Top Circuits Page 12
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A simple level of power meter can be arranged to give a bar or dot display for a hi-fi system. Use green LEDs for 0 to 7; yellow for 8 and red for 9 to indicate peak power. The gain control is provided to enable calibration on the equipment with which the....
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Use a pair of Maxim"s 5V-powered MAX231 RS-232C transmitters as drivers to obtain a 2-color LED. The transmitters require only a singleended, 5-V input to generate ± 10 V internally. Their outputs are short-circuit-proof and can supply as much as 10....
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The pull-up transistor of the totem-pole output is used-to turn on the LED and the pull-down transistor is used to turn ·off the LED. The lower impedance and higher current handling capability of the saturated pull-down transistor is used as an effective....
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When power is first turned on, two of the LEDs are on and the other two remain off until the timing cycle reverses. The LEDs flash in pairs, but by pressing and holding Sl closed until only one of the LEDs is on, and then releasing it, the four LEDs can be....
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Inserting two 1-MO resistors, R1 and R2, in the output stage of one of the circuit"s inverters limits the current needed by the oscillator tone more than a few pA. This circuit includes a CD4007 package, which has three CMOS inverters. It forms a standard....
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The timing components are Rl, R2, and C,. Cl is a bypass capacitor used to reduce the effects of noise. At start-up, the voltage across C, is less than the trigger level voltage (1/3 Vnn). causing the timer to be triggered via pin 2. The output of the....
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Uses a low cost CMOS IC to tum four LEDs on and off at a rate that is set by the values of R1, R2, Cl, and C2. The pulse rate for the component values given for R1 and R2 is about one cycle every four seconds. By lowering the values of Rl and R2 to 220 KO,....
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This indicator is basically a switch with hysteresis characteristics. If the input voltage momentarily (or permanently) exceeds the most positive reference level, LEDl is switched on. If, on the other hand, the voltage falls below the negative, or least....
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The ·circuit includes a peak detector that irrunediately drives the readout to any new higher signal level and slowly lowers it after the signal drops to zero. The readout is a moving dot or expanding bar display. The circuit can be expanded for a longer....
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The LED with integrated flasher is connected in series with the base-emitter junction of transistor Tl. Thus, the l..
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Many electronic circuits need an indication that they are under power; for most ac circuits, a neon lamp is ..
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When the mains voltage is present at the input terminals, the transistor in the optocoupler is on, T1 is off, and s..
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Battery-operated equipment can work on one set of batteries for a long time nowadays. However, if it is left on inadvertently,..
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The super LED flasher is actually two complete LED flasher circuits on one circuit board. The first, LED flasher is made up of 1C1 and LEDs D1 and D2. IC1 is a 555 timer IC configured as an astable (free-running) multivibrator with its output on pin 3. The....
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Three individual flashing circuits that use an LM3909 LED flasher/oscillator IC create the appearance of a pseudo-random firing order. The combination of CX!RV C.JRb, and C^R control the blink rate, which is between 0.3 and 0.8 s, and the inherent wide....
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A bar column of LEDs is arranged so that as the audio signal level increases, more LEDs in the column light up. The LEDs are arranged vertically in 6 dB steps. A fast response time and a one second decay time give an accurate response to transients and a low....
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L1C1 are selected to be resonant at a frequency below the desired crystal harmonic but above the crystal"s next lower odd harmonic. C2 should have a value of 30-70 pF, independent of the oscillation frequency. There is no requirement for any specific ratio....
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This circuit consists of a 2048 radio remote control transmitter and the corresponding wireless receiver with very high reception sensitivity and low consumption. The combination of the two above gives a high-reliability remote control, ideal for security....
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The circuit is built around the LM567 tone decoder IC that requires about 100 millivolts at its operating frequency. The frequency is set by a 10 K variable resistor and can be between 700 and 1500 He..
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This circuit provides power control without running line-voltage switch leads. The primary of a 6-volt filament transformer is connected between the gate and one of the main terminals of a triac. The secondary is connected to the remote switch through....
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The transmitter is built around two CMOS 555 timer ICs (TLC 555s). The transmitter generates a modulated 35-kHz ..
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This circuit can be used to operate a VCR or CD player from another room. It"s really an infrared signal repeater. The s..
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This 1-cable system carries composite video (NTSC, PAL, or SECAM), power, and channelselect signals. The interfa..
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A schematic diagram for the remote analyzer is shown. The circuit is powered from a simple 5-V supply, consisting of PL1, SI, Tl, a bridge rectifier (comprised of D1 through D4), capacitor CI, and a common 5-V regulator, Ul. Switch SI is the on/off control....
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This transmitter sends an FM signal in the 88-to 108-MHz range, with a tone of 19 kHz. This can be used to activate the FM MPX pilot carrier indicator, which can be interfaced to external devices. L4 is for use with a 15 CM wire antenna. LI is 9 turns of....
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Shown here arc several possible interface circuits that can be used with the remote-control transmitter. The one in A illustrates a typical FM stereo MUX decoder with a load connected directly to the open-collector output of a TA7343 PLL. The circuit in....
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CI in series with the crystal may be used to adjust the oscillator output frequency· Value may range between 20 pF and 0.01 µ¥, or may be a trimmer capacitor and will approximately equal the crystal load capacitance. X values are approximate and can vary....
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One section of the MC10101 is connected as a 100 MHz crystal oscillator with the crystal in series with the feedback loop. The LC tank circuit tunes the 100 MHz harmonic of the crystal and may be used to calibrate the circuit to the exact frequency. A second....
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This circuit employs an adjustable resonant tank circuit which insures operation at the desired crystal overtone. Cl and LI form the resonant tank circuit, which with the values specified as a resonant frequency adjustable from approximately 50 MHz to 100....
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The crystal element in this circuit is connected directly between the base and ground. Capacitor Cl is used to improve the feedback due to the internal capacitances of the transistor. This capacitor should be mounted as close as possible to the case of the....
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The crystal is in a feedback circuit from collector to base. A trimmer capacitor in series shifts the point on the reactance curve where the crystal operates, thus providing a frequency trim..
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The crystal operates into a complex load at series resonance. Ll, Cl, and C2 balance the crystal at zero reactance. Capacitor Cl fine-tunes the center frequency..
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This circuit is often used by amateur radio operations, shortwave listeners, and other operators of shortwave receivers to calibrate the dial pointer. The oscillator operates at a fundamental frequency of 100 kHz, and the harmonics are used to locate points....
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The crystal is placed between the collector of the output stage and the base of the input stage. The frequency of oscillation can be set to a precise value with trimmer capacitor CI. The range of operation for this circuit is 500 kHz to 10 MHz..
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For frequencies below 20 MHz, a fundamental-frequency crystal can be used and the resonant tank is no longer required. Also, at this lower frequency range the typical MECL 10,000 propagation delay of 2 ns becomes small compared to the period of....
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This low cost, crystal-controlled oscillator uses one TTL gate. Two factors ensure oscillator start-up: The connection of NAND gates G1, G2, and G3 into an unstable logic configuration and the high loop gain of the three inverters. Values of R1, R2, C1,....
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An on-board oscillator and a 17-stage divider compose IC1. By connecting a standard 3.58-MHz, television color-burst crystal as shown, an accurate source of 60-Hz squarewaves is generated at the IC"s output, pin 1. Those pulses are then fed to IC2, a 4024....
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This unit is easily tunable and stable, consumes little power, and costs less than other types of oscillators tlmt operate at the same frequencies. This unusual combination of features is made possible by a design concept that includes operation of the....
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This circuit uses LTC1043 to differentiate between a temperature sensing network and a de reference. The single-ended output biases a varactor-tuned crystal oscillator to compensate drift. ..
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Diagram shows a 100MHz oscillator operating on the fifth harmonic. Again to maintain the transistor"s gain, note the increase in the collector"s load resistance Rl because of the increase in the quartz crystal"s internal series resistance R5. C3 is needed....
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Diagram shows a 50MHz oscillator operating on a third harmonic. The collector"s load resistor R1 has been increased because the quartz crystal"s internal series resistance Rs increases with frequency in the VHF range. The crystal"s internal series....
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Although ceramic resonators are a good choice for low-power, low-frequency clock sources (if you can stand their 30-ppm te..
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CI capacitor in series with the crystal may be used to adjust the output frequency of the oscillator. The valu..
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This simple circuit will oscillate with a wide range of crystals. Connect several different types of crystal holders in ..
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Ql, Q2, and the associated circuitry form a modified astable multivibrator in which the loop gain is automatically adjusted to the threshold of oscillation by means of field effect transistor Q3. Q4 linearly amplifies the signal present at the collector of....
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On occasion, microprocessors/microcomputers and microprocessor crystals just aren`t compatible with each other. Many microprocessor data sheets specify maximum values for a crystal`s equivalent series resistance (Rs) that aren`t met by some crystals....
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A major feature of the PWM servo amplifier is elimination of a pulse transformer. A 150 kHz pulsewidth modulated signal is applied to U3, with its complementary outputs applied to identical circuits to drive the load. When point A increases, Q2 is on and....
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Two 555s and a quad NAND-gate IC can simulate an electrocardiograph signal and a -y-wave radioisotope signal for applications in nuclear medicine. This circuit synchronizes the radioisotope signal to the EKG signal. You can use the circuit"s outputs to....
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The mercury-in-rubber strain gauge is the detector of breathing. In the model device, the strain gauge produced by Medimatic, Demark was used. The change in the length of the strain gauge wrapped around the chest during breathing causes a varying....
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Most circuits that provide an electrical stimulus for research subjects are constant-voltage designs; this circuit is a constant-current design. Stimulator circuits must be isolated for two reasons: to ensure safety and to minimize interference. Isolated....
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The greatest sensitivity is achieved if R1 is approximately equal to the probe resistance. The circuit can be zeroed with R2, while the full-scale voltage is controlled by R5. The correlation between pH and output voltage might not be linear, which would....
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An IR photodiode, which senses IR skin reflectivity as a result of increased blood volume during the periods that the heart forcibly contracts, is used to pick up a signal that is correlated with the heartbeat...
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A sidetone oscillator is a special audio astable multivibrator. Keying is accomplished oscillator that is turned on and off with the by applying a positive dc potential, developed transmitter. The oscillator is rf-driven and bat- from the rf signal, to the....
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Laser-receiver circuits must bias their avalanche photo diodes (APD) to achieve optimal gain. Unfortunately, an APD..
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An input rectangular signal is differentiated and short impulses are formed from its edges. These impulses write the content of counter A to a latch that clears the counter after a very short time. Counter A counts impulses of the frequency fo that are much....
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Fixed-value capacitors are disc ceramics. CI, C4, C5, C6, and C8 are NPO ceramic or polystyrene. C2 is a 25-pF ceramic trimmer and C3 is a 15- pF miniature air variable capacitor. The resistors are -W carbon film or composition. The RF chokes are miniature....
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This circuit uses a VFO operating from 15 to 18 MHz (Ul), which feeds a balanced mixer (U2). A fixed oscillator signal is mixed with this signal to generate an output from 0.4 to 33 MHz. FL1 and FL2 are low- and high-pass filters that are used to eliminate....
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This basic VFO for the 3- to 6-MHz range is coirimonly used in amateur applications, using a Colpitis circuit. For 5 to 5.5 MHz, C = C2 = 70 pF and for 3.5 to 4.0 MHz, use 1000 pF. C3 is typically 10 to 220 pF, depending on the frequency. C4, C5, and C6,....
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Lamp LI stabilizes the loop gain at higher frequencies while the limiting action of R2, CRI, and CR2 prevents clipping at low frequencies and increases the frequency adjustment range from about 3:1 to greater than 10:1.
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A Wien-bridge oscillator can be made Vllriable by using two frequency-determining parts that are varied simultaneously at high tracking accuracy. High-quality tracking potentiometers or variable capacitors are, however, expensive and difficult to obtain.....
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Cascading two identical integrators will thus result in an overall phase shift of 180° and an amplification of unity (p..
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This circuit produces a pure, - 80-dB THD sine wave with a frequency that is equal to the fc of IC3"s filter. A TT..
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This compact LC oscillator offers a frequency range of about 1 kHz to almost 9 MHz and a low-distortion sine-wave ou..
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This oscillator uses two transistors and operates the crystal in the fundamental mode. CT and C2 should..
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This phase-shift oscillator is useful for audio oscillator applications. Adjust R7 for a good sine w..
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Using a Quad NAND Gate, the TTL oscillator can use fundamental crystals between 1 and 10 MHz. The sine..
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A highly-stable 60-Hz sine wave can be delivered with this circuit, which offers a different and much simpler approach to gaining a stable amplitude...
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A 555 timer operating in the astable mode generates the driving pulses and two 4518 dual BCD (binary coded decimal) counters provide the square waves. A TL081 op amp serves as an output buffer-amplifier, and potentiometers Rl and R2 are used in order to....
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In this circuit, a square wave is filtered by a high-order low-pass filter so that a -3-dB frequency will eliminate most harmonics of the waveform. As a result, the filter outputs a fundamental sine wave. This method is applied to generate a sine wave by....
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A TTL counter, an 8-channel analog multiplexer, and a fourth-order low-pass filter can generate 10- to 25-kHz sine waves with a THD better than -80 dB. The circuit cascades the two second-order, continuous-time Sallen-Key filters within ICS to implement the....
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In this circuit, an LM741 op amp drives a Wien-bridge network using two zener diodes as..
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This pulse generator produces square pulses from 1Hz to 100KHz with adjustable pulse width of nearly 0-100%. The generator is powered with a voltage of 5-15V and is therefore suitable for both TTL and CMOS circuits. If you want to measure the response of an....
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Symmetry of the square-wave output is maintained by connecting the right side of R2 through resistor R3 to the output of the third amplifier stage. This changes the charging current to the capacitors in proportion to the setting of frequency-adjusting....
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This self-starting fixed frequency oscillator circuit gives excellent frequency stability. Rl and Cl comprise the frequency determining network while R2 provides the regenerative feedback. Diode Dl enhances the stability by compensating for the difference....
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The circuit will provide both a sine-and square-wave output for frequencies from below 20 Hz to above 20 kHz. The frequency of oscillation is easily tuned by varying a single resistor. This is a considerable advantage over Wien-Bridge circuits where two....
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This circuit uses a positive-feedback loop closed around~a combined comparator and integrator. When power is applied, the output of the comparator will switch to one of two states, to the maximum positive or maximum negative voltage. This applies a peak....
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This circuit traps a single positive pulse from a square-wave train. Following the rising edge of an input command, the pulse-out signal emits a replica of one positive pulse of the clock signal simultane ous with the clock signal"s next rising edge. The....
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The NE555 is connected in the astable mode and uses only three timing components (RA, RB, and Ct. A 0.01-/aF bypass ..
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This circuit will generate a square wave of 2 Hz to 20 kHz. The circuit uses an op amp in a relaxation-oscil..
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When this circuit is turned on, the natural offset of the devices serves as an automatic starting voltage. Assume that ..
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When the output is high, R3 and R4 are in parallel, and CI charges via Rl until the current in R2 equals that a..
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The circuit will generate precision triangle and square waves. The output amplitude of the square wave is set by the output swing of op amp Al, xndRl/R2 sets the triangle amplitude. The frequency of oscillation in either case is approximately l/0.69ftC. The....
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The 566 can be wired as a positive or negative ramp generator. In the positive ramp generator, the external transistor driven by the Pin 3 output rapidly discharges Cl at the end of the charging period so that charging can resume instantaneously. The pnp....
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With the component values shown, the oscillator has a frequency of 8 kHz. When an input signal is applied to the base of Ql the current flowing through Ql is varied, thus varying the time required to charge Cl. Due to the phase inversion in Ql the direction....
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A voltage-variable capacitance tuning diode is placed in series with the crystal feedback path. Changing the voltage on VR varies the luning diode capacitance and tunes the oscillator. The 510-KO resistor, R1, establishes a reference voltage for VR -ground....
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This TMOS VCO operates in push-pull to produce 4 Wot 70 MHz. It consists of two MFE930 TMOS devices in a balanced VCO that generally provide better linearity than the single-ended types. Varactors are not used because the design takes advantage of the....
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You can transform a 7415124 multivibrator into a wideband VCO by replacing it conventional fixed capacitor with a variable-capacitance diode. The only disadvantage of this scheme is the 30-V biasing voltage that the diode requires. Capacitors C1 and C2....
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This circuit uses the output of the IGL8049 to control the frequency of the IGL3038 waveform generator; the 741 op amp is used to linearize the voltage-frequency response. The input voltage to the 8049 can be, for example, from the horizontal sweep signal....
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This simple circuit can convert a single supply voltage, such as a battery, into a bipolar supply. Sense resistors Rl and R2 establish relative magnitudes for the resulting positive and negative voltages. Their rail-to-rail value, of course, equals....
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At startup, the voltage in the trigger input at pin 2 is less than the trigger level voltage, "13 VDD. caus ing the timer to be triggered via pin 2. The output of the timer at pin 3 becomes high, allowing capacitor c, to charge very rapidly through diode Dl....
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The output frequency of the VCO, U1, varies inversely with the input voltage. With a 1 "V input, the oscillator output frequency is about 1500 Hz; with a 5-V input, the output frequency drops to around 300 Hz. The output frequency range of U1 can be....
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A 555 and a dual 556 timer generate a rudimentary video signal, as shown in the schematic. The first timer generates 4.7-8 synch pulses operating in the astable mode with a 64-8 period. The second timer generates a delay pulse, which triggers the third....
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This circuit uses Analog Devices` AD639 universal trigonometric function generator to convert a triangle waveform, the basic waveform of the VCO itself, into a very low-distortion sine wave. By using the AD639 in its frequency tripler mode [2], the....
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The output frequency of this simple low-cost active voltage-controlled oscillator circuit is based upon the inherent frequency dependent characteristics of our operational amplifier. The oscillator circuit shown uses a TL082 op amp. When power is applied,....
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In the circuit the frequency trimming component is arranged so that the voltage across it is in quadrature with the voltage V0 from the bridge so that as it is adjusted the attenuation of the bridge only changes a little, avoiding the need for a two gang....
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In FSK, two discrete frequencies are used to represent the binary digits 0 and 1. The heart of the circuit consists of two Wien-bridge oscillators built using a dual op amp LM 1458, for the two frequencies. The two frequencies are enabled corresponding to....
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This circuit utilizes an HA-5152 dual op amp and FET to produce a low-voltage, low-power, Weinbridge sine-wave oscillator. Resistors R and capacitors C control the frequency of oscillation; the FET, used as a voltage-controlled resistor, maintains the gain....
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A variable Wien bridge provides frequency tuning from 20 Hz to 20kHz. Gain control comes from the positive temperature coefficient of the lamp. When power is applied, the lamp is at a low resistance value, the gain is high, and oscillation amplitude....
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Ql is a fixed oscillator operating at 455 kHz. Ul is a mixer, with its own internal oscillator running at 45..
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The circuit"s frequency oscillation is /=2.8/ [Cix(/i + i2)]· Using the values shown, the output frequency can be varie..