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Two Identical Telephone Intercom Circuit

2016-02-15 06:57  
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Two telephones can be used as an intercom by using this circuit. Older style rotary phones that are nonelectronic might work best in this application.This circuit consists of two identical intercom units. Each unit contains a power supply, microphone preamplifier, audio amplifier and a Push To Talk (PTT ) relay circuit. Only 2 wires are required to connect the units together. Due to the low output impedance of the mic preamp, screened cable is not necessary and ordinary 2 core speaker cable, or bell wire may be used.An intercom using dual-modular wall jacks is shown in this circuit. If the wires are available in the home telephone cable,this system can be installed with little trouble.An intercom (intercommunication device), talkback or doorphone is a stand-alone voice communications system for use within a building or small collection of buildings, functioning independently of thepublic telephone network.
 

Telephone Intercom Circuit