Im in the brainstorming stages of a project that will control sequences insync with music. Here is the plan I've been brewing, i want your guys advice to see if i can get it done. Im going to play a stereo mp3 from an ipod. One side of the track will have the music and the other side of the track will have my "data stream." I would like to feed this data stream into a adc0803-lcn CMOS[SIZE=-1] 8BIT A/D converter. Which takes in an analog voltage and converts it into binary. This ic can take a very small [/SIZE]reference voltage. so if i set the reference voltage to 1v, then i can have 255 different voltages between 0-1VDc representing the digital steps. Where I need the advice is do you guys think i can produce accurate voltages from the ipod headphone jack? If not would any type of op amp configuration "square" up the voltage steps? Any advice is greatly appreciated.

 

You won't be able to output a DC voltage from the headphone jack because audio circuits block DC. You would be able to vary the volume of a 1KHz tone (for example) and rectify that to DC but I expect there would be nonlinearities which would make calibrating this method tricky. Perhaps a better method would be to vary the frequency and use a frequency to voltage converter or similar.

 

A thought just occurred that MP3s encode 1 channel and the difference between that and the other channel. I'm not sure if that applies to all MP3s but it might be worth checking or sound quality could suffer.