Top Circuits Page 16
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This touch switch does not rely on mains hum for switching-It-can be used with battery powered circuits. Schmitt trigger IC1 forms a 100 kHz oscillator and IC2a which is biased into the linear region, amplifies the output and charges CI via the diode. IC2b....
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An operational amplifier can be used as a convenient device for analog comparator applications that require two different trip points. The addition of a positiverfeedback network introduces a precise variable hysteresis into the usual comparator switching....
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This circuit can drive anLED display with constant current independently of wide power supply voltage changes. It can operate with a power supply range of at least 4V to 30V. With 10M resistances for R2 and R3 and the inverting input of the comparator....
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This circuit gives a positive output when the input voltage exceeds 8 volts. Between these limits the output is negative. The positive limit point is determined by the ratio of Rl, R2, and the negative point by Rl, R3. The forward voltage drop across the....
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This circuit gives an output (which in this case is OV) when an input voltage lies in between two specified voltages. When it is outside this window, the output is positive. The two op amps are used as voltage comparators. When Vin is more positive than Vref....
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The capacitor-diode output circuit is used here as a polarity converter to generate a - 5 volt supply from +15 volts. This circuit is useful for an output current of up to 20 mA with no additional boost transistors required. Since the output transistors are....
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This circuit has a 100 mV hysteresis which can be used in applications where very fast transition times are required at the output even though the signal is very slow. The hysteresis loop also reduces false triggering due to noise on the input..
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The NPD5566 monolithic dual is used in a differential multiplex application where Rds(ON> should be closely matched) for the monolithic dual tracks at better than ±1% over wide temperature ranges (-25° C to +125° C), this makes it an unusual but ideal....
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The triac will be gated on at the start of the positive half cycle by current flow through the 3 µf capacitor as long as the C103 SCR is off. The load voltage then charges up the 1 µF capacitor so that the triac will again be energized during the....
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When switching loads with the aid of a thyristor, a large amount of RFI can be generated unless some form of zero crossing switch is used. The circuit shows a simple single transistor zero crossing switch. Rl and R2 act as a potential divider. The potential....
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The circuit is a simple rf-actuated switch which will respond to any strong field in the region of the pickup wire. The length of the wire will depend on how much coupling is needed, but a 250-mm length wrapped around the outside of the coaxial cable....
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When the digital logic level at the control input is low, the PIN diode is forward-biased by the CMOS gates. The two 1-KO bias resistors limit this current to the PIN diode"s safe forward current limit. In this state, the switch is on. When the control....
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A basic circuit to trigger an SCR is shown in Fig. 67 -lA. This circuit has the disadvantage that the blocking voltage of the photon-coupler output device determines the circuit-blocking voltage, irrespective of higher main SCR capability. Adding....
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This circuit is effective for lamp and heater loads. Some circuits driving reactive loads require integral cycling and zero-voltage switching-when an identical number of positive and negative half cycles of voltage are applied to the load during a power....
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Snubber circuit R2C2, as shown, might be necessary since Rl and Cl are tailored for optimized triggering and not for dV!dt protection. Fiber-optic pairs can be used with discrete SCRs to switch thousands of volts. A photon coupler with a transistor output....
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Since standard CMOS logic operates down to 3-V supply voltages and is specified as low as 30 p.A maximum current sinking/sourcing capability, it is necessary to use a buffer transistor to provide the required current to the IRED if CMOS is to drive the....
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Detection of line-current flow and indicating the flow to an electrically remote point is required in line status monitoring at a variety of points in theJelephone system and auxiliary systems. The line should be minimally unbalanced or loaded by the....
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For higher speed applications, up to 1-MHz NRZ, the Schmitt-trigger output HllL series optoisolator provides many features. The 1.6-mA drive current allows fan-in circuitry to drive the IRED, ..
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Al and A2 are two sections of a quad comparator. The first, Al, functions as an amplifier and detector. Resistors R~and R6 set the gain at 100; the output of Al is an open collector to negative-peak-rectify the output with a decay time constant determined....
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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 VrEAK and 0.9 APEAK· The control input can come from CMOS, TTL, LS, etc., ..
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TTL inverter 74LS14 has an internal 16-Kohm, pull-up resistor that pulls the gate input high when the switch is open. As you close the switch, the 4.7uF capacitor discharges on the first contact. If the switch contacts bounce open, the internal resistor....
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This circuit provides the tum-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, !1, to be switched....
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Using four diode in an array allows using only one MOSPOWER transistor for analog switching. The current flow is controlled by keeping the source-base connection of the MOSFET towards the load. Be sure to use diodes capable of handling the load current....
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Each time the switch closes, the voltage on Cl causes inverter A to change state, with positive feedback from inverter B. Resistor Rl delays the charging and discharging of Cl, making the circuit virtually immune to contact bounce. The circuit works....
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A single op amp-one of four contained in the popular LM324-is operating in a variable pulsewidth, free-running squarewave oscillator circuit, with its timed output driving two transistors that control the on/ off cycle of the tape-drive motor. The....
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A sensitive electret microphone picks up the sound and feeds the signal to a two-stage amplifier circuit, consisting of Ula and Ulb. The amplified output of Ulb is fed ·to a voltage-doubler circuit (comprised of Dl, D2, C4, and C5). The output of the....
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This circuit can cause a cassette recorder to automatically tum on and record when a sound or noise is present. Another use, is when the sound-activated switch is used to tum on a cassette player so that it operates as a burglar-alarm detector and sounder.....
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At a predetermined level of declining terminal voltage, the circuit disconnects the battery from the load ..
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This circuit produces an output pulse when SW1 (pushbutton) is depressed. It also becomes a hysteresis ga..
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The reset switch on a computer is very important. If an operating instruction threatens to wreck the internal mana..
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Although this circuit uses a 74HC74, any CMOS variant of this flip-flop will work. IC1A acts as a true/ compleme..
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Relay K1 has a low-impedance coil and K2 has a high-impedance coil. When a sensor opens, current is routed throu..
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This circuit provides either latched switching or timed switching. U1A and UlB provide audio amplification from the ..
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This sound-operated switch will sense the ring of the phone and translate this to a lamp that will go on and off. The..
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This single-chip circuit adjusts its audio gain according to the ambient noise picked up by the microphone. When ..
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This circuit is a two-channel baseband video switcher. Buffer amps Ul/Ql, U4/Q4, and associated components produce a b..
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This signal tracker and lock detector combine to make a precision tone switch. Filter R3/R4/C2 determines..
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Some channels offer a separate audio mode (SAP) in a second language. It is usually transmitted on 6.8 MHz, whi..
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This switching circuit acts like a bank of interlocked mechanical switches; pushing one of the buttons latches its corres..
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This circuit uses low-cost IN4148 diodes and exhibits about 1.5 dB insertion loss from 10 to 1000 MHz w..
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When transistor Q1 is switched off, the circuit behaves as a voltage follower. By applying a positive vol..
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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..
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This circuit uses a CA3240 dual BiMOS op amp to sense small currents flowing between the contact points on a touch plat..
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The circuit is built around a 555 oscillator (Ul), which is turned on when a trigger is applied by touching the touch ..
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If your circuits experience frequency overvoltage conditions, continually replacing blown fuses can get pretty expensive. However, this shutdown circuit overcomes that deficiency by replacing the fuse with a relay and a low-current SCR. When the input....
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At the heart of the whistle swatch are a pair of tone detectors, each of which is built around an LM567 tone decoder, which are supported by a minimum of additional components. This whistle switch is designed to respond to only two or more occurrences of a....
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This circuit will switch off the line supply to audio or video equipment if there has been no input signal for about 2 seconds. SI provides manual operation and S2 acts as a reset. This circuit allows for time to change a tape or compact disc. ..
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This source is selected by pressing momentary-contact pushbutton switch SI. Switch SI is connected to the trigger of a 555 oscillator/timer (Ul) configured as a monostable multivibrator, wliich generates one short output pulse for each press of SI. That....
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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 Ql acts as the switch...
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ICl-c functions as a noninverting comparator, and ICl-a operates as an inverting comparator. Potentiometer Rl and fixed resistors R2 and R3 form a divider chain that delivers slightly different voltages to the two comparators. These voltages define the....
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Commutator circuit provides low impedance gate drive to the PN4091 analog switch for both on and off drive conditions..
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Hall-effect switches have several advantages over mechanically and optically coupled switches...
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A regulator allows you to power a 7.5-V cassette recorder or other device from a 12-Vdc au..
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This circuit outputs the maximum (or the minimum) of the four input voltages Vv V2, V3, and V4. Each of these input voltages is in the range 0 to 5 V. The output of the unit is the maximum of Vv V2, V3, and V4 if the control voltage input is 5 V (i.e.,....
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The LRC input network limits the anode dv/dt to a safe value—below 30 V/jus. Rl provides critical damping to prevent voltage overshoot. While a simple RC filter section could be used, the high current required by the squib would dictate a small value of....
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The circuit is an open loop rms voltage regulator that will provide 500 watts of power at 90 V rms with good regulation for an input voltage range of 110-130 V rms. With the input voltage applied, capacitor Cl charges until the firing point of Q3 is reached....
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This SCR pre-regulator keeps the filter capacitor Vc, in a variable output power supply, a few volts above the output voltage V0. The benefits include: less heat dissipated by the pass transistor and therefore small heatsink, cooler operation and higher....
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This .circuit for starting arc jets and controlling them in steady operation is capable of high power efficiency and can be constructed in a lightweight form. The design comprises a pulse-width-modulated power converter, which is configured in a closed....
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One of the control circuit"s triacs selects the tap on main transformer Tl, which provides the proper, preregulated voltage to the secondary regulator. T2 and its associated components comprise the secondary regulator. The ADC 0804, IC1, digitizes a....
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This circuit is basically tbe classic bucking regulator, except it uses a TMOS N-channel power FET for the chopper and creates its own supply for the gate control. Tht unique aspect of this circuit is how it generates a separate supply for the gate....
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Output voltage great enough to jump a l-inch gap can be obtained from a 12-V power source. A 555 timer IC is connected as an astable multivibrator that produces a narrow negative pulse at pin 3. The pulse turns Ql on for the duration of the time period.....
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This circuit takes as an input a signal from a 5-V CMOS logic circuit and outputs a high voltage of the same polarity. The high-voltage supply can be varied from ±30 V to ±150 V without the need to change circuit components. The input voltage is applied....
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This circuit can generate high-voltage pulses with an inexpensive auto ignition coil. Add a rectifier on the output and the circuit produces high-voltage de. The circuit"s input is 115 Vac. During the input"s positive half cycle, energy is stored in....
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The circuit converts a de voltage (V +) to a high-amplitude square wave in the audio-frequency range. The dual timer, IC2, provides an inexpensive alternative to the traditional transformer for providing complementary base drive to the power transistors,....
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The regulator delivers 100-V at 100 mA and withstands shorts to ground. Even at 100 V output, the LT317A functions in the normal mode, maintaining 1.2 V between its output and adjustment pin. Under these conditions, the 30-V zener is off and Ql conducts.....
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Using a charge pump and oscillator, this circuit uses a 7-kHz oscillator. When the clock is high, C and D..
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This inverter uses a 12.6-V to 120-V transformer to deliver a quasi-sine wave that has the same rms and peak voltage ..
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For back-lit LCD displays, this supply will drive a lamp. LT1072 drives Ql and Q2, and a sine wave app..
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This circuit detects low-voltage supply conditions, down to 0.6 V. Dl sets the trip point of the cir..
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Figure 99-l(a)"s circuit exhibits a high-output impedance as a result of the small effective capacitance of the series-c..
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A CMOS oscillator (U1A) drives. U1B through U1F, which drives Ql, which generates a 12-Vpp square wave across the primary ..
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During the first half-cycle (Fig. 99-5(a)), Dl conducts, D2 cuts off, CI changes to 170 V peak, and C2 discharges through ..
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In this circuit Ql, Q2, Rl, and CI form a multivibrator. The square wave that results from the oscillation..
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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....
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A TMOS MTM7N45 (Q2) is used as a series pass element in a linear high voltage supply that accepts +275-V unregulated and produces 250 V regulated with foldback current limiting. A 15-V zener, Dlf provides the dc reference for operational amplifier Ul, whose....
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Stepdown transformer T1 drops the incoming line voltage to approximately 48 Vac which is rectified by diode D1; the resultant de charges capacitor C1-through current limiting resistor Rl-to a voltage level preset by R4. When the voltage on R4"s wiper....
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The output voltage changes approximately linearly up to 20 KV as the input voltage is varied from 0 to 5 V. The oscillator is tuned by a 5-0 potentiometer to peak the output voltage at the frequency of maximum transformer response between 45 and 55 kHz. The....
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This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
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This project is an electronic lock with many combinations that you can easily change and opens only with the correct combination of four consecutive numbers. The big advantage of the electronic lock is that the four numbers must be entered in the correct....
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When button S12 (#) is pressed, a positive voltage fed through Rl appears at the base of transistor Ql, turning it on. When Ql is conducting, pin 1 of Ul is brought to ground 0ow) or the battery's negative terminal. With pin 1 low, two things occur: Pin 8 of....
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The door opener derives its power from a 9-V battery. A momentary-contact switch, 52, is provided in the event that manual opening and closing is required. Relay Kl is a 9-V type and relay K2 is a 117"Vac latching-type, which automatically latches with....
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A keypad enters a four-digit access code, which is programmed via jumpers on a 24-pin plug-in header and socket. Ul is a..
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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..
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A block pinout diagram of the LS7220 keyless-lock IC is shown. The keypad must provide each key with a contact to a common connection. In this case, the common connection goes to the positive supply rail so that when a key is pressed, a positive voltage is....
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For some applications it is important to have a tone decoder with narrow bandwidth and fast response time. This can be accomplished by the dual time constant tone decoder circuit shown. The circuit has two low-pass loop filter capacitors, C2 and C'2. With no....
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For other input structures see Figures 6 to 11; shown here with PC-filter (Figure ß). The micropoco capacitor has a temperature coefficient of 125.10"6i 60.10" k"1. In simplified circuits a fixed resistor (e.g. 620k) can be used for a guaranteed switching....
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A resistive voltage divider is used to establish a bias voltage for the input (Pins 2 and 3). The demodulated (multiplex) FM signal is fed to the input through a two-stage high-pass filter, both to effect capacitive coupling and to attenuate the strong....
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Readback data is applied directly to the input of the first NE592. This amplifier functions as a wide-band ac coupled amplifier with a gain of 100. By direct coupling of the readback head to the amplifier, no matched terminating resistors are required and....
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PLL (Ul) is set with R2 to desired tone frequency. LED lights to indicate lock-up of PLL. Reduce signal level (Rl) and readjust R2 to assure lock-up. Delay is selected from counter U3 output. Circuits latches (turns on Q1 to allow audio to speaker) when....
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A resistive voltage divider is used to establish a bias voltage for the input (pins 2 and 3). The demodulated (multiplex) FM signal is fed to the input through a two-stage high-pass filter, both to effect capacitive coupling and to attenuate the strong....
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The baseband-audio input comes from the pole of switch Sl in the stereo decoder, and is coupled to IC1 (a CA3089) via a 78.6 kHz bandpass filter that consists of capacitors Cl and C2, and inductor Ll. IC1 is a combination i-f amplifier and quadrature....
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Adding a pair of one shots to the output of a 567 tone decoder renders it less sensitive to out-of-band signals and noise. Without the one shots, the 56Tis prone to spurious output chatter. Other protection schemes, such as feeding back outputs or using an....
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The transducer circuit can be operated as either a tone encoder or decoder by changing the position of Sl. The operating frequency of that dual-purpose circuit is determined by C3 and R2. Capacitors Cl and C2 are not critical and can be of almost any....
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This circuit, which was developed to monitor the traffic of bumblebees in and out of the hive, differentiates a-to-b motion from b-to-b motion. When used with an optical decoder, the circuit distinguishes clockwise from counterclockwise rotation and....
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The piezo transducer operates as a sound-pickup device as well as a frequency-selective filter. By controlling the gain of the op amps, the oscillator can be transformed into a sensitive and frequency-selective tone-decoder circuit. With the gain of U1a....
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This electronic keyer uses four ICs (five, if the optional sidetone oscillator is desired) and operates from dc sources of 9 to 15..
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Apply a signal to each differential amplifier input pair. When the gate voltage is changed from one extreme to the ot..
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This circuit allows the effective power in a load to be controlled by varying the duty cycle of the on/off ratio of l..
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Teledyne Semiconductor"s Type TSC9402 IC is eminently suitable as an inexpensive current-to-frequency conver..
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This RF converter converts amateur TV signals in the 420- to 450-MHz region to VHF channel 3 or 4, allowing reception of those signals on a standard TV receiver. RF amplifier Ql feeds mixer Ml, and Q3 acts as an IF amplifier. ..