Top Circuits Page 14
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A limiter circuit that requires matched zener diodes can instead use one zener with a full-wave diode bridge. The..
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Q1 is an npn Darlington and Q2 is a prip Darlington. MOV1 is a metal-oxide varistor and R8 is an thermistor for limiting inrush current. This circuit limits ac line current to a load. When a predetermined interval has passed, RY1 shorts out thermistor or....
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A 7805 can be configured as a constant-current regulator, to serve as an inrush current limiter. Rl will have 5 V across it at all times so the total current through 11 will be 5 V/R1 + 5 mA, the 5 mA being the regulator operating current...
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The calibrator operates on exactly 100 kHz providing a reference for calibrating the variable time base oscillator of general purpose scopes. For example, if the scope is set so that one cycle of the signal fills exactly 10 graticule divisions then each....
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A clamp-on "current probe" such as the Tektronix P6021 is a useful means of displaying current waveforms on an oscilloscope. Unfortunately, the low-frequency response is somewhat limited, as shown in the Table. The more sensitive range on the P6021 is 2....
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The 650 MHz Prescaler Probe's input is terminated by resistor Rl and is fed through Cl to the diode limiter composed ofD1 through D4. Those diodes are forward-biased by the +5 volt supply for small-input signals and, in turn, feed the signal to Ul. However,....
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A single connection change permits division by any integer between 2 and 10. The RCA CD4017A Johnson decade counter is shown connected as a divide by 7 counter. The resistor is used to hold the reset line low. When the appropriate number is reached, that....
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To buffer a test generator to the outside world requires an amplifier with sufficient bandwidth and power handling capability. The circuit is a very simple unity gain buffer. It has a fairly high input impedance, a 50 ohm output impedance, a wide bandwidth,....
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The circuit employs a 100 ohm isolation resistor which enables the amplifier to drive capacitive loads exceeding 500 pF; the resistor effectively isolates the high frequency feedback from the load and stabilizes the circuit..
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With a constant current excitation, the voltage dropped across an inductance in-(in creases with frequency. Thus, an active device whose output increases with frequency can be characterized as an inductance. The circuit yields such a response with the....
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The monolithic quad operational amplifier provides an inexpensive way to increase display capability of a standard oscilloscope. Binary inputs drive the IC op amp; a dual flip-flop divides the scope"s gate output to obtain channel selection signals. All....
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The basis ofthe beam splitter is a 555 timer connected as an astable multivibrator. Signals at the two inputs are alternately displayed on the oscilloscope with a clear separation between them..
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Simple, portable phase-sequence indicator determines the proper phase rotation in polyphase circuits. Major components are two neon lamps, two resistors, and a capacitor. In operation, the leg voltages are unbalanced, so that the lamp with the maximum....
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This tester provides an audible indication of the logic level of the signal presented to its input. A logic high is indicated by a high tone, a logic low is indicated by a low tone, and oscillation is indicated by an alternating tone. The input is high....
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The DUT"s(Device Under Test) cathode, anode, and gate are connected to the unit"s K, A, and G terminals, respectively. Pressing switch ·Sl feeds a gate current to the D UT, which triggers it on. Resistor Rl limits the gate current to the appropriate....
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The pitch of the tone is dependent upon the resistance under test. The tester will respond to resistances of hundreds of kilohms, yet it is possible to distinguish differences of just tens of ohms in low-resistance circuits. Q1 and Q2 form a....
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Using inexpensive components, you can fit a simple probe circuit into a pencil-sized enclosure. When both LEDs are on, the probe indicates the presence of an ac voltage; either LED alone indicates the presence and polarity of a de voltage. The....
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This FET probe has an input impedance of 10 M!J shunted by 8 pF. Eliminating the protective diodes reduces this impedance to about 4 pF. The frequency response of the probe extends from de to 20 MHz ( -1 dB), although higher frequency operation is possible....
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This compact tester checks cables for open-circuit or short-circuit conditions. A differential transistor pair at one end of each cable line remains balanced as long as the same clock pulse generated by timer IC appears at both ends of the line. ..
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A designer often needs to know the value of the internal resistance of a battery. Quite a few testers gi..
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The battery low-voltage detector uses a CD4093 Schmitt trigger and a capacitor that acts as a 1-bit dynamic RAM. The c..
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This circuit allows a microprocessor system to measure its own battery voltage. A Texas Instrument TI43..
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This battery tester makes use of an LM3914 bar-graph driver IC. SI selects load on battery under test and programs the volta..
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This Nicad battery tester discharges the test battery at a rate of 500 mA. When the endpoint of 1 V (determined by set..
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The sensing circuit consists of a 741 op amp set up as a voltage comparator, using a zener diode as a voltage referen..
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Three-terminal regulator device (LM78LXX) has Vout = Vm until the input rises 1.5 to 2 V above the output when the ..
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This unit uses switches and resistors to provide a number of current ranges. It allows you to test most of the meters availabl..
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A 555 timer drives Ql through Q4 with a square wave. LED1 and LED2 light when an npn or pnp transistor respectively, are ..
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Ul is an op amp used as a comparator. When the test probes are shorted together, resistors R1 and R2 bias the noninverti..
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This circuit can be used to check up to an eight-conductor cable. IC1, a 555 timer, drives decade counter..
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The circuit consists of a 5-V regulator, constant-current source Dl, D2, and Ql, and op amp gain stage Ul. Power is provid..
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A high-gain amplifier using a UA741 is used to sense relative voltage drop in a conductor, and therefore current i..
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This circuit uses a dc amplifier (324) in a bar-graph circuit that uses an LM339 Quad comparator IC to sense dc levels. ..
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An LF356 op amp is used as a gain amplifier with the output taken across R5, When a full-scale current of 1 mA is flowing..
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This amplifier can transfer dc-to 5-MHz signals across a potential difference of 25 000 V. This circu..
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The input consists of two comparators that operate with different reference voltages supplied by separate potential dividers. ..
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This circuit outputs a TTL-compatible - pulse whenever the signal falls within the limits set by potentiometers ..
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This window generator uses a single LM324 op amp and features two adjustable set points. When the two comparators formed b..
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In Fig. 104-3(a), when Vin is between reference voltages Vi and Vu, output Vout goes low. If Vin> Vl, IC2 produces a low..
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The high switching speed, low offset current and low offset voltage of the HA-4900 series make this window detector extreme..
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The battery tester uses four transistors and two LEDs to indicate the condition of any battery you want to test. Q3 and Q4 are connected in a Darlington configuration that has extremely high gain. LED L2 lights when a small positive potential appears on the....
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This circuit uses a pair of Zener diodes to monitor battery voltage of a 12-V battery. If below 11 V, 1)1 ceases to conduct, pin 3 of 102 goes high, setting FF IC2 turning on Ql, Kl, and the battery charger...
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Using this circuit, tiiree levels of voltage can be displayednormal (11 to 15 V), liigh (>15 V), and low (11 V). When the voltage is low, the LED glows steadily. In the normal range, the LED is off. When the voltage is high, the LED blinks at a 1-Hz rate. ..
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The LM3914A bargraph LEDis used here as a voltmeter for battery testing. The circuit is powered by a 4.5-V battery and compares the battery under test with an internally derived reference, set by R1/R2/P1. Each LED of the 10 represent 10% of full scale...
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This circuit consists of a tri-color LED, a resistor, wire, and a coin-size test plate. You will have to build two such circuits one for each black clamp on a set of auto battery jumper cables. The author installed the circuits inside the black clamps....
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With SI open, base bias is supplied to Q2 through a voltage divider (formed by R2 and R3), thus turning on the green element in the LED. That indicates that power is being supplied to the project. If you close SI, current through R1 biases Ql on, thereby....
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By judging the rate at which a particular LED flashes, you`ll be able to estimate the resistance. The circuit consists of two IC`s (1 4011 CMOS quad 2-input, NAND gate, Ul; and a 4024 binary counter, U2), seven LEDs, and a handful of additional .components.....
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This decade box can be set for any resistance value between 10 and 11.1 in 10- stops. A switch can be used to configure several RC configurations. Use close tolerance components in the circuit. If possible, check components with-an accurate bridge or....
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At the heart of the cable tester are two op amps, which are used as a window- comparator to indicate a short- or open-circuit condition. A third op-amp comparator is used to indicate a good circuit (i.e., neither open nor shorted). Colored LEDs are used to....
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The circuit is built around a 741 general-purpose op amp that is configured as a voltage follower; with the components shown, the op amp has a voltage gain of one. The output of the 741 is used to drive a 50- meter movement. Potentiometer R7 is used to zero....
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The tester provides an audible indication of the logic level of the signal presented to its input. A logic high is indicated by a high tone, a logic low is indicated by a low tone, and oscillation is indicated by an alternating tone. The input is high....
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This electronic pressure gauge uses a Wheatstone bridge-type pressure sensor tb drive a 3 A digit A/D converter and a display. IC1 is a pump (quad) that interfaces the bridge sensor to the A/D converter. R16 provides zero adjustment and R6 provides....
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Transistors Ql and Q2, together with resistors Rl through R7, make up the input balancing stage, which senses the resistance between points X and Y. The input stage is essentially a bridge, consisting of Rl, R2, R6, R7, and the resistance between points X....
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The tester consists of a rectifier circuit and a multivibrator circuit. The ac voltage is half-wave rectified by diode D1 and stored in capacitor CI. Resistor Rl is used to limit the current through D1 to a safe value. The voltage stored across CI supplies....
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The circuit uses Ql to buffer the right-channel balance output while Q2 and Q3 form a VOX circuit. When the signal level from the microphone goes high, the output of the VOX also goes high and the multiplexer inside IC1 switches the high-gain left-channel....
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Transmitter operation. Operating power for the transmitter circuit is derived directly from the ac line. The dc power to operate the circuit is generated in two stages, one for an RF power-am-plifier stage, and the second for the remainder of the circuit.....
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Driving a D/A converter with an A/D converter provides an overall analog-hold function, which though limited in output resolution, offers zero voltage droop and infinite hold time. The A/D converter shown (IC1) includes a 12-bit compatible track/hold at its....
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To display an rf signal, connect LI to the transmitter and points A and B to the vertical plates of the oscilloscope. Adjust LI for minimum SWR and C3 for the desired trace height on the CRT..
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Though this setup can act as a cost-effective current source with an output accurate to 1%, the voltage offset will turn on the current source even when Vqq equals Vin. 2. Modifying the configuration of Figure 1 can rectify the problem of the current source....
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The dc values of op-amp offsets can`t always be taken for granted when delivering ac outputs. No device is ever exactly symmetrical for maximum positive slew rate versus maximum negative slew rate. Consequently, there is always some range of output slew....
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In essence, the circuit is nothing more than an auto ignition coil and a set of points which accomplishes the same thing. A pulsing circuit made from a single CMOS NOR integrated circuit (Ul), opens and closes the relay contacts to simulate the action of the....
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The silicon controlled rectifier (SCR) is rated to handle at least the current of the power supply. It is connected in parallel across the 12 V dc output lines, but remains inert until a voltage appears at the gate terminal. This triggering voltage is....
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The push button and potentiometer initiate a time delay that turns a light on then automatically turns it off again after a predetermined time. The potentiometer can be set for a delay of a few seconds to just under three minutes. When the push-button switch....
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This circuit checks the reliability of appliances so that the equipment may be used safely. The test circuit must be plugged into a properly wired three terminal wall outlet. When a two-lead or three-lead appliance is plugged into circuit outlet SOI, neon....
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Industrial applications sometimes require that power be only briefly applied to a load following the closure of a switch, such as a microswitch or foot switch. The load could be a heating element for use in sealing plastic bags, a de motor that is indexed....
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The spark developed by the circuit is suitable for a gas ignitor. Capacitor Cl is charged through Rl and Dl toward peak line voltage. C2 is simultaneously being charged at a slower rate through R5. When the charge on C2 is sufficient.to trigger the PUT,....
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To avoid grief when using 12-V power supplies with mobile transceivers, especially when there is a short -circuit failure of the series pass transistor, crowbar circuits provide protection by clamping the power line and blowing the fuse within microseconds....
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This circuit uses a type 741 op amp as a voltage comparator. One input of the 7.41 is connected to a reference voltage (a 12-V battery) through a resistor voltage divider. The potential at the noninverting input of the 741 is approximately 3 V. The....
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The adjustable circuit breaker responds in 0.02 sunder all conditions-provided you select a fast relay for Kl. For moderate overload conditions, it"s preferable to use the fuse or the fast-acting breaker. Toroid transformer Tl senses ac load current and....
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This circuit protects expensive portable equipment against all types of improper hookups and environmental hazards that could cause an overvoltage condition. It operates very quickly and does not latchup, that is, it recovers when the overvoltage condition....
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These two circuits are SSB generators. One uses a crystal filter by KVG Electronics at 9 MHz, the other uses a 455-kHz mecha..
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Most of the transistors in this speaker protector function as switches. Normally, Q4, Q5, and K1 are on and the speakers are connected to the amplifier. However, if a large dc voltage appears at an amplifier output, either Q3, or Ql and Q2 turn on, biasing....
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Basically, this circuit is an adjustable electronic circuit breaker, containing a toroidal transformer that senses 60-Hz load current. Tl has a two-turn winding for primary, and 100 turns of #30 gauge wire for the secondary. A high-low range switch selects....
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A speaker system can be protected against amplifier failure when dc voltages (on speaker line a-b) arc sensed by the circuit. Either positive or negative dc voltages are sensed. A relay opens in this case, removing the dc from the speakers...
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When testing a circuit, a source of voltage that is variable and has overvoltage shutdown is veiy useful. In this circuit, Rl is adjusted to 1 to 2 V below the eventual shutdown threshold. R2 sets the trip voltage. When this voltage is reached, the circuit....
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The ear protector is actually a peak audio-detector/shutdown circuit that disables the amplifier through its chip-disable input when the output volume of an amplifier reaches the set level. The circuit, although intended for the MC34119 amplifier,..
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Transistors Ql, Q2, and Q3 monitor the two outputs of the stereo amplifier. If the offsets exceed 2 V, Q7 is turned off, which turns off Q8 and the normally on relay. Diodes D2 and D5, together with Q4, provide a mains voltage monitor. As soon as the ac....
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This antenna tuner is suitable for use with low-power (less than 5 W) transmitters or SW receivers. S2 selects inductance and S2 connects the 365-pF capacitor to either the transmitter or the side of the inductor. The tiny tuner is comprised of a tapped....
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The HF/SW receiver preamplifier is comprised of a broadband toroidal transformer (LI-a and Ll-b), LC network (comprised of a 1600-kHz, high- pass filter-and a 32-MHz, low-pass filter), L2 and L3 (26 turns of #26 enameled wire wound on an Amidon Associates....
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A pair of diodes and a quarter-wave transmission line are used as an automatic TR switch. D1 and D2 conduct during transmit periods, short- circuiting the scanner input. In this mode,-the K-wave line appears as an open circuit...
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A circuit stabilizes the current-transfer ratio (CTR) of an optically coupled isolator used as a linear transducer. The optocoupler produces a voltage output that is proportional to—but electrically isolated from—the voltage input. However, the output....
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The application involves observing the light pulse emerging from a thick specimen after transillumination by a laser pulse. Pulses derived from the laser source are amplified using a Video Amplifier LM733. The reference level is set to 1 V in the comparator....
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Fiber Optic applications require analog drivers and receivers operating in the megahertz region. This complete analog transmission system is suitable for optical communication applications up to 3 MHz. The transmitter LED is normally biased at 50 mA....
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If you need a wide-range, resistor-programmable monostable multivibrator, you can program tbe circuit for pulse widths from 1 JlS to 10s-107:1 range. A high-to-low transition at tbe input causes IC1"s output to switch low, thereby turning off Q1 and Q2.....
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A positive-going trigger pulse can be used to start the timing cycle with the circuit shown. In this design, trigger input pin 2 is biased to 6V (1/z Vvv) by divider Rl and R2. Control input pin 5 is biased to 8 V (213 Vvvl by the internal divider circuit.....
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The circuit illustrates the usefulness of the HA-5151 as a battery-powered monostable. In this circuit, the ratio is set to .632, which allows the time constant equation to be reduced to: T=R1*C1. D2 is used to force the output to a defined state by....
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In this mode, the timer functions as a one shot. The external capacitor is initially held discharged by a transistor internal to the timer. Applying a negative trigger pulse to pin 2 sets the flip-flop, driving the output high, and releasing the short....
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Modems are devices that connect either remote devices to a computer, or two or more computers to each other. Their connection is usually wired. The GSM modem we present is wireless. It can connect two computers, a computer with the internet or even be the....
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This circuit features the ZTX450/ZTX550 transistors in a push-pull output stage. The following readings were taken at maximum volume: Input: 0.4 mV rms, Output: 1.8 V rms, Voltage gain: 4500, Max. output before distortion: 2.25 V rms -supply current ~ 3.5....
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A JFET transistor-is used as a high-to-low impedance converter and signal mixer. Input impedance is approximately 50.0 kQ but it can be increased by increasing R5 to R8 as high as 10 . Output is about 2 kQ, but it can be increased or decreased by changing....
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It is possible to simulate the balanced performance of a transformer electronically with a different amplifier. By adjusting the presets, the resistor ratio can be balanced so that the best CMRR is obtained. It is possible to get a better CMRR than from a....
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The detector uses three sections of an L144 and a DC4011 type CMOS NAND gate to make a very low power voltage monitor. If the input voltage, Vin, is above Vhigh or below Vlow, the output will be a logical high. If (and only if) the input is between the....
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Using a pickup coil to drive an amplifier (IC3A-B-C-D), this meter circuit can be directly calibrated in field-intensi..
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In this circuit, oscillator Ql runs at about 15 kHz and feeds mixer Ul. Ul has an internal oscillator that runs a..
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The circuit uses a Hall-effect sensor, which consists of an IC that resides in a small gap in a flux-collector ..
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The voltage required to ignite the neon tube is obtained by using an ordinary filament transformer (240-6 V) in reverse. Battery drain is quite low, around 1 to 2 milliamps for a nine volt battery. The pulses from Ql, unijunction transistor, operated as a....
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This circuit has been designed to drive an 8-W fluorescent lamp from a 12-V source using an inexpensive inverter based on the ZTX652 transistor. The inverter will operate from supplies in the range of 10 to 16.5 V, thus making it suitable for use in....
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For multiplying frequencies in the 1-to 150-Hz range, this circuit uses a 4046B and a 100 prescaler. The VCO output..
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A wideband high gain configuration using two SL550s connected in series. The first stage is connected in common emitter configuration, the second stage is a common base circuit. Stable gains of up to 65 dB can be achieved by the proper choice of Rl and R2..
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The JFET-bipolar cascode circuit will provide full video output for the CRT cathode drive. Gain is about 90. The cascode configura-tioneliminates Miller capacitance problems with the 2N4091 JFET, thus allowing direct drive from the video detector..
A limiter circuit that requires matched zener diodes can instead use one zener with a full-wave diode bridge. The..
Q1 is an npn Darlington and Q2 is a prip Darlington. MOV1 is a metal-oxide varistor and R8 is an thermistor for limiting inrush current. This circuit limits ac line current to a load. When a predetermined interval has passed, RY1 shorts out thermistor or....
A 7805 can be configured as a constant-current regulator, to serve as an inrush current limiter. Rl will have 5 V across it at all times so the total current through 11 will be 5 V/R1 + 5 mA, the 5 mA being the regulator operating current...
The calibrator operates on exactly 100 kHz providing a reference for calibrating the variable time base oscillator of general purpose scopes. For example, if the scope is set so that one cycle of the signal fills exactly 10 graticule divisions then each....
A clamp-on "current probe" such as the Tektronix P6021 is a useful means of displaying current waveforms on an oscilloscope. Unfortunately, the low-frequency response is somewhat limited, as shown in the Table. The more sensitive range on the P6021 is 2....
The 650 MHz Prescaler Probe's input is terminated by resistor Rl and is fed through Cl to the diode limiter composed ofD1 through D4. Those diodes are forward-biased by the +5 volt supply for small-input signals and, in turn, feed the signal to Ul. However,....
A single connection change permits division by any integer between 2 and 10. The RCA CD4017A Johnson decade counter is shown connected as a divide by 7 counter. The resistor is used to hold the reset line low. When the appropriate number is reached, that....
To buffer a test generator to the outside world requires an amplifier with sufficient bandwidth and power handling capability. The circuit is a very simple unity gain buffer. It has a fairly high input impedance, a 50 ohm output impedance, a wide bandwidth,....
The circuit employs a 100 ohm isolation resistor which enables the amplifier to drive capacitive loads exceeding 500 pF; the resistor effectively isolates the high frequency feedback from the load and stabilizes the circuit..
With a constant current excitation, the voltage dropped across an inductance in-(in creases with frequency. Thus, an active device whose output increases with frequency can be characterized as an inductance. The circuit yields such a response with the....
The monolithic quad operational amplifier provides an inexpensive way to increase display capability of a standard oscilloscope. Binary inputs drive the IC op amp; a dual flip-flop divides the scope"s gate output to obtain channel selection signals. All....
The basis ofthe beam splitter is a 555 timer connected as an astable multivibrator. Signals at the two inputs are alternately displayed on the oscilloscope with a clear separation between them..
Simple, portable phase-sequence indicator determines the proper phase rotation in polyphase circuits. Major components are two neon lamps, two resistors, and a capacitor. In operation, the leg voltages are unbalanced, so that the lamp with the maximum....
This tester provides an audible indication of the logic level of the signal presented to its input. A logic high is indicated by a high tone, a logic low is indicated by a low tone, and oscillation is indicated by an alternating tone. The input is high....
The DUT"s(Device Under Test) cathode, anode, and gate are connected to the unit"s K, A, and G terminals, respectively. Pressing switch ·Sl feeds a gate current to the D UT, which triggers it on. Resistor Rl limits the gate current to the appropriate....
The pitch of the tone is dependent upon the resistance under test. The tester will respond to resistances of hundreds of kilohms, yet it is possible to distinguish differences of just tens of ohms in low-resistance circuits. Q1 and Q2 form a....
Using inexpensive components, you can fit a simple probe circuit into a pencil-sized enclosure. When both LEDs are on, the probe indicates the presence of an ac voltage; either LED alone indicates the presence and polarity of a de voltage. The....
This FET probe has an input impedance of 10 M!J shunted by 8 pF. Eliminating the protective diodes reduces this impedance to about 4 pF. The frequency response of the probe extends from de to 20 MHz ( -1 dB), although higher frequency operation is possible....
This compact tester checks cables for open-circuit or short-circuit conditions. A differential transistor pair at one end of each cable line remains balanced as long as the same clock pulse generated by timer IC appears at both ends of the line. ..
A designer often needs to know the value of the internal resistance of a battery. Quite a few testers gi..
The battery low-voltage detector uses a CD4093 Schmitt trigger and a capacitor that acts as a 1-bit dynamic RAM. The c..
This circuit allows a microprocessor system to measure its own battery voltage. A Texas Instrument TI43..
This battery tester makes use of an LM3914 bar-graph driver IC. SI selects load on battery under test and programs the volta..
This Nicad battery tester discharges the test battery at a rate of 500 mA. When the endpoint of 1 V (determined by set..
The sensing circuit consists of a 741 op amp set up as a voltage comparator, using a zener diode as a voltage referen..
Three-terminal regulator device (LM78LXX) has Vout = Vm until the input rises 1.5 to 2 V above the output when the ..
This unit uses switches and resistors to provide a number of current ranges. It allows you to test most of the meters availabl..
A 555 timer drives Ql through Q4 with a square wave. LED1 and LED2 light when an npn or pnp transistor respectively, are ..
Ul is an op amp used as a comparator. When the test probes are shorted together, resistors R1 and R2 bias the noninverti..
This circuit can be used to check up to an eight-conductor cable. IC1, a 555 timer, drives decade counter..
The circuit consists of a 5-V regulator, constant-current source Dl, D2, and Ql, and op amp gain stage Ul. Power is provid..
A high-gain amplifier using a UA741 is used to sense relative voltage drop in a conductor, and therefore current i..
This circuit uses a dc amplifier (324) in a bar-graph circuit that uses an LM339 Quad comparator IC to sense dc levels. ..
An LF356 op amp is used as a gain amplifier with the output taken across R5, When a full-scale current of 1 mA is flowing..
This amplifier can transfer dc-to 5-MHz signals across a potential difference of 25 000 V. This circu..
The input consists of two comparators that operate with different reference voltages supplied by separate potential dividers. ..
This circuit outputs a TTL-compatible - pulse whenever the signal falls within the limits set by potentiometers ..
This window generator uses a single LM324 op amp and features two adjustable set points. When the two comparators formed b..
In Fig. 104-3(a), when Vin is between reference voltages Vi and Vu, output Vout goes low. If Vin> Vl, IC2 produces a low..
The high switching speed, low offset current and low offset voltage of the HA-4900 series make this window detector extreme..
The battery tester uses four transistors and two LEDs to indicate the condition of any battery you want to test. Q3 and Q4 are connected in a Darlington configuration that has extremely high gain. LED L2 lights when a small positive potential appears on the....
This circuit uses a pair of Zener diodes to monitor battery voltage of a 12-V battery. If below 11 V, 1)1 ceases to conduct, pin 3 of 102 goes high, setting FF IC2 turning on Ql, Kl, and the battery charger...
Using this circuit, tiiree levels of voltage can be displayednormal (11 to 15 V), liigh (>15 V), and low (11 V). When the voltage is low, the LED glows steadily. In the normal range, the LED is off. When the voltage is high, the LED blinks at a 1-Hz rate. ..
The LM3914A bargraph LEDis used here as a voltmeter for battery testing. The circuit is powered by a 4.5-V battery and compares the battery under test with an internally derived reference, set by R1/R2/P1. Each LED of the 10 represent 10% of full scale...
This circuit consists of a tri-color LED, a resistor, wire, and a coin-size test plate. You will have to build two such circuits one for each black clamp on a set of auto battery jumper cables. The author installed the circuits inside the black clamps....
With SI open, base bias is supplied to Q2 through a voltage divider (formed by R2 and R3), thus turning on the green element in the LED. That indicates that power is being supplied to the project. If you close SI, current through R1 biases Ql on, thereby....
By judging the rate at which a particular LED flashes, you`ll be able to estimate the resistance. The circuit consists of two IC`s (1 4011 CMOS quad 2-input, NAND gate, Ul; and a 4024 binary counter, U2), seven LEDs, and a handful of additional .components.....
This decade box can be set for any resistance value between 10 and 11.1 in 10- stops. A switch can be used to configure several RC configurations. Use close tolerance components in the circuit. If possible, check components with-an accurate bridge or....
At the heart of the cable tester are two op amps, which are used as a window- comparator to indicate a short- or open-circuit condition. A third op-amp comparator is used to indicate a good circuit (i.e., neither open nor shorted). Colored LEDs are used to....
The circuit is built around a 741 general-purpose op amp that is configured as a voltage follower; with the components shown, the op amp has a voltage gain of one. The output of the 741 is used to drive a 50- meter movement. Potentiometer R7 is used to zero....
The tester provides an audible indication of the logic level of the signal presented to its input. A logic high is indicated by a high tone, a logic low is indicated by a low tone, and oscillation is indicated by an alternating tone. The input is high....
This electronic pressure gauge uses a Wheatstone bridge-type pressure sensor tb drive a 3 A digit A/D converter and a display. IC1 is a pump (quad) that interfaces the bridge sensor to the A/D converter. R16 provides zero adjustment and R6 provides....
Transistors Ql and Q2, together with resistors Rl through R7, make up the input balancing stage, which senses the resistance between points X and Y. The input stage is essentially a bridge, consisting of Rl, R2, R6, R7, and the resistance between points X....
The tester consists of a rectifier circuit and a multivibrator circuit. The ac voltage is half-wave rectified by diode D1 and stored in capacitor CI. Resistor Rl is used to limit the current through D1 to a safe value. The voltage stored across CI supplies....
The circuit uses Ql to buffer the right-channel balance output while Q2 and Q3 form a VOX circuit. When the signal level from the microphone goes high, the output of the VOX also goes high and the multiplexer inside IC1 switches the high-gain left-channel....
Transmitter operation. Operating power for the transmitter circuit is derived directly from the ac line. The dc power to operate the circuit is generated in two stages, one for an RF power-am-plifier stage, and the second for the remainder of the circuit.....
Driving a D/A converter with an A/D converter provides an overall analog-hold function, which though limited in output resolution, offers zero voltage droop and infinite hold time. The A/D converter shown (IC1) includes a 12-bit compatible track/hold at its....
To display an rf signal, connect LI to the transmitter and points A and B to the vertical plates of the oscilloscope. Adjust LI for minimum SWR and C3 for the desired trace height on the CRT..
Though this setup can act as a cost-effective current source with an output accurate to 1%, the voltage offset will turn on the current source even when Vqq equals Vin. 2. Modifying the configuration of Figure 1 can rectify the problem of the current source....
The dc values of op-amp offsets can`t always be taken for granted when delivering ac outputs. No device is ever exactly symmetrical for maximum positive slew rate versus maximum negative slew rate. Consequently, there is always some range of output slew....
In essence, the circuit is nothing more than an auto ignition coil and a set of points which accomplishes the same thing. A pulsing circuit made from a single CMOS NOR integrated circuit (Ul), opens and closes the relay contacts to simulate the action of the....
The silicon controlled rectifier (SCR) is rated to handle at least the current of the power supply. It is connected in parallel across the 12 V dc output lines, but remains inert until a voltage appears at the gate terminal. This triggering voltage is....
The push button and potentiometer initiate a time delay that turns a light on then automatically turns it off again after a predetermined time. The potentiometer can be set for a delay of a few seconds to just under three minutes. When the push-button switch....
This circuit checks the reliability of appliances so that the equipment may be used safely. The test circuit must be plugged into a properly wired three terminal wall outlet. When a two-lead or three-lead appliance is plugged into circuit outlet SOI, neon....
Industrial applications sometimes require that power be only briefly applied to a load following the closure of a switch, such as a microswitch or foot switch. The load could be a heating element for use in sealing plastic bags, a de motor that is indexed....
The spark developed by the circuit is suitable for a gas ignitor. Capacitor Cl is charged through Rl and Dl toward peak line voltage. C2 is simultaneously being charged at a slower rate through R5. When the charge on C2 is sufficient.to trigger the PUT,....
To avoid grief when using 12-V power supplies with mobile transceivers, especially when there is a short -circuit failure of the series pass transistor, crowbar circuits provide protection by clamping the power line and blowing the fuse within microseconds....
This circuit uses a type 741 op amp as a voltage comparator. One input of the 7.41 is connected to a reference voltage (a 12-V battery) through a resistor voltage divider. The potential at the noninverting input of the 741 is approximately 3 V. The....
The adjustable circuit breaker responds in 0.02 sunder all conditions-provided you select a fast relay for Kl. For moderate overload conditions, it"s preferable to use the fuse or the fast-acting breaker. Toroid transformer Tl senses ac load current and....
This circuit protects expensive portable equipment against all types of improper hookups and environmental hazards that could cause an overvoltage condition. It operates very quickly and does not latchup, that is, it recovers when the overvoltage condition....
These two circuits are SSB generators. One uses a crystal filter by KVG Electronics at 9 MHz, the other uses a 455-kHz mecha..
Most of the transistors in this speaker protector function as switches. Normally, Q4, Q5, and K1 are on and the speakers are connected to the amplifier. However, if a large dc voltage appears at an amplifier output, either Q3, or Ql and Q2 turn on, biasing....
Basically, this circuit is an adjustable electronic circuit breaker, containing a toroidal transformer that senses 60-Hz load current. Tl has a two-turn winding for primary, and 100 turns of #30 gauge wire for the secondary. A high-low range switch selects....
A speaker system can be protected against amplifier failure when dc voltages (on speaker line a-b) arc sensed by the circuit. Either positive or negative dc voltages are sensed. A relay opens in this case, removing the dc from the speakers...
When testing a circuit, a source of voltage that is variable and has overvoltage shutdown is veiy useful. In this circuit, Rl is adjusted to 1 to 2 V below the eventual shutdown threshold. R2 sets the trip voltage. When this voltage is reached, the circuit....
The ear protector is actually a peak audio-detector/shutdown circuit that disables the amplifier through its chip-disable input when the output volume of an amplifier reaches the set level. The circuit, although intended for the MC34119 amplifier,..
Transistors Ql, Q2, and Q3 monitor the two outputs of the stereo amplifier. If the offsets exceed 2 V, Q7 is turned off, which turns off Q8 and the normally on relay. Diodes D2 and D5, together with Q4, provide a mains voltage monitor. As soon as the ac....
This antenna tuner is suitable for use with low-power (less than 5 W) transmitters or SW receivers. S2 selects inductance and S2 connects the 365-pF capacitor to either the transmitter or the side of the inductor. The tiny tuner is comprised of a tapped....
The HF/SW receiver preamplifier is comprised of a broadband toroidal transformer (LI-a and Ll-b), LC network (comprised of a 1600-kHz, high- pass filter-and a 32-MHz, low-pass filter), L2 and L3 (26 turns of #26 enameled wire wound on an Amidon Associates....
A pair of diodes and a quarter-wave transmission line are used as an automatic TR switch. D1 and D2 conduct during transmit periods, short- circuiting the scanner input. In this mode,-the K-wave line appears as an open circuit...
A circuit stabilizes the current-transfer ratio (CTR) of an optically coupled isolator used as a linear transducer. The optocoupler produces a voltage output that is proportional to—but electrically isolated from—the voltage input. However, the output....
The application involves observing the light pulse emerging from a thick specimen after transillumination by a laser pulse. Pulses derived from the laser source are amplified using a Video Amplifier LM733. The reference level is set to 1 V in the comparator....
Fiber Optic applications require analog drivers and receivers operating in the megahertz region. This complete analog transmission system is suitable for optical communication applications up to 3 MHz. The transmitter LED is normally biased at 50 mA....
If you need a wide-range, resistor-programmable monostable multivibrator, you can program tbe circuit for pulse widths from 1 JlS to 10s-107:1 range. A high-to-low transition at tbe input causes IC1"s output to switch low, thereby turning off Q1 and Q2.....
A positive-going trigger pulse can be used to start the timing cycle with the circuit shown. In this design, trigger input pin 2 is biased to 6V (1/z Vvv) by divider Rl and R2. Control input pin 5 is biased to 8 V (213 Vvvl by the internal divider circuit.....
The circuit illustrates the usefulness of the HA-5151 as a battery-powered monostable. In this circuit, the ratio is set to .632, which allows the time constant equation to be reduced to: T=R1*C1. D2 is used to force the output to a defined state by....
In this mode, the timer functions as a one shot. The external capacitor is initially held discharged by a transistor internal to the timer. Applying a negative trigger pulse to pin 2 sets the flip-flop, driving the output high, and releasing the short....
Modems are devices that connect either remote devices to a computer, or two or more computers to each other. Their connection is usually wired. The GSM modem we present is wireless. It can connect two computers, a computer with the internet or even be the....
This circuit features the ZTX450/ZTX550 transistors in a push-pull output stage. The following readings were taken at maximum volume: Input: 0.4 mV rms, Output: 1.8 V rms, Voltage gain: 4500, Max. output before distortion: 2.25 V rms -supply current ~ 3.5....
A JFET transistor-is used as a high-to-low impedance converter and signal mixer. Input impedance is approximately 50.0 kQ but it can be increased by increasing R5 to R8 as high as 10 . Output is about 2 kQ, but it can be increased or decreased by changing....
It is possible to simulate the balanced performance of a transformer electronically with a different amplifier. By adjusting the presets, the resistor ratio can be balanced so that the best CMRR is obtained. It is possible to get a better CMRR than from a....
The detector uses three sections of an L144 and a DC4011 type CMOS NAND gate to make a very low power voltage monitor. If the input voltage, Vin, is above Vhigh or below Vlow, the output will be a logical high. If (and only if) the input is between the....
Using a pickup coil to drive an amplifier (IC3A-B-C-D), this meter circuit can be directly calibrated in field-intensi..
In this circuit, oscillator Ql runs at about 15 kHz and feeds mixer Ul. Ul has an internal oscillator that runs a..
The circuit uses a Hall-effect sensor, which consists of an IC that resides in a small gap in a flux-collector ..
The voltage required to ignite the neon tube is obtained by using an ordinary filament transformer (240-6 V) in reverse. Battery drain is quite low, around 1 to 2 milliamps for a nine volt battery. The pulses from Ql, unijunction transistor, operated as a....
This circuit has been designed to drive an 8-W fluorescent lamp from a 12-V source using an inexpensive inverter based on the ZTX652 transistor. The inverter will operate from supplies in the range of 10 to 16.5 V, thus making it suitable for use in....
For multiplying frequencies in the 1-to 150-Hz range, this circuit uses a 4046B and a 100 prescaler. The VCO output..
A wideband high gain configuration using two SL550s connected in series. The first stage is connected in common emitter configuration, the second stage is a common base circuit. Stable gains of up to 65 dB can be achieved by the proper choice of Rl and R2..
The JFET-bipolar cascode circuit will provide full video output for the CRT cathode drive. Gain is about 90. The cascode configura-tioneliminates Miller capacitance problems with the 2N4091 JFET, thus allowing direct drive from the video detector..