Top Circuits Page 11
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A neon bulb and a CdS photocell enclosed in a light-tight enclosure form an optocoupler. A diac/triac combination is used to provide the snap- switch effect. A second CdS photocell acts as the main sensor. As darkness approaches, the resistance of K4 begins....
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The circuit can be used as a sensor that can trigger an alarm, without direct contact being made by the intruder. In this circuit, a visible or invisible light source radiates on the sensor, keeping the detection loop in what could essentially be called a....
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NOR gates a and b form a low-frequency oscillator that is activated when the CDS cell, under dark conditions, causes NOR gate a to see a logic zero at one input. This low-frequency (10 Hz) gates a high-frequency oscillator (c and d) to oscillate at around....
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This circuit can produce up to 1 W of audio power to drive a speaker or horn. When the CDS cell is struck by light, its resistance decreases thus activating NOR gate (a) thereby causing (a) and (b) to produce a low-frequency (10-Hz) square wave. This pulses....
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A circuit for isolating a variable resistor is shown. An optoisolator that has an LED arid a photo-conductive cell (or photoresistor) is used. The current through the LED controls its brightness, which in turn determines the resistance between terminals A....
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Null detector uses simple LED readout to indicate if test resistor R* is below, equal to, or greater than test resistance Rref. IfR* = Rref, the 741 output sits at midpoint value of 4 volts and LED A lights..
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The values of Rl, R2, and D1 are selected for the voltage applied. Using a 12-volt battery, Rl = 10 K, R2 = 5 K and D1 is a 5-volt zener diode, or a string of forward-biased silicon rectifiers equaling about 5 volts. Transistor Ql is a general-purpose UJT....
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The circuit has negative feedback only for positive signals. The inverting input can only get some feedback when diode Dl is forward biased and only occurs when the input is positive. With a positive input signal, the output of the op amp rises until the....
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A window detector is a specialized comparator circuit designed to detect the presence of a voltage between two prescribed limits; that is, within a voltage window. This circuit is implemented by logically combining the outputs of two single-ended....
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The primary advantage of this circuit, when compared to other comparators, is its ability to latch after the input has reached a predetermined threshold level. When the input exceeds the threshold level, the LM311N output increases. This transition enables....
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A quad comparator forms the basis of a frequency detector that is faster and less expensive than more complex versions designed around frequency-to-voltage converter chips. Positive feedback through a 5MO resistor allows the circuit to resolve changes as....
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When the upper or lower limit is exceeded, the LED lights up. Positive feedback to one of the nulling terminals creates 5 to 20 p,V of hysteresis on both amplifiers. This feedback changes to offset voltage of the LT1002 by less than 5 p,V. ..
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This window comparator generates an output pulse for each event that occurs within a specified window. That is, each output pulse signifies an input voltage pulse or level change that exceeds VREFLOW. but not VREFHIGH· The monostable multivibrators, IC2A....
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When operated as an open loop without compensation, the HA-2400 becomes a comparator with four selectable input channels. The clamping network at the compensation pin limits the output voltage to allow DTLor TTL digital circuits to be driven with a fanout....
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ICl and IC2 form an inverting half-wave precision-rectifier/peak-detector circuit. Negative input-signal, swings with peaks larger than the voltage on Cl, cause this capacitor to charge to the new peak voltage. The capacitor holds this voltage until a....
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Analog peak detection is accomplished hy repeatedly measuring the input signal with an a/d converter and comparing the current reading with the previous reading. If the current reading is larger than the previous, the current reading is stored in the latch....
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This circuit draws very little power, less than 5 mA with a single 6-V power supply. making it ideal for portable battery-operated equipment. The small size and low power consumption belie the 90-dB dynamic range and 10.5-I"V sensitivity. De output voltage....
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The heart of the electroscope is the two junction FETs Ql and Q2 connected in a balanced-bridge circuit. The gate input of Ql is connected to the wire pick-up antenna, while Q2"s gate is tied to the circuit"s common ground through R2. That type of bridge....
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The range of this ac-voltage monitor is 100 to 140 Vac, with a resolution of 1 V. The speech processor interprets an 8-bit binary input code from an analog-to-digital converter. The processor"s pulse-code-mod ulated output then passes through a filter and....
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This, circuit is a programmable current source in which op amp LT1102 (Linear Technology Corp.) is used..
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A simple voltage-controlled oscillator (VCO), coupled to your instrumentation by an optoisolator, allows you to mea..
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A method of boosting the output current of a reference and also protecting against overloads is shown..
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This is a 8048/IM80C48 Microcomputer with 8 character 16-segment ASCII triplex liquid crystal display. The two bit character address is merged with the data and written to the display driver under the control of the WR line.
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With this dataselector, only one RS-232 port is used to connect two RS-232 devices (i.e., printer, plotter, etc.) with a mini-or microcomputer. The operation is very simple. Power on will reset FFI (QFFT ~ Low), which enables gates N1, N5, and N7. Now....
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Circuits to interlace the Si7135 directly with two popular microprocessors are shown in Figs. 18-2a and b. The 8080/8048 and the MC6800 families with 8-bit words need to have polarity, overrange, and underrange multiplexed onto the digit 5 word. In each....
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The RGB blue box turns your PC"s RGB-monitor screen blue at the flip of a switch. That is, it makes your computer display bright white text on a blue background, instead of the usual low-intensity white on black. The RGB .blue box connects between your....
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This circuit determines whether more than one input in a group of digital inputs is active. It provides a digital measure of the number of active inputs, and it allows you to establish a threshold for majority-decision applications. That is, whether the....
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This RS-232 type line receiver to drive CMOS logic uses a Schmitt-trigger feedback network to ~give about 1-V input hysteresis for added noise immunity. A possible problem in an interface which connects two pieces of equipment, each plugged into a different....
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The circuit uses one-half of a dual D flip-flop as an inverter. When the input decreases, the flip-flop resets, and its Q output increases. When the input increases, the reset line is released and Q gets clocked low. The rc delay between applying the input....
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The IBM PC debugger plugs into the PC"s math-coprocessor socket.The 8288 bus controller, IC1, regenerates control signals from the processor"s status signals, SO, Sl, and S2. Reset LED Dllights if reset is active and holding the processor. Clock status LED....
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This text-to-speech converter is built around the SP0256-AL2 speech processor and the Cf6256AL2 text-to-speech converter chips~manufactured by General Instruments. The circuit is set up to receive standard ASCII code from virtually any microcomputer or....
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The circuit, a general-purpose system with many uses, vocalizes 59 allophones contained in the speech processor. After filtering and amplification, its pulse-code-modulated output can drive an 8-!l speaker. The processor"s address pins, Al to A6, define 64....
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The 555 acts as the tone generator configured in the astable mode. Its pin 3. square-wave output is transformed into a triangle wave by Rl and C2. The voice"s pitch is controlled by RL Transistor Ql can be 2N1086, 2N1091, or any other equivalent npn....
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This hardware-software combination deletes clocks from the slave until both /iPs synchronize. The firmware..
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This protection circuit is inserted between the reset switch and the motherboard. The earth connection of th..
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Getting microprocessor designs to work is notoriously difficult when both the software and hardware are new. The ..
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The circuit illustrates a way to power CMOS ICs from RS-232C lines. The MAX680 is normally used to genera..
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Glitch has been a universal slang expression among electronics people for an unwanted transient condition. In D/A converters, th..
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The I2C serial bus is a popular two-wire bus lor small-area networks. I2C Clock and Data lines have open collector (or drain) outputs for each device-on the network. Only a single pull-up resistor is needed. With this arcliitecture, each device can talk on....
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A laptop computer supply that has 9-V output, crowbar overvoltage protection, and operates i`rom a 12-V supply is shown above. The supply voltage should be at least 3.6 V above the expected output voltage. Ql should be heatsinked appropriately. R5 should....
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This circuit was designed on request to drive a Light-cluster formed by several LEDs that can be mounted in the vehicle as a tail and brake light. When SW1 is on, the cluster will illuminate at medium brightness. When brakes are operated, SW2 will be closed....
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This circuit keeps an automobile's headlights on temporarily. It also will turn the lights off, even if you forget to flip the light switch. The circuit's shut-off delay is actuated only after both the ignition and light switches have been on, and only if....
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Most car door switches are simply single-pole switches, with one side grounded. When the door is opened the switch grounds the other line thus completing the light circuit. In a car where the negative terminal of the battery is connected to the chassis, the....
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This circuit holds on the internal light for approximately one minute after the car doors are closed. When the door contacts open, a + VE pulse is applied to the base of Tl. This transistor turns on, turning off T2 and charging the 10-llF capacitor. T3....
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With both the ignition and the car lights on, piezo transducer BZl draws no current and remains silent. With only the ignition on, diode Dl is reverse-biased and so prevents current flow through BZL. However, when the lights are on and the ignition is....
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When the driver depresses pushbutton switch S1, timing capacitor C1 charges to 12 V and turns on transistor Q1, which drives power transistor Q2 into conduction. This, in tum, energizes the relay which has its contacts connected in parallel with the....
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The circuit keeps the courtesy light on for 30 seconds after you close the door. The lead from the door switch is removed and connected to the 555 circuit. The 555 is arranged in a monostable mode, and is triggered by the door switches. The output drives....
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When power is first applied, three things happen: light -driving transistor Ql is switched on due to a iow output from U2 pin 3; timer U1 begins its timing cycle, with the output, pin 3, becoming high, inhibiting U2"s trigger, pin 2, via D2; and charge....
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The base of Ql is connected to the car"s ignition circuit. One side of the piezoelectric buzzer is connected to the instrument-panellight fuse. When the headlights are off,. no current reaches the buzzer, and therefore nothing happens. What happens when....
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This circuit is for the purpose of monitoring automotive lighting. Two special ICs are available from Telefunken that ar..
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We assume that most of our readers are thoughtful drivers who do not switch on their rear fog lights w..
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The circuit is designed to light (via SCR1 and SCR2) only when both the left and right brake lights are activated. The ci..
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Because power for the circuit is obtained from the car"s side lights, the circuit can"t oscillate unless the lights are o..
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It is annoying to realize that you have left your car headlights on only to find that the battery is flat. One possib..
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This circuit turns on the brake lights of a parked car when the headlights of an oncoming car are detected, wa..
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The circuit can be used to give a visible or an audible warning that the headlights are on. It uses a 2N1305 ..
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When power is first applied, three things happen: the light-driving transistor (Ql) is switched on because of a low output from U2, pin 3; timer Ul begins its timing cycle, with the output (pin 3) going high, inhibiting U2`s trigger (pin 2) via D2; and....
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The headlight flasher is nothing more than a 555 oscillator/timer that`s configured as an astable multivibrator (oscillator). Its input is used to drive the gate of an IRF53IND hexFET, which, in turn, acts like an on/off switch, ..
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A normally open pushbutton switch (SI) delivers a positive input pulse to pin 4 of Ul, triggering the 1C into action. The output of Ul at pin 6 supplies base-drive current to a Darlington pair comprised of Q1 and Q2, activating . 10- capacitor and any....
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A relay and two diodes are all tliat is needed the relay performs the job of a buzzer so no annunciator is required. When the lights are left on, but the ignition is off, the normally closcd relay contacts are in series with the relay coil. That means the....
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The base of Ql is connected to the car`s ignition circuit; the easiest point to make that connection is at the ignition switch fuse in the car`s fuse panel. Also, one side of the piezoelectric buzzer is connected to the instrument-panel light fuse; when the....
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This circuit was designed as an aid in parking the car near the garage wall when backing up. LED D7 illuminates when bumper-wall distance is about 20 cm., D7+D6 illuminate at about 10 cm. and D7+D6+D5 at about 6 cm. In this manner you are alerted when....
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This project is a dedicated device. It dials a single phone number when the handset is lifted. There are two different modes of operation.. A slide-switch on the PC board allows the project to operate in automatic or manual mode. If the switch is in "auto....
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An LM556 dual oscillator/timer, U1, configured as a two-tone oscillator drives U2, a dual4-watt amplifier. One of the oscillators, pins 1 to 6, contained in U1 produces the upper frequency signal of about 200 Hz, while the second oscillator, pins 8 to 13,....
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NOTE: FOR BRIDGE CONFIGURATION: t install jumpers ju2 and ju4 2.remove j 1)3 3.remove rio 4replace ..
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Only one channel of this circuit is shown. The other is practically a carbon copy.The input to the circuit, taken from your car radio`s speaker output, is divided along two paths; in one path, a high-power divider network (consisting of R8 through R10)....
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The following is a method to allow day and night detection using Infrared/Visible light sensitive phototransistors and a simple LM339 voltage comparator circuit. A phototransistor is mounted between the rails so that it is covered by the train as it passes.....
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The simple modulator stage will accommodate most common LEDs. By adjusting the potentiometer, the bias of the transistor is varied until the LED is at its half output point. Then, audio will cause it to vary above and below this point..
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This circuit shows a 555 with its trigger and threshold inputs connected together used to energize a relay when the light level on a photoconductive cell falls below a preset value..
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R2 sets the circuit"s threshold. When the light intensity at PCI"s surface is decreased, the resistance of PCI a cadmium-sulfide photo-resistor is increased. This decreases the voltage at the inverting input of the 741. When the reference voltage at the....
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When the light incident on the LASCR is interrupted, the voltage at the anode to the 2N4990 unilateral switch goes positive on the next positive cycle of the power which in turn triggers the switch and the C230 SCR when the switching voltage of the....
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The basic circuit can be operated at 80 kHz and is limited by the PUT capacitor combination. 60 kHz is the maximum modulation frequency. The pulse repetition rate is a linear function of Vin, the modulating voltage. Lenses or reflectors minimizes stray light....
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An alternate LED driver which uses the 74F3040 line driver was incorporated in this particular application example. The 74F3040.has a higher current rating, but not the variable threshold capabilities at the NE522. The LED diode is operated in the....
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This receiver uses the NE5212, the Signetics 10116 ECL line receiver, and the Phillips/Amperex BPF31 pin diode. The circuit is a capacitor-coupled receiver and utilizes positive feedback in the last stage to provide the hysteresis. The amount of hysteresis....
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The circuit shows a simplex fiber link between the NE5080 transmitter and the NE5081 receiver. The components shown are for a center frequency of 5 MHz, although this frequency can be increased to 20 MHz with proper selection of external component values.....
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This two-chip receiver with minimum external component count has been designed for low-cost fiber optic applications to 100-M baud (50 MHz). The receiver is divided into pre-and postamplifier !Cs for increased stability. The preamplifier IC features low....
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The optical signal is coupled to the pin diode. Current flowing in the diode also flows into the input of the NE5211 preamplifier. The preamplifier is a fixed-gain block that has a 28-K!J differential transimpedance and does a single-ended to differential....
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A resonance-tuned narrow-band amplifier reduces this optical object detector"s sensitivity to stray light. C1 and L1 in IC2A"s feedback loop cause tbe op amp to pass only those frequencies at or near the LED"s 5-kHz modulation rate. ..
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A common method of transforming the output current of a photodiode into a voltage signal, paralleling the photodiode with a high-value load resistor, produces a nonlinear response. Also the combination of the load"s transresistance, Rr. and the....
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This circuit puts out a pulse when an object on the conveyor belt blocks the light source. The light source keeps the phototran-sistor turned on. This produces a high-logic-level voltage at the Schmitt-trigger inverter and a TTL-compatible low logic level at....
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Provides remote control for ac-powered devices by using the beam of a flashlight as a magic wand. The important aspect of this gadget is that it remembers. Activate it once to apply power to a device and it stays on. Activate it a second time and power goes....
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Both circuits use the GE. SC146B, 200 V, 10 A Triac as load current contacts. These triacs are triggered by normal SBS (2N4992) trigger circuits, which are controlled by the photo-Darlington, acting through the DA806 bridge as an ac photo switch. To operate....
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This transmitter uses a 741 op amp as a high-gain audio amplifier, which is driven by a microphone. The output of the 741 is coupled to Ql, which serves as the driver for a LED. Potentiometer R1 is the amplifier`s gain control. Miniature trimmer resistor R6....
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This light-wave receiver consists of a 741 operated as a preamplifier and an LM386 operated as a power amplifier. Potentiometer R2 is the gain control. Various kinds of detectors can be used as the front end of the receiver. Phototransistors are very....
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As before, there are two sections: the transmitter board and the receiver board, both powered by a separate 9V battery or a fixed voltage power supply, depending on your needs. The transmitter board has an electret microphone module at one end, and the laser....
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Ql and Q2 switch the primary windings of transformer Tl via a square wave at a frequency determined by its magnetic properties. Diodes Dl and D2 provide base return paths for the feedback current of Ql and Q2. The output winding of T1 is connected to a....
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The laser diode·pulser is a simple drive circuit capable of driving the laser diode with 10-A, 20-ns pulses. For a 0.1 % duty cycle, the repetition rate will be 50 kHz. A complementary emitter follower is used as a driver. Switching speed is determined by....
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These two circuits provide bias for the microwave preamps shown in this text. The circuit in Fig. 51-5(a)..
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ICl is a 555 timer running at about 16 kHz. This IC drives Ql, a TIP146, which produces a 12-V square wave across Tl pri..
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Driving Helium-Neon Lasers can be simplified considerably using This power-supply configuration. When power is applied, the laser doesn`t conduct and the voltage across the 190- resistor is zero. However, a resonant circuit and a voltage tripler then....
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The circuit uses a 555 timer IC to power an ultrabright LED. The output is a pulsing red light that can be projected using lenses. An ultrabright Stanley LED, capable of 300-millicandle output, is tied to pin 3 of the 555 timer IC. That IC has been....
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This supply generates an initial high voltage for ignition purposes. After ignition, the supply generates about 1300 to 1500 V. If a higher ignition voltage (than the 6000 V supplied) is necessary,..
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There are many 9V chaser circuits that seem to waste about 7V when driving LEDs that are only about 2V. This project is unique, because it uses only two inexpensive alkaline battery cells totaling 3V for power. Since most of the waste is eliminated, the....
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The LEDs are OSSV53E1A from OptoSupply and they have an 140° angle. This means that the first plane with uniform density can be obtained at a shorter distance from the LED, for a given spacing between LEDs which means smaller height for the board. Their peak....
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Have you ever wondered how many different colors can illuminate a LED? One, two or maybe three? Constructing this simple circuit, you will find it much more. The key component in this design is a dual LED. One such accessory includes two inside the 'slices'....
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Indicator was designed for displaying the peak level of small ac signals from a variety of transducers including microphones, strain gauges and photodiodes. The circuit responds to input signals contained within the audio frequency spectrum, i.e., 30 Hz to....
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The circuit uses CA3290 BiMOS dual voltage comparators. Non-inverting inputs of A1 and A2 are tied to voltage divider reference. The input signal is applied to the inverting inputs.
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When SI is on, power is applied to an oscillator composed of Ql, Rl, Cl, LI, and L2. Coil Ll is the primary winding of Tl, and L2 is the feedback winding. When Ql turns on, its collector current saturates Tl's ferrite core. That, in turn, removes the base....
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A 741 op amp is employed as a voltage comparator. The noninverting input is connected to zener reference source. Reference voltage is 5V. R2 is adjusted so that the voltage at the inverting input is half the supply voltage. When supply is higher than 10V,....
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The precision voltage-monitor chip contains a temperature-compensated voltage reference. R1 divides down the battery voltage to match the built-in reference voltage of ICl (15 volts). When the voltage at pin 3 falls below 15 volts, pin 4 supplies a constant....
A neon bulb and a CdS photocell enclosed in a light-tight enclosure form an optocoupler. A diac/triac combination is used to provide the snap- switch effect. A second CdS photocell acts as the main sensor. As darkness approaches, the resistance of K4 begins....
The circuit can be used as a sensor that can trigger an alarm, without direct contact being made by the intruder. In this circuit, a visible or invisible light source radiates on the sensor, keeping the detection loop in what could essentially be called a....
NOR gates a and b form a low-frequency oscillator that is activated when the CDS cell, under dark conditions, causes NOR gate a to see a logic zero at one input. This low-frequency (10 Hz) gates a high-frequency oscillator (c and d) to oscillate at around....
This circuit can produce up to 1 W of audio power to drive a speaker or horn. When the CDS cell is struck by light, its resistance decreases thus activating NOR gate (a) thereby causing (a) and (b) to produce a low-frequency (10-Hz) square wave. This pulses....
A circuit for isolating a variable resistor is shown. An optoisolator that has an LED arid a photo-conductive cell (or photoresistor) is used. The current through the LED controls its brightness, which in turn determines the resistance between terminals A....
Null detector uses simple LED readout to indicate if test resistor R* is below, equal to, or greater than test resistance Rref. IfR* = Rref, the 741 output sits at midpoint value of 4 volts and LED A lights..
The values of Rl, R2, and D1 are selected for the voltage applied. Using a 12-volt battery, Rl = 10 K, R2 = 5 K and D1 is a 5-volt zener diode, or a string of forward-biased silicon rectifiers equaling about 5 volts. Transistor Ql is a general-purpose UJT....
The circuit has negative feedback only for positive signals. The inverting input can only get some feedback when diode Dl is forward biased and only occurs when the input is positive. With a positive input signal, the output of the op amp rises until the....
A window detector is a specialized comparator circuit designed to detect the presence of a voltage between two prescribed limits; that is, within a voltage window. This circuit is implemented by logically combining the outputs of two single-ended....
The primary advantage of this circuit, when compared to other comparators, is its ability to latch after the input has reached a predetermined threshold level. When the input exceeds the threshold level, the LM311N output increases. This transition enables....
A quad comparator forms the basis of a frequency detector that is faster and less expensive than more complex versions designed around frequency-to-voltage converter chips. Positive feedback through a 5MO resistor allows the circuit to resolve changes as....
When the upper or lower limit is exceeded, the LED lights up. Positive feedback to one of the nulling terminals creates 5 to 20 p,V of hysteresis on both amplifiers. This feedback changes to offset voltage of the LT1002 by less than 5 p,V. ..
This window comparator generates an output pulse for each event that occurs within a specified window. That is, each output pulse signifies an input voltage pulse or level change that exceeds VREFLOW. but not VREFHIGH· The monostable multivibrators, IC2A....
When operated as an open loop without compensation, the HA-2400 becomes a comparator with four selectable input channels. The clamping network at the compensation pin limits the output voltage to allow DTLor TTL digital circuits to be driven with a fanout....
ICl and IC2 form an inverting half-wave precision-rectifier/peak-detector circuit. Negative input-signal, swings with peaks larger than the voltage on Cl, cause this capacitor to charge to the new peak voltage. The capacitor holds this voltage until a....
Analog peak detection is accomplished hy repeatedly measuring the input signal with an a/d converter and comparing the current reading with the previous reading. If the current reading is larger than the previous, the current reading is stored in the latch....
This circuit draws very little power, less than 5 mA with a single 6-V power supply. making it ideal for portable battery-operated equipment. The small size and low power consumption belie the 90-dB dynamic range and 10.5-I"V sensitivity. De output voltage....
The heart of the electroscope is the two junction FETs Ql and Q2 connected in a balanced-bridge circuit. The gate input of Ql is connected to the wire pick-up antenna, while Q2"s gate is tied to the circuit"s common ground through R2. That type of bridge....
The range of this ac-voltage monitor is 100 to 140 Vac, with a resolution of 1 V. The speech processor interprets an 8-bit binary input code from an analog-to-digital converter. The processor"s pulse-code-mod ulated output then passes through a filter and....
This, circuit is a programmable current source in which op amp LT1102 (Linear Technology Corp.) is used..
A simple voltage-controlled oscillator (VCO), coupled to your instrumentation by an optoisolator, allows you to mea..
A method of boosting the output current of a reference and also protecting against overloads is shown..
This is a 8048/IM80C48 Microcomputer with 8 character 16-segment ASCII triplex liquid crystal display. The two bit character address is merged with the data and written to the display driver under the control of the WR line. ..
With this dataselector, only one RS-232 port is used to connect two RS-232 devices (i.e., printer, plotter, etc.) with a mini-or microcomputer. The operation is very simple. Power on will reset FFI (QFFT ~ Low), which enables gates N1, N5, and N7. Now....
Circuits to interlace the Si7135 directly with two popular microprocessors are shown in Figs. 18-2a and b. The 8080/8048 and the MC6800 families with 8-bit words need to have polarity, overrange, and underrange multiplexed onto the digit 5 word. In each....
The RGB blue box turns your PC"s RGB-monitor screen blue at the flip of a switch. That is, it makes your computer display bright white text on a blue background, instead of the usual low-intensity white on black. The RGB .blue box connects between your....
This circuit determines whether more than one input in a group of digital inputs is active. It provides a digital measure of the number of active inputs, and it allows you to establish a threshold for majority-decision applications. That is, whether the....
This RS-232 type line receiver to drive CMOS logic uses a Schmitt-trigger feedback network to ~give about 1-V input hysteresis for added noise immunity. A possible problem in an interface which connects two pieces of equipment, each plugged into a different....
The circuit uses one-half of a dual D flip-flop as an inverter. When the input decreases, the flip-flop resets, and its Q output increases. When the input increases, the reset line is released and Q gets clocked low. The rc delay between applying the input....
The IBM PC debugger plugs into the PC"s math-coprocessor socket.The 8288 bus controller, IC1, regenerates control signals from the processor"s status signals, SO, Sl, and S2. Reset LED Dllights if reset is active and holding the processor. Clock status LED....
This text-to-speech converter is built around the SP0256-AL2 speech processor and the Cf6256AL2 text-to-speech converter chips~manufactured by General Instruments. The circuit is set up to receive standard ASCII code from virtually any microcomputer or....
The circuit, a general-purpose system with many uses, vocalizes 59 allophones contained in the speech processor. After filtering and amplification, its pulse-code-modulated output can drive an 8-!l speaker. The processor"s address pins, Al to A6, define 64....
The 555 acts as the tone generator configured in the astable mode. Its pin 3. square-wave output is transformed into a triangle wave by Rl and C2. The voice"s pitch is controlled by RL Transistor Ql can be 2N1086, 2N1091, or any other equivalent npn....
This hardware-software combination deletes clocks from the slave until both /iPs synchronize. The firmware..
This protection circuit is inserted between the reset switch and the motherboard. The earth connection of th..
Getting microprocessor designs to work is notoriously difficult when both the software and hardware are new. The ..
The circuit illustrates a way to power CMOS ICs from RS-232C lines. The MAX680 is normally used to genera..
Glitch has been a universal slang expression among electronics people for an unwanted transient condition. In D/A converters, th..
The I2C serial bus is a popular two-wire bus lor small-area networks. I2C Clock and Data lines have open collector (or drain) outputs for each device-on the network. Only a single pull-up resistor is needed. With this arcliitecture, each device can talk on....
A laptop computer supply that has 9-V output, crowbar overvoltage protection, and operates i`rom a 12-V supply is shown above. The supply voltage should be at least 3.6 V above the expected output voltage. Ql should be heatsinked appropriately. R5 should....
This circuit was designed on request to drive a Light-cluster formed by several LEDs that can be mounted in the vehicle as a tail and brake light. When SW1 is on, the cluster will illuminate at medium brightness. When brakes are operated, SW2 will be closed....
This circuit keeps an automobile's headlights on temporarily. It also will turn the lights off, even if you forget to flip the light switch. The circuit's shut-off delay is actuated only after both the ignition and light switches have been on, and only if....
Most car door switches are simply single-pole switches, with one side grounded. When the door is opened the switch grounds the other line thus completing the light circuit. In a car where the negative terminal of the battery is connected to the chassis, the....
This circuit holds on the internal light for approximately one minute after the car doors are closed. When the door contacts open, a + VE pulse is applied to the base of Tl. This transistor turns on, turning off T2 and charging the 10-llF capacitor. T3....
With both the ignition and the car lights on, piezo transducer BZl draws no current and remains silent. With only the ignition on, diode Dl is reverse-biased and so prevents current flow through BZL. However, when the lights are on and the ignition is....
When the driver depresses pushbutton switch S1, timing capacitor C1 charges to 12 V and turns on transistor Q1, which drives power transistor Q2 into conduction. This, in tum, energizes the relay which has its contacts connected in parallel with the....
The circuit keeps the courtesy light on for 30 seconds after you close the door. The lead from the door switch is removed and connected to the 555 circuit. The 555 is arranged in a monostable mode, and is triggered by the door switches. The output drives....
When power is first applied, three things happen: light -driving transistor Ql is switched on due to a iow output from U2 pin 3; timer U1 begins its timing cycle, with the output, pin 3, becoming high, inhibiting U2"s trigger, pin 2, via D2; and charge....
The base of Ql is connected to the car"s ignition circuit. One side of the piezoelectric buzzer is connected to the instrument-panellight fuse. When the headlights are off,. no current reaches the buzzer, and therefore nothing happens. What happens when....
This circuit is for the purpose of monitoring automotive lighting. Two special ICs are available from Telefunken that ar..
We assume that most of our readers are thoughtful drivers who do not switch on their rear fog lights w..
The circuit is designed to light (via SCR1 and SCR2) only when both the left and right brake lights are activated. The ci..
Because power for the circuit is obtained from the car"s side lights, the circuit can"t oscillate unless the lights are o..
It is annoying to realize that you have left your car headlights on only to find that the battery is flat. One possib..
This circuit turns on the brake lights of a parked car when the headlights of an oncoming car are detected, wa..
The circuit can be used to give a visible or an audible warning that the headlights are on. It uses a 2N1305 ..
When power is first applied, three things happen: the light-driving transistor (Ql) is switched on because of a low output from U2, pin 3; timer Ul begins its timing cycle, with the output (pin 3) going high, inhibiting U2`s trigger (pin 2) via D2; and....
The headlight flasher is nothing more than a 555 oscillator/timer that`s configured as an astable multivibrator (oscillator). Its input is used to drive the gate of an IRF53IND hexFET, which, in turn, acts like an on/off switch, ..
A normally open pushbutton switch (SI) delivers a positive input pulse to pin 4 of Ul, triggering the 1C into action. The output of Ul at pin 6 supplies base-drive current to a Darlington pair comprised of Q1 and Q2, activating . 10- capacitor and any....
A relay and two diodes are all tliat is needed the relay performs the job of a buzzer so no annunciator is required. When the lights are left on, but the ignition is off, the normally closcd relay contacts are in series with the relay coil. That means the....
The base of Ql is connected to the car`s ignition circuit; the easiest point to make that connection is at the ignition switch fuse in the car`s fuse panel. Also, one side of the piezoelectric buzzer is connected to the instrument-panel light fuse; when the....
This circuit was designed as an aid in parking the car near the garage wall when backing up. LED D7 illuminates when bumper-wall distance is about 20 cm., D7+D6 illuminate at about 10 cm. and D7+D6+D5 at about 6 cm. In this manner you are alerted when....
This project is a dedicated device. It dials a single phone number when the handset is lifted. There are two different modes of operation.. A slide-switch on the PC board allows the project to operate in automatic or manual mode. If the switch is in "auto....
An LM556 dual oscillator/timer, U1, configured as a two-tone oscillator drives U2, a dual4-watt amplifier. One of the oscillators, pins 1 to 6, contained in U1 produces the upper frequency signal of about 200 Hz, while the second oscillator, pins 8 to 13,....
NOTE: FOR BRIDGE CONFIGURATION: t install jumpers ju2 and ju4 2.remove j 1)3 3.remove rio 4replace ..
Only one channel of this circuit is shown. The other is practically a carbon copy.The input to the circuit, taken from your car radio`s speaker output, is divided along two paths; in one path, a high-power divider network (consisting of R8 through R10)....
The following is a method to allow day and night detection using Infrared/Visible light sensitive phototransistors and a simple LM339 voltage comparator circuit. A phototransistor is mounted between the rails so that it is covered by the train as it passes.....
The simple modulator stage will accommodate most common LEDs. By adjusting the potentiometer, the bias of the transistor is varied until the LED is at its half output point. Then, audio will cause it to vary above and below this point..
This circuit shows a 555 with its trigger and threshold inputs connected together used to energize a relay when the light level on a photoconductive cell falls below a preset value..
R2 sets the circuit"s threshold. When the light intensity at PCI"s surface is decreased, the resistance of PCI a cadmium-sulfide photo-resistor is increased. This decreases the voltage at the inverting input of the 741. When the reference voltage at the....
When the light incident on the LASCR is interrupted, the voltage at the anode to the 2N4990 unilateral switch goes positive on the next positive cycle of the power which in turn triggers the switch and the C230 SCR when the switching voltage of the....
The basic circuit can be operated at 80 kHz and is limited by the PUT capacitor combination. 60 kHz is the maximum modulation frequency. The pulse repetition rate is a linear function of Vin, the modulating voltage. Lenses or reflectors minimizes stray light....
An alternate LED driver which uses the 74F3040 line driver was incorporated in this particular application example. The 74F3040.has a higher current rating, but not the variable threshold capabilities at the NE522. The LED diode is operated in the....
This receiver uses the NE5212, the Signetics 10116 ECL line receiver, and the Phillips/Amperex BPF31 pin diode. The circuit is a capacitor-coupled receiver and utilizes positive feedback in the last stage to provide the hysteresis. The amount of hysteresis....
The circuit shows a simplex fiber link between the NE5080 transmitter and the NE5081 receiver. The components shown are for a center frequency of 5 MHz, although this frequency can be increased to 20 MHz with proper selection of external component values.....
This two-chip receiver with minimum external component count has been designed for low-cost fiber optic applications to 100-M baud (50 MHz). The receiver is divided into pre-and postamplifier !Cs for increased stability. The preamplifier IC features low....
The optical signal is coupled to the pin diode. Current flowing in the diode also flows into the input of the NE5211 preamplifier. The preamplifier is a fixed-gain block that has a 28-K!J differential transimpedance and does a single-ended to differential....
A resonance-tuned narrow-band amplifier reduces this optical object detector"s sensitivity to stray light. C1 and L1 in IC2A"s feedback loop cause tbe op amp to pass only those frequencies at or near the LED"s 5-kHz modulation rate. ..
A common method of transforming the output current of a photodiode into a voltage signal, paralleling the photodiode with a high-value load resistor, produces a nonlinear response. Also the combination of the load"s transresistance, Rr. and the....
This circuit puts out a pulse when an object on the conveyor belt blocks the light source. The light source keeps the phototran-sistor turned on. This produces a high-logic-level voltage at the Schmitt-trigger inverter and a TTL-compatible low logic level at....
Provides remote control for ac-powered devices by using the beam of a flashlight as a magic wand. The important aspect of this gadget is that it remembers. Activate it once to apply power to a device and it stays on. Activate it a second time and power goes....
Both circuits use the GE. SC146B, 200 V, 10 A Triac as load current contacts. These triacs are triggered by normal SBS (2N4992) trigger circuits, which are controlled by the photo-Darlington, acting through the DA806 bridge as an ac photo switch. To operate....
This transmitter uses a 741 op amp as a high-gain audio amplifier, which is driven by a microphone. The output of the 741 is coupled to Ql, which serves as the driver for a LED. Potentiometer R1 is the amplifier`s gain control. Miniature trimmer resistor R6....
This light-wave receiver consists of a 741 operated as a preamplifier and an LM386 operated as a power amplifier. Potentiometer R2 is the gain control. Various kinds of detectors can be used as the front end of the receiver. Phototransistors are very....
As before, there are two sections: the transmitter board and the receiver board, both powered by a separate 9V battery or a fixed voltage power supply, depending on your needs. The transmitter board has an electret microphone module at one end, and the laser....
Ql and Q2 switch the primary windings of transformer Tl via a square wave at a frequency determined by its magnetic properties. Diodes Dl and D2 provide base return paths for the feedback current of Ql and Q2. The output winding of T1 is connected to a....
The laser diode·pulser is a simple drive circuit capable of driving the laser diode with 10-A, 20-ns pulses. For a 0.1 % duty cycle, the repetition rate will be 50 kHz. A complementary emitter follower is used as a driver. Switching speed is determined by....
These two circuits provide bias for the microwave preamps shown in this text. The circuit in Fig. 51-5(a)..
ICl is a 555 timer running at about 16 kHz. This IC drives Ql, a TIP146, which produces a 12-V square wave across Tl pri..
Driving Helium-Neon Lasers can be simplified considerably using This power-supply configuration. When power is applied, the laser doesn`t conduct and the voltage across the 190- resistor is zero. However, a resonant circuit and a voltage tripler then....
The circuit uses a 555 timer IC to power an ultrabright LED. The output is a pulsing red light that can be projected using lenses. An ultrabright Stanley LED, capable of 300-millicandle output, is tied to pin 3 of the 555 timer IC. That IC has been....
This supply generates an initial high voltage for ignition purposes. After ignition, the supply generates about 1300 to 1500 V. If a higher ignition voltage (than the 6000 V supplied) is necessary,..
There are many 9V chaser circuits that seem to waste about 7V when driving LEDs that are only about 2V. This project is unique, because it uses only two inexpensive alkaline battery cells totaling 3V for power. Since most of the waste is eliminated, the....
The LEDs are OSSV53E1A from OptoSupply and they have an 140° angle. This means that the first plane with uniform density can be obtained at a shorter distance from the LED, for a given spacing between LEDs which means smaller height for the board. Their peak....
Have you ever wondered how many different colors can illuminate a LED? One, two or maybe three? Constructing this simple circuit, you will find it much more. The key component in this design is a dual LED. One such accessory includes two inside the 'slices'....
Indicator was designed for displaying the peak level of small ac signals from a variety of transducers including microphones, strain gauges and photodiodes. The circuit responds to input signals contained within the audio frequency spectrum, i.e., 30 Hz to....
The circuit uses CA3290 BiMOS dual voltage comparators. Non-inverting inputs of A1 and A2 are tied to voltage divider reference. The input signal is applied to the inverting inputs. ..
When SI is on, power is applied to an oscillator composed of Ql, Rl, Cl, LI, and L2. Coil Ll is the primary winding of Tl, and L2 is the feedback winding. When Ql turns on, its collector current saturates Tl's ferrite core. That, in turn, removes the base....
A 741 op amp is employed as a voltage comparator. The noninverting input is connected to zener reference source. Reference voltage is 5V. R2 is adjusted so that the voltage at the inverting input is half the supply voltage. When supply is higher than 10V,....
The precision voltage-monitor chip contains a temperature-compensated voltage reference. R1 divides down the battery voltage to match the built-in reference voltage of ICl (15 volts). When the voltage at pin 3 falls below 15 volts, pin 4 supplies a constant....