Newest Nokia cell phones can be charged via USB, even the wall charger has a Micro-USB plug. Since I wanted to charge the phone in the car, I bought a USB adapter for the car -- those ones that go into the cigarrete lighter socket and supply 5V for devices that can draw power via USB.
First, it was a FAIL: the CA-101 cable does not charge the cell phone just by connecting to a USB power source. The phone expects the USB handshake to actually happen, and then it draws power from USB. It even asked if it should use PC Suite or Mass Storage protocol.
But I had read somewhere that Nokia's wall charger "hints" the phone that it is a dummy voltage source just by shorting the USB data pins. Since I had two "cloned" CA-101 cables that I had bought from DX, I decided to try to build a "charger cable" by myself. It would be just a matter of shorting the data wires at phone connector's side.
Of course, the things went more complicated than expected. Those "generic" cables bought from DX do not follow the USB convention of wire colors (green and white for data, red and black for power). Once I opened the outer insulation, there was no black wire, there was a blue wire instead. Hmmm... too good I have a multimeter. Indeed the colors were non-standard: green and blue were data, white and red were power.
Finally, SUCCESS: the phone charges via USB and no longer asks about USB protocols. It behaves exactly like if it were plugged to the wall charger.
I guess the next step is to open up the USB adapter and short the data pins in there, in order to satisfy all devices that possibly understand shorted data wires as a dummy power source. Luckily I bought two USB adapters, so I can spare one for this experiment :)
And then I can throw that modded cable in trash; I am not comfortable about passing 500mA or more through that cable with incredibly thin wires and that unsoldered wire junctions that I made, which are kept together just by duct tape :)
