LM331 Frequency to Voltage Converter

The frequency to voltage converter circuit illustrated in the schematic diagram below produces a 10 V output for 10 kHz full scale input (square waves or pulses).  The simplicity of the circuit doesn’t mean a bad performance: this circuit has linearity about 0.06% at full scale. For your note, there is a trade-off between ripple versus response time. With Cfilter […]

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Solid State Relay (SSR) with Optocoupler and Triac

This solid state relay (SSR)  equivalent circuit is made of optocoupler and a triac. This SSR circuit is also designed with  LED protection from overvoltage and reverse polarity. The diode 1N4002 is the reverse polarity protector, as it will short the wrong polarity to null the voltage with the help of 150 Ohm series resistor.  The 2N4403 transistor will protect […]

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74S124 High Frequency VCO with Varactor

The following schematic diagram shown a conventional which is modified to become a VCO (voltage-controlled oscillator) circuit. By replacing the conventional fixed capacitor with a variable capacitance diode (varactor), we can turn a 74S124 multivibrator into a wide-band VCO. High speed logic 74S series is used here to enable this circuit for high frequency operation. Here is the schematic diagram […]

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High/Low Voltage Probe

Simple voltage probe circuit shown in the schematic diagram below very useful in testing, testing, or troubleshooting discrete  or integrated circuits, especially logic circuitry. This voltage probe circuit gives two indication, “high” or “low”. Here is the schematic diagram of the circuit: When the “high” condition is probed, Q2 and Q1 transistor will be activated shorting R2 and LED1 to […]

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