Need some simple electronics help for an iPhone adapter

[TX297]

I may have posted a thread about this last year, and since Sparkfun finally got around to stocking female dock connectors (albeit in SMD form) and parts in general for this generation of iPod hardware are getting plentiful and cheaper, it's time to forge ahead with my crazy plan!

 

I'm currently prototyping a pass-through adapter that will do the following things:

1. Charge the iPhone

--This is done by pulling FW+ down to 5V with a voltage regulator and feeding it to USB+ (This is a little crude because it may require a heatsink, but I haven't poked around the CD-IB100II to see if 12V or 5V is more stable/present)

2. Remove the "This accessory is not made to work with iPhone" nag

--This is done by pulling USB Data- to 2.8V, and USB Data+ to 2V

3. Allow serial data pass-though for music control from the head unit

--Feeding the right voltage the the accessory indicator pin (I have a variety of peripherals to test this with and find the right value)

4. Add a switch that disables the data lines and removes the "Accessory connected" screen so you can use the iPhone to browse songs instead of the slow Pioneer interface. When the switch is on, head unit and steering wheel control works as normal, as well as the fancy song display.

 

For the first version I'm going to hack it together with off-the-shelf parts, meaning #4 will be accomplished by using a simple SPST switch. For future versions though I plan on creating a PCB and would like to use those tiny little push button switches to make things nice and neat. Initially, I'd probably just throw in a SPST on the Serial+ line, but I don't know if that would be enough. I might also need to change the voltage going to the accessory pin, and I don't know how to do that since those switches only come in SPST/momentary flavors. Essentially, I need to perform 2 functions with the same switch and have no clue how the electronics for that would go (in the absence of a DPST, so I'm guessing a momentary push button with a little bit of "magic" [iE stuff I don't know yet] would get the job done).

 

By keeping the design that way, it opens up a possible expansion to enabling composite AV out. I would just wire in the right connectors, pull the accessory pin to the right voltage again and sneak in an apple authentication chip ripped from a cheap dealextreme cable. If I can use that momentary switch, I can make it remote and house it nice and neatly in a small cable so you can hide the composite connectors and the huge ugly Pioneer dock connector behind the dash.

 

So yeah, some pretty fun stuff but it seems I'm hung up on a really simple problem. I'll keep this space updated once I finish building and testing the prototype.

 

Edit: Upon further research, it seems I'm going to have to switch the Tx/Rx lines from the pass-through to the authentication chip for video output, but I won't be needing to do that until version 3-ish.