An autopilot system using an android phone. The PPM signal goes to the microphone input on the phone and and a modified PPM signal comes out of the audio jack to drive the servos.
The android phone stabilizes the plane using the built-in gyroscopes and GPS functionality is also going to be implemented, with the RTH (return to home) function upon signal loss.
PPM (Pulse Position Modulation) Is used by RC transmitters and recievers to transmit data for the Rc channels. Old FM recievers (The one I have) use this type of signal. I hacked the FM reciever and located the PPM output, then I used an arduino based serial oscilloscope to check the signal.
at Thomas: you are wrong, the sampling frequency is enough. 48 steps is more than what you have on your radio control throttle stick. consider there is software like smartpropplus for windows that uses audio sampling.
at Pedro: i created a discussion to create a PPM encoder library:
please share your code if you wrote it. anyway It will be easy to create the encoder library.