How could you transfer data over an audio line?
I'm trying to make my Android phone talk to my robot which uses an Atmega8535L chip. The idea is to use the phone's camera as a line follower's sensor (already done) and send information to my robot's wheels.
As of now I have a quite naive idea of how it'll work: I'll use left audio channel as clock and right as data over a simple scavenged audio cable which I'll connect to analog pins (as the audio jack doesn't put out much voltage, the threshold will be low). Since I cannot output digital signal from my Android phone (I think) I'll use some noise as 1 and no noise as 0.
I'd like to use no electronics whatsoever between my phone and my robot... if that's even possible. I've heard about FSK, but it seems complicated, especially the demodulation part.
Is this even feasible without additional electronics?