technical diversions

a place to document my current project of connecting an iPod to a Saab 9-3 convertible with the factory audio system.

Monday, January 17, 2005

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)

onStar activeiPod activeradio TEL-MUTEradio input Lradio input R
101onStar audioonStar audio
011iPod audio LiPod audio R
111onStar audioonStar 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.


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