LED serial debugging for cell phone hacking


[Barry] needed some way to get serial output to help debug his efforts to port Linux to the HTC TytnII (Windows mobile Pocket PC phone). He wrote some code to send serial output via one of the LEDs on the phone and rigged up an AVR to pic up the output and provide a USB interface to the computer. It runs at about 200bps – perfect for the quick debug session.

Comments

  1. BlizzardDemon says:

    Cool topic, I think I saw this done to a camera once to dump its firmware via a LED reading USB device. Think it was one of the new cannon’s…

  2. Wolf says:

    http://www.hackaday.com/2008/05/27/porting-chdk-to-new-cameras/

    Yep, this method was on HAD a little while ago.

  3. James says:

    Camera flash != cell phone IR-LED

    Neat trick, though he probably could have done it easier over the headphone jack — HTC uses a special 11-pin port that looks kind of like mini-B USB, but has additional pins for a headset. I would think it would be easy to find a software modem package, though maybe it’s not trivial to route the system terminal to it.

  4. Barry Carter says:

    Thanks for the kind words!

    @wolf yes, been done a few times, but as far as I could tell never quite like this.

    @james You assume we have audio :)

    Also you are right, (assuming we had audio) routing to the headphone port after decoding the incoming console data would be a nasty job. I decided to do it this way as it was very simple to do, 9 lines of code in the Linux kernel and a chunk in an avr.

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