# Bidirectional Digital Communication over Audio Signal?

I am trying to figure out a way to achieve low speed digital communication over an audio line. I have two devices that are connected with a two wire audio cable. Audio and Ground. From my research, I can't find any current solution to achieve bidirectional digital communication over a single audio signal.

Does anyone know of any IC's or designs that can accomplish this task? I only need something very basic and low speed.

• Morse coding, that is. Oh, well, the modem/fax communication is working this way. Upd: Or you mean modulating a signal in addition to the audio? Than DSL is doing this. It's called FDM (frequency division multiplexing) – Eugene Sh. Nov 3 '15 at 17:01
• Does this actually have to be audio? If it's just a 2 wire cable, you could use any number of digital encodings - the fact that you're using a cable normally used for audio is irrelevant. – Nick Johnson Nov 3 '15 at 17:06
• Bi-directional could be a real problem due to contention over who is driving the line. I think you want some kind of simple modulation technique. There is simple on-off keying, frequency shift keying (FSK), and all kinds of other stuff. What are you doing, anyway? Do you have control of the design of both devices? – mkeith Nov 3 '15 at 18:01
• Look at a 1Wire protocol. – MadHatter Nov 3 '15 at 18:13
• do you want to record it, so must fit within audio channel? With bidirectional, could suggest two different frequency ranges, one for out, one for return, seperated by filtering. – Neil_UK Nov 3 '15 at 18:48

You can just feed a low speed (low enough that it can be handled by opamps) signal to "In A" and it should come out at "Out B". Correspondingly, "In B" to "Out A".