I had an Ipod FM transmitter, tonight, and I wanted an android one. I fixed it. This is my method and the specifics for this model. The main reason I couldn’t just buy one is because I have an otterbox defender on my phone which is great for protection but eliminate most docks.
This dock is the Belkin TuneBase FM model F87176 (mostly there to get indexed by search engines because when I searched for a hack for it I didn’t find anything). Opening it up I find a whole pile of test points very well labeled, interesting things like RX_IRQ, C2CLK, C2D, LCD_D0, a bunch of voltages and a bunch of others (pics in the album). I didn’t touch any of them. I’m sure there’s something cool there, maybe the interface between the 8051 (not kidding) and the fm transmitter, maybe the screen’s display (almost certainly), maybe even something more interesting. I can’t imagine what I would add to this with that data, so I just filed it away for later. The first thing I did was pin out the ipod connector:
Luckily the connector was less blurry in person and pith the help of pinouts.ru I worked out what all the pins did. One of the things I noticed was that I couldn’t change the station when the ipod wasn’t plugged in which told me that the ipod was probably connecting a pin to ground (connecting the ground pins together is what it looks like from an analytical point of view) and I determined what one it was. When I shorted those pins together I could trick the dock into letting me control it without an ipod attached. The grounds get all connected, the 5 volt output that went to the ipod now goes to the android phone and the analog audio inputs go there too. The challenge now is to make the android phone output audio on it’s usb connector.
The phone I have now is the Samsung Galaxy S4 (t-mobile)and it’s similar but not identical to the S3 and previous galaxy phones. I found it here that the samsung phones set the mode with a resistor on the id pin (some of them do a massively more complex scheme, which is awesome but not relevant here). The pin numbering is laid out here for left and right audio (It turns out that this dock outputs something on the order of two amps which is great for navigation). The S4 specific data is… somewhere, but the main point was that car mode and desk mode got combined. The final pinout had a 365k ohm resistor between ID and GND, I used a 5% 360k and it worked fine.
The test setup piped audio to my speakers and worked perfectly. After that I soldered up the car dock to the adapter (power and all) and tested it in my car. I can’t overpower the obnoxious station near me, but on empty bands it works ok. It’s a bit more quiet than I would like but whatever. After I cut the ipod connector off I widened the connector hole for the usb micro connector and glued it in place with the phone plugged it. Once it wouldn’t move much I finished potting the connector. Now I had a car adapter, but since usb micro connectors are the shittiest connector on the planet full stop I decided to bend a bit of sheet metal into a holder to prevent side stresses when I drive around corners. Glued that on and now it’s done. Very simple hack, but some people don’t have the experience to know how easy it is. The documentation is a bit sparse, but I’ve got some keywords and sources so I think this can probably be accomplished by anyone.