Supplies: From Radio Shack: * 1 pack assorted LEDs * 1 pack assorted resistors (I use 40, 1.5k, 10k, and 100k) * 1 pack NPN transistors (an op-amp would also work, but we won't do that) * 1 power transistor * 2 pairs of infrared emitters and detectors (2 emitters and 2 detectors) * Some wire * 4 D, C, or AA batteries and a holder (so they connect in series) * Some means to connect wires to each other (eg twisting them together, electrical tape, circuit board and soldering iron, or breadboard) From Amazon.com or a toy store: * 1 motorized water gun (I bought a Speed Shark gun for <$10)
