I am hacking some old phones into my arduino project. I am currently controlling all of the ringers, dials, and hooks through my board.
At a certain point, I would like to connect the two handsets and let them function kind of like a basic intercom. There are four wires into each handset, two for the microphone, and two for the speaker. As I understand it they function much like any cheap microphone or headphones you could plug into your computer.
My initial thought is that I could just connect the mic of one to the speaker of the other, but I don't know audio circuits very well and am not sure if additional circuitry or op-amps would be required. What is the simplest way to do this?
Also, what would be the best way to toggle this connection, so I can control if the lines are open or closed?
Best Answer
Your microphone will need to have a simple amplifier in order to power the speaker. This might depend a little bit on what speaker is actually being used in the headset but an op-amp circuit should work for you. You will just have to make sure that the op-amp can output enough power to power the headset. If standard op-amps are not powerful enough to power to speaker you will need to go with a more complicated amplifier.
As for the toggling the connection, are you wanting to just have a dedicated 1-1 connection that can either be on or off? If so, you could do this by powering off the amps with a simple switch. If you are wanting some switch capabilities, such as 1 phone can be routed to 2 different locations, you should look into analog multiplexers.