In my search for a dynamo- and batteryless bike light, I found only 2 brands working on the same principle. I had to come up with an other idea using the movement of some bike parts.
Playing with coils and magnets I discovered a new phenomenon. I toke a mechanical relay and put a strong magnet against the iron around the coil. By pressing the contact lever I changed the magnetic flux inside the core of the relay and induced an electric pulse inside the coil. First I used a small 12 volt relay. Later I used a bigger relay and placed the strong ceramic magnet directly agains the coil. The pulse that came out by tipping the contact lever was about 30 volt. A LED was flashing with a serious amount of light. The RattleGen was born. A nice feature is that the linear movement is only 1 mm. I never saw this principle used for vibrational energy harvesting, but I don't know all. The power output of the RattleGen is quit high.
So, how to make this RattleGen useful for my bike lights? The best is as light and generator are placed in the same lamp housing. In this project I show you the prototype and the way I solved some construction problems. The linear movement I get from the spokes of the wheel, near the rim. A lever hits the spoke and that movement presses the contact lever of the relay. I didn't try the profile of the tire as vibrational source. The video instructable show's you how easy the RattleGen can be made. To get the same relay as I used can be hard. The few other accessories you can find in most electronic parts shops.