I was inspired by w2aew's excellent video to check out the Ears To Our World humanlight project. It's a good cause, although shipping costs kill the idea of buying one myself - better just to make a direct donation.

It's also an interesting circuit - a variation on the many "joule thief" circuits out there - and also demonstrates some of the basics that under-pin boost converter power supplies.

As always, all notes, schematics and code are in the Little Arduino Projects repo on GitHub.

With my particular mix of components, I'm getting almost 40% duty cycle which actually produces an apparently very bright LED on just 1.5V supply.