My bike light stopped working recently, and putting in new batteries didn’t help. It didn’t look like I could really take it apart without permanent damaging it, so I conceded to buying a new bike light and tore apart the old one.There are a couple of really cool things going on inside this guy, and actually a lot of taking it apart wasn’t terribly destructive. Probably the coolest thing I found was a Reed Switch, which is how the switch most bike lights have at the back works. Basically it’s a moving part that you push to the side and changes if the light is on, blinking, or off. If you take off the back all you see is a small magnet that moves–no physical contact to anything. On the inside of the bike light, there’s a small hermetically sealed glass envelope with two wires that barely don’t touch. When the magnet gets close, the wires touch! That’s the signal, and that’s how a Reed Switch works. Cool.
The general mechanical design of getting the electrical contacts in the right place is also pretty cool. The bike light is 95% batteries, so the trick is to fit the electronics around the batteries in a space-efficient way.
Unfortunately taking it apart didn’t help me fix it. I can’t really check the electrical contacts without the batteries being in place, but when they are you can’t really access the circuit board. I guess I was just being a bit lazy. I could go back and check that the LEDs still work, and then rig it up to supply the circuit with power and check the different components. Maybe next time.