We are always thinking about ways to improve our circuit boards activity set so that there are interesting components that can also survive the wear and tear of the museum floor in a semi-facilitated environment.
One kind of component that we really like are hand crank generators. These are geared down motors with cranks that can subsitute for batteries and show how rotational motion can be transformed into electricity. We usually use something like the ones above for workshops, but they tend to not be robust enough for the museum floor. Also at 30$ to 60$ we cannot afford to continuously replace broken generators.
But yesterday I went to IKEA and saw a huge-o bin of these LJUSA hand powered emergency flashlights. I bought one and at $4.99 and figured it would be worth seeing if I could hack it to make a hand crank generator to try out with our circuit board set.
I started by prying off the top of the flashlight with a utility knife and a tiny screwdriver. I cut off the button and attached the two protruding wires to alligator clips to see what would happen.
When we cranked the flashlight it did power the component! However, once we stopped turning the handle, the light or mechanism kept working, although dimmer and dimmer or slower and slower. We realized that this was because the flashlight was meant to be spun and then powered on for a set period of time. We figured there was some sort of capacitor or other circuit board inside the bottom half making it do that.
While this was an interesting phenomenon to us, we thought that it would be too confusing for someone just starting out learning about electricity. So I decided to see if I could remove the circuit and find out how to make the crank directly power one of our outputs.
I was nervous that prying off the bottom part with the handle would wreck the device, but I went ahead and tried it anyways and was relieved to see that the handle was just press-fit on the gears with a hexagonal connection. I also discovered that there was a little circuit board with a battery (rechargable?) on it and some other components that looked like resistors and capacitors.
One thing that I was confused about was that the motor had three wires coming off of it and the circuit board somehow turned that into just two wires (labeled positive and negative). I color coded the wires and tested it out with a light bulb and figured out which two of the three worked together to power the bulb.
So I soldered the wires together and then put everything back together. I ran the two wires out little holes that I drilled in the clear cover and added alligator clips to the ends. We tested it out and it seemed to work great.
However, once we tested it with a wide variety of circuit boards, we noticed some strange things. It wouldn't power any motor or mechanical toy part. It also seemed to work either way with the piezo buzzer (which usually only makes a sound when connected in one direction. We hooked it up to a multimeter and although we don't completely understand all the bells and whistles it seems to give us a value when its on AC current and nothing when it's measuring DC current.
This makes a bit of sense to us (although none of us as a solid grasp of how electricity really works) because a light could be powered with pulses in each direction, but a motor couldn't spin if it was constantly getting equal pushes in opposite directions.
The next step may be to add a diode to the system which may limit the current to only going in one direction. We're not sure how this might affect the generation of electricity but we'll find out!
So, there is still potential for the LJUSA to be a part of our circuit exploration set, but more experimentation is required to make it work the way we want it to and interact well with all of the other conponents.