Digital Circuit

SQUELCH_CIRCUIT_FOR_AM_OR_FM

Published:2009/6/26 3:50:00 Author:May

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FM_STEREO_DEMODULATION_SYSTEM

Published:2009/6/26 3:40:00 Author:May

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COMBINATION_VOLTAGE_AND_CURRENT_REGULATOR

Published:2009/6/26 3:35:00 Author:May

This voltage-regulator/current-limiter combination can be made from two 7805 regulators as shown. R1, R2, and R3 should be selected for a 5-V drop at the maximum allowable current limit. S1 selects one of the three current values. Do not forget that U1 requires 5 mA to operate and this means that the minimum current limit setting should be 10 mA or more (R1 = 1.25 kΩ). Resistor values are as follows:   (View)

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CLOCK_RADIO

Published:2009/6/26 3:14:00 Author:May

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BEAM_SPLITTER_FOR_OSCILLOSCOPE

Published:2009/6/26 2:27:00 Author:May

The basis of the beam splitter is a 555 timer connected as an astable multivibrator.Signals at the two inputs are alternately displayed on the oscilloscope with a clear separation between them. The output is controlled by the tandem potentiometer RV1a/b which also varies the amplitude of the traces.   (View)

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100_kHz_FREE_RUNNING_MULTIVIBRATOR

Published:2009/6/26 2:08:00 Author:May

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MONOSTABLE_MULTIVIBRATOR

Published:2009/6/26 2:08:00 Author:May

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BISTABLE_MULTIVIBRATOR

Published:2009/6/26 2:07:00 Author:May

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ONE_SHOT_MULTIVIBRATOR_

Published:2009/6/26 2:07:00 Author:May

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1MONOSTABLE_CIRCUIT

Published:2009/6/26 2:04:00 Author:May

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UJT_MONOSTABLE

Published:2009/6/26 2:02:00 Author:May

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DUAL_ASTABLE_MULTIVIBRATOR

Published:2009/6/26 2:02:00 Author:May

This dual astable multivibrator provides versatility not available with single timer circuits. The duty cycle can be adjusted from 5% to 95%. The two outputs provide two phase clock signals often required in digital systems.It can also be inhibited by use of either reset terminal.   (View)

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DIGITAL_THERMOMETER

Published:2009/6/26 1:41:00 Author:May

The sensor consists of two series-connected 1N914s, part of the circuit of a 555 multivibrator. Wired as shown, the output pulse rate is proportional to the temperature of the diodes. This output is fed to a simple frequency-counting circuit.   (View)

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PRECISION_FULL_WAVE_RECTIFIER

Published:2009/6/25 23:42:00 Author:May

Circuit Notes The circuit provides accurate full wave rectification. The output impedance is low for both input polarities, and the errors are small at all signal levels. Note that the output will not sink heavy current, except a small amount through the 10 K resistors. Therefore, the load applied should be referenced to ground or a negative voltage. Reversal of all diode polarities will reverse the polarity of the output. Since the outputs of the amplifiers must slew through two diode drops when the input polarity changes, 741 type devices give 5% istortion at about 300 Hz.   (View)

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AC_MOTOR_BRAKE

Published:2009/6/25 23:37:00 Author:May

A shot of direct current will instantly stop any ac power tool motor. Switch S1 is a center-off, one side spring return. With S1 on, ac will be fed to the motor and the motor will run. To brake the motor, simply press S1 down and a quick shot of dc will instantly stop it. The switch returns to the center off position when released. This Power Brake can only be used with ac motors; it will not brake universal (ac-dc) motors. A heat sink must be provided for the diode.   (View)

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FM_DEMODULAT0_R_AT_12_V__

Published:2009/6/25 23:28:00 Author:May

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80_METER_DIRECT_CONVERSION

Published:2009/6/25 23:28:00 Author:May

Portabl e receiver with directional ferrod antenna and ver-tical sense antenna was developed for radio foxhunting at 1975 Bov Scout World Jamboree in Norway, in competitions for locating four low-power crystal-controlled transmitters hid-den along 4-km course. Varactor-tuned oscillator provides 20-kHz tuning range with R9, ade-quate for the frequency used-3.566, 3.585, 3.635, or 3680 MHz. T1 is subminiature auto-transformer with 8-ohm and 2000-ohm sec-tions, for 8-ohm headphones. For high-imped-ance headphones, connect headphone jack J1 to lug 9 of T1. ON/OFF switch is not needed, L1 is 22 turns No. 28 enamel wound over two 10×95 mm ferrite rodstaped together. 01-06 are NPN high-frequency small-signal transistors.-N. K. Holter, Radio Foxhunting in Europe, QST, Nov. 1976, p 43-46.   (View)

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5_STEP_ATTENUATOR

Published:2009/6/25 23:27:00 Author:May

AppIication s indude comparing performance of various rece Mng an-tennas and measuring gain of preamp used abead of receiver. Dashed lines represent required shield partitions. All resistors are 1/4-W composition with 5% tolerance.-D.DeMaw, What Does My S-Meter Tell Me?, QST,June 1977,p 40-42.   (View)

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SELF_EXCITED_SWR_BRlDGE

Published:2009/6/25 23:19:00 Author:May

Portable bridge has built-in signal sources for each band from 80 through 10 meters, for tuning antenna on tower before transmission line is connected.Oscillators are crystal controlled at desired antenna tuneup frequencies. Separate oscillators for each band simplify switching problems, so only supply voltage from J1 and oscillator outputs to meter circuit need be switched. Current drain from 9-V battery is maximum of 12 mA.R17 and R18 should be closely matched, while R1, and R20 should have 5% tolerance.-T.P.Hulick, An S.W.R.Bridge with a Built-In 80 Through 10 Meter Signal Source, CQ1 June 1971,p 64-66 68, and 99.   (View)

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HALF_WAVE_RECTIFIER

Published:2009/6/25 23:06:00 Author:May

Circuit Notes This circuit provides for accurate half wave rectification of the incoming signal. For positive signals, the gain is 0; for negative signals, the gain is -1. By reversing both di-odes, the polarity can be inverted. This circuit provides an accurate output, but the output impedance differs for the two input polarities and buffering may be needed. The output must slew through two diode drops when the input polarity reverses. The NE5535 device will work up to 10 kHz with less ttan 5% distortion.   (View)

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