Modify a generic USB car charger to charge a 3rd gen iPod Nano

Step 3 Add the resistors

You need to add two resistors. You should do a continuity test first to determine if your two central pins are connected to any others. If they are, you've likely got a different charger and this probably won't work.

According to the USB charging and power spec I should be able to simply short the two central pins (the data lines) and the device will detect that it's connected to a charging device and start charging.

I tried this first of all, but it didn't work (the iPod detected it had been plugged in to something, but refused to charge). I knew the iPod charged from my MintyBoost!, and after a quick look at the schematic and some playing with the multimeter, I decided it would be worthwhile adding a couple of pull-up resistors.

I don't think the values are that vital (the USB spec is quite forgiving), but I decided to try matching roughly what the MintyBoost! was giving, apart from the V+ to D- resistor, which was guesswork.

Don't forget to check that you've got the correct resistance between the pins, and that they're not connected to anything they shouldn't be!

Comments

[mopk47]

with 3 resistors added between 4 pins, works well according to simulation and actually test. the value of resistors would be: 5V-39k-12k-33k-GND. This config with produce a nice 2.7V and 2.0V.

[endolith]

iPods don't follow the USB-IF charging spec. They use voltages on D+ (2.0 V) and D- (2.7 V) to tell the iPod how much current it's allowed to draw. You can just measure the pins on a Griffin charger or whatever to test this.

Cell phones don't follow the USB-IF charging spec, either. I'm not sure if anything does. :)