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Simple Door Intercom

2015-01-10 04:55  
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Thisintercom circuitsuitable for accompanying? door bell. This circuit uses the speakers both as microphones and as loudspeaker. This intercom is made simple by using only a singleamplifierIC LM390 to serve two-way communication. This circuit is based on master controlledhalf-duplexoperation.? With LM390, a 6V battery supply would produce loud enough volume. Here is theschematic diagramof the circuit:

Intercom circuit schematic diagram

The switch for this intercom circuit is ideally a push button PTT switch, but any double SPDT should work. The interaction scenario between the guest (remote)? and the host (master) can be like this:

  • The guest press the door bell
  • The host press the intercom switch to talk position and then say: “who’s that?”,? then release the switch to return to the listen position.
  • The guest then answer: “This is me bla bla bla.. “
  • The host press the button and say: “OK, wellcome bla bla bla..”

    The simplicity of this intercom circuit is achieved by using half-duplex method, so we can use only a single amplifier for two way communication. This simplicity is further improved by utilizing the loudspeaker to act both as a microphone and as speaker. [Circuit's schematic diagram source: National Semiconductor Application Notes]

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