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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Square Wave Oscillator using Comparator/Op-Amp

The circuit shown in this schematic diagram is a square-wave oscillator circuit.  The main component of this oscillator circuit is LP165/365 comparator. As timing component, it uses capacitor and resistor to determine the frequency operation, generating square waves signal. Here is the schematic diagram of the circuit: We can change the values of R and C to produce different frequencies. […]

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Simple Door Intercom

This intercom circuit suitable for accompanying  door bell. This circuit uses the speakers both as microphones and as loudspeaker. This intercom is made simple by using only a single amplifier IC LM390 to serve two-way communication. This circuit is based on master controlled half-duplex operation.  With LM390, a 6V battery supply would produce loud enough volume. Here is the schematic […]

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