3, T4	455 kHz	microminiature (7mm) Mouser PN 42IF203 IF transformer, black core
Ul, U3	NE602	double-balanced mixer
U2	MC3340	variable attenuator
U4	LM380N-8	audio amplifier
U5	78L05	100mA miniature +5V regulator

* C10 and Cl 1 can range from 0.1 to 0.22 pf. Values greater than 0.33 cause distortion.

Other: Printed stripboard, DSE PN H5614 or equivalent, cabinet, plastic stick-on feet, 4-40

hardware, etc.

In this circuit, Ul is a frequency converter that feeds the 455-kHz IF stage U2 and detector U3. U4 is the audio output stage. R9 is a gain control that varies the gain of U2. Coil data is given in the part list.

(73 Amateur Radio Today)


ONE-TUBE AM RECEIVER
ONE-TUBE AM RECEIVERFF76-19

This radio uses an untuned RF stage to boost the signal voltage up to the linear portion of the crystal diode's characteristic curve. The circuit's distortion and wide bandpass and a good-quality transformer make for a great-sounding AM radio. Ll is a winding of #22 enameled wire 2" long on a 2" diameter plastic pipe. Tl is a tube-type radio output transformer, rated at 2000 Ω to the speaker voice coil. (Reprinted with permission from Popular Electronics, 10/94, p.62. (C) Copyright Gernsback Publications, Inc.,1994)


SCA RECEIVER DEMODULATES ADDITIONAL SUBCARRIERS
SCA RECEIVER DEMODULATES ADDITIONAL SUBCARRIERSFG218

A simple PLL-based FM demodulator can be made to demodulate two subcarriers and provide a source of background music. The input to this receiver is fed from the wideband audio output from an FM radio's first FM detector. This is the point that feeds the FM stereo demodulator in an FM receiver. Care should be taken so that the signal is tapped off at a point which hasn't yet been filtered (the subcarrier(s) are still present). This FM input signal is then passed through 2 second-order high-pass filter and peaker stage (Q1), which serves to bandpass and provide additional gain within the input spectrum prior to the FM demodulator input. The FM detection is accomplished by a simple LM565 PLL IC (Ul) operating as an FM demodulator. The PLL's VCO is tuned to 91 kHz via RT/CT. The demodulated output signal is available at pin 7, which is followed by a second-order LPF/buffer combination (Q4). The characteristics of this filter can be modified to suit the user. The design shown has an audio corner frequency of about 5kHz. The filtered output is the recovered audio output and is the input to an audio amplifier. To choose the second subcarrier (67 kHz), the peaker and VCO are gang-tuned by the Q2 and Q3 saturating switch transistors. These devices switch inappropriate-valued parallel capacitors to re-tune the peaker and VCO to the proper frequency for reception of the second subcarrier signal. Circuit values shown are for an FM level of about 50 to 300 mV rms at the input to the peaker stage. In addition, the PLL dynamic characteristics can be altered as desired by modifying the loop filter. The typical recovered audio level at pin 7 of Ul is 200 mV rms. To receive SCA signals, the FM receiver can simply be tuned to normal FM stations and then the presence of either or both subcarriers can be checked. (Electronic Design, February 3, 1997, p. 154-156)


RADIO CIRCUITS

AM RADIO USES ONE CHIP

BROADCAST-BAND RF AMPLIFIER

NE602 DIRECT-CONVERSION RECEIVER

RECEIVER PREAMPLIFIER

SIMPLE 1.5-V AM BROADCAST RECEIVER

SIMPLE 225-400 MHZ AIR BAND RECEIVER

SIMPLE AM RADIO

SOLID STATE REGENERATIVE RECEIVER

TWO-CHIP AM RECEIVER


AM RADIO USES ONE CHIP
AM RADIO USES ONE CHIPFG222

The ZN414 IC contains a complete AM radio, with AGC, except for an audio section. Like an MMIC, it is powered through its output terminal. (Electronics Now, December 1995, p. 8)


BROADCAST-BAND RF AMPLIFIER
BROADCAST-BAND RF AMPLIFIERFB85-7

The circuit has a frequency response ranging from 100 Hz to 3 MHz; gain is about 30 dB. Field-effect transistor Ql is configured in the common-source self-biased mode; optional resistor R1 sets the input impedance to any desired value. Commonly, it will be 50 ohms. The signal is then direct-coupled to Q2, a common-base circuit that isolates the input and output stages and provides the amplifier's exceptional stability. Q3 functions as an emitter follower, to provide low output impedance (about 50 ohms). For higher output impedance, include resistor R8. It will affect impedance according to this formula: R8 ~ Rout -50. Otherwise, connect output capacitor C4 directly to the emitter of Q3. (Radio Electronics, 3/87, p. 42)


NE602 DIRECT-CONVERSION RECEIVER
NE602 DIRECT-CONVERSION RECEIVERFE83-7

An NEC602 is used as a mixer with zero IF frequency output. U2 acts as an audio amplifier. This receiver is primarily for SSB and CW signals. T1 and T2 are 10.7 MHz IF coils used  in AM/FM transistorized radios, etc. or in any similar indicator.( Reprinted with permission from Popular Electronics, 3/93, p.79. (C) Copyright Gernsback Publications, Inc.,1993)


RECEIVER PREAMPLIFIER
RECEIVER PREAMPLIFIERFG34

Here is a preamplifier that lets you use a short antenna over the range from 100 kHz to well over 55 MHz, with excellent sensitivity, using a vertical 30-inch piece of number 12 wire, or a few feet of wire laying on the floor. Transistor Ql (NPN) is directly coupled to PNP transistor Q2. Feedback from the collector of Q2 to the emitter of Ql is accomplished by resistors RF and RA. Because of the high open loop gain of the amplifier, the gain of the amplifier is RF/RA, or 20 dB maximum. A l K potentiometer changes the effective value of RA, resulting in a minimum gain of near unity. (73 Amateur Radio Today, January 1997, p. 26)


SIMPLE 1.5-V AM BROADCAST RECEIVER
SIMPLE 1.5-V AM BROADCAST RECEIVERFE83-5

This receiver uses the ZN416E made by GEC Plessey. The tuning is via C1. (Reprinted with permission from Popular Electronics, 8/93, p.70. (C) Copyright Gernsback Publications, Inc.,1993)


SIMPLE 225-400 MHZ AIR BAND RECEIVER
SIMPLE 225-400 MHZ AIR BAND RECEIVERFG219

Tuning-coil L2 can be wound with 2 turns of No. 22 wire on a 5/32-inch drill bit. This circuit is well behaved as long as a good component layout is used. The component leads must be kept short and neat, especially the leads of the transistor. The lengths should not exceed 3/16 of an inch. Audio could be tapped off the tuning coil with a 5-μF or so electrolytic capacitor, but the 1N82 diode circuit seems to produce less signal loss. The RF signal from ANT1, an approximately 18-inch antenna, can be introduced through a small capacitor of 1 pF or less to the emitter of the 2N918. Other high-frequency transistors can be used but might require different resistance in the regeneration circuit. The output of this circuit must go to an audio amplifier. (Popular Electronics, September 1995, p. 31)


SIMPLE AM RADIO
SIMPLE AM RADIOFD71-9

An AM radio can be built of a simple diode detector and an audio amplifier. A random length of wire always serves as an antenna. L1 is an adjustable ferrite loopstick of the type used in transistor radios. (Reprinted with permission from Popular Electronics, 10/89, p.22. (C) Copyright Gernsback Publications, Inc.,1989)


SOLID STATE REGENERATIVE RECEIVER
SOLID STATE REGENERATIVE RECEIVERFG220

You will need to modify the coil shown to use it with the regenerative receiver. Place a single layer of electrical tape around the bottom winding of the coil (Ll); wind 6 turns of 19- or 20-gauge wire over the taped winding, leaving 4-inch pig tails. Tape the winding in place. Then connect the modified coil to the receiver circuit as shown in the Figure. The two 2N3904 transistors are connected in a Darlington high-input-impedance circuit configuration to reduce loading of the tuned circuit. Potentiometer R2 controls the positive RF feedback. If the receiver seems dead, and only weak signals are heard, try reversing the leads on the 6-turn feedback coil. (Popular Electronics, December 1996, p. 64)


TWO-CHIP AM RECEIVER
TWO-CHIP AM RECEIVERFF76-15

This receiver is comprised of a TDA7000 single-chip FM receiver (Ul), an LM386 low-voltage audio-power amplifier (U2), a pair of hand-wound coils (L1 and L2), and a few additional components. L1 and L2 are 100 turns of #28 wire on toroidal cores (about 240 μH each). L1 is tapped at 30 turns. (Reprinted with permission from Popular Electronics, 5/94, p.79. (C) Copyright Gernsback Publications, Inc.,1994)


REGULATOR CIRCUITS

DUAL-OUTPUT REGULATOR

LOW-COST STEP-DOWN REGULATOR

LOW-DROPOUT THREE-TERMINAL REGULATORS FOR NEW MICROPROCESSOR APPLICATIONS

VARIABLE VOLTAGE REGULATOR


DUAL-OUTPUT REGULATOR
DUAL-OUTPUT REGULATORFF78-4

If load can go to zero, an optional preload of 1 to 5 kΩ can be used to improve regulation. Many modern circuit designs still need a dual polarity supply. Communication and data acquisition are typical areas where both 5 V and -5 V are needed for some of the IC chips.

The current mode architecture and saturating switch design allow the LTl376 to deliver up to 1.5-A load current from the 8-pin SO package. Ll is a 10-μH surface-mount inductor from Coiltronics. The second winding is used to create a negative-output SEPIC (Single-Ended Primary Inductance Converter) topology using D3, C4, C5, and the second half of Fl. This converter takes advantage of the fact that the switching signal driving Ll as a positive buck converter is already the correct amplitude for driving a -5-V SEPIC converter. During switch-off time, the voltage across L is equal to the 5-V output plus the forward voltage of D1. An identical voltage is generated in the second winding, which is connected to generate -5 V using D3 and C5. Without C4, this would be a simple flyback winding connection with modest regulation. The addition of C4 creates the SEPIC topology. Note that the voltages swing at both ends of C4 is theoretically identical-even without the capacitor. The undotted end of both windings goes to a zero ac voltage node, so the equal -windings will have equal voltages at the opposing ends. Unfortunately coupling between windings is never perfect, and load regulation at the negative output suffers as a result. The addition of C4 forces the winding potentials to be equal and gives much better regulation.

(Linear Technology Design Note #98)


LOW-COST STEP-DOWN REGULATOR
LOW-COST STEP-DOWN REGULATORFF78-3

This inexpensive and efficient discrete step-down regulator is based on a complementary transistor arrangement that uses both positive and negative feedback and is referenced to a Zener diode. Inductor Ll is selected to maintain the switching frequency above the audible range for the intended operating load. The output filter L2 and C4 reduces ripple to less than 10 mV p-p over a large range of loads, with only a slight decrease in efficiency. (Reprinted with permission from Electronic Design 2/95, p 118, Copyright 1995 Penton Publishing)


APPLICATIONS
LOW-DROPOUT THREE-TERMINAL REGULATORS FOR NEW MICROPROCESSOR APPLICATIONSFF78-7

The LT1584/LT1585/LTLI587 are high-performance, low-dropout regulators designed to meet the demands of the newest high speed, low voltage microprocessors. These devices are designed to regulate from 5-V supplies to output voltages between 1.25 V and 3.6 V. The LT1584 can provide up to 7 A of current, making it ideal for powerful Pentium processor- or similar applications. The LTl585 can supply up to 4 A, while the LT1587 supplies up to 3 A. The excellent transient response capability allows them to maintain good regulation even with significant load steps. Fixed 3.3 V, 3.45 V, 3.6 V and adjustable output voltages are available. (Linear Technology, Advertisement LT/1294)


VARIABLE VOLTAGE REGULATOR
VARIABLE VOLTAGE REGULATORFD74-3

The op amp is wired as a x 2 noninverting dc amplifier with a gain that is determined by the R3/R2 ratio. The input voltage to the op amp is variable between 0 and 15 V via R5. The output voltage is therefore variable over the approximate range from 0.5 to 30 V. The available output current has been boosted by adding transistor Ql to the output. (Reprinted with permission from Radio-Electronics, 12/88. p. 72. (C) Copyright Gernsback Publications, Inc.,1988)


RELAY CIRCUITS

HIGH-IMPEDANCE RELAY DRIVER

LATCHING RELAY ALARM CIRCUIT

LATCHING RELAY DRIVER FOR +12-V LOADS

LOW-CONSUMPTION MONOSTABLE RELAY

MOMENTARY RELAY CIRCUIT

POLARITY SENSITIVE RELAY CIRCUIT

SOLID-STATE RELAY CIRCUIT


HIGH-IMPEDANCE RELAY DRIVER
HIGH-IMPEDANCE RELAY DRIVERFF79-4

A CMOS gate is used to drive a switching transistor and relay. (William Sheets)


LATCHING RELAY ALARM CIRCUIT
LATCHING RELAY ALARM CIRCUITFF79-1

Momentarily closing any sensors will cause K1 to latch. S1 must be depressed to reset circuit. If any sensor is still closed circuit will not reset. (William Sheets)


LATCHING RELAY DRIVER FOR +12-V LOADS
LATCHING RELAY DRIVER FOR +12-V LOADSFF79-3

A 4-V signal will cause the relay to pull in when Q1 turns on. Latching is obtained by feedback through a 4.7Ω resistor. A switch is used to select latching or nonlatching operation. A NO pushbutton releases the circuit. (William Sheets)


LOW-CONSUMPTION MONOSTABLE RELAY
LOW-CONSUMPTION MONOSTABLE RELAYFD75-3

A monostable relay has two states: operative when a large enough current flows through its coil and quiescent when no current flows. A relay contact that assumes a certain position after the supply voltage has been switched on is required in many applications. Of course, many relays operate in that manner.

However, most of these relays require an energizing current of 50 mA or more and that normally precludes a battery supply. The circuit presented here, which uses a bistable relay, can solve that problem.

The contact of a bistable relay normally remains in the position it is in after the supply is switched off. This circuit, however, makes the bistable relay behave like a monostable type, at a modest current. When the supply voltage is switched on, Cl charges via Dl and the relay coil. The current then flowing through the coil causes the relay contact to assume one of two positions. The forward drop across Dl ensures that the base of T1 (in this condition) is more positive than its emitter so that Tl, and thus T2, is switched off.

When the supply voltage is switched off, the emitter of Tl is connected to the positive terminal of Cl, while the base is connected to the negative terminal of the capacitor via Rl and the relay coil. This results in Tl, and thus T2, switching on so that Cl discharges via T4 and the relay. The current flows through the relay coil, then flows in an opposite direction and this causes the contact to change over.

The bistable relay thus behaves exactly as a monostable with the advantage, however, that the operational current is determined by Rl, which amounts to only 130 μA.

To ensure reliable operation, the rating of the relay coil should be 65 to 75% of the supply voltage. In the prototype, a 9-V relay was used with a battery supply voltage of 12 V.

(Elektor Electronics, 12/90, p. 525)


MOMENTARY RELAY CIRCUIT
MOMENTARY RELAY CIRCUITFF79-2

The charging current of a capacitor can be used if a momentary relay-on circuit is needed. Depending on the relay characteristics, C will vary from 1000 to 4000 μF or so for a 1-s hold time if a 500-Ω relay is used. RD discharges capacitor C to ready the circuit for the next operation. The value should be high enough so as not to maintain the relay closure at highest expected supply voltage. (William Sheets)


POLARITY SENSITIVE RELAY CIRCUIT
POLARITY SENSITIVE RELAY CIRCUITFG224

When a positive voltage is input to the circuit, relay RY1 is activated; when a negative voltage is input, RY2 is activated. (Popular Electronics, May 1996, p. 65)


SOLID-STATE RELAY CIRCUIT
SOLID-STATE RELAY CIRCUITFE84-2

R1 limits input current while Q1 acts as a current sink to protect IC1. D1 serves as a polarity protector. IC1 provides a triac output to trigger the main triac TR1. (Reprinted with permission from Electronic Design, 8/92, p.69)


REMOTE CONTROL CIRCUITS

REMOTE-CONTROL EXTENDER

SIMPLE REMOTE CONTROL

SIMPLE REMOTE CONTROL INTERFACE CIRCUITS

ULTRASONIC REMOTE-CONTROL TRANSMITTER


REMOTE-CONTROL EXTENDER
REMOTE-CONTROL EXTENDERFE85-4

A signal from an IR remote control is converted from IR radiation to a frequency pulse that can be transmitted through coaxial TV cable or any other two conductor wire to another room, where its converted back into an IR signal. (Reprinted with permission from R-E Experimenters Handbook 1991, p. 30)


SIMPLE REMOTE CONTROL
SIMPLE REMOTE CONTROLFG226

Here is a remote-control transmitter and receiver. The theory of the circuit's operation is very simple. The transmitter (Fig. A) generates IR light pulses at a frequency of 320 Hz (set in part by R2). The pulses arrive at the collector of the phototransistor and are amplified by the 2N2222 transistor. An NE567, IC2, is tuned to 320 Hz (by R6), so if pulses of any other frequency arrive at the phototransistor, the NE567's output will remain high. When the 320 Hz signal enters the phototransistor,  the NE567 recognizes this frequency and pulls its output low. If you wish to change the NE567's operating frequency, you'll have to adjust R2 and R6 to the same value. Keep in mind that the NE567 will work between 100 Hz and 1 kHz. You can also add more resistors (for more frequencies) instead of R2, and more NE567's tuned at the desired frequencies in order to make a multi-channel remote control system. (Popular Electronics, May 1997, p. 68)


SIMPLE REMOTE CONTROL INTERFACE CIRCUITS
SIMPLE REMOTE CONTROL INTERFACE CIRCUITSFG225

If you want to control a DC motor, a momentary load or an on/off load, these are some useful interface circuits. Figure A shows a DC-motor controller that requires the outputs of two different channels (CH1 and CH2). Note that it doesn't matter if the channel outputs are active low or high; what matters is that CH1 must be different from CH2 for the motor to be energized. The circuits in Figs.B and C are momentary load controllers for both active high and low channel outputs, respectively. The circuit in Fig. D is a toggled-load controller. If you have an active-high channel output, you must add the inverter shown (Popular Electronics, May 1997, pp. 68-69)


ULTRASONIC REMOTE-CONTROL TRANSMITTER
ULTRASONIC REMOTE-CONTROL TRANSMITTERFE85-5

A GC Electronic P/N J4-815 ultrasonic transducer is used in this 4--kHz transmitter for remote control application. (Reprinted with permission from Popular Electronics, 3/93, p.45. (C) Copyright Gernsback Publications, Inc.,1993)


SAMPLE AND HOLD CIRCUITS

HIGH-SPEED SAMPLE-AND-HOLD

LOW-DRIFT SAMPLE AND HOLD

SAMPLE-AND-HOLD CIRCUITS II

TRACK-AND-HOLD/SAMPLE-AND-HOLD


HIGH-SPEED SAMPLE-AND-HOLD
HIGH-SPEED SAMPLE-AND-HOLDFC87-3

This circuit uses the speed and drive capability of the HA-5190 coupled with two high-speed DMOS FET switches. The input amplifier is allowed to operate at a gain of - 5, although the overall circuit gain is unity. Acquisition times of less than 100 ns to 0.1% of a 1-V input step are possible. Drift current can be appreciably reduced by using FET input buffers on the output stage of the sample-and-hold. Harris, Analog Data Product Data Book, 1988, p. 10-54.


LOW-DRIFT SAMPLE AND HOLD
LOW-DRIFT SAMPLE AND HOLDFF80-2

(Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 1202)


SAMPLE-AND-HOLD CIRCUITS II
SAMPLE-AND-HOLD CIRCUIT IIFE88-2

Driving a D/A converter with an A/D converter provides an overall analog-hold function, which though limited in output resolution, offers zero voltage droop and infinite hold time. The A/D converter shown (IC1) includes a 12-bit compatible track/hold at its input. The track/hold specifies a 6-MHz full-power bandwidth, a 30-ns aperture delay, and a 50-ps aperture jitter. The direct connections shown allow the D/A converter to reconstruct signal levels within the input range of 0 to 5 V. (Reprinted with permission from Maxim Journal, Vol. 3, p. 22)


TACK-AND-HOLD/SAMPLE-AND-HOLD
TRACK-AND-HOLD/SAMPLE-AND-HOLDFC87-7

Channel 1 is wired as a voltage follower and is turned on during the track/sample time. If the product of R x C is sufficiently short compared to the period of maximum output frequency, or sample time; C will charge to the output level. Channel 2 is an integrator with zero input signal. When channel 2 is then turned on, the output will remain at the voltage across C. (Harris, Analog Data Product Data Book, 1988, p. 10-14)


 SAWTOOTH GENERATOR CIRCUIT

LINEAR SAWTOOTH GENERATOR

SAWTOOTH GENERATOR


LINEAR SAWTOOTH GENERATOR
LINEAR SAWTOOTH GENERATORFG227

Ql is connected in a simple constant-current generator circuit. The value of Ql's emitter resistor sets the constant-current level flowing from the transistor's collector to the charging capacitor, Cl. One op-amp of a LM324 quad op-amp IC, Ul-a, is connected in a voltage-follower circuit. The input impedance of the voltage follower is very high and offers little or no load on the charging circuit. The follower's output is connected to the input of Ul-b, which is configured as a voltage comparator. The comparator's other input is tied to a voltage divider setting the input level to about 8 volts. The output of Ul-b at pin 7 switches high when the voltage at its positive input, pin 5, goes above 8 volts. That turns on Q2, discharging Cl. The sawtooth cycle is repeated over and over as long as power is applied to the circuit. The sawtooth's frequency is determined by the value of Cl and the charging current supplied to that capacitor. As the charging current increases, the frequency also increases, and vice versa. To increase the generator's frequency range, decrease the value of Cl, and to lower the frequency, increase the value of Cr. The output is about 3-5 volts. (Popular Electronics, November 1994, pp. 75-76)


SAWTOOTH GENERATOR
SAWTOOTH GENERATORFF81-2

A sawtooth waveform generator circuit, using a 555 IC, is shown. The IC is connected in all astable oscillator circuit with the majority of the output contained in the positive portion of the cycle. The negative output is a very brief pulse.

Capacitor C2 charges through R3 in a positive direction during the time that the ICs output (at pin 3) is high. When the output goes negative, C2 is rapidly discharged through D1 and the IC's output.

Peak-to-peak sawtooth output is about 1 V The linearity of this circuit is best when R3 is as large as possible. The oscillator's frequency is about 200 Hz and can be increased by lowering either the value of R1 or Cl; to decrease the frequency, increase the values of those components. (Reprinted with permission from Popular Electronics, 11/94, p.75-76. (C) Copyright Gernsback Publications, Inc., 1994.


SIRENS, WARBLERS, WAILERS AND WHOOPERS CIRCUITS

ELECTRONIC SIREN

HEE-HAW ELECTRONIC SIREN

PROGRAMMABLE-FREQUENCY ADJUSTABLE-RATE SIREN

SIREN GENERATOR

TWO-TONE SIREN

WAILING SOUND GENERATOR

WARBLE GENERATOR

YELPING SIREN


ELECTRONIC SIREN
ELECTRONIC SIRENFC90-9

The wailing sound of a siren is generated by a VFO consisting of Ql and Q2. Capacitor C2 provides the feedback for the oscillator. The frequency of the oscillator is varied by the voltage applied to the base of Ql through R3. When switch S1 is closed, capacitor Cl charges, thus increasing the oscillator frequency. When S1 is released, capacitor Cl discharges, and the oscillator frequency decreases. Capacitor C3 limits the maximum oscillator frequency. The average battery current drain is about 15 mA. (Radio Electronics, 12/81, p. 53)


HEE-HAW ELECTRONIC SIREN
HEE-HAW ELECTRONIC SIRENFD80-1

The oscillator based on IC2 is responsible for producing the sound. Its output is connected to the base of TR1, which amplifies it to drive the speaker. Resistor R4 is included in the circuit to limit the current through TR1 to a safe and reasonable level. The oscillation frequency of IC2 is partially dependent on the values of R3 and C2. Another factor that governs the frequency of oscillation is the magnitude of voltage fed to pin 5 of IC2. If a voltage of varying magnitude is fed to pin 5, the internal circuitry of the IC is forced to reset at a different rate, which changes the frequency.

IC1 is also connected as an oscillator but it runs much slower than IC2: around 1 Hz. Each time the IC triggers, the voltage at pin 3 goes high. As pin 3 is connected to pin 5 of IC2, this forces IC2 to change its note. That produces the "hee-haw" sound of the siren.

(Hands-On Electronics, 1-2/86, p. 67)


PROGRAMMABLE-FREQUENCY ADJUSTABLE-RATE SIREN
PROGRAMMABLE-FREQUENCY ADJUSTABLE-RATE SIRENFC90-4

The LM380 operates as an astable oscillator with the frequency determined by R2/C2. Adding Q1 and driving its base, with the output of an LM3900 wired as a second astable oscillator, acts to gate the output of the LM380 on and off, at a rate fixed by R1/C1. (National Semiconductor Corporation, Audio/Radio Handbook 1980, p. 4-29)


SIREN GENERATOR
SIREN GENERATORFG228

An adaptable Siren Generator circuit with a multitude of uses is shown. It is based around a 556 twin timer chip, IC1. An audio tone is created by one timer section and is directly coupled to the driver transistor TR1. The other half of the timer is used to modulate the frequency of the audio tone using the control voltage pin terminal of the audio oscillator section, pin 11. If capacitor C2 is omitted from the circuit, a twin-tone alarm generator will be created. However, with C2 in place as shown, a "wailing" tone is produced. Capacitor Cl governs the rate of tone change and the LED Dl flashes, for extra effect. A waterproof Mylar-coned 8 ohm loudspeaker was used for LS1 and the volume may be adjusted for different impedances by altering the value of resistor R5. The circuit operates from approximately a 9V rail. (Everyday with Practical Electronics, November 1995, p. 88)


TWO-TONE SIREN
TWO-TONE SIRENFC90-2

This siren provides a constant audio output, but alternates between two separate tones. The LM13080 is set to oscillate at one basic frequency; this frequency is changed by adding a 200-KΩ charging resistor in parallel with the feedback resistor, R2. (National Semiconductor Corporation, Linear Databook 1982, p. 3-289)


WAILING SOUND GENERATOR
WAILING SOUND GENERATORFF83-4

In this circuit, C2 and T1 determine the tone generated and C1/R2 control the blocking rate. The signal produced is an interrupted tone, like a police whistle or toy ray gun, depending on C1 and C2. (William Sheets)


WARBLE GENERATOR
WARBLE GENERATORFB89-1

The circuit uses a pair of 555 timers or a single dual timer. Capacitor C1 controls the speed of the warble, while C2 determines the pitch. The values shown should produce quite a distinctive signal. (Popular Electronics, 12/74, p. 68)


YELPING SIREN
YELPING SIRENFC90-3

Unijunction transistors Ql and Q2 are both connected as relaxation-type, sawtooth oscillators. Transistor Ql is the low-frequency control oscillator and Q2 is the tone generator. Sawtooth waveforms are produced at the emitter terminals. Without R4 connecting the two emitters, each oscillator operates independently, with its frequency determined mainly by the RC time constant. With the values shown, Ql operates from 1. to 1.5 Hz and Q2 operates from 400 to 500 Hz. When R4 is connected between the two emitters, it couples the low-frequency sawtooth from Ql directly across capacitor C2. That coupling causes the frequency of the tone generator to increase, along with the rise in sawtooth voltage from Ql. The tone generator's frequency drops to its lower design value when Cl discharges and produces the falling edge of the sawtooth. (Hands-On Electronics, Spring 1985, p. 35)


SOUND EFFECT CIRCUITS

BIRD-CHIRP SOUND-EFFECT GENERATOR

COMPUTER VOICE

ELECTRONIC TROMBONE

GUNSHOT SOUND-EFFECTS GENERATOR

RACE-CAR MOTOR/GRASH

ROBOTIC CHATTER SOUND GENERATOR

SOUND EFFECTS GENERATOR

SOUND-EFFECTS GENERATOR

SPACE-AGE SOUND MACHINE


BIRD=CHIRP SOUND-EFFECT GENERATOR
BIRD-CHIRP SOUND-EFFECT GENERATORFF84-5

A low frequency oscillator modulates a higher frequency oscillator, which drives the speaker. (Sound, Light and Music, Delton T. Horn, McGraw-Hill, pp. 98-100)


COMPUTER VOICE
COMPUTER VOICEFG230

This circuit will enable one to simulate the "computer voice" effect commonly heard in films, ads, and TV programs. It consists of two sections: an oscillator to provide the modulation signals, and the modulator itself. The oscillator uses a 555 timer chip in the astable multivibrator mode, and the frequency of operation has been set at about 10 Hertz by the values given to Rl, R2 and Cl. A very simple modulator is used, but this is quite acceptable. Distortion produces new frequencies that help to change the voice's signal and make it sound less like the original. A large amount of distortion is obviously not desirable as it would severely impair the intelligibility of the output signal. Transistor TRl is used as a sort of voltage controlled resistor, and, in conjunction with R4, it forms a voltage and controlled attenuator. (Electronic Experimenters Handbook, 1996, p. 61)


ELECTRONIC TROMBONE
ELECTRONIC TROMBONEFG229

The heart of the trombone is R3, a slide potentiometer. Two gates of a quad two-input NAND gate, ICl-a and ICl-b, make up a simple audio-oscillator circuit with Rl, R3, Cl, C2, and C3 setting the oscillator's frequency. The oscillator's output is buffered by ICl-c, which also supplies the drive signal for the power amplifier, IC2. The trombone's output level is set by R4. A slide handle made of plastic or wood should be attached to the slider of R3, and the complete circuit enclosed in a small plastic cabinet with the three push button switches, Sl-S3, mounted in a convenient location for playing. Just press one or more of the tone-control switches, S1-S3, and work the slide. (Popular Electronics, February 1996, pp. 27, 77)


GUNSHOT SOUND-EFFECTS GENERATOR
GUNSHOT SOUND-EFFECTS GENERATORFF84-8

Gunshot sound effects generator built around a Texas Instruments SN76477 sound chip. An input pulse causes IC1 to generate a gunshot sound. (Sound, Light, and Music, Delton T. Horn, McGraw-Hill, pp. 105-106)


RACE-CAR MOTOR/GRASH
RACE-CAR MOTOR/CRASHFC93-5

For two simultaneous race car sounds, the mixer can be multiplexed between the SLF and VCO functions. (Texas Instruments, Complex Sound Generator Bulletin No. DL-S 12612, p. 11)


ROBOTIC CHATTER SOUND GENERATOR
ROBOTIC CHATTER SOUND GENERATORFF84-6

lCl-IC4, IC6	LM3909 LED flasher/oscillator	R5	6.8 kΩ 1/4 W 5% resistor
IC5	74LS138 three-line to eight-fine decoder	R6	10 kΩ potentiometer
SPKR	small loudspeaker	R7	2.2 kΩ, 1/4W 5% resistor
C1	10 μF 10 V electrolytic capacitor	R8	33 kΩ 1/4 W 5% resistor
C2	22 μF 10 V electrolytic capacitor	R9	3.9 kΩ 1/4 W 5% resistor
C3	33 μF 10 V electrolytic capacitor	R10	4.7 kΩ 1/4 W 5% resistor
C4	100 μF 10 V electrolytic capacitor	R11	100kΩ 1/4 W 5% resistor
C5	0.01 μF capacitor	R12	470 kΩ 1/4 W 5% resistor
C6	0.1 μF capacitor	R15	100 Ω potentiometer
Rl,R3, R14	10 kΩ potentiometer	R16	33 Ω 1/4 W 5% resistor
R2,R4, R13	3.3 kΩ 1/4 W 5% resistor	R17	1 MΩ 1/4 W fixed resistor

The circuit simulates sound effects of a robot, for toy or novelty applications.

(Sound, Light and Music, Delton T. Horn, McGraw-Hill, pp. 114-115)


SOUND EFFECTS GENERATOR
SOUND EFFECTS GENERATORFB91-1

This circuit can generate a European police-car siren, bird noises, spaceship sounds, etc. In addition, it can be put to use as a doorbell, an alarm, etc. The circuit consists of four parts: a binary counter, a D/A converter, a VCO, and an audio output amplifier. The initial frequency of oscillation is determined by potentiometer R11. The VCO first oscillates at a relatively low frequency, and gradually picks up speed as the control voltage supplied by the D/A converter increases. The D/A converter is the group of resistors R1-R8. When none of IC1's outputs is active, little current will flow into the base of Ql, so the VCO's control voltage will be low. As more and more counter outputs become active, base current increases, and thereby so does the VCO's frequency of oscillation. The VCO itself is composed of IC2-a, IC2-b, Ql, and the timing network comprising Dl-D4, Cl, RIO, and R11. The buffer amplifier is made up of the four remaining gates from IC2, all wired in parallel. (Hands-On Electronics, 6/87, p. 40)


SOUND-EFFECTS GENERATOR
SOUND-EFFECTS GENERATORFC93-1

A variable clock-pulse generator is made up of two sections of IC1 (a 4069 CMOS hex inverter), R1, S1, and capacitors  Cl through C6. By adjusting R1 and switching one of the capacitors into the circuit, the clock's pulse rate can be varied over a wide range.

The TL507C converts analog signals-in this case the output of IC3, an LM386 audio amplifier-into digital signals. The conversion is accomplished using the single-slope method; it involves comparing an internally generated ramp signal to the analog input signal and a 200-mV reference voltage.

The square-wave output from the a/d converter is fed to IC3 through a network consisting of R2, R3, and C7. Resistor R2 controls the amplitude of the pulses. Resistor R3 and capacitor C7 form a variable tone-control filter and a differentiator circuit that converts a square wave into a spiked waveform. That waveform is amplified by IC3, and the resulting output is fed back into the analog input of IC2, as well as to an 8-Ω speaker. By adjusting R1 and selecting one of the six capacitors with S1-thus varying the clock frequency-and by varying R2 and R3, you can produce many sounds.

(Gernsback Publications 42 New Ideas 1984 p. 4)


SPACE-AGE SOUND MACHINE
SPACE-AGE SOUND MACHINEFE93-8

The space-age sound device uses a 556 dual-times IC to produce a phasor sound. That IC is actually two 555 timer ICs in one 14-pin package, as shown in the schematic. Each timer inside the 556 is connected in an astable multivibrator mode.

The first timer has its frequency set by R1, R2, and Cl. Its output appears on pin 5 and it is coupled through C2 and R5 into the trigger input of the second timer. The second timer has an adjustable frequency that is controlled by Pl, R6, and C3.

In the second timer, the first frequency mixes with the second frequency and produces the phasor-like sounds. The output of the second timer, which has the two signals mixed together, is brought from pin 9 through limiting resistor R7 to the input of Ql. The function of pnp germanium power transistor Q1 is to amplify the signal to the level that is needed to drive the speaker. The green LED, Ll, converts electrons directly into visible photons (light) in time with the pulses from the speaker. The purpose of resistor R8 is to limit the current through the LED to a safe level.

(Reprinted with permission from PE Hobbyist, 1991, p.77. (C) Copyright Gernsback Publications, Inc.,1991)


SOUND- AND VOICE-CONTROLLED CIRCUITS

AUDIO DRIVEN XENON TUBE FLASH CIRCUIT

AUDIO-CONTROLLED SWITCH

AUDIO-CONTROLLED SWITCH II

BASIC COLOR ORGAN

MELODY SOUND TO LIGHT CIRCUIT

SOUND-OPERATED SWITCH

VOICE ACTIVATED TAPE RECORDER SWITCH


AUDIO DRIVEN XENON TUBE FLASH CIRCUIT
AUDIO DRIVEN XENON TUBE FLASH CIRCUITFG233

This circuit uses a Xenon flashtube to create a very real lightning effect and can be driven one of two ways: Either by sound input or by straight repeated flashes, depending on where switch 2 is positioned. When producing straight flashes, the rate is determined by pot R7. If the switch is set to trigger by sound, the sensitivity is determined by the level of the sound driving the transformer TX2 and the setting of pot R10. This circuit uses high voltages (over 4000 volts for the trigger) and extreme care should be taken by anyone that builds it. The high voltage capacitors can hold dangerous voltages for some time (even after the circuit has been unplugged). Strong caution to part polarity is highly urged. (Nuts and Volts, June 1995, p. 77)


AUDIO-CONTROLLED SWITCH
AUDIO-CONTROLLED SWITCHFE92-9

The audio controlled switch combines a pair of 741 op amps, two 2N2222 general purpose transistors, a hexFET and a few support components to a circuit that can be used to turn on a tape recorder, a transmitter, or just about anything that uses sound. (Reprinted with permission from Popular Electronics, 6/93, p.72. (C) Copyright Gernsback Publications, Inc.,1993)


AUDIO-CONTROLLED SWITCH II
AUDIO-CONTROLLED SWITCH IIFF88-20

The audio-controlled switch combines a pair of 741 op amps, two 2N2222 general-purpose transistors, a HEXFET, and a few support components to produce as circuit that can be used to turn on a tape recorder, a transmitter, or just about anything using sound. (Reprinted with permission from Popular Electronics, 6/93, p.72. (C) Copyright Gernsback Publications, Inc.,1993)


BASIC COLOR ORGAN
BASIC COLOR ORGANFB90-5

Transformer Tl can be any matching transistor type in the range of 500/500 to 2500/2500 ohms. No connections from the SCR or its components are connected to ground. For safety's sake, keep the 117-V line voltage from the amplifier connections-that is the reason for using T1. To adjust, set potentiometer Rl "off" and adjust the amplifier volume control for a normal listening level. Then adjust the potentiometer until the lamp starts to throb in step with the beat. (William Sheets)


MELODY SOUND TO LIGHT CIRCUIT
MELODY SOUND TO LIGHT CIRCUITFG231

A method of synchronizing a simple light show to a musical chip is given the circuit diagram shown. Here a display of eight rows of four LEDs advances with each musical note. IC2 is a UM66 3-pin melody chip selected to generate the desired tune. When power is applied to IC2, the sequence plays one and then stops. Power must be re- applied to initiate a further rendition. IC1 is a 555 astable which will constantly re-enable the tune chip and repeat the melody. However, the maximum supply voltage of the UM66 range is 3.3V, hence a simple Zener diode supply is used based around two 500mW 2V7 types (Dl, D2). TRl is a directly driven transistor amplifier and the melody is played through loudspeaker LS1. Each musical note when present also biases transistor TR2 on, which shunts capacitor C2 to ground. In the absence of a note C2 charges which causes the op amp IC3 to change state at a point determined by preset potentiometer VR1. The output from IC3, pin 6, provides a clock pulse for IC4, a 4022 divide-by-eight counter. Each of its outputs drives a buffer transistor sequentially to illuminate a series of four LEDs. The light display then advances with each note. (Everyday with Practical Electronics, November 1995, p. 878)


SOUND-OPERATED SWITCH
SOUND-OPERATED SWITCHFD82-2

 This sound-operated switch will sense the ring of the phone and translate this to a lamp that will go on and off. The amplified signal across R2 reaches Dl through capacitor C2. The rectified audio signals provide a negative bias for Q2, a pnp transistor. This causes Q2 to conduct so the current that triggers SCR1 is provided at the gate. Potentiometer R4 sets the sensitivity. R3 and C3 delay the operating voltage for Ql so that the circuit will not be triggered on by the sound of the on/off switch, Sl or by the current surge.

Set the lamp atop a TV receiver, turn it on and set the potentiometer so that a finger snap at two feet will trigger the lamp on. Place the speaker close to the telephone and give it a try.

(Hands-On Electronics, 11/86,p. 32))


VOICE ACTIVATED TAPE RECORDER SWITCH
VOICE ACTIVATED TAPE RECORDER SWITCHFG232

A schematic of the Tape-Recorder Switch is shown. The circuit can be powered by Bl, which is four AA batteries in series, or by any 6-volt DC supply. Audio signals from the electret microphone, MIC1, are coupled via capacitor Cl to two audio-amplification stages centered around transistors Q1 and Q2. A 5000-ohm potentiometer, R12, provides a sensitivity control that sets the audio level at which the switch will activate a tape recorder. The audio input to the digital switching section of the circuit is biased at half the supply voltage by two 1 %, 1-megohm, metal-film resistors (R6 and R7). Integrated-circuit Ul is a 74HC14 hex Schmitt trigger inverter. With a 6-volt power supply, the Schmitt inverter gates will have a 1-volt hysteresis gap between 2.2 volts and 3.2 volts. That means that the input to a Schmitt inverter must rise above 3.2 volts for the output to g low, but must fall below 2.2 volts for the output to return to a high. The low on pin 3 of Ul-b in the presence of audio is presented to pin 11 of Ul-e and ends up at pin 8 of Ul-d. That will pull pin 1 low in the absence of an audio signal from the microphone, making pin 2 high. Diode D2 blocks the discharging of C5 through its original charging path, so C5 starts to discharge through R9. After that delay, the voltage at pin 3 rises above 3.2 volts, thus removing the connection from terminal A to ground, and turning off the tape recorder. A continuous audio input to pin 1 will hold pin 4 high, but soon as it ceases, the time-out process begins. When power is applied to the circuit using switch S2, LED1 lights. However, if the ground connection to R11 is removed, and that end of the resistor is then connected to terminal X (pin 6 of Ul-c), the LED will instead light only when the output of the circuit is active. (Popular Electronics, January 1996, pp. 35-36)


SQUARE-WAVE GENERATOR CIRCUITS

1-KHZ SQUARE-WAVE GENERATOR

555 SQUARE WAVE GENERATOR

ADJUSTABLE DUTY CYCLE SQUARE WAVE OSCILLATOR

CMOS SCHMITT TRIGGER SQUARE WAVE OSCILLATOR

SCHMITT TRIGGER R-C OSCILLATOR

SCHMITT TRIGGER SINE-/SQUARE-WAVE GENERATOR

SQUARE-WAVE GENERATOR

VARIABLE DUTY-CYCLE SQUARE-WAVE GENERATOR

VARIABLE-FREQUENCY SQUARE-WAVE GENERATOR


1-KHZ SQUARE-WAVE GENERATOR
1-KHZ SQUARE-WAVE GENERATORFD83-10

When the output is high, R3 and R4 are in parallel, and Cl charges via Rl until the current in R2 equals that at the noninverting terminal. This action occurs when Cl's voltage rises to 2/3 of the supply voltage. At that point, the circuit switches regeneratively. The output switches low and Cl starts to discharge via Rl. Now, R4 is effectively disabled and the current to the noninverting terminal is determined solely by R3, so Cl discharges until the current through R2 falls slightly below that of R3. This happens when the voltage across Cl falls to about 1/3 of the supply Voltage. At that point, the circuit again switches regeneratively, and the output again goes high. This circuit is useful for generating symmetrical square waves with maximum frequencies of only a few kHz. Because of the poor slew-rate characteristics of the LM3900 (0.5 V/μs), the output waveforms have rather slow rise and fall times.(Reprinted with permission from Radio-Electronics, 12/88. p. 76. (C) Copyright Gernsback Publications, Inc.,1988)


555 SQUARE WAVE GENERATOR
555 SQUARE WAVE GENERATORFG237

The 555 can be connected in either monostable or astable configurations, but for continuous square waves, the astable circuit in use. The square-wave signal appears at pin 3 of the 555. The output frequency of the 555 astable multivibrator is found from:

fo = 1.44/((Rl + 2R2)Cl)

The duty cycle of the 555's square-wave output is determined by the relationship between Rl and R2, and is given by:

Duty Cycle = (Rl + R2)/R2

(Electronics Hobbyists Handbook, Fall 1995, p. 99)


ADJUSTABLE DUTY CYCLE SQUARE WAVE OSCILLATOR
ADJUSTABLE DUTY CYCLE SQUARE WAVE OSCILLATORFG236

Use R5 to adjust this variable-duty cycle square wave generator. That potentiometer controls I2 to vary the timing. (Electronics Hobbyists Handbook, Fall 1995, p. 100)


CMOS SCHMITT TRIGGER SQUARE WAVE OSCILLATOR
CMOS SCHMITT TRIGGER SQUARE WAVE OSCILLATORFG234

A CMOS inverting Schmitt-trigger square wave oscillator requires very few components to function. Frequency = 1.4/(R1C1). (Electronics Hobbyists Handbook, Fall 1995, p. 96)


SCHMITT TRIGGER R-C OSCILLATOR
SCHMITT TRIGGER R-C OSCILLATORFG238

Here's another square-wave oscillator that uses a CMOS IC with input hysteresis. In this R/C oscillator circuit, a single gate of a quad 2-input NAND Schmitt trigger IC is the active element. (Popular Electronics, June 1997, p. 64)


SCHMITT TRIGGER SINE-/SQUARE-WAVE GENERATOR
SCHMITT TRIGGER SINE-/SQUARE-WAVE GENERATORFE94-6

A sine wave input can produce a square wave output by this Schmitt trigger circuit based on a 555 IC. (William Sheets)


SQUARE-WAVE GENERATOR
SQUARE-WAVE GENERATORFD83-5

This relaxation oscillator circuit uses diodes to produce charge and discharge paths for C1. The duty cycle is set via R2 and the frequency via R4. C1 can be varied to vary the frequency range, which, for this circuit is approximately 300 to 3000 Hz. (Reprinted with permission from Radio-Electronics, 7/89. p. 53. (C) Copyright Gernsback Publications, Inc.,1989)


VARIABLE DUTY-CYCLE SQUARE-WAVE GENERATOR
VARIABLE DUTY-CYCLE SQUARE-WAVE GENERATORFD83-4

C1 alternately charges via R1/D1 and the upper half of R5, and discharges via R1/D2 and the lower half of R5. The duty cycle can be varied over the range from 1:10 to 10:1 via R5. (Reprinted with permission from Radio-Electronics, 12/88, p.76. (C) Copyright Gernsback Publications, Inc.,1988)


VARIABLE-FREQUENCY SQUARE-WAVE GENERATOR
VARIABLE-FREQUENCY SQUARE-WAVE GENERATORFE94-5

This simple square wave generator produces a variable output of 2800 Hz to 80 kHz with the values shown. Frequency is adjust with potentiometer R1. (William Sheets)


STAIRCASE GENERATOR CIRCUITS

FREE-RUNNING STAIRCASE WAVE GENERATOR

STEPPED TIRIANGLE WAVEFORM GENERATOR

UA2240 STAIRCASE GENERATOR

UP/DOWN STAIRCASE WAVE GENERATOR

VIDEO STAIRCASE GENERATOR


FREE-RUNNING STAIRCASE WAVE GENERATOR
FREE-RUNNING STAIRCASE WAVE GENERATORFF86-3

This free-running staircase generator uses all four of the amplifiers-which are available in one LM3900 package. Amp 1 provides the input pulses that "pump up" the staircase via resistor R1. Amp2 does the integrate and hold function  and also supplies the output staircase waveform. Amps 3 and 4 provide both a compare and a one-shot multivibrator function. Resistor R4 is used to sample the staircase output voltage and to compare it with the power supply voltage (V+) via R3. When the output exceeds approximately 80% of V+ the connection of Amps 3 and 4 causes a 100-μs reset pulse to be generated. This is coupled to the integrator (AMP2) via R2 and causes the staircase output voltage to fall to approximately 0 V. The next pulse out of Amp 1 then starts a new stepping cycle. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 235)


STEPPED TIRIANGLE WAVEFORM GENERATOR
STEPPED TRIANGLE WAVEFORM GENERATORFF86-1

Two gates of a 4011 quad two-input NAND gate (Ul) are connected in a pulse generator circuit. The square output at pin 4 of Ul-b, connects to the clock input, pin 14, of a 4017 decade counter IC (U2). For each input clock pulse, the 4017 takes a single step. Because the 4017 counter is set up to count ten and then repeat the count, the stepped output frequency will only be 1/10 of the clock frequency. For a 100-Hz output, the clock generator must operate at 1 kHz. The 4017's positive output pulses begin at pin 3 and progress to pin 11 in a serial manner. The first output pulse, at pin 3, passes through D1 and R8 and appears across R4 to produce the first step up the triangle. The second pulse is routed through D2 and R7 to produce the second step. The out puts at pins 10 and 1 form the top of the waveform and outputs at pins 5, 6, 9, and 11 produce the down steps. (Reprinted with permission from Popular Electronics, 11/94, pp. 76 and 91. (C) Copyright Gernsback Publications, Inc.,1994)


UA2240 STAIRCASE GENERATOR
UA2240 STAIRCASE GENERATORFC97-1

The uA2240 timer/counter, combined with a precision resistor ladder network and an op amp, form the staircase generator. In the astable mode, once a trigger pulse is applied, the uA2240 operates continuously until it receives a reset pulse. The trigger input at pin 11 is tied to the time base output at pin 14, resulting in automatic starting and continuous operation. The frequency of the time-base oscillator, TBO, is set by the time constants RI and Cl (f = 1/R1 C1).For this example, a 10-KΩ resistor and a 0.01-μF capacitor form the timing network.

The counter outputs are connected to a precision resistor ladder network with binary-weighted resistors. The current sink through the resistors connected to the counter outputs correspond to the count number. For example, the current sink at Q7, the most significant bit, is 128 times the current sink at Q0, the least significant bit. As the count is generated by the uA2240 eight-bit counter, the current sink through each active binary-weighted resistor decreases the positive output of the op amp in discrete steps. The feedback potentiometer is set at a nominal 10 KΩ to supply a maximum output voltage range. An input of 12 V allows a 10-V output swing. With a 0.5-V input reference on pin 3 of the TCL271, the output will change from 10.46 V maximum, in 256 steps of 38.9 mV per step, to a 0.5 V minimum. Each step has a pulse duration of 100 μs and an amplitude decrease of 38.9 mV. The waveform output is repeated until a reset is applied to the uA2240.

(Texas Instruments, Linear and Interface Circuits Applications, 1985, Vol. 1, p. 7-28)


UP/DOWN STAIRCASE WAVE GENERATOR
UP/DOWN STAIRCASE WAVE GENERATORFF86-4

This staircase waveform first steps up and then steps down by the circuit shown. An input pulse generator provides the pulses that cause the output to step up or down, depending on the conduction of the clamp transistor, Ql. When this is ON, the "down" current pulse is diverted to ground and the staircase then steps "up." When the upper voltage trip point of Amp 2 is reached, Ql goes OFF and as a result of the smaller "down" input resistor (one-half the value of the "up" resistor, Rl), the staircase steps "down" to the low-voltage trip point of Amp 2. The output voltage, therefore, steps up and down between the trip voltages of the Schmitt trigger. (Reprinted with permission of National Semiconductor Corporation, National Semiconductor Linear Applications Handbook, 1991, p. 23)


VIDEO STAIRCASE GENERATOR
VIDEO STAIRCASE GENERATORFF86-2

Using a 74HC161 counter and a simple D-A converter using an op amp and resistor network, a very simple video staircase generator for gray scale generation (12 bars) can be obtained. The output is clean and mostly free of glitches. (William Sheets)


STROBE CIRCUITS

FREEZE FRAME STROBE

SAFETY FLARE

SOLID STATE STROBOSCOPE


FREEZE FRAME STROBE
FREEZE FRAME STROBEFG241

A sensor input from a mike or photodetector is amplified and used to trigger an SCR which in turn triggers a camera strobe. This circuit is useful for freeze frame photos of phenomena such as drops of water , explosions, shots, etc. (1994 Electronic Experimenters Handbook, p. 68)


SAFETY FLARE
SAFETY FLAREFB95-2

 When S1 is on, power is applied to an oscillator composed of Ql, Rl, Cl, L1, and L2. Coil L1 is the primary winding of Tl, and L2 is the feedback winding.  When Ql turns on, its collector current saturates Tl's ferrite core. That, in turn, removes the base drive to Ql through L2. Transistor Ql then turns off. As the field around L1 and L2 decays, Ql will eventually turn on again, and the cycle repeats over, and over. Transformer Tl is a step-up, ferrite-core, potted-type unit whose secondary-winding (L3) output is rectified by D2 and filtered by C2. That capacitor charges up to around 250 to 300 volts, which is applied to the resistor divider composed of R3 and R4, along with the flash tube FX1. Capacitors C3 and C4 will charge up to around 200 and 100 volts, through R3 and R4, respectively. Flash rate is adjustable via R4. When the charge on C4 gets to around 100 volts, neon lamp NE1 fires discharging C4 into the gate circuit of silicon control rectifier SCR1. The SCR1 turns on discharging C3 into the primary winding of trigger-pulse transformer T2. Transformer T2 is another step-up, pulse-type unit providing an output of around 4 kW across transformer T2's secondary winding. The xenon gas inside FXl is ionized and a bright flash is emitted. Finally, C3 quickly discharges through L4, and the cycle repeats over, and over. (Hands-On Electronics, Fall 1984, p. 65)


SOLID STATE STROBOSCOPE
SOLID STATE STROBOSCOPEFG242

The schematic diagram for the stroboscope is shown, When switch S2 is closed, a 9-volt battery, Bl is connected to IC3, a 78L05 voltage regulator, which provides a 5-volt source to the circuit. Capacitors C8 and C9 filter the supply. A CD4046 phase-locked loop, IC1, provides a low-frequency square-wave to the circuit. Potentiometer R4 - a 5000 ohm, 10-turn, precision potentiometer with a built-in turns counter - provides a way to adjust and get a direct readout of the FPM rate from 0 to 1000. Switch S1 lets you select the multiplier affecting that rate. Setting Sl to xl therefore gives you a 0- to 1000-FPM range, while setting S1 to x10 results in a 0- to 10,000-FPM range. The values of the multiplier settings are determined by capacitors Cl and C2. A 555-timer, IC2, configured in a monostable mode, provides a pulse with a width that is adjustable via R8. That audio-taper potentiometer allows the duration or pulse width to be varied from 10 microseconds at the minimum setting to 1000 microseconds at the maximum setting. An MPSA14 Darlington transistor, Ql, is configured as a capacitive discharge-type current sink, which provides an approximately 90-milliampere pulse (for the pulse duration set by R8) through LED1, the flash output. The super-bright LED specified for LED1 has a maximum rating of 100 milliamperes. (Popular Electronics, September 1996, pp. 51-52, 56)


SWITCHING CIRCUITS

AC POWER CONTROLLER FOR VCR

ANALOG SWITCH

AUTO-OFF POWER SWITCH

BASIC PIN DIODE RF SWITCH

ELECTRONIC SAFETY SWITCH

HIGH TOGGLE RATE HIGH FREQUENCY ANALOG SWITCH

LOAD-DISCONNECT SWITCH

TRANSCEIVER T/R SWITCH


AC POWER CONTROLLER FOR VCR
AC POWER CONTROLLER FOR VCRFG243

This circuit can be used to switch on a manual control TV when a VCR signal is present. When the tape starts, video is present at J1 from the VCR video output jack. This is detected and the DC produced in the detector (D1) circuit turns on Q1, cutting off Q2, allowing relay driver Q3 to actuate the relay K1. (Popular Electronics, May 1996, p. 74)


ANALOG SWITCH
ANALOG SWITCHFF88-8

This design takes advantage of the strobed output stage of a CA3140 amplifier. With the strobing capability, the circuit's output voltage can be set to either of the input voltages by grounding one of the control inputs, either A or B.

When the strobe input at pin 8 is taken below 1 V, that amplifier is disabled. The remaining amplifier then acts as a unity-gain high-impedance buffer.

The 10-kΩ output resistor enables the output voltage to swing down to 20 mV from ground. The Zener-diode clamps and associated resistors connected at the strobe inputs can be omitted for the lowest-cost applications. However, experience has shown that they allow the amplifiers to shrug off the effect of high transient voltages.

The circuit is particularly suited to 8-bit microcontroller applications, where the strobe inputs can be driven directly from two open-collector output ports under software control.

The use of Schottky diodes for D1 and D2 makes possible an output swing of 2.5 V when the circuit is powered from a 5-V supply.

(Reprinted with permission from Electronic Design 1/94, p 118, Copyright 1994 Penton Publishing)


AUTO-OFF SWITCH
AUTO-OFF POWER SWITCHFF88-16

This timed switch circuit can be used where a timed power source is needed. The on-time is approximately 4.6 RC. (Maxim, Vol. III, New Releases Data Book, 1994. p. 3-125)


BASIC PIN DIODE RF SWITCH
BASIC PIN DIODE RF SWITCHFG244

D1 is a pin diode (MV3404) used as a switch with DC bias supplied via R1. L1 and L2 are RF chokes. An alternate approach eliminating RF chokes is also shown. (Popular Electronics, December 1994, p. 41)


ELECTRONIC SAFETY SWITCH
ELECTRONIC SAFETY SWITCHFE97-5

S1 and S2 must be depressed within 200 ms of each other to activate K1. The hold time is adjustable via R7. S1 and S2 overlap time can be changed by changing C1 and C2 or R1 and R2. (Reprinted with permission from Popular Electronics, 9/93, p. 70. (C) Copyright Gernsback Publications, Inc.,1993)


HIGH TOGGLE RATE HIGH FREQUENCY ANALOG SWITCH
HIGH TOGGLE RATE HIGH FREQUENCY ANALOG SWITCHFA84-2

Commutator circuit provides low impedance gate drive to the PN4091 analog switch for both on and off drive conditions. This circuit also approaches the ideal gate drive conditions for high frequency signal handling by providing a low ac impedance for off drive and high ac impedance for on drive to the PN4091. (Reprinted with permission from National Semiconductor Corporation, Transistor Databook 1982, p. 11-33)


LOAD-DISCONNECT SWITCH
LOAD-DISCONNECT SWITCHFE97-8

Deep discharge can damage a rechargeable battery. By disconnecting the battery from its load, this circuit halts battery discharge at a predetermined level of declining terminal voltage. Transistor Q1 acts as the switch. The overall circuit draws about 500 μA when the switch is closed and about 8 μA when the switch is open. (Reprinted with permission from Maxim Engineering Journal, Vol. 4, p. 10)


TRANSCEIVER T/R SWITCH
TRANSCEIVER T/R SWITCHFF88-14

This transceiver's transmit/receive switch uses PIN-diode instead of a relay. On receive, D1 is cutoff, D2 is cut off and the antenna connects to the receiver. During transmit, D1 is forward-biased, as is D2. This connects the receiver input. This causes the input impedance of the transmission line to be high, so little transmitter power reaches the receiver. Although not shown in the schematic, the 12-V supply should have a series resistor of 100 Ω to 2.2 kΩ, depending on diode current, to limit diode current to a safe value. (Reprinted with permission from Popular Electronics, 12/94, p.41. (C) Copyright Gernsback Publications, Inc.,1994)


TAPE RECORDER CIRCUITS

EXTENDED-PLAY CIRCUIT

SOUND-ACTIVATED TAPE SWITCH


EXTENDED-PLAY CIRCUIT
EXTENDED-PLAY CIRCUITFC101-1

A single op amp-one of four contained in the popular LM324-is operating in a variable pulse width, free-running squarewave oscillator circuit, with its timed output driving two transistors that control the on/off cycle of the tape-drive motor.

The oscillator's positive feedback path holds the secret to the successful operation of the variable on/off timing signal. The two diodes and pulse width potentiometer R8 allows the setting of the on and off time, without affecting the oscillator's operating frequency. One diode allows only the discharge current to flow through it and the section of R8 that it's connected to. The other diode, and its portion of R8, sets the charge time for the timing capacitor, C3. Since the recorder's speed is controlled by the precise off/on timing of the oscillator, a simple voltage-regulator circuit (Ql, R3, and D4) is included. Connecting the speed control to most cassette recorders is a simple matter of digging into the recorder and disconnecting either of the motor's power leads, the ground or common side might be best, and connecting the recorder through a length of small, shielded cable to the control circuit. In some recorders, a remote input jack is furnished to remotely turn on and off the recorder. Before going in and modifying a recorder with a remote jack, try connecting the circuit to the external remote input.

(Hands-On Electronics, 11/87, p. 84)


SOUND-ACTIVATED TAPE SWITCH
SOUND-ACTIVATED TAPE SWITCHFC101-3

This circuit can cause a cassette recorder to automatically turn on and record when a sound or noise is present. Another use, is when the sound-activated switch is used to turn on a cassette player so that it operates as a burglar-alarm detector and sounder. Op amps Ula and Ulb are connected in tandem to amplify the sounds picked up by the detector's mike. The amplified audio voltage, output at pin 7 of Ulb, is fed to a voltage-doubler circuit, consisting of D1 and D2. The elevated voltage from the doubler circuit is input to the positive input of op amp Ulc, which is operating as a simple comparator circuit. The other input of Ulc is connected to a voltage divider that sets the switching point for the dc signal voltage, to turn on when the signal level is greater than about 1.5 V. As the comparator switches on, its output at pin 8 becomes positive and supplies a forward bias to turn on D3 and Q1, which in turn, starts the recorder. The RC combination of C4/R9 sets the cassette's run time after the input sound has ceased, preventing the recorder from chopping-up or turning-off between closely, spaced sounds or words picked up by the mike. The delay time is roughly 6 to 8 seconds. R11 sets the circuit's gain. Connect a low-impedance cassette mike to the amplifier's input, and connect the output of Ql to the cassette's remote input or to the internal input and set the recorder to the record position. Talk and adjust the amplifier's gain with R11 for the desired sensitivity.

(Popular Electronics/Hands-On Electronics, 5/89, p.87)


TELEPHONE RELATED CIRCUITS

AUTOMATIC TELEPHONE-CALL RECORDING CIRCUIT

FM TELEPHONE TRANSMITTER

LINE-ACTIVATED SOLID-STATE SWITCH

SIMPLE PHONE IN-USE INDICATOR

TELEPHONE BELL INDICATOR CIRCUIT

TELEPHONE CALL RESTRICTOR

TELEPHONE HOLD CIRCUIT

TELEPHONE LINE TESTER

TELEPHONE MESSAGE TAKER

TELEPHONE RING SIGNAL DETECTOR

TELEPHONE SCRAMBLER

TELEPHONE-CONTROLLED TAPE STARTER (TCTS)


AUTOMATIC TELEPHONE-CALL RECORDING CIRCUIT
AUTOMATIC TELEPHONE-CALL RECORDING CIRCUITFE100-2

The dc voltage present on a telephone line is usually around 45 to 50 V on-hook and 6 V off-hook. This circuit uses this drop in voltage to activate a relay. The relay controls a cassette tape recorder. Audio is taken off through a network to the microphone input of the cassette. (Reprinted with permission from Radio-Electronics, 10/89, p. 8)


FM TELEPHONE TRANSMITTER
FM TELEPHONE TRANSMITTERFG245

The circuit connects in series with either the Tip or Ring (green or red) telephone line. Power for the circuit is full-wave bridge rectified from the phone line by diodes Dl through D4. Transistor Ql, capacitors Cl and C8, and inductor L3 form an FM oscillator that operates at a frequency of around 93 Mhz. Variable-capacitor C8 allows the oscillator frequency to be adjusted between 90 and 95 Mhz. To move the tuning area up to the 98- to 105-Mhz range, Cl must be replaced with a 10-pF capacitor. Audio from the phone line is coupled through R3 and C2 to the base of Ql where it frequency modulates the oscillator. Transistor Q3, inductor Ll, and capacitor C6 form a power amplifier. The signal tapped off L3 in the oscillator circuit is fed to the base of transistor Q2 and the FM signal is transmitted from Q2's collector. Inductor L2 is a radio-frequency shunt that decouples power and audio from the amplifier circuit. (Popular Electronics, January 1996, p. 37)


LINE-ACTIVATED SOLID-STATE SWITCH
LINE-ACTIVATED SOLID-STATE SWITCHFC102-22

Each and every time a phone on the same line or calling number is taken off-hook, the circuit will be activated to control an external electronic circuit. If several extension telephones are used on one phone line, the circuit can be useful as a busy indicator. LED1 contains a special flashing red LED that makes an excellent indicator for a busy circuit condition.

The solid-state switch can be used for several other phone-activated applications, such as automatically turning on a cassette recorder, starting a phone-use timer or counter, etc. A small relay can be connected at points A and B, in place of LED1, to control external circuits. A 117-Vac-to-6-Vdc plug-in power supply can be substituted for the battery to keep the operating cost at a minimum.

The 48-Vdc, on-hook, phone-line voltage keeps Ql in the cut-off condition, allowing no current to flow through resistor R4, hence Q2 remains off. Resistors R1 and R2 keep the solid-state switch circuit from causing any problems with the telephone's central-office equipment. When a phone is taken off-hook, the line voltage (tip to ring) drops to 10 V or less, which forces Q1 to turn on; this, in turn, causes Q2 to trigger LED1, or a relay which might be used in lieu of LED1.

(Hands-On Electronics, 9-10/86, P. 88)


SIMPLE PHONE IN-USE INDICATOR
SIMPLE PHONE IN-USE INDICATORFG246

The LM741 op-amp is used as a voltage comparator, comparing the telephone line voltage to the battery voltage. The telephone line drops below 9 volts when it is in use. That drop turns the op-amp on, which lights the LED. Resistor R1 prevents the circuit from loading the telephone line excessively. n my location the in-use circuit drops the line voltage approximately 5 volts. That leaves quite a bit of reserve because a telephone line operates at approximately 40-48 volts, Resistor R2 limits the current to the LED. A 1000-ohm resistor will brighten the Led. However, the total circuit current draw will increase. The circuit as shown consumes 1.15 mA in standby, and 3.80 mA when indicating a line use. (Popular Electronics, November, 1996, p. 65)


TELEPHONE BELL INDICATOR CIRCUIT
TELEPHONE BELL INDICATOR CIRCUITFG248

This circuit uses a 555 timer to gate a SCR. The SCR passes 12V to an alarm bell. The bell should be of the mechanical type so it will reset and only ring when ring signals are on the telephone. (Popular Electronics, November, 1996, p. 66)


TELEPHONE CALL RESTRICTOR
TELEPHONE CALL RESTRICTORFF90-3

This circuit is designed to restrict phone calls with the area codes: 900, 976, and 540. This device uses a microcontroller to compare the DTMF decoded tones with telephone numbers stored in EEPROM (IC3). This device requires a programmed microcontroller. Software and details of programming can be found in the original magazine article (Reprinted with permission from Electronics Now, 10/94. (C) Copyright Gernsback Publications, Inc.,1994)


TELEPHONE HOLD CIRCUIT
TELEPHONE HOLD CIRCUITFF90-14

When the hold button S1 is pressed, SCR1 fires via R1 and R2, firing SCR1, and seizing the line via the path through R3, D1, and SCR1. (William Sheets)


TELEPHONE LINE TESTER
TELEPHONE LINE TESTERFF90-1

The telephone-line tester shown in the figure is connected to the telephone line through modular connector P1. Because the tester's LED polarity indicator is always connected when the tester is plugged in, the instant that the unit is connected, you will have an indication of the polarity. If it is correct-that is, if the green wire is the positive side and the red wire is the negative side-nothing will happen. If the situation is reversed, the LED will light

With switch S1 set for LINE/RING, both S1-a and S1-b, are open and the meter indicates the condition of the line voltage. Any line-voltage reading in the LINE OK range (more on the meter in a moment) indicates a line voltage that, is higher than 40 Vdc. If the telephone is caused to ring, either by using a ringback number or by dialing from another phone, the meter will indicate RING OK, and the LED will pulse (indicating ac), if the ringing voltage/current is correct. The actual position of  the meter's pointer depends on how many ringers are connected across the line.

When S1 is closed the voltage range of the meter is changed and a nominal load resistance of 230 Ω (R5 and R6) is connected across the line to emulate the off-hook load of the telephone. If the meter indicates LOOP OK, you can be certain that you have sufficient loop voltage for satisfactory telephone operation. If you place another load on the line, perhaps by taking an extension telephone off hook, the meter reading will almost invariably drop below the LOOP OK range. If lifting the hand set causes the meter reading to drop you can at least be certain that the telephone's hook switch is working and that the repeat coil is connected to the line.

(Reprinted with permission from 1987 Radio-Electronics Experimenters Handbook, p. 51. (C) Copyright Gernsback Publications, Inc.,1994)


TELEPHONE MESSAGE TAKER
TELEPHONE MESSAGE TAKERFD86-22

This circuit operates on the ringing voltage of the telephone to trigger a tape recorder to record messages. K1 can be made to latch using extra contacts, if the tape recorder requires a constant closure. (Reprinted with permission from Popular Electronics, 2/91, p.25-26. (C) Copyright Gernsback Publications, Inc.,1991)


TELEPHONE RING SIGNAL DETECTOR
TELEPHONE RING SIGNAL DETECTORFF90-13

 Discriminating between telephone-ring signals on a phone line can be accomplished by using dedicated ICs, such as AT&T's LB1006AB or Texas Instruments' TMS1520A. However, if the system already is using a microcontroller, those dedicated chips can be replaced with simpler hardware and a few bytes of code.

Looking at the setup, the ringing voltage pulses the optoisolator's LED, which, in turn, pulses the low-asserted RD line to the microcontroller. The firmware analyzes the pulses to determine whether a valid ringing signal is present.

The frequency limits of a valid signal are 20 to 80 Hz, which is modulated 2 seconds on and 4 seconds off (with distinctive ringing, though, this cadence can vary). Therefore, the simplest analysis is to count down at least 20 pulses of  RD in 1 second.

The routine could be expanded to determine what type of ring signal is present in a distinctive ring setting. Such a system could switch the phone line to various output jacks. As a result, several phone devices could use the same line, without first picking up the line to determine if it's a voice, fax, or data call.

(Reprinted with permission from Electronic Design 8/94, p 116, Copyright 1994 Penton Publishing)


TELEPHONE SCRAMBLER
TELEPHONE SCRAMBLERFF90-4

This circuit uses the usual speech inversion algorithm, implementing it with a COM9046 ASIC. This unit is designed to fit between the handset and base of a standard telephone. It is powered by a 9-V battery. (Electronics Experimenters Handbook,1994, p.123)


TELEPHONE-CONTROLLED TAPE STARTER (TCTS)
TELEPHONE-CONTROLLED TAPE STARTER (TCTS)FA85-13

 This circuit converts a tape recorder into a completely automatic telephone conversation recording instrument that needs no external power source. Voltage at the switch terminals of tape recorder applied to a pair of Darlington-connected transistors, Ql and Q2, will turn on and start the tape recorder. To turn the transistors off, and thereby stop the machine, apply a negative voltage to the base of Q1 from the phone line. When the telephone receiver is on the hook, there is typically about 50 volts dc across the phone divided across R1, R2, and R4 in such a way that the base of Ql is sufficiently negative to keep the tape recorder off. When the phone's receiver is picked up, the voltage on the telephone line drops to about 5 volts, which leaves insufficient negative voltage on the base of Ql to keep it cut off, so the tape recorder starts and begins to record. (The Build It Book Of Electronic Projects, TAB Book No. 1498. p3)


TEMPERATURE CONTROLLER CIRCUITS

TEMPERATURE CONTROLLED FAN

TEMPERATURE CONTROLLER


TEMPERATURE CONTROLLED FAN
TEMPERATURE CONTROLLED FANFG249

The circuit described here needs only three ICs to smoothly increase fan speed as temperature rises above an easily set trip point. Low-dropout voltage regulator IC1 provides power to the fan and to temperature sensor IC2 (see the figure). IC2 drives the middle of the resistor divider across voltage reference IC3. Because the LM45's output stage can only source current, its output voltage will remain at about 610 mV until IC2's temperature rises above 61°C, IC2 will drive the 500-Ω Thevenin resistance of the divider, which will cause IC2's supply current to increase rapidly with rising temperature. As temperature rises above the point where IC2's output voltage exceeds the Thevenin voltage set by R4 and R5, IC2's supply current increases. IC2's supply current flows through R1 and directly affects the regulator's output voltage. If  temperature rises 200°C above the nominal 61°C threshold, the regulator's output voltage will rise to 12V and the fan will operate at full speed. (Electronic Design, August 19, 1996, pp. 114 - 116)


TEMPERATURE CONTROLLER
TEMPERATURE CONTROLLERFF91-27

 A proportional temperature controller can be made with an LM34 and a few additional parts. The complete circuit is shown. Here, an LM10 serves as both a temperature-setting device and as a driver for the heating unit (an LM395 power transistor). The optional lamp driven by an LP395 transistor, is for indicating whether or not power is being applied to the heater. (Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 1079)


TEMPERATURE SENSOR CIRCUITS

FREEZE-UP SENSOR

ISOLATED TEMPERATURE SENSOR

TEMPERATURE DIFFERENTIAL DETECTOR

TEMPERATURE MONITOR


FREEZE-UP SENSOR
FREEZE-UP SENSORFF91-29

Using a bridge circuit to provide an accurate activation temperature, this circuit will turn on a heating unit or other device when the temperature drops below the trip point set by R2. Use a 10-kΩ resistor in place of the thermistor to calibrate it for 32°F activation. (Reprinted with permission from Popular Electronics, 1/95, p.29. (C) Copyright Gernsback Publications, Inc.,1995)


ISOLATED TEMPERATURE SENSOR
ISOLATED TEMPERATURE SENSORFC104-3

(Linear Technology Corp. Linear Databook, 1986, p. 8-43)


TEMPERATURE DIFFERENTIAL DETECTOR
TEMPERATURE DIFFERENTIAL DETECTORFF91-25

This circuit measures temperature differences, not temperature. Once the difference passes a certain threshold, the timer is triggered, activating the solid-state relay.

Op amp Ul is placed in a comparator configuration, with two thermistors-one located at the ceiling, one at the floor. The IC senses the temperature difference between the ceiling and floor, but is unaffected by the overall room temperature differential increases. The upper thermistor will decrease in resistance, eventually causing the voltage at pin 2 of Ul to exceed that of pin 2 of Ul to go low and trip the timer. This adds hysteresis to the op amp's output, preventing the motor from chattering. When tripped, the timer activates the relay, which activates the fan.

(Reprinted with permission from Popular Electronics, 1/95, p.28. (C) Copyright Gernsback Publications, Inc.,1995)


TEMPERATURE MONITOR
TEMPERATURE MONITORFG250

The temperature sensor is a resistor, R4, with negative temperature coefficient--NTC, the resistance of such a resistor drops when its temperature rises. Resistors R4 and R3 are part of a resistance bridge whose variable branch consists of R1, R2 and P1. The metering diagonal is connected to the inputs of comparator IC1a. The voltage at the inverting input of IC1a is set with P1 to a level that with normal temperatures is a little lower than that at the non-inverting input. When the temperature rises, the resistance of R4 falls. This results in the comparator changing state (to low), which causes the piezo buzzer to sound. Care should be taken to ensure that the voltage across the metering diagonal does not drop below 3.5V to prevent the common-mode dynamic range of the LM393 being exceeded. The NTC may be a 5 kΩ or a 10kΩ  type. It must be in good thermal contact with the heat source. Preset P1 must be set o a position where, after the part or device being monitored has attained normal operating temperature, the buzzer just does not sound. The buzzer must be a 5V type. (Elektor Electronics, July-August 1996, p. 84)


TESLA COIL CIRCUITS

SOLID STATE TESLA COIL

TESLA COIL


SOLID STATE TESLA COIL
SOLID STATE TESLA COILFG252

A TV flyback transformer can double as Tesla coil. The Tesla circuit consists of a pulse generator, a driver circuit, and a high-voltage transformer. Resistors Rl and R2 determine the time duration that the output at pin 3 is off, while R3 and R4 along with Rl and R2 determine the on time. Inductor Ll and regulator IC2 provide a clean, stable power source for the timer. Transistor Ql acts as a buffer. Resistor R6 determines the rise time based on the time constant developed by R6 and the inherent gate capacitance of Q3. Resistor R8 limits current so that excessive current will not damage Tl's primary winding. Capacitor C15 absorbs some of the back EMF generated in Tl's primary. The pulse waveform from ICl is applied to Ql, which provides the high current necessary to offset the high capacitance of Q3. Capacitor C5 partially absorbs the primary EMF, reducing the stress on Q3. The spike produced in the secondary creates a ringing oscillation. When this oscillation begins to decay, Q3 is once again switched into its on state. This dumps the energy in C5, and builds the magnetic field in Tl. If the timing of both the on and off states of the pulse train are adjusted correctly, the secondary of Tl produces a nearly constant, high-frequency, high-voltage current. (Electronics Now, November 1994, p. 61)


TESLA COIL
TESLA COILFG251

The traditional Telsa coil is connected as shown. The primary capacitor a HV AC type, typically 500 pf to 5000pf, and the inductance of the primary winding should resonate around the resonant frequency of the secondary coil. (Electronics Now, November 1994, p. 61)


THERMOMETER CIRCUITS

BASIC DIGITAL THERMOMETER, KELVIN SCALE WITH ZERO ADJUST

CENTIGRADE THERMOMETER (0 DEGREE C-100 DEGREE C)

CENTIGRADE THERMOMETER WITH COLD-JUNCTION COMPENSATION

HIGH-ACCURACY THERMOMETER

IMPLANTABLE INGESTIBLE ELECTRONIC THERMOMETER

LM3911 TEMPERATURE CONTROLLER

SIMPLE LED THERMOMETER

SINGLE-DC SUPPLY THERMOMETER

TEMPERATURE ADAPTER FOR DVM


BASIC DIGITAL THERMOMETER, KELVIN SCALE WITH ZERO ADJUST
BASIC DIGITAL THERMOMETER, KELVIN SCALE WITH ZERO ADJUSTFB103-5

This circuit allows zero adjustment as well as slope adjustment. The ICL8069 brings the input within the common mode range, while the 5 k ohm pots trim any offset at 218°K (-55°C), and set the scale factor. (Intersil, Component Data Catalog, 1987, p. 6-11)


CENTIGRADE THERMOMETER (0 DEGREE C-100 DEGREE C)
CENTIGRADE THERMOMETER (0 DEGREE C-100 DEGREE C)FB103-6

The ultra low bias current of the ICL7611 allows the use of large-value gain resistors, keeping meter-current error under 1/2 % and therefore saving the expense of an extra meter-driving amplifier. (Intersil, Component Data Catalog, 1987, p. 6-8)


CENTIGRADE THERMOMETER WITH COLD-JUNCTION COMPENSATION
CENTIGRADE THERMOMETER WITH COLD-JUNCTION COMPENSATIONFF91-8

This electronic thermometer has a 10-mV/°C output from 0°C to 1300°C. The trimming procedure is as follows: first short out the LM329B, the LM335 and the thermocouple. Measure the output voltage (equal to the input offset voltage times the voltage gain). Then apply a 50-mV input voltage and adjust the GAIN ADJUST pot until the output voltage is 12.25 V above the previously measured value. Next, short out the thermocouple again and remove the short across the LM335. Adjust the TC ADJUST pot so that the output equals 10 mV/°K times the absolute temperature  Finally, remove the short across the LM329B and adjust the ZERO ADJUST pot so that the output voltage equals 10 mV/°C times the ambient temperature in °C.

(Reprinted with permission from National Semiconductor Corporation, National Semiconductor Linear Applications Handbook 1991, p. 500)


HIGH-ACCURACY THERMOMETER
HIGH-ACCURACY THERMOMETERFD89-5

This circuit combines a current source and a platinum RTD bridge to form a complete high-accuracy thermometer. The ground-referred RTD sits in a bridge that is composed of the current drive and the LT1009 biased resistor string. The current drive allows the voltage across the RTD to vary directly with its temperature-induced resistance shift. The difference between this potential and that of the opposing bridge leg forms the bridge output. The RTD's constant drive forces the voltage across it to vary with its resistance, which has a nearly linear positive temperature coefficient. The nonlinearity could cause several degrees of error over the circuit's 0°C - 400°C operating range.

The bridge's output is fed to instrumentation amplifier A3, which provides differential gain, while simultaneously supplying nonlinearity correction. The correction is implemented by feeding a portion of A3's output back to Al's input via the 10- to 250-kΩ divider. This causes the current supplied to Rp to slightly shift with its operating point, compensating sensor nonlinearity to within ±0.05°C. A1B, providing additional scaled gain, furnishes the circuit output. To calibrate this circuit, follow the procedure given in the diagram.

(Linear Technology, 10/90, Design Note #40)


IMPLANTABLE INGESTIBLE ELECTRONIC THERMOMETER
IMPLANTABLE INGESTIBLE ELECTRONIC THERMOMETERFC107-5

This oscillator circuit includes a quartz crystal that has a nominal resonant frequency of 262,144 Hz and is cut in the orientation that gives a large linear coefficient of frequency variation with the temperature. In this type of circuit, the oscillation frequency is controlled primarily by the crystal-as long as the gain- bandwidth product is at least four times the frequency. In this case, the chosen component values yield a gain-bandwidth product of 1 Mhz. Inductor. Ll can be made very small: 100 to 200 turns with a diameter of 0.18 in. (4.8 mm) and a length of 0.5 in. (12.7 mm). Although the figure shows two transistors in parallel, one could be used to reduce power consumption or three could be used to boost the output. The general oscillator circuit can be used to measure temperatures from - 10 to + 140°C. A unit made for use in the human body from about 30 to 40°'C operates at 262,144 ± 50 Hz with a frequency stability of 0. 1 Hz and a temperature coefficient of 9 Hz/°C.( NASA, NASA Tech Briefs, 10/87, p. 34)


LM3911 TEMPERATURE CONTROLLER
LM3911 TEMPERATURE CONTROLLERFF91-19

The LM3911 requires only a few resistors and a capacitor to turn into a full-function temperature controller. The LM3911 requires very few external components to implement a full-function temperature controller. The figure illustrates the simplicity of the freeze fighter circuit. The resistor network consisting of Rl, R2, and R3 is used to provide the set point voltage for the feedback input of the LM3911.

Resistor R4 limits the current through the internal voltage reference of the LM3911 and can be selected from a wide range of values. 7.5 kΩ is specified in most of the application notes.

Resistor R5 pulls the output of the IC high when the temperature is below the set point. The internal resistor is in series with a diode that allows a switching voltage up to 35 V to be used with the device.

(Reprinted with permission from Popular Electronics, 5/93, p. 43. (C) Copyright Gernsback Publications, Inc.,1993)


SIMPLE LED THERMOMETER
SIMPLE LED THERMOMETERFG253

As shown, the circuit is powered by a 9-volt battery, Bl, but can easily run off any 7- to 10-volt DC power supply. At the heart of the Thermometer is IC1, an LM34 temperature sensor. That device produces a voltage between the Vout and GND terminals that is linearly proportional to temperature, Although the output is usually 10 millivolts per degree Fahrenheit, IC1 is connected in a resistor network (made up of Rl-R3) with a gain that provides an output of 40 mV/°F. Capacitor Cl is used as a noise bypass across Rl and R2. Because the voltage output by IC1 will be used by the rest of the circuit to "determine" what the temperature in the room is, potentiometer Rl will have to be calibrated exactly (but more on that later). The output of IC1 is fed to pin 5 of IC2, an LM3914 LED bar- or dot-graph driver, which is where the actual temperature-determining process occurs. IC2 has ten internal comparators, the output pins of which are connected to LEDl-LED10. The voltage input to pin 5 is compared by IC2 to the voltages at pins 4 and 6; that process determines which LED or LEDs light. The LEDs can be set to light either one at a time (dot mode) or progressively (bar mode). When jumper JUI is not installed, dot mode is enabled, and when the jumper is installed, the chip is in bar mode. In dot mode, the LED that corresponds to the correct input voltage lights by itself. When the input voltage increases, an LED representing a higher temperature will light, and the LED previously lit will extinguish. In bar mode, the LED representing the temperature and all the lower LEDs stay lit. Each mode has its advantages-the dot mode uses less current because only one LED is lit at a time, but the bar mode is easier to read at a glance. Resistor R8 and capacitor C2 provide decoupling for the LED7 supply circuit. If bar-mode operation is desired, it is recommended that you reduce the value of R8 to 15 ohms, In order to display a range of 60°F to 78°F, pin 6 must have a reference of 3.345 volts and pin 4 should have a reference of 2.545 volts. Those values are obtained through adjustments of potentiometers R5 and R7. (Popular Electronics, July, 1996, p.p. 45-46, 74)


SINGLE-DC SUPPLY THERMOMETER
SINGLE-DC SUPPLY THERMOMETERFD89-3

Using a J-type thermocouple, this circuit can indicate temperatures from -350° to 400° with a 6-V supply or -50° to +100° with a 3-V lithium battery. The AD954 produces 10 mV/°C output to the MAX 138 digital voltmeter chip, which drives the LCD display. (Reprinted with permission from Electronic Design 4/90, p 85-88, Copyright 1991 Penton Publishing)


TEMPERATURE ADAPTER FOR DVM
TEMPERATURE ADAPTER FOR DVMFG252A

A schematic for the temperature adapter is shown. The circuit outputs 0.01 volt per degree Fahrenheit. To determine temperature you ignore the decimal point in the display, and the temperature readout is to the tenth of a degree. For example, if the temperature in a room is 75.5 degrees, your DMM would read +0.755 volt. The voltage input for op-amp IC1 is obtained from a transistor Ql used as a diode in this application. The linear voltage drop is measured and used to indicate temperature. LM78L05 (IC2) low-power regulator provides a fixed 5-volt source for the circuit. The voltage drop across Ql is detected and amplified by IC1, an LM1458 op-amp. The output of IC1 is then fed to the input terminals of a DMM. Put the positive lead of a voltmeter on pin 7 of IC1, and the negative lead on ground. Adjust R2 for a reading of 2.5 to 3 volts. Connect the output of the adapter circuit to a voltmeter set to the 2-volt DC scale. Adjust R8 so that the multimeter reads the same as a stabilized thermometer in the same vicinity as the temperature probe (ignore the decimal point). (Popular Electronics, January 1997, pp. 48-50)


TIMER CIRCUITS

DUAL TIMER

LAMP TIMER

LONG-PERIOD TIMER

SCR TIMER

SIMPLE VERY LONG PERIOD TIMER

TIME-OUT CIRCUIT

TIMER USING CD4050

WIDE-RANGE TIMER-1 MINUTE TO 400 HRS


DUAL TIMER
DUAL TIMERFG254

Two are sometimes better than one. This dual timer contains a 556 IC, which contains two 555 timers in one package. (Popular Electronics, September, 1996, pp. 57-58)


LAMP TIMER
LAMP TIMERFF92-2

A timed switch uses a 555 oscillator/timer wired to operate in the astable mode. The timer supplies a positive pulse to the clock input of a 74193 4-bit binary up/down count every five minutes. Because the 74193 is set to operate in the count-down mode, the output of the 555 is connected to the count-down input of the 74193. As the binary counter is reset, it starts counting at nine and counts down to zero with each clock pulse. When the counter hits zero, the output from the 74193 goes low, turning off the relay and the light. The light can be turned back on by pressing the reset button again. (Reprinted with permission from Popular Electronics, 2/94, p.25. (C) Copyright Gernsback Publications, Inc.,1994)


LONG-PERIOD TIMER
LONG-PERIOD TIMERFF92-3

Adding a transistor to the 555 timer can create long timer periods, which is a key factor when the timer is operating at low speed. The transistor basically acts as a current divider or capacitance multiplier. The problem with low speed, however, is that the timing resistors and capacitors must be large and the charging current must be small, particularly when the desired timing period is in the range of seconds. Typically, electrolytic capacitors are used in these situations, but their leakage current tends to aggravate or even prohibit operation at very low charging currents. This problem can be solved by adding a transistor. In effect, the transistor is used as a current divider or a capacitance multiplier. The normal charging current (emitter current) is divided by the transistor's current gain so that the capacitor charging current (base current) is reduced considerably. For example, 10 μA of emitter current will require approximately 0.1 μA of base current, based on a current gain of 100. In this circuit, the capacitor will be charged with such a low charging current that timing periods will typically be 100 times longer than usual. This means that substantial time periods can be achieved with film or ceramic capacitors that have much better leakage characteristics and are physically smaller. The circuit's output period was approximately 6 seconds, compared to 80 ms without the transistor. The transistor multiplied the normal time period by a factor of approximately 75. (Reprinted with permission from Electronic Design 3/95, pp. 114-116, Copyright 1995 Penton Publishing)


SCR TIMER
SCR TIMERFD90-6

Depending on the R1 (adjustable) C1 time constant, when C1 charges up to certain level, Q1 conducts, triggers SCR1, and sounds BZ1. A push-button resets the circuit. (Hands-On Electronics Fact Card No. 49)


SIMPLE VERY LONG PERIOD TIMER
SIMPLE VERY LONG PERIOD TIMERFG256

The circuit is straight forward (see the figure). An RC oscillator consisting of R1, R2, and C1, with the internal gates on the CD4060, generates a 1.5 second clock thats subsequently divided to a 12-hour clock at the output. Other times are available for output or for ANDing with the longer duration signals. The output is capacitively coupled to the two-transistor driver to provide a several second pulse every 12 hours. (Electronic Design, June 26, 1995, p. 108)


TIME-OUT CIRCUIT
TIME-OUT CIRCUITFD90-11

This circuit operates in the astable mode and at the end of the first period (up to several minutes), it produces a tone. When Sl is placed in the time position, Q3 is cut off because pin 3 of Ul is high and Dl holds Q3 in cutoff. Q2 is off, and Ql is on, which grounds the negative end of D2 and C2. Therefore, Cl and C2 are returned to ground.

After a time of about 1.1 R6 (Cl + C2), the timer cycle completes and pin 3 Ul goes low. This turns on Q3 and Q2, cuts off Ql, and effectively disconnects C2. Now, the circuit oscillates with a period determined by R7 and Cl, because D2 is forward-biased. A tone is then generated and can be heard from SPKR1. Closing S2 resets the circuit.

(Reprinted with permission from Popular Electronics, 1/91. Gernsback Publications, Inc., 1991)


TIMER USING CD4050
TIMER USING CD4050FG257

Three stages are used to produce three consecutive time delays. The time delay for each stage is very close to 1.1 RnCn. Diode Dn allows quicker reset of stage n. (Popular Electronics, September, 1996, p. 58)


WIDE-RANGE TIMER-1 MINUTE TO 400 HRS
WIDE-RANGE TIMER-1 MINUTE TO 400 HRSFE102-6

This ultra-wide range timer uses a 555 timer base, two 4017Bs and a 4020B that act as frequency dividers that can be switch in and out. S1 is a SP3T range switch. (William Sheets)


TONE CIRCUITS

REPEATER-TONE BURST GENERATOR

THREE TONE GENERATOR

TWO-TONE ENCODER


REPEATER-TONE BURST GENERATOR
REPEATER-TONE BURST GENERATORFE103-1

Integrated circuit gates IC1-A and IC1-B form a monostable, whose time constant is determined by C2 and R3. When the transmitter is dekeyed (and then almost immediately rekeyed) point TX+ goes low and takes pin 1 low for a short time. This triggers the start of the timing period controlled by C2/R3. The capacitor C2, charges via R3 until the trigger point of gate IC1-B is reached. At this point, the monostable changes state and pin 3 goes low again. On the prototype, this time was about 700 ms. The pulse occurs each time after dekeying and it is normally inaudible. If, however, point TX+ goes high again (as in immediate rekeying) the monostable is still in the enabled state and the oscillations of IC1-C are present in the transmission. During this time period, the buffer gate, IC1-d, is enabled and the tone is therefore passed to the output. (Reprinted with permission from Practical Wireless, 2/91, p. 49)


THREE TONE GENERATOR
THREE TONE GENERATORFG258

The three-tone generator makes a great warning device. It has a lot of uses; for example, if the appropriate switch is used for Sl, the circuit can be used as a burglar alarm. When Sl is pressed, it turns on the circuit. The tone frequencies depend on resistor Rl and capacitors Cl through C3. Switch S2 lets you select between those capacitors. Capacitor Cl produces the highest frequency because it has the lowest capacitance, while C3 generates the lowest frequency. (Popular Electronics, July, 1996, p. 65)


TWO-TONE ENCODER
TWO-TONE ENCODERFE103-2

Using an XR2206 oscillator, this circuit can generate two audio tones. Switching between tones can be done with a logic level to either the base of the PN2222 or pin 9 of the XR2206. (Reprinted with permission from 73 Amateur Radio Today, 7/88, p. 14)


TONE CONTROL CIRCUITS

ACTIVE BASE- AND TREBLE-TONE CONTROL

ACTIVE TONE CONTROL

COMBINED BASS AND TREBLE CONTROL

TREBLE BOOSTER CIRCUIT

TREBLE BOOSTER FOR GUITARS


ACTIVE BASE- AND TREBLE-TONE CONTROL
ACTIVE BASE- AND TREBLE-TONE CONTROLFF93-4

A single transistor used as a feedback amplifier is connected with an ac feedback through the tone controls, which determine the frequency response of the stage. (William Sheets)


ACTIVE TONE CONTROL
ACTIVE TONE CONTROLFD91-2

The use of a low noise LM387 in a feedback circuit provides 20-dB boost or rejection of treble and bass. The supply voltage is +24 V. (Reprinted with permission from Radio-Electronics, 2/90. p. 58. (C) Copyright Gernsback Publications, Inc.,1990)


COMBINED BASS AND TREBLE CONTROL
COMBINED BASS AND TREBLE CONTROLFF93-3

This positive tone control system uses two pots to control bass and treble. (William Sheets)


TREBLE BOOSTER CIRCUIT
TREBLE BOOSTER CIRCUITFG259

The circuit diagram for the Treble Booster is shown. The circuit is basically a non- inverting mode amplifier. Resistors R2 and R3 bias ICl's non-inverting input (pin 3), and R1 plus R4 act as a negative feedback network that set the closed-loop voltage gain of IC1 at unity. However, Rl and R4 are only used to set the operating conditions of ICl at DC and low to middle audio frequencies. The high frequency voltage gain in governed by a more complex negative feedback network which is comprised of resistors R5, R6, potentiometer VRl and capacitors C4, C6. R5, VR1, and R6 form a conventional negative feedback network which enables the voltage gain of the circuit to be varied. With the wiper (w) of VRl towards the top end of its track the circuit provides losses of nearly 20dB. Moving it down to the bottom gives almost 20dB of gain. It is coupled to the inverting input via capacitor C4, which has quite a low value. Consequently, C4 only provides an efficient coupling at high frequencies, At middle and bass frequencies capacitor C4 has a very high impedance, and provides only a loose coupling to IC1's inverting input, Therefore, control VRl is ineffective at these lower frequencies, where the voltage gain of the circuit is largely governed by resistors Rl and R4. This permits the required boost and cut to be obtained at high frequencies, but keeps the gain at about unity at middle and low frequencies. (Everyday with Practical Electronics, October 1995, p. 782)


TREBLE BOOSTER FOR GUITARS
TREBLE BOOSTER FOR GUITARSFG260

The circuit diagram shown was designed to increase the treble content of an electric guitar's output. It boosts frequencies above 1 kHz and helps to restore any higher frequency losses. IC1 is a TL071 op amp connected as a non-inverting amplifier which is connected in line between the guitar and main amplifier. Potentiometer Vrl determines the level of Treble Boost applied and, with the values of components shown, will give between 3dB to 20dB. Resistor R6 and the potentiometer VRl could be replaced by a fixed resistor if required. The actual boost frequency is set by the values of resistor R4 and capacitor C2. With switch Sl open, the circuit acts as a voltage follower with no effect on the guitar signal. Closing Sl grounds C2 to the 0V line, which introduces the boost. Resistor R5 holds the "earthy" end of C2 at 0V when switch Sl is open, and prevents switching noise appearing on the signal when Sl is operated. Resistors R2 and R3 set the input impedance of the circuit at 50 kilohms, which should suit most electric guitars. If the circuit is housed in a die cast case, Sl can be a foot-operated switch and SK1 could be a stereo jack socket with the sleeve and ring connections connected to the battery negative and 0V rail respectively. Thus the unit will switch on automatically whenever the guitar is plugged in. Connect the case to the "earth" side of the circuit. Expect reasonable life from a PP3 battery. (Everyday with Practical Electronics, March 1995, p. 193)


TOUCH-CONTROL CIRCUITS

SIMPLE TOUCH SWITCH

TOUCH SWITCH

TOUCH SWITCH WITH ALTERNATE LIGHT OPERATED TURNOFF

TOUCH SWITCH WITH LIGHT OPERATED TURNOFF


SIMPLE TOUCH SWITCH
SIMPLE TOUCH SWITCH FF94-1

Q2 is held cut off since Q1 normally is conducting. When the touch plate is contacted by a large object (human body, etc) stray 60-Hz pickup is rectified by D1 and D2, and produces a negative voltage across R2-C2 and the gate of Q1, Q1 cuts off, causes Q2 to conduct, and the output goes low. (William Sheets)


TOUCH SWITCH
TOUCH SWITCHFD92-2

This switch reacts to the touch of a finger to turn lights and/or appliances on or off. The device uses the human body as an antenna to pick up 60-Hz hum, which is applied to a metal plate by your finger. The signal is fed to the input of Ul, an LM380 audio-power amplifier. An LM386 should work as well.

The 60-Hz output from the amplifier is rectified by D1 and D2, then filtered by C3. Potentiometer R3 sets the trigger voltage used to saturate Ql. When Ql turns on, the collector end of R4 goes almost to ground and provides the needed voltage to turn on Q2. Transistor Q2 turns on and clocks. The flip-flop is configured for toggle-mode operation, so its output switches states with each clock pulse.

The 4027 (U2) is wired to toggle by tying the J and K inputs high and the set and resets low. Transistor Q3 is connected to the Q output through the 4.7-kΩ resistor. Transistor Q3 drives Q4, the relay driver. Be sure that the load does not exceed the relay ratings. (Reprinted with permission from Popular Electronics, 2/91, p.23-24. (C) Copyright Gernsback Publications, Inc.,1991)


TOUCH SWITCH WITH ALTERNATE LIGHT OPERATED TURNOFF
TOUCH SWITCH WITH ALTERNATE LIGHT OPERATED TURNOFFFG262

When the touch plate is touched, it turns the output of IC1 on, giving a positive potential to the base of Q2. In turn, that turns on pins 4, 5, and 6 of IC2, therefore triggering the SCR's gate and energizing RY1. With RY1 energized, its contacts pull in, turning on the AC bulb. When Rl is hit by strong light, it turns on the SCR and energizes RY1. To turn the AC bulb off, just point a strong flashlight at R2, decreasing the base resistance of Q3, making its base positive, and therefore energizing RY2. When the contact of RY2 pulls in, it disconnects the anode of the SCR from the positive supply, therefore turning it off, or you can press S2 to energize RY2 and turn off the AC bulb. (Popular Electronics, October 1996, p. 66)


TOUCH SWITCH WITH LIGHT OPERATED TURNOFF
TOUCH SWITCH WITH LIGHT OPERATED TURNOFFFG261

When R5 is illuminated by a flashlight, its resistance lowers, leaving only 10,000 ohms as the minimum base resistance. That process gives a positive potential to the base of Q1, therefore turning on the transistor, activating RY2, and turning off the SCR. Or you can press S1 to turn the circuitry off. (Popular Electronics, October 1996, p. 65)


TRANSMITTER CIRCUITS

AM TONE TRANSMITTER

LOW-POWER 40-METER CW TRANSMITTER

LOW-POWER VHF BEACON TRANSMITTER

MICRO TV TRANSMITTER

TRACKING TRANSMITTER

VACUUM-TUBE LOW-POWER 80/40-METER TRANSMITTER

WIRELESS AM MICROPHONE

WIRELESS CAMCORDER MICROPHONE

WIRELESS FM MICROPHONE

WIRELESS FM MICROPHONEII


AM TONE TRANSMITTER
AM TONE TRANSMITTERFG264

Power for the circuit is supplied by Bl, a 9-volt battery. Two sections of a 4011 NAND gate, Ul-c and Ul-d, are used as part of a radio-frequency (RF) oscillator (carrier). The other two sections, Ul-a and Ul-b, are used in an audio frequency (AF) oscillator (modulator). Switch Sl enables and disables the modulation to allow the transfer of an intelligent message with the transmitter. When you press Sl, the AF oscillator composed of U1-a, U1-b, R4, and C1 starts generating an audio signal. That signal gates the RF oscillator composed of Ul-c, Ul-d, R2, R3, and C2 on and off. When on, the RF oscillator runs at 1 Mhz. The resulting output is sent out ANT1 as an AM signal. (Popular Electronics, November 1995, p. 43)


LOW-POWER 40-METER CW TRANSMITTER
LOW-POWER 40-METER CW TRANSMITTERFE106-12

This CW transmitter has an output of up to 3 W. By using 24 V on Q2, up to 10W output can be obtained If a 24-V supply is used, Q1 must not see more than 12 V. Connect 12 V between junctions C3, R2 and L2, and remove L5, L1 should be a low-Q 18- to 20 μH inductor. R6 can be used (up to 47 Ω) to reduce the Q further. (Reprinted with permission from 73 Amateur Radio Today, 4/92, p. 25)


LOW-POWER VHF BEACON TRANSMITTER
LOW-POWER VHF BEACON TRANSMITTERFF96-6

A crystal oscillator and tripler make up the low power beacon transmitter. U1 generators a pulse that keys the transmitter at a 10:1 duty cycle (100ms on 1s off) to conserve battery power. This transmitter was used as a locator beacon. (Reprinted with permission from 73 Amateur Radio Today, 5/93, p. 56)


MICRO TV TRANSMITTER
MICRO TV TRANSMITTERFF96-2

For very low power, noncritical applications, this small TV modulator can be useful as a short-range (50 feet) transmitter for video signals. A small camera module can be used as a source. R11 is  used to vary dc offset of the modulator. (Reprinted with permission from Electronics Now, 12/93, p. 29. (C) Copyright Gernsback Publications, Inc.,1993)


TRACKING TRANSMITTER
TRACKING TRANSMITTERFE106-7

This tracking transmitter consists of four distinct subassemblies; a free-running multivibrator, a transmit switch, an audio-tone generator, and an FM transmitter. The multivibrator (which produces a pulse width with a pulse separation of 1500 ms) is built around Ql and Q2. The multivibrator output is coupled through R5 to the base of Q3, whose emitter feeds Q4, which controls the circuit's transmitter section. (Reprinted with permission from Electronics Hobbyist Handbook, 1993, p. 24)


VACUUM-TUBE LOW-POWER 80/40-METER TRANSMITTER
VACUUM-TUBE LOW-POWER 80/40-METER TRANSMITTERFE106-6

Using a 6BW6 vacuum tube, the above transmitter delivers about 5 W output. C1 is adjusted for cleanest CW note. C8 and C9 are 365 pF and dual-365 pF (paralleled) tuning capacitors. L1 is 35 turns of #24 enameled wire on a 1" plastic tube. FT-243 crystals for 3.5 or 7 MHz are used. Do not use this circuit to produce a 7-MHz output from a 3.5-MHz crystal--it is not intended to "double over" crystal frequencies. (Reprinted with permission from 73 Amateur Radio Today, 11/92, p. 8)


WIRELESS AM MICROPHONE
WIRELESS AM MICROPHONEFA90-1

Transistor Ql and its associated components comprise a tuneable RF oscillator. The RF signal is fed to transistor Q2, the modulator. Operational amplifier IC1 increases the audio signal and applies it through resistor R4 to the base of Q2. Tune an AM radio to an unused frequency between 800 to 1600 kHz. Tune L1 for a change in the audio level coming from the radio. Peak the output by adjusting L2. If L1 is disturbed, it may be necessary to readjust L2 for peak performance. Depending on the impedance of the microphone audio sensitivity can be increased by decreasing the value of R10 and vice versa. (Radio Electronics, 12/81, p. 52)


WIRELESS CAMCORDER MICROPHONE
WIRELESS CAMCORDER MICROPHONEFG265

A 741 op amp acts as an audio amplifier and frequency modulates VHF oscillator Q1 via varactor D2. L1 is 2.5 turns of No. 18 wire on a 5/16 inch diameter form. The turn spacing can be varied to adjust the transmitter frequency. (1994 Experimenters Handbook, p. 104)


WIRELESS FM MICROPHONE
WIRELESS FM MICROPHONEFC115-9

Transistor Ql acts as an amplifier for condenser microphone MIC1. The output of Ql is applied to the base of transistor Q2 through a 4.7-μF capacitor. C2 and Ll form an LC tank circuit, which is used to set the frequency at which the transmitter operates. Coil Ll is a variable inductor, centered a bit below μH, that is used to adjust the modulating frequency of the circuit. Capacitors Cl and C2 are 4.7 pF units. A lower value can be used to raise the circuit's operating frequency. The microphone and Ql provide a varying voltage at the base of Q2, with the output of Q2 applied to the LC tank circuit. That causes a modulating action in the tank circuit that, when applied to the antenna, a short piece of wire 6- to 8-inches long, will provide a good, clear FM signal somewhere in the range of 88 to 95 MHz with a range of about 100 feet. Popular Electronics, 8/89, p.43.


WIRELESS FM MICROPHONE  II
WIRELESS FM MICROPHONEIIFD103-2

Q1 amplifies the output from an electret microphone MIC1. Audio is fed into oscillator Q2, which modulates the signal. L1C1 is a tank circuit for operation in the 88-Mhz region. The antenna is a 6- to 8-inch piece of wire. L1 is a variable inductor in the 1-μH range. (Reprinted with permission from R-E Experimenters Handbook 1990. p 155. (C) Copyright Gernsback Publications, Inc., 1987)


ULTRASONIC CIRCUITS

SIMPLE ULTRASONIC GENERATOR

ULTRASONIC PEST-REPELLER

ULTRASONIC SOUND SOURCE

ULTRASONIC GENERATOR USES PLL IC

ULTRASONIC MOTION DETECTOR

ULTRASONIC MOTION DETECTOR

ULTRASONIC REMOTE-CONTROL TESTER

ULTRASONIC SOUND RECEIVER


SIMPLE ULTRASONIC GENERATOR
SIMPLE ULTRASONIC GENERATORFF97-5

This basic ultrasonic generator can be built easily and quickly. An NE555 drives a speaker. The frequency range is 12 to 50 kHz. SPKR1 is a piezo tweeter, etc. (Reprinted with permission from Popular Electronics, 12/94, p.72. (C) Copyright Gernsback Publications, Inc.,1994)


ULTRASONIC PEST-REPELLER
ULTRASONIC PEST-REPELLERFC117-3

This circuit is a 555 timer IC connected as a square-wave generator. Its base frequency is approximately 45 kHz, as determined by the values of R1, R2, and Cl. The 45-kHz carrier is frequency modulated by a modified trapezoidal voltage waveform applied to pin 5 of the 555 timer. That modulating voltage is developed by a network consisting of C2, R3, and R4 connected across one leg of the bridge rectifier. The sweep is approximately 20 kHz on each side of the base frequency. The speaker is a 2-inch piezoelectric tweeter. (R-E Experimenters Handbook, p. 92)


ULTRASONIC SOUND SOURCE
ULTRASONIC SOUND SOURCEFD94-1

Using two NE555 timer IC devices, this circuit generates either pulsed or continuous ultrasonic signals. The sound frequency is:

f   =   1.44

                Ct(Rt1 + Rt2)

The values for Ct for both pulse rate and ultrasonic frequencies can be calculated this way. SPKR is a small hi-fi tweeter.

(Reprinted with permission from R-E Experimenters Handbook 1987. (C) Copyright Gernsback Publications, Inc., 1987)


ULTRASONIC GENERATOR USES PLL IC
ULTRASONIC GENERATOR USES PLL ICFG266

This ultrasonic generator is built around a 567 PLL. By adding  telegraph key as described in the text, it can be turned into an ultrasonic transmitter. (Popular Electronics, December 1994, p. 74)


ULTRASONIC MOTION DETECTOR
ULTRASONIC MOTION DETECTORFF97-2

A 567 PLL IC operates in a dual-function mode as a signal generator and an FM receiver. The 567's square-wave output at pin 5 is coupled to the base of Ql, and from Ql's emitter to the input of the power amplifier (Q2 and Q6). The output drives the piezo speaker, SPKR1.

The receive portion of the circuit operates as follows: transistors Q3 and Q4 are connected in a two-stage, high-gain, audio-frequency amplifier circuit, with the input connected to a second piezo speaker (SPKR2) operating as a sensitive microphone. The amplifier's output is coupled to the 567's input at pin 3. When an in-band signal is received, the LED lights.

The 567s FM output is coupled from pin 2 to the input of a very-low-frequency single-transistor amplifier, Q5. The amplifier's output at Q5's collector drives a voltage-doubler circuit (C11, D1, D2, and C12). The dc output feeds a 0- to 1-mA analog meter.

By placing the two piezo speakers one foot apart and aiming them in the same direction, toward a nonmoving solid object, the signal from the transmitter's speaker will reflect back into the receiver's speaker, and the frequency at the 567's input will be the same as the one being transmitted.

The ac output at pin 2 is zero when the outgoing and incoming frequencies are the same. However, when the signal is reflected from a moving object, the received frequency will be either lower or higher than the transmitted one. If the object is moving away from the speakers, the received frequency will be lower; if the object is moving toward the speakers, the frequency will be higher.

The pin-2 signal is fed through a 470-μF capacitor to the base of Q5, where the signal is amplified and fed to a voltage doubler, and then on to a meter circuit.

If you wish, the voltage doubler and meter can be removed and replaced with headphones connected between the negative side of C11 and circuit ground. That will allow you to listen to the difference-frequency signal as objects move in front of the speakers.

(Reprinted with permission from Popular Electronics, 1/95, pp.72-73. (C) Copyright Gernsback Publications, Inc.,1995)


ULTRASONIC MOTION DETECTOR
ULTRASONIC MOTION DETECTORFG267

The receiver section of the circuit is made up of four AC-coupled stages, each built around one of four sections of an LM324 op-amp, IC1. At the input to the third state-a differential amplifier built around ICl-c-there are two diodes, D2 and D3. They detect both positive and negative pulses. When there is no movement, the voltage at pin 7 of ICl-b is half the supply voltage and neither D2 or D3 can conduct. The voltage at pin 8 of ICl-c is then low. If the signal rises above +0.7 volt, D3 conducts causing the output on pin 8 to go high. If the signal falls below -0.7 volt, D2 conducts, which also causes the output to go high. The fourth stage, built around IC1-d, is set up as a monostable flip-flop. That stage converts any signal that gets through the filter into a pulse substantial enough to turn on transistor Ql. When Ql conducts, LED1 turns on and an output signal is provided to drive a separate relay or any other device connected to the circuit. (Popular Electronics, March 1996, pp. 52-55)


ULTRASONIC REMOTE-CONTROL TESTER
ULTRASONIC REMOTE-CONTROL TESTERFF97-1

This circuit picks up the ultrasonic tone via MIC1, amplifies it, and divides it by 10 in IC U2, a 74LS90. The output of U2 drives and audio amplifier and a piezoelectric element is used as a speaker. (Reprinted with permission from Popular Electronics, 5/95, p. 29. (C) Copyright Gernsback Publications, Inc.,1995)


ULTRASONIC SOUND RECEIVER
ULTRASONIC SOUND RECEIVERFF97-6

You won't be disappointed with the performance of this sensitive ultrasonic receiver. It can let you listen to bugs, bats, engines, and virtually any other source of ultrasonic sounds. This circuit uses a piezo tweeter as an ultrasonic microphone, amplifier stages Q1, Q2, and an LO using a 567 IC. Q3 is a mixer that heterodynes the ultrasonic sounds down to the audible range. U2 is an amplifier that will drive a pair of headphones. (Reprinted with permission from Popular Electronics, 12/94, p.74-75. (C) Copyright Gernsback Publications, Inc.,1994)


VIDEO CIRCUITS

SIMPLE NTSC GRAY-SCALE VIDEO GENERATOR

SYNC STRIPPER

VIDEO DC RESTORE CIRCUIT

VIDEO LINE DRIVER

VIDEO DRIVER/AMPLIFIER


SIMPLE NTSC GRAY-SCALE VIDEO GENERATOR
SIMPLE NTSC GRAY-SCALE VIDEO GENERATORFF98-8

A 4.032-MHz crystal oscillator (256 x horizontal line scan rate) drives a BCD counter. The binary outputs of the counter are fed to R2 through R5, a simple weighting network for D/A conversion, resulting in a staircase video output with a rep rate of 15.75 kHz. This circuit should be useful for amateur TV linearity testing and setup purposes. (Reprinted with permission from 73 Amateur Radio Today, 7/93, p. 74)


SYNC STRIPPER
SYNC STRIPPERFG272

This circuit provides synch stripping function. Output is positive going TTL compatible. (Analog Dialog, Vol. 26 #1, 1192, p. 13)


VIDEO DC RESTORE CIRCUIT
VIDEO DC RESTORE CIRCUITFE108-10

This circuit restores the black level of a monochrome composite video signal to 0 V at the beginning of every horizontal line. This circuit is also useful with CCD scanners to set the black level. (Reprinted with permission from Linear Technology Application Note #57)


VIDEO LINE DRIVER
VIDEO LINE DRIVERFF98-18

This video buffer/line driver operates at a gain of +2 and drives a pair of 75 Ω lines with a 75 Ω back terminations. The overall terminated gain is unity. (Analog Devices)


VIDIO DRIVER/AMPLIFIER
VIDEO DRIVER/AMPLIFIERFF98-17

This simple circuit has a voltage gain of about 5x and will drive low-impedance loads (75 W) to 1.5 V p-p or better. (Analog Dialogue, Analog Devices, Vol. 26, No. 1, 1992, p.11)


WEATHER RELATED CIRCUITS

ACID RAIN MONITOR

ANEMOMETER

RAIN ALARM

RAIN SENSOR


ACID RAIN MONITOR
ACID RAIN MONITORFC59-9

A simple bridge rectifier and a 12-V regulator powers the MOSFET sensing circuit. The unregulated output of the bridge rectifier operates the drain solenoid via switch S1. The sensor itself is built from two electrodes: one made of copper, the other of lead. In combination with the liquid trapped by the sensor, the electrodes form a miniature lead/acid cell whose output is amplified by MOSFET Ql. The maximum output produced by our prototype cell was about 50 μA.

MOSFET Ql serves as the fourth leg of a Wheatstone bridge. When sensed acidity causes the sensor to generate a voltage, Ql turns on slightly, so its drain-to-source resistance decreases. That resistance variation causes an imbalance in the bridge, and that imbalance is indicated by meter M1.

(R-E Experimenter's Handbook, 1989, p. 41)


ANEMOMETER
ANEMOMETERFG274

Here's a really simple and inexpensive anemometer. You can use any small DC motor for MOT1. Meter Ml can be any milliamp or microamp meter with markings from 0 to 50 or 100. The parts, including the 1000-ohm, 15-turn potentiometer, at hobbyist sources. A three-paddle wheel for the motor can be made with golf-ball-sized "wiffle" balls. Cut two of them in half, and bolt three of the halves to a PVC hub, using 6-32 machine screws. Calibrate the circuit by holding it out of a car window while someone drives steadily between 20 or 30 miles per hour on a still day. (Popular Electronics, February 1996, pp. 67-68)


RAIN ALARM
RAIN ALARMFG276

This rain detector circuit closes the relay when water bridges the gap between the metal electrodes. (Electronics Now, May 1996, p. 10)


RAIN SENSOR
RAIN SENSORFG275

The figure shows a simple Rain Sensor design which incorporates pitch and volume controls in the alarm signal. Whenever the sensor is bridged by droplets of water, the Darlington transistor TRl/TR2 will conduct. This enables IC1, a 555 astable tone generator, to function, powering a small loudspeaker through a driver transistor TR3. VR2 determines the pitch of the audio tone which can be anything from about 25 Hz to 18 kHz, whilst VR3 adjusts the volume. The sensitivity of the circuit is set by VR1. The Darlington pair could be constructed with two separate ZTX300s or a single TIP122. For the sensor use a small piece of stripboard, linking alternate strips into an interlocking design. The circuit will operate from a standard 9V PP3-type battery. (Everyday Practical Electronics, March 1996, p. 201)


WINDOW COMPARATOR/DISCRIMINATOR CIRCUITS

LOW-VOLTS ALARM

MULTIPLE APERTURE WINDOW DISCRIMINATOR

POWER SUPPLY MONITOR

REGULATED DC-DC CONVERTER

VARIABLE DUTY CYCLE TIMER

WINDOW COMPARATOR DRIVING HIGH/LOW LAMPS

WINDOW GENERATOR


LOW-VOLTS ALARM
LOW-VOLTS ALARMFB74-2

This inexpensive dc supply-voltage monitor sounds a warning when the voltage falls below a preset value. It is ideal for monitoring rechargeable batteries since it draws only a few microamperes when not sounding. The voltage at which the alarm sounds is determined by the zener diode. When the voltage falls below the zener voltage, the alarm sounds. The alarm tone is determined by the RC time constant of the 39 k resistor and 0.01 mf capacitor. (William Sheets)


MULTIPLE APERTURE WINDOW DISCRIMINATOR
MULTIPLE APERTURE WINDOW DISCRIMINATORFC126-7

The circuit shown here uses μA4136 comparators and FETs Q1 through Q3. (Fairchild Camera & Instrument Corporation, Linear Databook, 1982, p. 4-180)


POWER SUPPLY MONITOR
POWER SUPPLY MONITORFB74-1

This circuit uses a tricolor LED display to indicate acceptable and unacceptable output voltages. One to set the upper voltage limit, the other, the lower voltage limit. When the monitored voltage is above the set maximum, the LED display turns red. Yellow turns on for voltages below the set minimum, and green turns on for voltages between the high and the low settings. The circuit does not need a separate power supply. It is powered by the voltage it monitors. The circuit can be adapted to monitor voltage differences between two power supplies. Should the monitored voltages differ by more than a set value, a visual or an audible alarm would warn the operator about the difference. The circuit can also be modified for remote monitoring and the use of a separate power supply. (NASA Tech Briefs, Winter 1985, p. 52)


REGULATED DC-DC CONVERTER
REGULATED DC-DC CONVERTERFC19-16

The regulated dc-dc converter produces 15-Vdc outputs from a +5 Vdc input Line and load regulation is 0.1%. (Reprinted from EDN, 3/3/88. Copyright 1989 Cahners Publishing Co., a division of Reed Publishing USA)


VARIABLE DUTY CYCLE TIMER
VARIABLE DUTY CYCLE TIMERFG255

This NE555 circuit produces a variable duty cycle output. (Electronics Now, September 1995, p. 14)


WINDOW COMPARATOR DRIVING HIGH/LOW LAMPS
WINDOW COMPARATOR DRIVING HIGH/LOW LAMPSFA16-8

(Reprinted with permission from National Semiconductor Corporation, Linear Databook 1982, p. 10-215)


WINDOW GENERATOR
WINDOW GENERATORFD104-2

 This window generator uses a single LM324 op amp and features two adjustable set points. When the two comparators formed by UlB go high, LED1 lights. When UlC goes high, the LED extinguishes. Some hysteresis is provided by the 10-mΩ resistors. As shown in Fig. (b), LED1 can be replaced by an optoisolator (etc) for use in several applications. (Reprinted with permission from Popular Electronics, 1/90, p. 26. (C) Copyright Gernsback Publications, Inc.,1990)


PROBE CIRCUITS

CURRENT PROBE AMPLIFIER

LOGIC PROBE

SINGLE INJECTOR-TRACER

SUPER-SIMPLE SHORTWAVE RECEIVER

WWV RECEIVER! ChangeButtonBinding("btn_view", "ExecProgram(`view.exe  FF72-1',0) ")CURRENT PROBE AMPLIFIERFF72-1

A clamp-on current probe, such as the Tektronix P6021, is a useful means of displaying current waveforms on an oscilloscope. A less-expensive and simple alternative is shown in the figure.

The more sensitive range on the P6021 is 2 mA/mV, but it has a roll-off of 6-dB per octave below 450 Hz. The purpose of the compensator is to counteract the low-frequency attenuation, which is achieved by means of C3 and R4 + P1 in the feedback around op amp Nl. It's important that the latter is a low-noise type, such as the LM725 shown in the figure. On top of that, it's necessary at some point to limit the increasing gain with decreasing frequency; otherwise, amplifier noise and drive will overcome the signal. The values shown for C3 and R3 give a lower limit of less than 1 Hz.

A test square wave of ±1 mA is fed to the current probe so that P1 can be adjusted for minimum droop or overshoot in the output waveform. It's vital that the sliding core on the probe is fully closed. At high frequencies, the response begins to fall off at 100 kHz. Therefore, for most waveforms, switch Sl is moved to "direct," above a fundamental frequency of, for example, 10 kHz.

This circuit's current consumption is quite low, and it can be battery powered. If a mains power supply is built-in, it must be well screened to prevent hum problems.

(Reprinted with permission from Electronic Design 1/95, p 133, Copyright 1995 Penton Publishing)


LOGIC PROBE
LOGIC PROBEFD67-7

By connecting this circuit to a logic device that's under power, you can get an indication as to its status. If the circuit is open, neither of the test lamps will fight. If the circuit is grounded, the low (or zero) lamp will light. If 3 to 6 V are present, the high-voltage lamp will light.

Other than its application in logic testing, the probe is also convenient for checking supply voltages and grounds. You can select resistors to turn the lamps on at any desired threshold voltage within the component limits.

(Reprinted with permission from Popular Electronics/Hands-On Electronics, 5/89, p.28. (C) Copyright Gernsback Publications, Inc.,1989)


SINGLE INJECTOR-TRACER
SINGLE INJECTOR-TRACERFB75-2

This circuit provides a dc output to a meter and an audio output (if necessary) for checking transmitters or modulated signals. It can be used also as a field strength meter or transmitter monitor. (William Sheets)


SUPER-SIMPLE SHORTWAVE RECEIVER
SUPER-SIMPLE SHORTWAVE RECEIVERFE83-10

Integrated circuit Ul (an NE602 double-balanced mixer) is a combination oscillator and frequency mixer. Signals from the antenna input (at J1) are fed through de-blocking capacitor Cl to the RF-gain control, Rl, and fed to the input of U1 at pins 1 and 2.

The local-oscillator frequency, which varies with the settings of R2 and L2, is mixed internally within Ul, resulting in an output. The mixer output at pin 4 of Ul is applied to a tunable 260-kHz band-pass intermediate-frequency (IF) transformer, L3, through dc-blocking capacitor C7. Therefore, signals that are roughly 260 kHz above and below the local-oscillator frequency are passed while others are effectively blocked. The IF frequencies are now, amplified by Q2 and Q3. The AM audio signal is detected by D2 and its associated components, which bypass the RF signals, and leave only the audio signals. The signals are preamplified by U1-a (half of an LM358 dual op amp). The audio is then boosted to speaker level by the LM386 low-voltage audio power amplifier, U3.

(Reprinted with permission from Popular Electronics, 8/93, p. 32. (c) Copyright Gernsback Publications, Inc., 1993)


WWV RECEIVER
WWV RECEIVERFG221

This receiver is a crystal controlled superheterodyne receiver with a MPF102 RF amplifier, NE602 mixer, ceramic IF filter, MC1350 IF amplifier, NZ414 AM detector, and MC34119 audio output. The AGC system uses a CA3140E op-amp. A 9545 kHz crystal is used in the L. O. (Electronics Experimenters Handbook, 1996, pp. 27-31)