What Saab CD Changer is this for?

[lbilharz]

Sorry, come out of the blue, but I'm looking for ways to "CDC Fake" for the AS3 (2004 Aero) Kenwood SVT-M700 head unit to replace the KCA-S220A AUX in and properly integrate with the CDC protocol.

[ozgunawesome]

@lbilharz Hey! This is for emulating the factory CD changer on a 2001 Saab 9-5 entertainment system.

The head unit has a stereo input port on the back, but it's not for AUX. The port becomes active if the car is ordered with the 6 disc CD changer option.

The CD changer sits in the trunk and sends a message roughly every second on the CAN bus to indicate that it's installed and present, and if the head unit receives this message, it enables the CD changer as an input source.

Communication with the CD changer (play/pause, select disc, previous/next track, volume control messages) is over the CAN bus, but audio is transmitted analog, so if you emulate that CD changer present message, you can then use the stereo input signal for something else.

Additionally you can listen for the control messages & use them for something else if you want. Putting these together in an Arduino + CAN shield + Bluetooth audio transceiver allows for a cheap way of adding Bluetooth support to the car.

I wrote this over 10 years ago, when I had that vehicle in college & wanted a cheap way of adding BT audio support. You could use this to inject any message into a vehicle CAN bus. But you'll need at least a CAN dump from a vehicle that has the head unit and CD changer that you have.

IIRC the CD changer (1) sends the CDCcmd message with ID 3C8 about every second, and (2) when it receives a message with ID 6A1 it sends the ninefivecmd message with ID 6A2. There are other CAN messages that I dumped from the bus (some steering wheel control commands etc) but which one does what I can't remember right now.

The most challenging part was the non-standard I-Bus bit rate, which requires initializing the MCP2515 registers manually to set it correctly. The register values also depend on the MCP2515 clock frequency, IIRC this sketch was for a 16 MHz clocked CAN shield. The values would change if your CAN shield crystal is 8 MHz.