when i was growing up here in aus dicksmith was the electronics store with all the parts. they had a kit for kids that you could make about 200 kits out of. 1 of the kits i have been trying to track down a schematic for. it converted sound (through the speaker of course) to energy (well it made an analogue meter twinge a little). it was like a decibel meter but it used no batteries. if anyone can give me something similiar that would be awesome. as stated no power for this circuit.