I'm wondering about trying to communicate with an iPhone over its headphone jack. I'm kind of curious what voltage you get from a microphone normally, and if there's any other issues with feeding data into the iPhone that way?
I think i can get ahold of an oscilloscope in the next couple of days, and could use that to measure it.
Ideally i want to create a passive component system (in the first case a photodiode) which can be powered by a tone on the headphone out, and read back on the microphone in (all tested away from the iPhone to begin with of course!).
I know the Apple branded headphones have play/stop/skip/volUp/volDown controls via audio jack. So there is some kind of non-audio interface there. Let us know what you find!
Well you are in the AC audio realm. Audio headphones out is usually just a couple of volts AC at 20-20,000 hz at most. Most mic inputs are millivolt AC signals with a narrower frequency range.
been fiddling around today with no positive results, and haven't got a concrete enough log of notes to give my findings in a usable way. but here's what i remember:
Noticed that the headphone (iPhone 4) can give about 1.5V of power peak to peak on each channel, that the signal's midline seems to be offset from ground by about 2V (though this might disappear when you actually put a load on it other than the oscilliscope).
Noticed that the headphone (iPhone 4) can give about 1.5V of power peak to peak on each channel, that the signal's midline seems to be offset from ground by about 2V (though this might disappear when you actually put a load on it other than the oscilliscope).