Gimmee some help here mp3car.com members. I want this FAQ to cover as many cars or types of controls as possible. Post links to either FAQs or to your installs. I'll incorporate them in this initial post as they come in. Right now, I've only got CDrSkull's BMW I-Bus how to.
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So you'd like to use those steering wheel controls to send commands to your PC? Say, turn the volume up or down, change the song, move the cursor? It's possible and many of our member have done it. (Note that due to my lack of knowledge in this area because my car has no steering wheel buttons this FAQ is a work in progress, likely containing erroneous information and is incomplete for now)
There are a couple of different types steering wheel controls out there.
1. Straight wired buttons. This is the easiest to understand as each button has a traceable wire that you can tap into. The challenge will be to A) figure out how to tap into that wire; B) once you've tapped into it, using it to send a signal to your PC.
Tapping into the buttons requires you to solder wires to them. Depending on your car, you may be able to solder them directly to the switch, or you may have to find and trace the wiring harness and tap into the wire farther downstream [some examples of people who've done this would be good right here]
To convert the button presses into keyboard commands that your PC can understand, you need to use a device such as an IPAC
keyboard emulator. This emulator allows you to attach the various wires you have tapped into the controls and spit them out as keyboard commands. The IPAC emulator is designed for use by people who want to build their own gaming controls using custom hardware, but can be adapted easily for the car.
If you don't use an IPAC, long time member
StevieG has written software that allows you to run each wire to a hacked USB gamepad. His access control software will then allow you to control your car.
2. The second type of system used in cars to detect button presses is a simple and elegant voltage divider network. A voltage is run through a circuit that measures the resistance. Each button introduces a different resistance when pressed. The car's circuitry can deduce which button has been pushed and respond accordingly. This is elegant because it does not require a separate wire for each button to be run down the center of the steering column.
To decode the network and convert it into something your PC can understand, you need a device like
this.
It converts the resister network inputs into remote control outputs. You can use an infrared receiver on your computer and software such as Girder to interpret the outputs and convert them into commands for your applications.
3. Tapping into your car's system bus. Some cars have an electronics bus that you can tap a device into that will receive/transmit signals generated by the switching circuitry and convert them into serial port messages that your computer can understand. This allows you to make the car controls your interface to the PC. The BMW is such a car and
here is a thread describing how to connect to the I-Bus in the car.