The problem with non-standard USB charging (was: Re: Price of the Freerunner spare parts)

steve steve at
Fri Mar 28 20:02:01 CET 2008

Ya this nailed it for me.  thx Michael.

-----Original Message-----
From: joerg [mailto:joerg.twinklephone at] 
Sent: Friday, March 28, 2008 11:43 AM
To: Michael Shiloh
Cc: List for Openmoko community discussion; steve
Subject: Re: The problem with non-standard USB charging (was: Re: Price of
the Freerunner spare parts)

this is a perfect description of the current situation.
You have to wear the t-shirt yourself! :-)


Am Fr  28. März 2008 schrieb Michael Shiloh:
> Correct me if I'm wrong, but I think the big problem is that there is no 
> standard for reporting current capacity other than the USB protocol, 
> which is not supported by dumb chargers.
> What this means is that the various tricks that we and others play 
> (shorting unused data pins, adding resistors of specific values between 
> two pins, etc.) are all completely non-standard meaning there is no 
> agreement between manufacturers and most importantly NO PROM
> In other words we could test a given Motorola charger today, find that 
> they have a resistor of value x between two pins, write the code to test 
> for this value and then bump up the current draw to the value that we 
> know the Motorola charger can provide.
> But then next month Motorola might change the value of this resistor. 
> They might send a firmware update over the air to all their phones to 
> make existing phones compatible with the new charger.
> We, of course, do not get this update, and suddenly the charger that we 
> had tested no longer works.
> For a good example of this problem see Lady Ada's discussion on her 
> Minty Boost. You will see a string of reports from people saying they 
> needed to modify the resistor value and/or location in order to get 
> Minty Boost to work with different models of iPods. And any solution is 
> always temporary, until Apple changes something and then the resistor 
> must change again.
> Thus the only way we can guarantee safe charging at higher than the USB 
> maximum of 500mA is with our own charger.
> I would love to see a technical report, a white paper, written on this 
> issue. Would anyone like to take on the challenge? Winner gets an 
> Openmoko t-shirt (
> Michael
> Kevin Dean wrote:
> > O> > community at
> >

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