Top Circuits Page 8
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The HA7210 oscillator 10 combines with an IOL7642 quad CMOS op amp to produce a sleep-mode control circuit. The circuit is put into the sleep mode with a logic high applied to the Reset input or with an RC timer for automatic reset...
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The microphone input, MIC1, is fed through C3 and R4 to inverting amplifier U2-a; the gain of U2-a is controlled by potentiometer R5. The output of U2-a is fed through C4 to the remaining op-amps (U2-b, U2-c, U2-d), which are all configured as....
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In this circuit, audio fed to the control channel is amplified and rectified by Dl and D2. This dc level activates LED D3 via Q2. The light from D3 causes R9, a light-dependent resistor to decrease resistance. As Rll (audio gain) is set higher, more audio....
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At the heart of this simple circuit is the well-known type KTY10 temperature sensor from Siemens. This silicon sensor is essentially a temperature-dependent resistor that is connected as one arm in a bridge circuit here. Preset PI functions to balance the....
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Here`s an effective for a temperature sensor to receive power from a 4-to-20 mA loop without actually affecting the loop current (see the figure). This particular temperature sensor IC (AD590F) conducts 1 / when powered by a supply in the range of 4 V to 40....
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Figure A shows the circuit of a direct-trigger timing light. The trigger voltage is -taken from the car's ignition circuit by a direct connection to a spark plug. A circuit using an inductive pickup is shown in Fig. B. A trigger transformer is used to....
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Pulses from the distributor points are passed through a current limiting resistor, rectified, and clipped at 4 volts. Via Q1 and the diode pump, a dc voltage proportional to engine rpm is presented to RV1; the sharp transfer characteristic of a CMOS gate,....
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ICl is connected in the astable mode, driving RLA, C3, Dl, and D2 prevent spikes from the relay coil and the wiper motor from triggering ICl. VR2 is adjusted to give the minimum delay time required. VR1 is the main delay control and pro vides a range of from....
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A1 amplifies and regulates the signal from the spark coil. A2 converts frequency to voltage so that its output is a voltage proportional to engine rpm. A3 compares the tachometer voltage with the reference voltage and turns on the output transistor at the....
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This op-amp analyzer can measure the current drawn by any device in a car. The analyzer works by measuring the very small voltage that develops across the battery cables when current flows..
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This circuit provides complete speed control over car"s windshield wipers. They can be slowed down to any rate even down to four sweeps per minute..
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This circuit will operate a car"s headlights for a predetermined time to light up the driveway or path after the driver has left the car. SQl is pushed and Q2 is turned on closing the relay and turning on the car"s headlights. Cl begins to charge through VR1....
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This circuit relies upon the minute current between two conductive probes suspended in a washer fluid reservoir..
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This circuit uses an LED and 4081 CMOS integrated circuit. The variable resistor sets the voltage at which the LED turns on. Set the control so that the LED lights when the voltage from the car"s ignition switch drops below 13 volts..
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An op-amp comparator is used to compare the converter output with a dc threshold voltage. The circuit flashes the LED when the input frequency exceeds 100 Hz. Increases in frequency raise the average current out of terminal 3 so that frequencies above 100 Hz....
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When the turn signal switch SI is closed, lamp #1 will be activated and capacitor Cl will charge to the triggered voltage of Ql. As soon as the anode voltage on Ql exceeds its gate voltage by 0 V, Ql will switch into the low resistance mode, thereby....
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This circuit is a high performance charger for gelled electrolyte lead-acid batteries. Charger quickly recharges battery and shuts off at full charge. Initially, charging current is limited to 2A. As the battery voltage rises, current to the battery....
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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....
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This locater is made up of two parts. The first is an rf oscillator, whose circuit is shown in Fig. 8-4a. The second is a sensitive receiver shown in Fig. 8-4b. The heart of the oscillator is a 555 timer !C. Tank circuit C2 and L1 is used to tune the....
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The heart of the circuit is ICZ, a 4046 micropower phase-locked loop (PLL). The incoming signals are fed to the PLL after being buffered by IC1a and its associated components. The frequency of the incoming signal is multiplied by either 90, 60, or 45,....
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This circuit disables the air conditioner compressor when additional engine power is required. It does so by monitoring the engine vacuum at the intake manifold. Ifthe vacuum drops to 40% of its normal level, the compressor clutch is disabled, removing the....
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The monitor senses an ajar door and, if the situation isn"t corrected within 20 seconds, sounds a beeping alarm. The circuit is controlled by a magnetic reed switch and magnet on the door. With the door closed, the switch is closed and the alarm is....
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A monolithic 555-type timer is the heart of this simple automobile voltage regulator. When the timer is off so that its output at pin 3 is low, the power Darlington transistor pair is off. If battery voltage becomes too low, less than 14.4 V in this case,....
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A unijunction transistor audio oscillator drives a small speaker. The oscillator"s frequency is determined by resistor R2 and capacitor C2. The ope rating voltage is supplied from the car"s turn-signal circuit(s) through Dl and D2. ..
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This gauge uses a sensor in conjunction with R1 to develop a dc voltage proportional to oil pressure. IC1 and IC..
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This little tester is useful for checking vehicle electrical circuits. Two LEDs indicate whether one of the cl..
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A bridge circuit is used to produce a signal from the output of vacuum sensor IC1. IC2b provides about a 0.2 V offset ..
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This circuit uses a digital voltmeter (formed from IC1 and IC3) to display fuel quantity as a percentage of a full tank...
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Using an intersil ICL 7106 A/D converter chip and an LED display module, this gauge uses a Sensym Corp. pressure tra..
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This circuit uses an RCA CA3162E (IC2) A/D converter. This converter has 12-bit output (BCD) which is sent to display decoder..
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Using an SCR/relay combination, this circuit can be made to cut off ignition, unless a positive voltage is applied to..
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In this circuit, IC1A and IC1B act as a monostable multivibrator. Any input from the sensors SI through..
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With a single IC, you can build a simple, reliable auto burglar alarm or a similar alarm. See (a) for the timing informatio..
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In the wiper-delay schematic shown, with the ignition on, Dl maintains regulated +12 Vdc. When SI closes..
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This electronic ignition circuit is intended to be inserted into a car"s conventional ignition system. In effect, it re..
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The windshield wiper interval circuit presented here is very compact and is noteworthy for its use of ..
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At the heart of the CD4-MX is an astable multivibrator, built around Q1 and Q2, that feeds step-up transformer Tl. The output of 1 is rectified by D3 to D6 and used to charge capacitor C4. When the points close, a small voltage is fed to the gate of SCR1,....
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STS schematic. The Q2 gate voltage increases with the charge on C3. After 15 seconds of charging, the buzzer will warble. As the charging continues, the sound will grow louder.Circuit waveforms. Point A shows the signal from the flasher. The voltage at....
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If you live in the frozen north, knowing your engine-block heater is working is a comfort. This device will let you know if yours is okay. Plug in PL1 to your power outlet. NE1 should light. Then, plug in the block heater. Depressing SI should cause the....
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This alternator regulator uses a 3-transistor dc amplifier, and is designed for a pulled up field system, where one side of the alternate field returns to the +12-Vsupply, and the other end is pulled toward ground...
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This regulator is for the purpose of controlling a dc generator. The field configuration is that one side of the field is grounded. D4 prevents the battery from discharging through the generator and takes the place of the mechanical cut-out relay...
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This battery saver circuit can automatically turn off a small piece of test equipment after a desired period of time, allowing you to leave your shop worry free.This circuit uses a CD4011IC to act as a simple timer. One section acts as an RC discharge timer....
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This circuit uses the 555 timer in the asta-ble or oscillatory mode. The length of time the timer is off is a function of the values of CI, R2, and R3. The potentiometer which controls the amount of "hesitation"..
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A diode (IN4148) is used as a temperature sensor. IC2 is an A/D converter with BCD output. A refere..
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The circuit, is based on a commercial temperature sensor (TS6178) and an MC3334P ignition chip, When the radiator temperature increases, the sensor pulls the base of Q2 low via Ql, which is wired as a diode. Q2`s collector thus goes high and triggers IC1,..
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Because the power controller is powered from the vehicle`s accessory switch, the load can receive power only when the ignition key is on. Using half of a dual flip-flop (CD4013), a load of up to 10 A is controlled by a momentary pushbutton. This circuit was....
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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 Rl and CI. With the values shown approximately a 1 minute....
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This circuit determines the cold cranking amps of a battery by first discharging the surface charge, then checking the internal resistance. This gives a more realistic measurement than simply measuring the instantaneous drop in voltage with a load. A....
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The monitor is a simple voltage comparator in which a car battery serves as the battery for operation. The input voltage to the comparator is set by adjustment potentiometer PI, which must be adjusted so that the green LED L2 is on when the alternator is....
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It is very interesting and convenient to be able to control everything while sitting at your PC terminal. Here, a simple hardware circuit and software is used to interface a 7-segment based rolling display. The printer port of a PC provides a set of points....
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This page describes my home-built ICOM CI-V interface. In order to connect most all ICOM radios to a computer, an additional interface is required. The interface bridges the gap between the RS-232 electrical levels used by the computer serial port, and the....
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This circuit allows a remote microprocessor to be reset by a controlling host over a remote RS-232 or similar protocol serial line. With the use of a program loader on the remote host, a program may be downloaded and run. This allows a target processor to....
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Here`s a simple project that sends continuous or switch controller MIDI messages that correspond to the position of a potentiometer. Given a few parts and a cannibalized volume or wah-wah pedal, you can build this MIDI controller pedal and have the ultimate....
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The MIDI Drum Machine began in the Fall of 1991 as a project for a microprocessor system design course, shortly after I wrote PAULMON1, the 8051 monitor/debugger. A friend, Rod Seely, both a musician and electronics hobbiest suggested I design something....
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The data separator is intended for use with 8" flexible diskettes with IBM 3870 soft sectored format. The circuit delivers data and clock (B) and clock pulses (D). These two signals must be in such a sequence that the negative edge of the clock pulse is at....
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An op amp is used to interface between a fiberoptic system and the MOS SCR to multi-cycle, half-wave control of a load. This receiver has two complementary outputs, one at a quiescent level of about 0.6 V and the second at 3 V. By adding a 4.7 V zener in....
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This circuit draws only 4 mA from a 5-V supply while driving a standard RS-232C receiver. The system clock drives a de-de converter that produces -3.4 V. The frequency can range from 0.5 to 8 MHz, but a range of 0.5 to 1 MHz will minimize power....
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When driving MOSPOWER in a totem-pole output configuration, it is necessary to have the gate voltage 10 to 15 V positive with respect to the source in order to handle load currents near the MOSPOWER maximum ratings. The D169 lends itself to....
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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....
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A 5.1-V zener diode clamps positive-going transients, and a Schottky rectifier clamps negative-going transients. Th..
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Process-control applications often require a monostable multivibrator (one-shot) with a pulse width that c..
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Keyboards can be slotted into two categories, at least as far as the manner that the switches are connected is co..
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A microcomputer-to-triac interface uses a phototriac optoisolator to Jet 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....
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These are simple AVR programmers. I designed and built four different programmers for various envilonments: LPT controlled parallel programmer, LPT controlled ISP adapter, COM controlled ISP adapter and COM controlled generic SPI bridge. Additionaly, COM....
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The best human ear can capture sounds from 20Hz to 20KHz. These limits are known to be the broadest that can exist. Normally the normal limits range from 100Hz to about 13KHz and depend on the age and health of the individual. We for our measurements and to....
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With a constant current excitation, the voltage dropped across an inductance increases with frequency. Thus, an active device whose output increases with frequency can be characterized as an inductance. The circuit yields such a response with the effective....
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Applications such as photoelectric control, temperature detection and moisture sensing require a circuit that can accurately detect a given resistance ratio. A simple technique that uses an op amp as a sensing element can provide 0,5% accuracy with low parts....
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The ^generator output is rectified then filtered and applied between the positive supply voltage and the base of the detector transistor. This provides a negative voltage which reduces the base-voltage when the speed increases. In normal operation, if the....
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This simple three-phase tester, uses only a small current thyristor as a main element for testing the right or wrong succession of the three phases, and there is no need for a supplementary power supply. The basic circuit is shown in Fig. 69-4A. When....
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This tester is for tracing wiring on Printed Circuit Boards. Resistors below 50 ohms act as a short circuit; above 100 ohms as an open circuit. The circuit is a simple multivibrator switched on by transistor T3. The components in the base of T3 are Dl, Rl,....
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Electrodes are immersed in an electrolyte that remains level while the sensor follows the tilt of the body on which it is placed, more of one outer electrode and less of the other are immersed and their resistances fall or rise, respectively. The resistance....
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The circuit is not frequency sensitive. Its calibration will be accurate over a wide frequency spectrum, such as the entire amateur hf spectrum, if the values of L2, the voltage divider capacitors Cl-2 and C3, and the resistances of Rl-2 are chosen properly.....
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A suitable pilot larnp is illuminated by a small sample of rf and energizes an inexpensive solar cell; the dc current generated by the cell is a measure of relative rf power, and may be routed to a low-current meter located at any convenient point. A....
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This tachometer can be set up for any number of cylinders by linking the appropriate timing resistor as illustrated. A 500 ohm trim resistor can be used to set up final calibration..
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An electrical signal taken from the low tension side of the distributor is converted into a voltage proportional to engine rpm and this voltage is displayed on a meter calibrated accordingly. The 555 timer IC is used as a monostable which, in effect,....
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The indicator flashes an LED when the battery voltage drops below a certain threshold. 2N4274 emitter-base junction serves as a zener which establishes about 6V on the L161"s positive input. As the battery drops, the L161 output goes high. This turns on the....
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Use this circuit for checking fundamental oscillates, Q2 conducts and the LED lights. A3 HF crystals on a "Go-No-Go" basis. An untuned or 6V, 40mA bulb could be substituted for the Colpitts oscillator drives a voltage multiplier LED..
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A very sensitive pico ammeter (— 1 V/pA) employs the amplifier in the inverting or current summing mode. Care must be taken to eliminate stray currents from flowing into the current summing mode. It takes approximately 5 for the circuit to stabilize to....
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The circuit may be used as a sensitive current detector or as a voltage detector having high input impedance. Rl is set so that the voltage at point (A) is V2 to % volts below the level that fires the 2N494C. A small input current (Iin) of only 40....
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The 2N5457 and PN2222 bipolar serve as voltage isolation devices between the output and the current sensing resistor, Rl. The LM101 provides a large amount of loop gain to assure that the circuit acts as a current source..
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The 2N5457 JFET and PN2222 bipolar have inherently high output impedance. Using Rl as a current sensing resistor to provide feedback to the LM101 op amp provides a large amount of loop gain for negative feedback to enhance the true current sink nature of....
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When operating, a waveguide directs energy onto a crystal detector. The diode shown is for X-band operation. The waveguide is a 1H inch piece of plastic tubing with the ends flared. The plastic is coated with an elec-troless copper solution to provide a....
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Increased sensitivity gives field strength reading from low power transmitters. Operating range 3-30 MHz..
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The tuning range is determined by coil (L) dimensions and setting of Cl. Coils can be plugged in for multirange use or soldered in place if only limited frequency range is of interest. Cl = 36 pF variable, C2 = 047 disc, D = 1N60 (germanium) and M=0-1 mA meter..
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The circuit is frequency selective. It has been used from 2 meters through 160 meters. The telescoping antenna may be adjusted to its shortest length when working at 2 meters to keep the needle on the scale, Meter should be a 100 microamp to a 500 microamp....
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This ten-step adjustable analog level detector is capable Of sinking up to 40 milliam-peres at each output. The voltage range at the input pin should range from 0 to 2 volts. Circuits of this type are useful as liquid-level indicators, pressure indicators,....
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This circuit uses LEDs to display the beat frequency of two-tone oscillators. Only one LED is on at a time, and the apparent rotation of the dot is an exact indication of the best frequency..
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This circuit makes a very compact level indicator where a meter would be impractical or not justified due to cost. Resistor values will depend on type of LED used. For MV50 LEDs the resistors are 2 K for steps of approx 2 V and current drain with all three....
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This circuit provides a visual indication of the input analog voltage level. It has a high input impedance at pin 8 and open-collector outputs capable of sinking up to 40 milliam-peres. It is suitable for driving a linear array of 5 LEDs to indicate the....
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Light-emitting diodes connected with reverse polarity provide a visual indication of zero-beat frequency. Each LED is on for only half a cycle of the input. When the input frequency is more than 1 kilohertz away from the zero-beat frequency, both LEDs appear....
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This circuit employs a potentiometer as the weight sensing element. An object placed upon the scale displaces the potentiometer wiper, an amount proportional to its weight..
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This circuit provides a low cost and reliable method of testing zener diodes. RVl can be calibrated in volts, so that when LED 1 just lights, the voltage on pins 2 and 3 are nearly equal. Hence, the zener voltage can be read directly from the setting of RVl.....
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The circuit tests whether or not a diode is open, shorted, or functioning correctly. If lamp A lights, the diode under test is functional. When lamp B is lit, the diode is good but connected backwards..
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This circuit measures RF voltages beyond 200 MHz and up to about 5 V. The diode should be mounted in a remote probe, close to the probe tip. Sensitivity is excellent and voltages less than 1 V peak can be easily measured..
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An external power supply that gives a voltage higher than the highest expected rating of the zener diodes to be tested is required. Potentiometer RVl is adjusted until the meter reading stabilizes..
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Indicator lamp brightness varies in step with modulated RF signal. Adjust R2 with transmitter on (modulated) until the lamp flashes in step with modulation..
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The circuit is intended for 117 Vac ± 50 Vac operation, but can be easily modified for higher or lower voltages. It measures true (nonreactive) power beingdeliveredto the load and requires no external power supply. Idling power drain is only 0 W. Load....
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This tester can be used to check IC printed circuit boards. Two 4 K resistors and the transistors connected to them prevent current flow through the operational amplifier until the probe circuit is completed..
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One preset resistor is used for all the ranges, simplifying the setting up. Diode clamping is included to prevent damage to the meter if the unknown resistor is higher than the range selected..
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If the voltage at the input exceeds the voltage on the capacitor, then the output of the 741 goes positive, the diode conducts, and the capacitor is charged up to the input voltage-forward voltage drop of diode. When the voltage at the input is less than....
The HA7210 oscillator 10 combines with an IOL7642 quad CMOS op amp to produce a sleep-mode control circuit. The circuit is put into the sleep mode with a logic high applied to the Reset input or with an RC timer for automatic reset...
The microphone input, MIC1, is fed through C3 and R4 to inverting amplifier U2-a; the gain of U2-a is controlled by potentiometer R5. The output of U2-a is fed through C4 to the remaining op-amps (U2-b, U2-c, U2-d), which are all configured as....
In this circuit, audio fed to the control channel is amplified and rectified by Dl and D2. This dc level activates LED D3 via Q2. The light from D3 causes R9, a light-dependent resistor to decrease resistance. As Rll (audio gain) is set higher, more audio....
At the heart of this simple circuit is the well-known type KTY10 temperature sensor from Siemens. This silicon sensor is essentially a temperature-dependent resistor that is connected as one arm in a bridge circuit here. Preset PI functions to balance the....
Here`s an effective for a temperature sensor to receive power from a 4-to-20 mA loop without actually affecting the loop current (see the figure). This particular temperature sensor IC (AD590F) conducts 1 / when powered by a supply in the range of 4 V to 40....
Figure A shows the circuit of a direct-trigger timing light. The trigger voltage is -taken from the car's ignition circuit by a direct connection to a spark plug. A circuit using an inductive pickup is shown in Fig. B. A trigger transformer is used to....
Pulses from the distributor points are passed through a current limiting resistor, rectified, and clipped at 4 volts. Via Q1 and the diode pump, a dc voltage proportional to engine rpm is presented to RV1; the sharp transfer characteristic of a CMOS gate,....
ICl is connected in the astable mode, driving RLA, C3, Dl, and D2 prevent spikes from the relay coil and the wiper motor from triggering ICl. VR2 is adjusted to give the minimum delay time required. VR1 is the main delay control and pro vides a range of from....
A1 amplifies and regulates the signal from the spark coil. A2 converts frequency to voltage so that its output is a voltage proportional to engine rpm. A3 compares the tachometer voltage with the reference voltage and turns on the output transistor at the....
This op-amp analyzer can measure the current drawn by any device in a car. The analyzer works by measuring the very small voltage that develops across the battery cables when current flows..
This circuit provides complete speed control over car"s windshield wipers. They can be slowed down to any rate even down to four sweeps per minute..
This circuit will operate a car"s headlights for a predetermined time to light up the driveway or path after the driver has left the car. SQl is pushed and Q2 is turned on closing the relay and turning on the car"s headlights. Cl begins to charge through VR1....
This circuit relies upon the minute current between two conductive probes suspended in a washer fluid reservoir..
This circuit uses an LED and 4081 CMOS integrated circuit. The variable resistor sets the voltage at which the LED turns on. Set the control so that the LED lights when the voltage from the car"s ignition switch drops below 13 volts..
An op-amp comparator is used to compare the converter output with a dc threshold voltage. The circuit flashes the LED when the input frequency exceeds 100 Hz. Increases in frequency raise the average current out of terminal 3 so that frequencies above 100 Hz....
When the turn signal switch SI is closed, lamp #1 will be activated and capacitor Cl will charge to the triggered voltage of Ql. As soon as the anode voltage on Ql exceeds its gate voltage by 0 V, Ql will switch into the low resistance mode, thereby....
This circuit is a high performance charger for gelled electrolyte lead-acid batteries. Charger quickly recharges battery and shuts off at full charge. Initially, charging current is limited to 2A. As the battery voltage rises, current to the battery....
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....
This locater is made up of two parts. The first is an rf oscillator, whose circuit is shown in Fig. 8-4a. The second is a sensitive receiver shown in Fig. 8-4b. The heart of the oscillator is a 555 timer !C. Tank circuit C2 and L1 is used to tune the....
The heart of the circuit is ICZ, a 4046 micropower phase-locked loop (PLL). The incoming signals are fed to the PLL after being buffered by IC1a and its associated components. The frequency of the incoming signal is multiplied by either 90, 60, or 45,....
This circuit disables the air conditioner compressor when additional engine power is required. It does so by monitoring the engine vacuum at the intake manifold. Ifthe vacuum drops to 40% of its normal level, the compressor clutch is disabled, removing the....
The monitor senses an ajar door and, if the situation isn"t corrected within 20 seconds, sounds a beeping alarm. The circuit is controlled by a magnetic reed switch and magnet on the door. With the door closed, the switch is closed and the alarm is....
A monolithic 555-type timer is the heart of this simple automobile voltage regulator. When the timer is off so that its output at pin 3 is low, the power Darlington transistor pair is off. If battery voltage becomes too low, less than 14.4 V in this case,....
A unijunction transistor audio oscillator drives a small speaker. The oscillator"s frequency is determined by resistor R2 and capacitor C2. The ope rating voltage is supplied from the car"s turn-signal circuit(s) through Dl and D2. ..
This gauge uses a sensor in conjunction with R1 to develop a dc voltage proportional to oil pressure. IC1 and IC..
This little tester is useful for checking vehicle electrical circuits. Two LEDs indicate whether one of the cl..
A bridge circuit is used to produce a signal from the output of vacuum sensor IC1. IC2b provides about a 0.2 V offset ..
This circuit uses a digital voltmeter (formed from IC1 and IC3) to display fuel quantity as a percentage of a full tank...
Using an intersil ICL 7106 A/D converter chip and an LED display module, this gauge uses a Sensym Corp. pressure tra..
This circuit uses an RCA CA3162E (IC2) A/D converter. This converter has 12-bit output (BCD) which is sent to display decoder..
Using an SCR/relay combination, this circuit can be made to cut off ignition, unless a positive voltage is applied to..
In this circuit, IC1A and IC1B act as a monostable multivibrator. Any input from the sensors SI through..
With a single IC, you can build a simple, reliable auto burglar alarm or a similar alarm. See (a) for the timing informatio..
In the wiper-delay schematic shown, with the ignition on, Dl maintains regulated +12 Vdc. When SI closes..
This electronic ignition circuit is intended to be inserted into a car"s conventional ignition system. In effect, it re..
The windshield wiper interval circuit presented here is very compact and is noteworthy for its use of ..
At the heart of the CD4-MX is an astable multivibrator, built around Q1 and Q2, that feeds step-up transformer Tl. The output of 1 is rectified by D3 to D6 and used to charge capacitor C4. When the points close, a small voltage is fed to the gate of SCR1,....
STS schematic. The Q2 gate voltage increases with the charge on C3. After 15 seconds of charging, the buzzer will warble. As the charging continues, the sound will grow louder.Circuit waveforms. Point A shows the signal from the flasher. The voltage at....
If you live in the frozen north, knowing your engine-block heater is working is a comfort. This device will let you know if yours is okay. Plug in PL1 to your power outlet. NE1 should light. Then, plug in the block heater. Depressing SI should cause the....
This alternator regulator uses a 3-transistor dc amplifier, and is designed for a pulled up field system, where one side of the alternate field returns to the +12-Vsupply, and the other end is pulled toward ground...
This regulator is for the purpose of controlling a dc generator. The field configuration is that one side of the field is grounded. D4 prevents the battery from discharging through the generator and takes the place of the mechanical cut-out relay...
This battery saver circuit can automatically turn off a small piece of test equipment after a desired period of time, allowing you to leave your shop worry free.This circuit uses a CD4011IC to act as a simple timer. One section acts as an RC discharge timer....
This circuit uses the 555 timer in the asta-ble or oscillatory mode. The length of time the timer is off is a function of the values of CI, R2, and R3. The potentiometer which controls the amount of "hesitation"..
A diode (IN4148) is used as a temperature sensor. IC2 is an A/D converter with BCD output. A refere..
The circuit, is based on a commercial temperature sensor (TS6178) and an MC3334P ignition chip, When the radiator temperature increases, the sensor pulls the base of Q2 low via Ql, which is wired as a diode. Q2`s collector thus goes high and triggers IC1,..
Because the power controller is powered from the vehicle`s accessory switch, the load can receive power only when the ignition key is on. Using half of a dual flip-flop (CD4013), a load of up to 10 A is controlled by a momentary pushbutton. This circuit was....
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 Rl and CI. With the values shown approximately a 1 minute....
This circuit determines the cold cranking amps of a battery by first discharging the surface charge, then checking the internal resistance. This gives a more realistic measurement than simply measuring the instantaneous drop in voltage with a load. A....
The monitor is a simple voltage comparator in which a car battery serves as the battery for operation. The input voltage to the comparator is set by adjustment potentiometer PI, which must be adjusted so that the green LED L2 is on when the alternator is....
It is very interesting and convenient to be able to control everything while sitting at your PC terminal. Here, a simple hardware circuit and software is used to interface a 7-segment based rolling display. The printer port of a PC provides a set of points....
This page describes my home-built ICOM CI-V interface. In order to connect most all ICOM radios to a computer, an additional interface is required. The interface bridges the gap between the RS-232 electrical levels used by the computer serial port, and the....
This circuit allows a remote microprocessor to be reset by a controlling host over a remote RS-232 or similar protocol serial line. With the use of a program loader on the remote host, a program may be downloaded and run. This allows a target processor to....
Here`s a simple project that sends continuous or switch controller MIDI messages that correspond to the position of a potentiometer. Given a few parts and a cannibalized volume or wah-wah pedal, you can build this MIDI controller pedal and have the ultimate....
The MIDI Drum Machine began in the Fall of 1991 as a project for a microprocessor system design course, shortly after I wrote PAULMON1, the 8051 monitor/debugger. A friend, Rod Seely, both a musician and electronics hobbiest suggested I design something....
The data separator is intended for use with 8" flexible diskettes with IBM 3870 soft sectored format. The circuit delivers data and clock (B) and clock pulses (D). These two signals must be in such a sequence that the negative edge of the clock pulse is at....
An op amp is used to interface between a fiberoptic system and the MOS SCR to multi-cycle, half-wave control of a load. This receiver has two complementary outputs, one at a quiescent level of about 0.6 V and the second at 3 V. By adding a 4.7 V zener in....
This circuit draws only 4 mA from a 5-V supply while driving a standard RS-232C receiver. The system clock drives a de-de converter that produces -3.4 V. The frequency can range from 0.5 to 8 MHz, but a range of 0.5 to 1 MHz will minimize power....
When driving MOSPOWER in a totem-pole output configuration, it is necessary to have the gate voltage 10 to 15 V positive with respect to the source in order to handle load currents near the MOSPOWER maximum ratings. The D169 lends itself to....
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....
A 5.1-V zener diode clamps positive-going transients, and a Schottky rectifier clamps negative-going transients. Th..
Process-control applications often require a monostable multivibrator (one-shot) with a pulse width that c..
Keyboards can be slotted into two categories, at least as far as the manner that the switches are connected is co..
A microcomputer-to-triac interface uses a phototriac optoisolator to Jet 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....
These are simple AVR programmers. I designed and built four different programmers for various envilonments: LPT controlled parallel programmer, LPT controlled ISP adapter, COM controlled ISP adapter and COM controlled generic SPI bridge. Additionaly, COM....
The best human ear can capture sounds from 20Hz to 20KHz. These limits are known to be the broadest that can exist. Normally the normal limits range from 100Hz to about 13KHz and depend on the age and health of the individual. We for our measurements and to....
With a constant current excitation, the voltage dropped across an inductance increases with frequency. Thus, an active device whose output increases with frequency can be characterized as an inductance. The circuit yields such a response with the effective....
Applications such as photoelectric control, temperature detection and moisture sensing require a circuit that can accurately detect a given resistance ratio. A simple technique that uses an op amp as a sensing element can provide 0,5% accuracy with low parts....
The ^generator output is rectified then filtered and applied between the positive supply voltage and the base of the detector transistor. This provides a negative voltage which reduces the base-voltage when the speed increases. In normal operation, if the....
This simple three-phase tester, uses only a small current thyristor as a main element for testing the right or wrong succession of the three phases, and there is no need for a supplementary power supply. The basic circuit is shown in Fig. 69-4A. When....
This tester is for tracing wiring on Printed Circuit Boards. Resistors below 50 ohms act as a short circuit; above 100 ohms as an open circuit. The circuit is a simple multivibrator switched on by transistor T3. The components in the base of T3 are Dl, Rl,....
Electrodes are immersed in an electrolyte that remains level while the sensor follows the tilt of the body on which it is placed, more of one outer electrode and less of the other are immersed and their resistances fall or rise, respectively. The resistance....
The circuit is not frequency sensitive. Its calibration will be accurate over a wide frequency spectrum, such as the entire amateur hf spectrum, if the values of L2, the voltage divider capacitors Cl-2 and C3, and the resistances of Rl-2 are chosen properly.....
A suitable pilot larnp is illuminated by a small sample of rf and energizes an inexpensive solar cell; the dc current generated by the cell is a measure of relative rf power, and may be routed to a low-current meter located at any convenient point. A....
This tachometer can be set up for any number of cylinders by linking the appropriate timing resistor as illustrated. A 500 ohm trim resistor can be used to set up final calibration..
An electrical signal taken from the low tension side of the distributor is converted into a voltage proportional to engine rpm and this voltage is displayed on a meter calibrated accordingly. The 555 timer IC is used as a monostable which, in effect,....
The indicator flashes an LED when the battery voltage drops below a certain threshold. 2N4274 emitter-base junction serves as a zener which establishes about 6V on the L161"s positive input. As the battery drops, the L161 output goes high. This turns on the....
Use this circuit for checking fundamental oscillates, Q2 conducts and the LED lights. A3 HF crystals on a "Go-No-Go" basis. An untuned or 6V, 40mA bulb could be substituted for the Colpitts oscillator drives a voltage multiplier LED..
A very sensitive pico ammeter (— 1 V/pA) employs the amplifier in the inverting or current summing mode. Care must be taken to eliminate stray currents from flowing into the current summing mode. It takes approximately 5 for the circuit to stabilize to....
The circuit may be used as a sensitive current detector or as a voltage detector having high input impedance. Rl is set so that the voltage at point (A) is V2 to % volts below the level that fires the 2N494C. A small input current (Iin) of only 40....
The 2N5457 and PN2222 bipolar serve as voltage isolation devices between the output and the current sensing resistor, Rl. The LM101 provides a large amount of loop gain to assure that the circuit acts as a current source..
The 2N5457 JFET and PN2222 bipolar have inherently high output impedance. Using Rl as a current sensing resistor to provide feedback to the LM101 op amp provides a large amount of loop gain for negative feedback to enhance the true current sink nature of....
When operating, a waveguide directs energy onto a crystal detector. The diode shown is for X-band operation. The waveguide is a 1H inch piece of plastic tubing with the ends flared. The plastic is coated with an elec-troless copper solution to provide a....
Increased sensitivity gives field strength reading from low power transmitters. Operating range 3-30 MHz..
The tuning range is determined by coil (L) dimensions and setting of Cl. Coils can be plugged in for multirange use or soldered in place if only limited frequency range is of interest. Cl = 36 pF variable, C2 = 047 disc, D = 1N60 (germanium) and M=0-1 mA meter..
The circuit is frequency selective. It has been used from 2 meters through 160 meters. The telescoping antenna may be adjusted to its shortest length when working at 2 meters to keep the needle on the scale, Meter should be a 100 microamp to a 500 microamp....
This ten-step adjustable analog level detector is capable Of sinking up to 40 milliam-peres at each output. The voltage range at the input pin should range from 0 to 2 volts. Circuits of this type are useful as liquid-level indicators, pressure indicators,....
This circuit uses LEDs to display the beat frequency of two-tone oscillators. Only one LED is on at a time, and the apparent rotation of the dot is an exact indication of the best frequency..
This circuit makes a very compact level indicator where a meter would be impractical or not justified due to cost. Resistor values will depend on type of LED used. For MV50 LEDs the resistors are 2 K for steps of approx 2 V and current drain with all three....
This circuit provides a visual indication of the input analog voltage level. It has a high input impedance at pin 8 and open-collector outputs capable of sinking up to 40 milliam-peres. It is suitable for driving a linear array of 5 LEDs to indicate the....
Light-emitting diodes connected with reverse polarity provide a visual indication of zero-beat frequency. Each LED is on for only half a cycle of the input. When the input frequency is more than 1 kilohertz away from the zero-beat frequency, both LEDs appear....
This circuit employs a potentiometer as the weight sensing element. An object placed upon the scale displaces the potentiometer wiper, an amount proportional to its weight..
This circuit provides a low cost and reliable method of testing zener diodes. RVl can be calibrated in volts, so that when LED 1 just lights, the voltage on pins 2 and 3 are nearly equal. Hence, the zener voltage can be read directly from the setting of RVl.....
The circuit tests whether or not a diode is open, shorted, or functioning correctly. If lamp A lights, the diode under test is functional. When lamp B is lit, the diode is good but connected backwards..
This circuit measures RF voltages beyond 200 MHz and up to about 5 V. The diode should be mounted in a remote probe, close to the probe tip. Sensitivity is excellent and voltages less than 1 V peak can be easily measured..
An external power supply that gives a voltage higher than the highest expected rating of the zener diodes to be tested is required. Potentiometer RVl is adjusted until the meter reading stabilizes..
Indicator lamp brightness varies in step with modulated RF signal. Adjust R2 with transmitter on (modulated) until the lamp flashes in step with modulation..
The circuit is intended for 117 Vac ± 50 Vac operation, but can be easily modified for higher or lower voltages. It measures true (nonreactive) power beingdeliveredto the load and requires no external power supply. Idling power drain is only 0 W. Load....
This tester can be used to check IC printed circuit boards. Two 4 K resistors and the transistors connected to them prevent current flow through the operational amplifier until the probe circuit is completed..
One preset resistor is used for all the ranges, simplifying the setting up. Diode clamping is included to prevent damage to the meter if the unknown resistor is higher than the range selected..
If the voltage at the input exceeds the voltage on the capacitor, then the output of the 741 goes positive, the diode conducts, and the capacitor is charged up to the input voltage-forward voltage drop of diode. When the voltage at the input is less than....