Apple makes such nice sexy products but dam them for making it so hard for us to work with them. Apple has vendors who make accessory products that work with Apple products and to give them a leg up Apple has incorporated some ridiculous technology. This additional technology adds speed bumps to generic electronic products from working properly with their devices. Limor Fried has reverse engineered what needs to be done to control charging an iPhone and iPod.
“We did some experimenting (see the video up top) and determined that in fact the different voltages/resistances did effect the charging rates! Using the 2.8V&2.0V setup resulted in a 1 Amp charge rate and the 2.0V&2.0V setup resulted in a 500mA charge rate. This made us very happy, because 500mA is within the capability of the MintyBoost chip. We redesigned the PCB to allow us to have 4 resistors on the datalines and put two 75K and two 49.9K resistors in each kit.”