For a Highschool physics project, I built a circuit that varies a current to a infrared LED based on input to an electret microphone. A second circuit that is not connected to the first receives the signal with an infrared photoresistor and changes it back into a signal that is then played through a speaker.
This was my entry into the Fall 2010 Awesome Things Competition. It uses compressed air to shoot a 6x8ft. lightweight fishing net and is constructed entirely out of PVC pipe. The tractors which are used to spread the net as it travels through the air are covered with pipe insulation in order to prevent injury to the targeted victim.
This is a longboard constructed from 4 plies of 1/8" baltic birch. It was pressed using Titebond III wood glue, stained using RIT fabric dye, and coated with Minwax Water-based Polyurethane. It was then wet-sanded, polished, and waxed for a mirror-smooth finish. Tred-Tex paint additive was used to increase traction on top. SPECS Length: 38" Width: 9.5" Concave: 0.25"