Thread: iPod Car Adapter Hacked for Carputer Use

Heres a schematic. I figured this out the hard way, by using a digital multi meter and dissecting the iPod cable and adapter and using a pin out diagrams for the iPod dock connector.



For the 3.3V pin, I used a voltage divider (1k and 2k resistors) using the 5VCC on the USB TTL adapter header. However, as I've already mentioned, this forces my head unit into CD Changer (aka carpc) mode always. This means if I try to listen to AM/FM or CD, it will switch back to CDC (aka carpc) mode within a few seconds. So it would be better to use a 3.3V switched source possibly using a relay. I've also noticed that even if I unplug the USB adapter from the carpc, so that pin 6 on the 8 mini din connector gets no 3.3V, the iPod adapter will still automatically switch to CDC/carpc mode. My guess is that for this adapter, simply grounding or grounding through a resistor is enough to trigger the pin, but I have not verified this. It may even be possible to ignore this pin altogether. I have not experimented yet, since I've already ordered jbors car2pc adapter. If it doesn't work, I may look into this some more.

Now, to get the serial communication working on your carpc, just install the drivers for the USB TTL adapter. The drivers register the adaptor as a standard com port. Here's what I did in Girder. You should use 19200 8N1 as the com port settings.



I set the Girder serial plugin to detect variable length messages with a 100ms timeout. I set the terminator to "aa", since that should not appear in the packet. After 100ms, the plugin will just return the full HEX string.

Now you can just configure Girder as normally would with any other remote or device. Just use the "Learn Event" button. Add a command to Girder. Click the Learn Event Button. Press the radio or steering wheel control you want to train. Girder will record the packet string, and thats it. Now just set the keyboard map or whatever else you want to do this with event. The best part is you don't have to know anything about the iPod serial protocol. Just enjoy

However, if you plan to use the advanced remote features, for example to send text/track/playtime to the Head Unit, you will need to learn to decode/encode the protocol. I've attached a link to a wiki where you can learn more about that.

Parts List:

• An OEM iPod Car Adapter.
  - Usually connects to the bus, CDC, or SAT connector on the HU. I recommend that you choose one that supports the simple remote protocol. You can tell by if you can still use the iPod click wheel and radio controls at the same time. The usa spec adaptor I'm using has a little toggle switch I can use to set the mode. The honda music link does not.
• USB TTL 3.3V Serial Adapter
• Optional parts
  - A few resistors for the voltage divider I'm using to convert 5V to 3.3V
  - Possibly a relay for the 3.3V pin
  - An 8 pin din cable or connector for easier hacking.
  I used non-stranded copper wires from an old ethernet cord for testing. Fits perfectly in the mini-din pin holes.

Mainly you just need something to decode the Serial TTL 3.3V signals. I recommend the one I've posted, as its pretty simple to use and only $20. However, you could also hack up most cell phone data cables (like those at radio shack) to do the same thing. They typically work on the same principle (3.3V TTL to USB Com port adapter), and may even use the same chip inside the cord.


Useful references:
iPod Pinouts
iPod Accessory Protocols
Acura Music Link Pinouts
Acura Music Link hacking

Your adapter might be trying to use the "Advanced" Apple protocol where it sends commands to the ipod and expects responses. You can get some details from the Apple protocol page that is linked further up. If that's the case then you'll have to write some code to work correctly since the method above is setup for the simple remote protocol.