shake flashlight

Thursday and Friday June 22 and 23 2006 I got to spend some time on a grant developing curriculum. A few other teachers and I worked on projects to try out some engineering activities.

We started with an activity written by undergraduates on the idea of making a shake flashlight. During the first day, we searched online for any instruction about how to make a shake flashlight. There wasn't much available, but we did find one or two sites. On the second day, two of us brought shake flashes. They had the same plastic mold, but their circuitry was different.

The basic convenience store shake flashlight was more smoke and mirrors than electronic novelty. The other one was a bit more completely manufactured, with the rectifier soldered in and the coil actually connected to the flashlight circuit. The better light also had two 3v button batteries like the cheapie, but it had a capacitor soldered to the circuit board.

That said, it is possible to make your own shake flashlight. We used a whole lot of enamelled magnet wire, a blue LED, a dead whiteboard marker and four small ceramic magnets. We also tried a rare earth magnet, but it was very expensive compared to the cheaper disk mags.

Next phase is to add the rectifier and capacitor so that the charge generated by the shake can be stored. Without any storage, you get a flickering light only while you shake the magnet inside the race.

One of the goals was to create a project that actually worked and used cheap or readily available supplies. The magnet wire was raided from the Physics department, and we brought in the magnets and LEDs. The soldering iron and hookup wire was supplied, and we snagged a couple of well worn white board markers.

We made three flashlights, one that didn't have enough coil, one that did have enough coil to work and one that just had a couple of AA batteries and a switch to control the LED.

Saturday night I played around with the flashlights over dinner with friends and made a few discoveries. The number of magnets makes a difference. The optimum is 4 little mags for the big coiled light. 3 mags and there isn't enough field to force the electrons, 5 mags and the magnets don't move far enough to do the work. If you switch the polarity of the magnets by flipping them end over end, then it doesn't light the LED, must have to do with the whole diode thing.

The kids enjoyed playing with all the lights and it definitely captured everybody's attention. This will be a great project when it gets the bugs worked out. Just knowing that it can actually be done is a rather exciting and magical thing. The cost for the parts of the project is under $5, and it gets to a lot of useful aspects of electricity, circuit design and the design process.