Alpine CD Changer Emulator

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CategoryPlugin: Alpine CD changer emulator ( documentation) [Player, Recorder]

This plugin emulates an Alpine CD changer. It allows to plug the Archos to a compatible head unit and control the playback from there, too. Currently implemented is track change, shuffle, seek, but no disk change (dunno how to handle that best). The plugin us a TSR, it silently operates in the background once started. It will keep doing so until kicked out by a new plugin being started. I use the autostart.rock feature (a special compilation of Rockbox) to run this plugin automatically on boot.

Alpine also did M-Bus as OEM for other brands (Honda, Acura, Volvo, BMW, etc.) Nowadays Alpine uses a different protocol, called Ai-Net, not subject of this. (As well as all other protocols, please don't ask me for such!)

Hookup to Archos works by connecting the headphone output including the remote pin (you need a 4-ring 3.5 mm plug for that) to the changer jack of the radio. M-Bus radios have a DIN-style circular jack with 8 pins (7 in a ~270 degree circle, one in the center). A standard 5-pin DIN plug is OK for us, since we don't use the other (power) pins.

As OEM, they shuffled the pins around a bit, better check first if it's not genuine Alpine. The bus pin is pulled high to 12 volts with a ~2kOhm resistor, pulses driven low. Because it's open collector, this is not harmful to the Archos.

ASCII art of the 4-pin headphone plug: (available in Germany from Reichelt for 1.95 EUR)
/ \
\_/ left -> Alpine pin 5
|_| right -> Alpine pin 4
|_| remote -> Alpine pin 1
|_| ground -> Alpine pin 2 + 3

The remote pin can be programmed bidirectional, that's the reason this works. Very luckily the M-Bus uses a single wire communication and the two radios I tried are happy with the 3.3 Volt level the Arcos can deliver. So the connection is a simple cable! For all protocols requiring more lines, an external controller would be necessary. Archos FMs don't have the remote pin connected, but the one I looked into was internally prepared for it, a matter of closing a bridge.