HOW TO – Use old telephones as an intercom

HOW TO – Use old telephones as an intercom

Img413 212
Have some old phones laying around? You can turn them into an intercom system, shows you how – “Talking over the phones is easy. You put DC current through the phone and it transmits and receives audio. So two phones and a current source (about 25mA) all in series will give you a talking circuit. A suitable current source can be as simple as a 9V battery and a series resistor whose value is adjusted (with both phones offhook) till about 25mA flows. You can then bypass the battery and the resistor with a capacitor to couple the audio straight across and get a loud and clear connection.” Thanks kryten007! [via] Link.

4 thoughts on “HOW TO – Use old telephones as an intercom

  1. Rockingham says:

    A good place to get old telephones to make this work is at
    Antique Telephones

  2. Ajay says:

    Which type of capacitor we need to use in this?
    Have anyone used it?

Comments are closed.

Discuss this article with the rest of the community on our Discord server!

current: @adafruit - previous: MAKE, popular science, hackaday, engadget, fallon, braincraft ... howtoons, 2600...

View more articles by Phillip Torrone


Maker Faire Bay Area 2023 - Mare Island, CA

Escape to an island of imagination + innovation as Maker Faire Bay Area returns for its 15th iteration!

Buy Tickets today! SAVE 15% and lock-in your preferred date(s).