Charging Neo Freerunner via USB port

Michael Shiloh michael at
Fri Apr 18 23:19:31 CEST 2008

Alexey Feldgendler wrote:
> On Fri, 18 Apr 2008 21:06:26 +0200, Michael Shiloh 
> <michael at> wrote:
>>>    * you mention 'other manufacturers' that 'identify their own 
>>> chargers' with various resistors... if I have one of those chargers,
>>> is there a way to get the phone to ID it?
>> There are two issues here: First of all, you have to know the value 
>> and location (i.e. between which two pins) of the resistor. There is 
>> no standard, no gathering place of all this information. You can 
>> search the Internet in case someone has posted this.
>> I'm not sure how we measure the resistor. My guess is we measure the 
>> current and deduce from this. Measuring the current requires an analog 
>> to digital converter (ADC), which we must have wired up to the pin in 
>> question. If an arbitrary charger uses a different pin, and if we 
>> don't have an ADC on that pin, we won't be able to detect the resistor 
>> there.
>> That said, the most common location for a resistor is the same as 
>> ours, so you're in good shape.
>> Next, you have to modify the code to do this. Trivial for all you 
>> developers.
> This could actually be done by an application downloadable by a user who 
> knows what he's doing. The user starts the application, plugs in the 
> charger, the application measures the resistance. If it's not something 
> identifiable, too bad. Otherwise, the user reads the output current 
> specification on the charger and adds the pair (ID resistance, current) 
> to the table.

That's a great idea. Find the code that checks for the specific 
Freerunner resistance, and modify it to simply report the value of 
whatever it sees. If it is anything different from an open or short 
circuit (within reasonable tolerances) assume it is a resistor, and note 
the value. Post to the wiki, and if a few other people see the same 
value for the same charger, this seems safe to code.

>> The reason I think this is of limited use is that I would guess that 
>> most of you will simply read the label on the charger, and then use a 
>> utility to override all the automatic detection and simply tell the 
>> charging logic that 500mA or 1A is available. Automating this is a lot 
>> of work for little gain.
> Not so little if you have a particular charger (say, Motorola) and use 
> it to charge Neo every time. You'd really want it to auto-detect the 
> charger instead of choosing the charging current manually every time.

Yes, that's a really good point, and one I had overlooked.


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