USB, enumerate to draw power

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Hi guys,


I need to draw power from USB and do very little beside that. Could you help me find a dirt simple solution for that?


Basically, think about the end solution as a USB fan. It must enumerate on the bus and request up to 500mA. The USB plug on the fan can be connected to a proper USB Host or to a silly power supply with only 5V and no data lines. Successful enumeration or no USB data sets a bit which turns on the fan motor.


It would be nice to use my own VID/PID and device description. Recycling an existing VID/PID from some standard class compliant demo project would be even better.


I was thinking along the lines of using an FTDI device. But have quite a bit of experience with AVRs and wouldn't mind using a minimalistic USB+MCU solution. It should be programmable over the USB cable.


I appreciate your help in finding a starting point for such a project.