I replaced the stock internals of an Ultrafire 90 degree single AA flashlight i bought on eBay with a Pololu step up converter board and an ATTiny 85 micro controller. I reused the original cree LED and the stock switch as they fit nicely in the lights body. The wiring was ugly and dead bug style with a lot of electrical tape to stop shorts but it has worked pretty well for a year or so now even did a few miles on the Appalachian trail . The original light had variable intensity and strobe mode neither of which i wanted. I decided that all i need was a low mode with one click and a high with another click and off with a third. I used the Arduino software to program the ATTiny using the following sketch