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February 7, 2007

iPod Dock Extender

Update: You can buy one of these Dock Extender Cables for iPod or iPhone at CableJive

The most frequent request I get from folks reading about building a SoundDock Aux Input cable is if I might build an extension cable that would allow them to connect their iPod to a dock without having to put the iPod directly on the docking cradle. You see, if you've put any kind of case on your iPod there's a good chance that it no longer fits on the dock. This is true for my iPod and the iSkin it is in. The idea for the extension cable is to have a female iPod connector on one end and a male iPod connector on the other...a flexible extension of the dock cradle.

I've been tossing around the idea of making one of these cables for awhile, poking at the connector docs for a few weeks now. Tonight I got around to doing it. It's a bit more tedious soldering than the aux input cable, but doesn't require any special circuitry so didn't take quite as long to figure out.

The supplies...a male and female iPod connector, available from Ridax or Sparkfun. You'll also need a multi-conductor cable, depending on what features you want to have available through the cable. For my cable I want everything that the iPod has when docked on the Bose SoundDock. This is audio, charging, and some minimal control (pause, next/previous track).

I also can't emphasize enough having a decent soldering iron. There's no way I could have pulled this off with my $5.99 iron from Radio Shack.

The connections are pretty well explained at pinout.ru. Ground on pin 1 & 2 and audio comes from the iPod on pins 3 (right) and 4 (left). From previous experience with SoundDock hacks I know that it charges the iPod using 12V Firewire powerp on 19 & 20 and that the SoundDock powers on when it senses 3.3V coming from the iPod on pin 18. The last question was how control signals are sent from the SoundDock to the iPod. Turns out this is all done on the serial interface on pins 11,12, & 13. So I needed an 8-conductor wire. I used some Apple serial cable I had handy, which is shielded 9-conductor that fit the bill prefectly (except the one extra conductor).

I started with the female SMD and attached the cable to pins 1/2, 3, 4, 11, 12, 13, 18, & 20.

Soldering to the male connector is much easier as the pins are significantly wider and are staggered in two rows to provide a little more space between the pins.

Once I had everything soldered I did some testing to make sure that there were no crossed wires or touching connectors. When I knew everything was right and that the functions were all working I put a quick shot of glue on each end to hold the conductors and pins in position. The only thing left to do at this point is stick each end of the cable into a shell and enjoy.

And it works beautifully. I have my iPod in the iSkin while it is connected to the SoundDock, playing music, charging, and changing tracks as I use the remote control.


I might consider making up a few more of these if anyone is interested. Drop me an email.

Posted by mike at February 7, 2007 12:14 AM