Relay Circuit Detects Light Change

Configured with capacitive coupling (by inserting a small cap between photo-transistor and bipolar transistor), this relay circuit will respond only to rapid changes  in light while ignoring normal gradual changes in ambient light. Rapid changes can be produced by light interruption or turning on/off lamps, while gradual light changes can be produced by clouds or  sunrise.  Here is the schematic […]

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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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Remote On-Off Switch through Small Transformer

This is a remote on-off switch circuit. With this circuit, we can take the benefit of using small switch to control larger AC current from high power devices. Safer operation is the other benefit, since this circuit is control the power without running line-voltage switch leads, only low voltage exposure for human operator. Here is the  schematic diagram of the […]

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