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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VOX (Voice-Operated Switch)

This schematic diagram below show a circuit of VOX Box (voice-operated switch). This circuit consist of a Schmitt trigger, a relay driver, and microphone preamplifier. The microphone preamplifier(U1) receive input signal which will be amplified. THRESHOLD control (R8) is fed by the amplified signal. The trigger’s output goes high when the preselected threshold voltage level is exceeded. Here is the […]

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