The goal was to make a small USB interface board which could easily be connected to microcontroller boards. It should support USB-powered as well as externally-powered operation. External components are kept at a minimum (but there are still quite a lot of them). The board may be used as USB-powered device (externally connect pins 1 and 2 on the S
UPPLY pin header) and as externally-powered (leave pin 1 open and apply 5V to pins 2 and 3).