9 Volt, Battery Powered, Telephone Intercom System

9V Telephone Project

When I was developing the VoIP Fundamentals course, I wanted a demonstration to illustrate the simplicity of the public switched telephone network. After combing through the internet, I came across this ingenious little project. With just a 9V battery, a resistor, a telephone cord, and a couple of phones you can create a simple little intercom system. The video explains it fully.

Like I said in the video, I’m sure you could work out a simple signaling method if you did wanted to use the setup as an honest to goodness telephone. I toyed with the idea of using an Arduino to produce the ringing signal, but that signal would need to be amplified significantly.

3 thoughts on “9 Volt, Battery Powered, Telephone Intercom System”

  1. Jason
    What is the current required to ring the phone AFTER the transformer coil? I’m looking for the DC current after the AC current has energized it’s side of the transformer. Any way to figure that out?

    1. Jason Baird

      I’m not entirely sure I understand what you are asking. In the ring circuit there is no DC current present that I’m aware of. DC current only comes into play after the phone was been taken off-hook. At that point the phone pulls 30mA to 40mA from the central office.

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