Chan has a great site and he has put up a lot of interesting projects, incidentally many of them based on AVR. One of his projects (not based on AVR) is a pocket LED light. He describes a blocking oscillator based single cell, white LED torch. This and rusty nail project got me thinking and I started experimenting with Chan circuit. The circuit is very robust and it worked with a wide variety of transistors; I tried BC547, 2N2222 and 2n3904.
But the real fun and challenge was in building an enclosure for this torch. I have been a big fan of matchboxes; as a kid I used to collect empty matchboxes everywhere I went. I thought the art on matchboxes reflected the local culture.
Long ago, I built a data logger that could fit in a match box (I never completed it in that form, settling to find a much larger enclosure). But now I was determined to fit the white LED torch circuit AND the AA cell in a matchbox.