You can make those buttons on your steering wheel much more functional if you have a way of monitoring them. Don’t even think of cracking open the factory finish to get to the solder points, just tap into the CAN bus and monitor the data traffic.
The small board seen above is the result of a project [Peter Shabino] calls the CAN sniffer. The connector on the left will plug into the Control Area Network system on your car, giving the chips on board something to do. There’s an MCP2551 CAN transceiver (hidden under that linear regulator) and an SPI controlled MCP2515 CAN controller which take care of the particulars of the CAN protocol. The big chip in the middle is a PIC 16F876, responsible for making sense out of the data. From there a MAX232 chip is used to provide a serial interface to connect the device to a computer.
This really isn’t tied down to one particular function. Once you have access to the bus for a microcontroller you’ll only be limited by your firmware writing skills. [Peter] has posted an archive with all of the open source files, as well as an illustrated step-by-step board assembly. We’ve embedded the schematic from that archive after the break.