Apparently many USB charger units—you’ve probably got at least one that came free with a gizmo: I’ve got three—won’t work to charge the iPhone. That’s ’cause Apple’s lovely design engineers made the phone’s electronics look for the standard USB D+ and D- lines, which lots of USB chargers omit. Thanks to a simple hack, however, you can add these lines in by spoofing reference voltages instead. All it takes is a few resistors, some wire cutting and soldering, and the ability to have no fear that you’re precious iPhone is going to go up in an expensive puff of smoke. The magic resistor formula is revealed below.
The project was designed to work on 12V car USB units, and it’s pretty neat, hey? Interestingly, with just a few extra tweaks you can adapt it so the circuit works with high-capacity batteries. That’ll let you run your iPhone almost anywhere in the world away from power sockets. [Tzywen via Makezine]
Leonard
Tuesday, August 26, 2008 at 3:09 AMIf the only thing you need is a differential voltage of 0.5V across the D- and the D+ at 2.5V and 2V then you could do this with 3 resistors. 50K from +5V to the D- then 10K from the D- to the D+ then 40K from D+ to ground. This will have the same voltage as before of 2.5V at D- and 2V at D+
BeeJay
Monday, November 17, 2008 at 1:29 PMwhats the charge app yopu have on your iphone? were can i get it looks hot.
Man-wai Chang
Friday, April 29, 2011 at 11:44 PMGood suggestion, Leonard. Saves a resistor.