I was at that Science Fair. Unfortunately I didn't get to see this one but I heard them announce it over the intercom.
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There was actually another really cool design there where this kid had a device that could prolong battery life and even power an LED out of a dead battery. The way he described it was the device would build up a charge then release it and it would do this really fast so the LED would be blinking 300000 times per second which is to fast for the human eye to detect so it looked like constant stream of light.