A little solar powered pendulum that I made a few years back. It uses a very simple circuit with just 2 transistors, a couple of resistors, a diode and some capacitors. Power is supplied by a two calculator solar panels wired in parallel for faster charging. The power is dumped into a coil which repels a magnet (disguised by some old brass gears) hanging from some fishing line. As the magnet swings back towards the coil the EMF generated lights a red LED in the top post and the power from the capacitors is dumped into the coil again giving the pendulum a little kick, forcing it higher.
Video, more pics and the schematic after the jump.
The frame is made of brass tubing that I soldered together, then threaded the wires for the solar panel and LED through into the box. The box is an old one that I had. It needs some glue on the seams as the constant rocking motion tends to pull it apart slightly. The other little brass bits are from a box of watch parts that I got cheap off ebay and the magnet hidden under the gears is a flat, round neodymium type. I used fishing line to suspend the magnet and found that the nicest way to keep this in place on the post above was to wrap it tightly in thin cotton thread, which has the bonus of looking quite good too.
The circuit is based on the following Solarbotics schematic that I found.
Here is the parts list for the circuit:
- Two 3-5V solar panels, in parallel
- 1mH coil
- 3300uF Electrolytic Capacitor
- 1000uF Electrolytic Capacitor
- 2N3904 Transistor
- 2N3906 Transistor
- Two 100kΩ Resistors
- 1N914 Diode
- Red LED
- Neodymium Magnet
- Fishing line
- Copper wire
Update – 24th June 2011: Added a parts list.