USB cable hacking

Michael Shiloh michael at
Fri Aug 29 01:52:38 CEST 2008

Daniel Dadap wrote:
> Hello Community,
> I just bought a portable USB battery pack ( one of these:
> ) to use with my
> FreeRunner so that I could keep tangogps running to log a track for me
> during a bike ride. It worked quite well: I was able to keep the unit
> powered on for over 12 hours and still had some juice left over to
> make some phone calls at the end of the day. However, I noticed that
> the FR was only drawing 100mA. I was sort of hoping that the battery
> pack would emulate a USB host and negotiate current, but it looks like
> it just has available power.
> Anyway, I saw on that the
> included AC adapter has a 47.5 kOhm resistor betwen ID and GND. Like
> many other people on this list, I have dozens of USB A to Mini-B
> cables cluttering the house, and I figured it might be a neat idea to
> cut a cable, splice it short (about 20cm or so), and add a resistor.
> This cable would be used only for charging with the battery pack. I
> don't like the idea of having to switch the FR to force fast charge,
> possibly forgetting to switch it back before plugging it into a
> computer, and possibly destroying the USB port on the computer and/or
> the FR. A dedicated charging cable would make this simpler.
> Problem is, the ID pin apparently exists only on the Mini-B connector,
> and doesn't have a corresponding wire inside the USB cable. Has
> anybody on the list done USB connector hacking, and have any tips on
> how to get a resistor in there without interfering with plug in
> operation?
> Also, what part of the software exactly is responsible for charger
> detection? I guess another possibility is to hack the software to
> recognize shorted data pins as a charger. I have another device with a
> charger that identifies itself by shorted data pins, but more
> importantly, shorting the data pins is a much easier mod to perform on
> a USB cable.
> I suppose the easiest option would be to cut off the end of a FR
> charger (or other compatible charger with a resistor across GND and
> ID) and splice it with a USB cable... but I would like to hear other
> suggestions that people may have.

1. I'm working on an adapter using a 5 pin mini USB connector from 
Digikey (p/n H2958-ND  	CONN PLUG MINI USB2.0 5POS )

2. Belkin makes a 5-conductor mini-USB to USB cable, useful as a start 
for another hacking project.

3. It's possible that the ID resistor in the FR charger is in the 
wall-wart portion and not at the mini USB connector.

4. I'm composing a detailed wiki page to gather all of this info, and I 
welcome contributions.

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