Here's my project in a nutshell: I'm building a quadcopter and I need to control each of the four motors independently. I'm using an iPhone as the "brain" of the quadcopter, with of all the control logic being implemented in software on the phone.
Somehow, I need to interface my iPhone with the ESCs for each of the brushless motors. I don't have access to the Lightning port (or the money to join Apple's MFI program), so that leaves me with the headphone jack. It would be reasonably simple to control the frequency/amplitude of the two audio channels and convert the signals to PWM, but I need to extract FOUR signals from the two channels.
My idea is this: "encode" two signals per channel by dedicating two different frequencies (say, 100Hz and 1000Hz) and modulating their amplitude in the software. Then I need a way to split the frequencies into their own independent signals to convert to PWM, before reaching the ESCs. What could I do to make this work?
Or, is there an easier way to accomplish what I need? I'm a Software Engineer by trade and a wanna-be EE by hobby, so my electronics experience is limited. A Fourier Transform would be the answer in the digital world, but I'm not sure how to make this work in the analog world. If somebody has a better solution, I'd love to hear it!