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Cheap USB charging devices only provide a +5VDC rail. Nothing on the data lines - not connected. This works for a lot of things, but my Motorola Milestone and iPod won't charge because they expect to see some life on the data lines.

I had a quick Google and found a number of solutions, of which this was the simplest.

                    +5VDC
                    |
                    |
               +----+----+
               \         \
          150k /         / 50k
               \         \
               /         /
      USB D+ --+         +-- USB D-
               \         \
          100k /         / 50k
               \         \
               /         /
               +----+----+
                    |
                    |
                   GND

Of course, I didn't have any 50k or 150k resistors in my junque box, so I subbed 47ks in for the 50ks and a 100k+47k for the 150k. Too easy. Still works just fine. Both iPod and Milestone charge away nicely.

I've been told this won't work for the iPhone 3G or newer because they're _really_ fussy about the voltages they expect. I'm not too fussed since I'm unlikely to buy an iPhone.

Credit where credit is due: I looked at a quite a few ideas while poking around with this, but this link was the most obvious and clear: http://tzywen.com/modules.php?name=News&file=article&sid=683

(I'm stashing this note here because I don't trust forums to be here in the future.)

Alright, and a snapshot of the hackjob before I clean it up for e^ipi.