Microscope Light Source
A simple PWM capable constant current source for a high brightness LED based around an ATtiny13 and an LM317 voltage regulator.
The board has been designed to be primarily one-sided, it should be possible to etch it DIY. This hasn't been tested though. The top copper layer only has a ground fill and the extra unused pins brought out to pads for possible use at a later date.
You can find out more here.