the actual interface

with almost all the information, it is now time to start designing the electronics to interface to the radio, or head-unit.

Goals (revised):

* iPod wired interface to the factory radio
* no modifications to the iPod
* as few, and as reversible as possible, modifications to the car
* radio input switching to the iPod when the iPod is active
* onStar phone still usable
* charging the iPod battery

with this very preliminary goals, turned into specifications, my friend SQ designed a circuit that will implement the following logic: (this is the logic, actual voltage levels will be handled by the circuit)

inputs		outputs
onStar active	iPod active	radio TEL-MUTE	radio input L	radio input R
0	0	0	any	any
1	0	1	onStar audio	onStar audio
0	1	1	iPod audio L	iPod audio R
1	1	1	onStar audio	onStar audio

and here is the preliminary circuit. I still need to figure how to detect the iPod presence. This circuit assumes that the iPod announces itself with a +12V signal, i need to research this to adjust the resistors on the circuit for the actual voltage.