Top Circuits Page 13
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The circuit uses a dual LED. When power is applied to the probe throughthe power leads, and the input is touched to a low level or ground, Ql is cut off. This will cause Q2 to conduct since the base is positive with respect to the emitter. With Ql cut off....
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The injector is a CMOS oscillator with period approximately equal to 1 x Cl x R2 seconds. The values are given for 1 kHz operation. Resistors R3 and R4 divide theoutput to 1 V; Whereas the oscillator employs the gates in their digital mode, the tracer used....
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The unit has a separate amplifier and oscillator section allowing them to be used separately if need be. The injector is a multivibrator running at 1 kHz, with R5 andR6 dividing down the output to a suitable level («1V). The tracer is a single-stage....
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The logic probe can indicate four input states, as follows: floating input—all LEDs off..
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A 741 op amp is used with 100% ac and dc feedback to provide a typical input impedance of 1011 ohm and unity gain. To avoid hum and rf pickup the input leads should be kept as short as possible and the circuit should be mounted in a small grounded case.....
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Transistors Q1 and Q2 form a buffer, providing the probe with a reasonable input impedance. Q3 and Q4 form a level detecting circuit. As the voltage across the base-emitter junction of the Q3 rises above 0,6 V the transistor turns on thus turning on Q4 and....
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There are two switches: a memory disable switch and a pulse polarity switch. Memory disable is a push-button that resets the memory to the low state when depressed. Pulse polarity is a toggle switch that selects whether the probe responds to a high-level or....
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The probe indicates a high or low at 70% and 30% of V+ (5 to 12 V). One section of the voltage comparator (LM393) senses V in over 70% of supply and the second section senses V in under 30%. These two sections direct-drive the appropriate LEDs. The pulse....
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This economical signal tracer is useful for servicing and alignment work in receivers and low power transmitters. When switched to RF, the modulation on any signal is detected by the diode and amplified by the FET..
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Gates Gl and G2 together with resistors Rl and R2 form a simple voltage monitor that has a trip point of 1 volts. Gate G3 is simply an inverter. The display section of the tester consists of a common anode alphanumeric LED and current-limiting resistors..
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The low Rds and high peak current capability ofthe DG419 makes it ideal for discharging an·integrator capacitor. A high logic input pulse disconnects the integrator from the analog input and discharges the capacitor. ..
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When a large number of channels are multiplexed, the outputs of two or more multiplexers can be connected together and each multiplexer sequentially enabled. In the inhibit mode. the multiplexer draws less power and its output and inputs act as open....
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This circuit reconstructs and separates analog signals which have been time-division multiplexed. The conventional method, shown on the left, has several restrictions, particularly when a short dwell time and a long, accurate hold time is required. The....
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This circuit shows a typical multiplex system intended to carry one of 8 inputs into a remote location. A 5-V pulse train is sent down a separate channel to perform timing and synchronizing functions. A 15-V reset pulse is superimposed on the 5-V clock,....
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The probe relies on the power supply of the CUT (circuit-under-test). The input to the probe, at probe tip, is fed along two paths. One path flows to the clock inputs of U2a and U2b. The other path feeds both the inverting input of Ulc, which is set up as....
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The pulser generates pulses at a user-selected frequency of 0.5 or 500 Hz, with a pulse width of about 5 ms. If the input to be pulsed is already being driven high or low by another output, the pulser automatically pulses the input to the opposite logic....
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Using this simple resistor circuit, you can trick your oscilloscope into displayin..
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The HA-4900 series comparators can be used as versatile logic interface devices, as shown in these circuits. Negati..
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Some circuits that add binary numbers have problems with time delay caused by carry propagation. This has been ..
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The compact test probe provides rapid "measurement" of voltage levels at digital gates, fuses, diodes, batteries, and ..
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This logic probe uses a CD4009 CMOS hex inverter. The characteristic high-input impedance of CMOS gives the advantage..
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· This circuit is used for analog signal selection or time division multiplexing. As shown, the feedback signal places the selected amplifier channel in a voltage follower (noninverting unity gain) configuration, and provides very high input impedance and....
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This circuit for a test set contains a signal injector (U1A/U1B) and associated com..
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Amplifying and limiting of the AM carrier is accomplished by the if gain block providing 55 dB of gain or higher with a limiting of 40 µ\. The limited carrier is then applied to the detector at the carrier ports to provide the desired switching function.....
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Transistor Ql and its associated components comprise a tuneable rf oscillator. The rf signal is fed to transistor Q2, the modulator. Operational amplifier ICl increases the audio signal and applies it through resistor R4 to the base of Q2. Tune an AM radio....
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Built around an Intersil 7216 frequency-counter IC, this counter has a basic range of 10 MHz, a 100-MHz prescaler, and an..
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This receiver uses an IR-sensitive phototransistor (Clairex, HP, etc.) mounted in a light-tight enclosur..
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Using a Signetics NE602 in a varactor-tuned front end, the circuit of a shortwave receiver can be very simple and yet g..
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Two MC1408—8-bit D/A converters, A and in the circuit diagram, are used. The four least-significant bits of A are tied to zero. The four most significant bits of the 12-bit data are connected to the remaining four input pins. The eight least significant....
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The step size of the converter is variable by selection of the high order data bits. The first DAC, A, has a stable reference current supplied via the 10.24 V reference IC and Rl. R2 provides bias cancellation. As shown, only the first 4 MSB inputs are used,....
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This circuit will convert four-bit BCD into a variable voltage from 0-9 V in 1 V steps. The SN74141 is a Nixie driver, and has ten open-collector outputs. These are used to ground a selected point in the divider chain determined by the BCD code at the input,....
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The following applications circuits are intended to illustrate the following points: A 2-KO resistor should be in series with V + to limit supply current with negative ringing oi the bit. inputs. Temperature compensation for Rns(on) can be provided in the....
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The front end of the DAC is configured differentially using dual eight-input IC multiplexer 1H6216 and three LM156 op amps. Following the differential amplifier is the programmable gain stage discussed earlier, with a low-pass filter on the output feeding....
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Three CD4007 A IC packages perform the switch function using a 10-V logic level. A single 15-V supply provides a positive bus for the follower amplifier and feeds the CA3085 voltage regulator. The scale adjust function is provided by the regulator output....
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Where N is the binary number from 0 to 15 formed by the digital input. If the analog input is a fixed de reference, the circuit is a conventional 4-bit D to ac signal, in which case the output is the product of the analog signal and the digital signal. The....
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This peak detector uses a CA3100 BiMOS op amp as a wide-band noninverting amplifier to provide essentially constant gain for a wide range of input frequencies. The IN914 clips the negative half of VfN (R4)/(R3) (R5). ..
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Figure A is an R/2R resistor ladder. Each switch that is closed increases the amount of current at . A simple channel A/D converter is shown in Fig. B. The voltage reference (D2) is common to all channels, but-the value of the dropping resistor (R9) varies....
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A heat-sensitive sensor can be used to construct a direction detector. Such a sensor reacts to all an..
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A four output Hall sensor combined with a few logic gates produce this digital compass. The NOR gates resolve the four Hall..
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This RDF circuit consists of a square-wave oscillator (IC1), which switches two antennas alternately at an audio rat..
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A talking compass is made up using a Hall-effect direction sensor (MODI) and an ISD1016 analog audio storage device. It is possible to program eight two-second announcements, for each of the eight main compass directions. The Talking Compass is comprised of....
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The very simple circuit uses only two CD4001 packages, i.e., eight NOR gates and operates in the following way: Pulse streams are fed to an RS flip flop generating an output waveform wliich has a small or large duty cycle depending on the direction of....
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This self-starting fixed-frequency oscillator circuit gives excellent frequency stability. R1 and C 1 comprise the frequency-determining network, while R2 provides the regenerative feedback. Diode D 1 enhances the stability by compensating for the....
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Capacitor C1 is charged through timing resistor R1 when the clock output is high. When C1 reaches the upper threshold voltage, the output signal decreases, and then C1 discharges through R1 until its voltage reaches the lower threshold point. When this....
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This free-running TTL square-wave oscillator has a variable frequency output over a 20:1 range or better through use of four of the six inverters in an SN7404 chip and the additional components shown. Frequency of oscillation is determined by the capacitor....
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The 20-MHz clock phase-locks to Apple"s Mac II 10-MHz NuBus clock. It uses a simple, inexpensive CMOS circuitry to generate 10-and 20-MHz square waves. The output duty cycle settings are insensitive to Vee variations. The input to the circuit is a NuBus....
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This simple circuit generates a dual-speed clock for personal computers. The circuit synchronizes your asynchronous switch inputs with the master clock to provide glitch-free transitions from one clock speed to the other. The dual-speed clock allows some....
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1. THE INPUT CLOCK frequency fed into this circuit is divided by 2n-l. The circuit consists of clocked flip-..
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One leg of the photocell (Rl) is tied to the +15 volt supply and the other end is connected to ground through resistor R2, forming a voltage-divider network. The non-inverting input of the 741 op amp, IC1, is tied to the junction formed by Rl and R2, while....
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The circuit arrangement consists of a photo-amplifier which feeds a voltage derived from varying light levels in an enlarger to a pair of peak detectors. One follows the peak positive voltage and the other the peak negative voltage. The capacitors used for....
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The darkroom timer/controller uses few external components: a display, a digit driver, keyboard, and output switching devices. A 4-digit common-cathode LED display is desirable for dark room environments. The time base is provided by shaping up the 50/60 Hz....
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This circuit gives multiple "stop-action" photographic effects like showing a bouncing ball in up to nine locations in a single photograph. The circuit will automatically fire the bulbs sequentially with the time between each firing variable. The circuit is....
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Take strobe-flash pictures the instant a pin pricks a balloon, a hammer breaks a lamp bulb or a bullet leaves a gun. Use a transistor amplifier of 1-watt rating or less. (It must have an output transformer) The amplifier is terminated with a resistor on its....
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In photography r a separate flash, triggered by the light of a master flash light, is often required to provide more light, fill-in shadows etc. The sensitivity of this circuit depends on the proximity of the master flash and the value of Rl..
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Transistor Ql is a light-activated silicon-controlled rectifier (LASCR). The gate is tripped by light entering a small iens built into the top cap. To operate, provide a 6-in. length of stiff wire for the anode andcathodeconnections and terminate the wires....
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You can set the interval from about 5-30 seconds. A relay operates the slide-change mechanism. Op amp Ul forms a sort of Schmitt trigger. Resistors Rl and R2 bias the noninverting input at pin 3 of Ul to half the supply voltage. Feedback resistor R3....
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Transistor Ql remains off until the magnetic switch connected to Jl closes. When that happens, the 9 Vis connected through Rl to Ql"S base. Ql turns on, thereby charging C2 through relay Kl, which causes Kl "s contacts to close. Since the contacts connect....
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The NE555 circuit is a basic one-shot timer with a relay connected between the output and ground. It is triggered with the normally open momentary contact switch, which when operated, grounds the trigger input at pin 2. This causes a high output to....
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Insulated-gate, field-effect transistor (IGFET), Q2 and silicon photo cell Zl form the heart of this circuit. Transformer T1 is an audio-output type, but it"s reversed in the circuit. A sudden flash from a photoflash unit detected by Zl sends a voltage....
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This circuit is used for remote photographic flash units that flash at the~ame time as the flash attached to the camera. This circuit is designed to the trigger cord or hot shoe connection of a commercial portable flash unit and triggers the unit from the....
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This circuit will record commentary and/ or music on one track of a tape and put the beeps that change the slides on another track. Gate U2a is used to trigger U1, which is configured as a timer when a pulse is received from either the tape input or via....
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Using the CA3164A BiMOS control chip consumes less than 15 pA during standby, yet it can provide 100 mA of chopped current to the de-to-de converter during the energy-reservoir charging cycle. The CA3164A drives tbe primary of T1 with symmetrically chopped....
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The HA2541 is well-suited for use as the heart of an oscillator. In spite of the rudimentary diode limiting that is ..
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S2 is used to initiate timing. A light-to-dark or dark-to-light transition stops this timer, depending on the setting of ..
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Ql is a phototransistor that is normally illuminated by a beam of light. When the beam is intercoupled, pin ..
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This circuit was used to trip a camera shutter. Grounding pin 2 of U1 makes pin 4 of U1 go high. This triggers both tim..
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A 4001 CMOS Quad NORgate is set up as an astable multivibrator, which drives a simple differentiator and relay..
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By using a low-cost RS-170 camera and this circuit, a voltage that trades the position of an object in ..
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Meter Ml, a +/-50-uA zero-center D`Arsonval meter movement is driven by Ul, a TL081 FET op amp, through R3. The gain of Ul is set at 11 by Rl and R2, while capacitor 01 is used to restrict the bandwidth of Ul to 1.6 Hz. Power for the circuit is derived from....
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Sound or light sensors corniected to J2 produce a voltage that is amplified by ICl-a and ICl-b. A positive trigger voltage that is developed by D1 and 1)3 and amplified by ICl-d, drives 1C2 and 1C1 to trigger SCR1. SCR1 is connected to a strobe. ..
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The electronic darkroom timer is built around a 555 oscillator/timer, a pair of general-purpose transistors, a buzzer, and an LED. The 555 (Ul) is configured as an astable multivibrator (free-running oscillator). The frequency of the oscillator is....
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Two gates of a 4011 arc used as a comparator. When the resistance of R4 decreases the voltage at pin 1 and 2 increases, producing a logic zero at pin 3, causing pin 4 to go high and activating the LED. R3 is calibrated in light units, or seconds exposure....
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It is common that sometimes we need to power some devices σuccessively one after the other. This function forces us to handle a large number of switches, which are located where the access is difficult, especially in the case of informational devices and....
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The purpose of this circuit is to control the water temperature in a hot-water heating system. What it does is to lower the boiler temperature as the outside air temperature increases. The op amp is used as a comparator. Thermistor TH2 and R2 form a voltage....
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The sensor is a standard TO-5 or TO-46 package. For surface or air temperature sensing. Small clip-on heat sinks can be used. A simple probe can be made using heat-shrink tubing and RTV silicon rubber. Three-leads-plus-shield cable is a good choice for wire....
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Temperature control is achieved using the REF-02 +5 V Reference/Thermometer and a CMP-02 Precision Low Input Current Comparator. The CMP-02 turns on a heating element driver (Ql) whenever the present temperature drops below a setpoint temperature determined....
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This converter can accommodate wide inputvoltage swings, such as the 8 to 15-V swing typical of a 12-V sealed lead/acid battery. The low battery output indicates when input voltage drops below 8V. ..
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The SCR is wired across the trigger circuit of the flash gun. Normally, the SCR is off, so the flash gun is able to cha..
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This solid-state switch senses and interrupts an overcurrent condition within 2 /is. II allows the circuit to float. IC..
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This circuit allows a 4-to 20-mA current loop to control an isolated SCR drive. IC1A and are one-shots. Q2 detect..
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In both circuits, the SCR (and thereby the lamp) can be latched on by momentarily closing SI, thereby fe..
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This switch uses four CD4013 BE dual flip-flops, an inverter, and an optoisolator to drive a triac. The circuit can switch 25-A ac load current. A standard 4x3 telephone keyboard is used to enter a 6-digit code. In case of a wrong code, a signal is....
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This circuit senses the video from the VCR. When the VCR is turned on, video signal is amplified by U3A and to drive Ql, activating Kl. In this manner, it is not necessary to turn on and off two video devices every time. In many cases, this avoids the use....
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This circuit, adds a power-down function to analog I/O ports (for example, the AD7769 and AD7774). Moreover, the diodes ordinarily needed to protect the devices against power-supply mis-sequencing can be eliminated (see the figure).In the circuit, MOSFETs....
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The amplifier picks up the TV"s audio output signal and amplifies it to drive a set of earphones for private listening. It is built around an LM324 quad op amp and an LM386 low-power audio amplifier. ..
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This circuit provides a simple, low-cost crosshatch generator tor convergence and geometry adJUStments on color TVs. The generator is driven by two clocks, one for the horizontal drive, IC1ab, and one for the vertical drive, IC2ab. The clock outputs are....
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CI and LI resonate on the 1750 meter band, with coverage from 150 kHz to 500 kHz. LI can be slug-tuned for 160-to-190 kHz coverage alone or a 2.5 mH choke can be used for LI, if desired, using CI for tuning. A 1N270 germanium diode rectifies the RF signal....
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The bug tracer is made up of a simple rf-injector circuit consisting of Ql and Q2, and a pocketsize, AM broadcast receiver. The two-transistor rf-injector circuit supplies a constant rf signal to one end of a cable. Then the AM receiver is used as a....
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This rf detector can locate low-power transmitters (bugs) that are hidden from sight. It can sense the presence of a 1-mW transmitter at 20 feet. which is sensitive enough to detect the tiniest bug. As you bring the rf detector closer to the bug, more and....
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The circuit is based on operational amplifier IC1 used in the noninverting amplifier mode. Rl and 2 set the gain at about 500. RV1 (sensitivity) biases the noninverting input to the negative supply. Ql provides the relatively high trigger current required by....
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A stereo power amp designed for use in portable players and radios. A 3V supply can be used to drive headphones providing 20mW in 32 Ohms per channel. ..
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This generator will supply sine, triangular, and square waves from 2Hz to 20kHz. This complete test instrument can be plugged into a standard 110 Vac line for power. VoVT will be up to ±25 V (50 V pk-pk across loads as small as 10 0 (about 2.5 A maximum....
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This inverter can deliver .high-voltage ac or de, with a rectifier and filter, up to several hundred volts. The secondary and primary of T1-a 12.6 to 440 V power transformer, respectively-are reversed; e.g., the primary becomes the secondary and the....
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The most elementary application is a half-wave control circuit. The thyristor is acting both as a power control device and as a rectifier, providing variable power to the load !luring the positive half cycle and no power to the load during the negative....
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Here is a simple tachometer circuit for use with a hand-held DVM or portable chart recorder. A novel feature is that the source frequency pulse/rev rate can be directly set on a ten-turn potentiometer to provide a convenient calibration of one V per 1000....
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This circuit provides a cheap alternative to the LM3915 series LED displays. The meter relies on a square-wave oscillat..
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U2 is a decade counter /divider, Ul is used as a switch debouncer. For a self-generating system, connect a resisor..
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A simple solenoid driver uses incandescent lamp filaments as on-indicators to limit power consumption. High magnetic reluctance (opposition to flux) in the coil of an armature-driven device, such as a solenoid or relay, calls for a surge of activation....
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This circuit controls a solenoid by the operation of a single push-button switch. The circuit will supply loads of over 1 A and can be operated up to a maximum speed of once every 0.6 second. When power is first applied to the circuit, the solenoid will....
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In many applications, a solenoid driver must first briefly supply a large amount of pull-in cnrrent, which quickly actuates the solenoid. Thereafter, the driver must supply a much lower holding cnrrent to avoid burning the solenoid out. To avoid using the....