tejesh83

copied from my post on mp3car.com

Problem Statement: How to connect a carpc to your stock audio system and use radio controls and steering wheel controls to control carpc. Specifically, I started this for my 2005 Acura TL with Navigation, but this should work for most vehicles that have a iPod car adapter that can be controlled via the headunit.

Solution: A few vendors have developed iPod adapters for my vehicle. I currently own a USA Spec PA11 HON2 iPod Adapter. It plugs into my headunit and acts like a CD changer but controls my iPod.

Instead of hooking the adaptor to an iPod, I have replaced the connection to my carpc notebook using a TTL 3.3V serial to USB adapter. Now when I hit a radio control, such as next track, the iPod adapter translates the Honda bus data to a serial command that the iPod can understand. Instead of this command going to an iPod, the TTL adapter sends the serial command to my carpc. In my carpc, I read the serial command using the program Girder and its serial plugin. Girder will translate the serial command to a keypress that I can use in Road Runner or any other event/program for that matter.



Current Status

• I have successfully mapped the next and previous track buttons from the radio and steering wheel to Girder and key-presses.
• There is still a quirk with the iPod detection. Normally, the iPod adapter will automatically switch the headunit whenever I turn on the hooked up iPod. I've currently hardwired this detection to pin to always on, so the headunit will always default to cd changer (now carpc) mode. Even if I hit AM/FM or CD, it will switch back to my carpc. I need to add a relay or something to make it switch only when I want it too.
• My current iPod adaptor doesn't not display any text, track info, etc on the head unit. However, Dice has just released a new unit for my car that would allow this, which I could then use to send text from my carpc to the headunit such as track name, time, playlist, etc.

I'm putting this project on hold indefinitely. Initially, I thought jbors' car2pc adapter was not compatible with my car. After doing some more research and talking with jbors, I think I will be able to use his car2pc adapter right out of the box and get a little more functionality. I've ordered one of his adapters to try out. If it doesn't work, I'll keep working on this. But for now, here's what I learned for those who may want to build their own.

tejesh83

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

tejesh83

If I had more hardware skills, I'd love to figure out how to decode the CAN (I think thats what its called) bus. I believe it has all the events used by the car to turn on lights, roll down windows, odb data, etc. I'm not sure what I'd do with it yet, but it would be super neat.

I haven't posted pics of my carpc yet. Its nothing too different from the one's we've seen here already, and I've borrowed some from all of them. I'll get to it one of these days when I finish wrapping up my install and making an amp rack or something to hold/hide the new audio and carpc equipment.

datmrman

Impressive!

Thanks for sharing your hard work. Good luck getting the other adapter working.

dennisil

do you know if there is a ipod cable extender avalable anywhere, i need a few extra feet to make this work and i would need a one side female and one side male ipod cable.


datmrman congrats on the 4k posts!!!

dennisil

oh yes and i t has to play video through the cable i forgot to mention that i know there is a 65 dollar audio extention ( by, Mike Kruckenberg) avalable and that wont do.

tejesh83

These guys sell some stuff that might work or parts to make your own:
http://home.swipnet.se/ridax/connector.htm

Their extender cable claims to use all pins.

You could make your own, but it requires some serious soldering skills.

lembowski

iTrader: (1)

he's a post whore......

tejesh83

Just an update. I tried jbors car2pc adapter this weekend but couldn't get it working. I'll contact him to see if its a quick fix, but otherwise I plan to go back to my original idea.

TrashCan

jbors is having problems hooking up a TL navi unit to test his car2pc unit. I am sending him the schematics and hopefully he'll resolve the issue soon. The issue I am having is trouble switching to CD-C mode. But if I unplug the car2pc unit, then turn on the ignition and wait 10 seconds, then plug in the car2pc unit, I was able to switch to CD-C mode. If I leave it in CD-C mode, it will stay in CD-C the next time you turn on your car untill you switch to another souce, then it won't go back to CD-C again unless you do the power delay trick.