However, when salvaging the solar cell and battery from a cheap solar garden light to make a charging circuit, I realised the electronics are in fact a simple LED driver. The only part involved in the charging is a diode. So I took a new diode for the charging project and used the complete little circuit board as a Joule Thief for a cyborg zombie.
I used solar garden light bought in a package of 4 for 10 euros at [www.conrad.be Conrad] under nr. 572759. If you happen to have another use for the solar cell, on-off switch and battery, as I do, this comes very cheap for LED + driver circuit. You can simply cut the wires from the solar cell and just leave them like that. Replace the battery with the one of your choice (or keep the one from the solar garden light) and you're ready.
The circuit from the solar garden light is bound to be at least somewhat more efficient than the famous three-parts-joule-thief. The latter is great with almost dead batteries, but so is the solar garden light circuitry. Tests show it works till the battery voltage drops to about 0.6V. While toroid three-parts-joule-thieves are reported to go to 0.3 V, the ones I managed to build mine also need about 0.6 V.
For the cyborg zombie I cut the wires to the battery and fitted them to a connecting block. As the wire connections on this kind of circuit boards is quite fragile, I fixed the connecting block on the back with hot melt glue. You can leave on the switch and its wiring and glue it to the assembly in the on-position. This way no soldering is required. Of course you soldering a little bridge on the printed circuit board, replacing the switch.
To make a cyborg eye, I desoldered the led, ran the legs through a button and resoldered it on the printed circuit. Because this way the cyborg zombie misses the cool toroid-thingy, I first left the complete circuit on the outside of the zombies face, which is pretty cool to. However as the sharp edges are not very child-friendly, I implanted the board, leaving just the LED + button outside.
The cyborg zombie is an entry in Halloween Contest, so please check it out, and if you like it, do not forget to vote Nomember 9th and 15th 2009. Thanks!