Joule-Thief

This is a silly litle thing, that I enjoyed making quite a lot. "Joule-Thief" is a common name for an electric schematic that allows single 1.5V batteries to feed one or even more LEDs. Normally that wouldn't work because LEDs need a certain higher voltage to start lighting. The level needed varies depending on color. Red is the one that goes down most (1.6-2.0V). The other colors require even higher voltage levels. However, 1.5V is normally not enough!
This is where the "Joule-Thief" comes in. It transfers low voltage levels in higher ones by use of an oscillator. This allone would not have tempted me to build this little guy, but there is more! This thing even works with batteries that are to "empty" to feed normal equipment! I own a Ansmann battery-tester and even cells that show to be down to 0% capacity, still work on this schematic. So what this thing does is sucking the last bit of energy out of the battery. That's where the name "Joule-Thief" comes from.
As I have a constant pileup of empty AA-batteries, I thought it worth to give it try. It's fun, I can tell you.
Look-up "joule-thief" at the internet in case you need more details regarding the little transformer or the schematic in general. There is plenty of information.
Or you may go here: http://www.galepp.com/basteln/joule-thief/joule-thief.htm
It's a page (sorry for the German) where I show my built in detail (page in progress). And of course feel free to ask, if you have questions.

-