Circuit Diagram

METAL_DETECTOR_1

Published:2009/7/10 3:26:00 Author:May

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 fteld of L1, 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 L1 and verify that Q1 is operating on or near 455 kHz.   (View)

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SCR_REPLACING_LATCHING_SWITCH

Published:2009/7/10 3:25:00 Author:May

This circuit provides the turn-on characteristics of an SCR, but turns off with ease. The switch is comprised of three transistors with descending current ratings: Q3 has a high-current rating and Q2 has a medium rating. The current, I1, to be switched is 15 A. Momentarily depressing S2 removes Q1's base drive, turning Q1 off and allowing Q2 to turn on. Q2 then drives the base-emitter junction of Q3, turning Q3 on. Q3's collector-emitter voltage, which serves as Q1's base drive, is essentially zero, keeping Q1 off. To turn Q3 off, depress S1; this action momentarily shunts Q2's base current to ground, reversing the chain of events that turned Q3 on.   (View)

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METAL_DETECTOR

Published:2009/7/10 3:24:00 Author:May

An NE602 acts as a heterodyne detector and Q1 as a sense oscillator. When L1 is brought near metal, it causes a charge in loop inductance, shifting the resonant frequency of L1 C6/C7. L1 is 5 turns #20 wire on a 9 diameter wood or plastic form.   (View)

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RELAXATION_OSCILLATOR

Published:2009/7/10 3:23:00 Author:May

This oscillator runs at about 150 Hz, but C1 and/or R4 can be proportionately changed to alter this frequency. Rise and fall times are 12 and 7 μs, respectively.   (View)

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SWITCH_DEBOUNCER

Published:2009/7/10 3:23:00 Author:May

TTL inverter 74LS14 has an internal 16-KΩ,pull-up resistor that pulls the gate input high when the switch is open. As you close the switch, the 4.7-μF capacitor discharges on the ftrst contact. If the switch contacts bounce open, the internal resistor limits the capacitor's recharge to a rate sufficiently slow to prevent an undesired gate transition before the contacts again close. Note that the circuit correctly debounces the switch for both opening and closing. If you add an external pull-up resistor, you can use a CMOS Schmitt-trigger gate, 74HC14, and a smaller, 0.1-μF, capacitor.   (View)

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FREQUENCY_METER

Published:2009/7/10 3:22:00 Author:May

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.   (View)

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TWO_SHEETS_DETECTOR

Published:2009/7/10 3:22:00 Author:May

Using the principle of capacitance between two plat-es this circuit senses when more than one sheet of paper goes between the sensing electrodes ai a time. C1 is the, sensing capacitor formed of two plates. It consists of two plates 2 x15 with 0.1 spacing. A change, of capacitance causes a change in oscillator frequency of the IC1 circuit, which is detected by IC2 and IC3.   (View)

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BIKE_SPEEDOMETER_1

Published:2009/7/10 3:21:00 Author:May

A TIL414 photo transistor senses reflection from a spoke-mounted reflector, generates a pulse, and sends it to U1 and U2, a monostable multivibrator, which drives meter M1.   (View)

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RF_POWER_SWITCH

Published:2009/7/10 3:20:00 Author:May

This rf power switch operates at 1.7 MHz with a 50-V Source and load.Its on loss is 0.2 dB and its off isolation is 30 dB.It provides 40-W PEP,45 VPEAK and 0.9 APEAK. The control input can come from CMOS ,TTL,LS,etc.,to turn on Q1,which turns on Q2,a TMOS MTP3N35.   (View)

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CODE_PRACTICE_OSCILLATORⅠ

Published:2009/7/10 3:20:00 Author:May

U1 is used as an oscillator; the frequency is determined by C2 and R3.Use an 80 Ω or similar highimpedance speaker, and a 1.5-V battery for a power source.   (View)

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VARIABLE_STROBE_LIGHT

Published:2009/7/10 3:18:00 Author:May

In this strobe-light, two circuits are needed; one circuit charges a capacitor placing 320 Vdc between the cathode and anode of the flashtube. The other circuit provides bursts of approximately 4000 V to trigger the flashtube into conduction. The voltage-doubler works by summing two equal voltages in series, which results in a doubling of the voltage. The 4000 V needed to trigger the flashtube is provided by transformer T1-a voltage step-up transformer that develops 4000 V across its secondary coil when current flows in the primary coil. Silicon-controlled rectifier SCR1 controls the current flow in the primary coil of T1. When SCR1 conducts, current flows suddenly in the primary coil and 4000 Vac spikes appear across the secondary coil. For conduction, SCR1 needs a negative and positive voltage on the cathode and anode, respectively, and a positive voltage on the gate. It is the function of components R2, R3, C3, and NE1 to provide that positive gate voltage and turn on SCR1. Potentiometer R2, resistor R3, and capacitor C3 form an rc timing circuit. Control of charging time of C3 is accomplished by varying that resistance in the circuit.When the voltage on C3 reaches the firing voltage of the neon bulb, it causes NE1 to conduct, thus placing a positive voltage, from C3, on the gate of SCR1. The SCR now turns on and C3 discharges through SCR1 and the primary coil of T1. The 4000 V that is developed across the secondary coil of T1 fires the xenon tube, causing a bright flash. The whole process then repeats itself with C3 charging up, NE1 firing to short out SCR1, and T1 developing 4000 V to trigger the xenon flashtube.   (View)

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THERMALLY_OPERATED_DIRECTION_DETECTOR

Published:2009/7/10 3:16:00 Author:May

A heat-sensitive sensor can be used to construct a direction detector. Such a sensor reacts to all ani-mal 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 is, of course, exactly the opposite. Circuit IC1B forms a symmetric supply. Terminal s of the sensor is its output. The signal at s is ampli-fied 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 multifacetted mirror. The circuit draws a current of only a few mA from a 5-V supply.   (View)

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SOUND_OPERATED_SWITCH

Published:2009/7/10 3:16:00 Author:May

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 D1 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 Q1 so that the circuit will not be triggered on by the sound of the on/off switch, S1 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.   (View)

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TRANSISTOR_TESTER

Published:2009/7/10 3:16:00 Author:May

A 555 timer drives Q1 through Q4 with a square wave. LED1 and LED2 light when an npn or pnp transistor respectively, are connected to the text terminals. If LED3 and LED4 light equally as LED1 and LED2, the transistor is functional. If LED3 and LED4 are brighter than LED1 or LED2, the transistor is shorted.   (View)

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STAIRCASE_GENERATOR

Published:2009/7/10 3:15:00 Author:May

This circuit is a high-input impedance version of the so-called diode pump or staircase generator. Note that charge transfer takes place at the negative-going edge of the input signal. The most common application for staircase generators is in low-cost counters. By resetting the capacitor when the output reaches a predetermined level, the circuit can be made to count reliably up to a maximum of about 10.   (View)

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PERMANENT_MAGNET_DETECTOR

Published:2009/7/10 3:14:00 Author:May

In this circuit, oscillator Q1 runs at about 15 kHz and feeds mixer U1. U1 has an internal oscillator that runs at around 15 kHz.C15 is used to zero-beat both oscillators. When a magnet is brought near L1 or L2, the magnetic field shifts the permeability of their respective cases. This changes the oscillator frequency, and the audio note is passed through ftlter L3, C16, and C10/R7 to amplifter Q2. There the audio is ampli-fied and drives meter M1 via rectiflers D1 and D2.   (View)

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AUDIO_OSCILLATOR

Published:2009/7/10 3:14:00 Author:May

The circuit's frequency oscillation is f=2.8/ [C1x(R1+R2)]. Using the values shown, the out-put frequency can be varied from 60 Hz to 20 kHz by rotating potentiometer R2. A portion of IC1's output voltage is fed to its noninverting input at pin 3. The voltage serves as a reference for capacitor C1, which is connected to the noninverting input at pin 2 of the IC. That capacitor continually charges and discharges around the reference voltage, and the result is a square-wave output. Capacitor C2 decouples the output.   (View)

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ANALOG_DATA_SIGNALS_ISOLATER

Published:2009/7/10 3:13:00 Author:May

By converting analog data to digital and usmg optocouplers，this circuit can be used to transmit analogsignals across barriers，such as voltage levels，different ground systems，etc．   (View)

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AUDIO_MODULATED_1_MC_TUNED_TD_OSCILLATOR

Published:2009/7/19 22:27:00 Author:Jessie

Uses silicon tunnel diode that, with no surface protection, may be dipped in liquid nitrogen, placed in furnace, or immersed in acid, with only minor change in oscillator and modulation frequencies.-I. A. Lesk, N. Holonyak, Jr., and U. S. Davidsohn, The Tunnel Diode-Circuits and Applications, Electronics, 32:48, p 60-64.   (View)

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DIODE_MATCHING_CIRCUIT

Published:2009/7/10 3:11:00 Author:May

This circuit can be used to match diodes for use in circuits where such a balance is necessary (a balanced modulator, for instance).The diode matching circuit will indicate the forward-voltage drop of the two diodes in millivolts.   (View)

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