Brit John Goldsmith sent in this example of an el cheapo shake-to-light flashlight he purchased at a filling station - it was a discounted offer if you bought enough petrol. Well, he got what he paid for, though given the price of petrol in the UK, the station probably could have given away a Surefire flashlight.
“As the closeup photo shows, the power comes from a magnet and coil, being stored in a 0.22 Farad (not microfarad!) capacitor on the PCB. The on/off switch has a little magnet on the slider and a reed switch on the PCB. This maintains the integrity of the watertight housing. The operating magnet is actually some small powerful magnets embedded in a larger lump, presumably steel. A nuisance as it drags all the recent UK coinage out of your pocket. I’m sure the unit would be more efficient with metal springs as end stops - the rubber used seems to absorb all the energy. I recently bought a wind-up 3 LED unit which is much brighter and much longer running (and less embarrassing to operate).”
Having looked closely, John also discovered a problem with the magnet. Like most high strength magnets, it is plated for corrosion protection, but the plating is peeling off. So far it is not impeding operation.
Note this post originally appeared on Made by Monkey’s British cousin (twice removed) Electronics Weekly.