Alternatively, using this circuit, you can use a regular 1.5V AA cell to light up a white LED which normally only wake up at around 3V. Very clever!
To learn the how and why of it all, visit Wikipedia
JP helped me do the soldering on this. He was in charge of the solder (new lead free solder by the way). I plumped for a big fat ferrite core that I had lying around. It can be done with teensy tiny cores but I didn't fancy the fiddle - especially with JP and it being my first attempt.
The circuit is built freeform - that is to say without a circuit board. Heatshrink comes in handy here. It fired up first time.
Here's a trace of the waveform on the oscilloscope. If I'm reading it right, it's peaking at around three volts.
The AA cell, under load, is putting in 1.3V at about 40mA
Putting the 'scope into XY mode produces this gorgeous trace. Fascinating - especially when you realise it's running quite fast... by my calculations, this is running at about 70kHz — 70,000 pulses a second!
For thems that wants to know mores... I was following the circuit diagram and recipe here.