Projects: Clapper

The circuit will flip the switch after hearing two claps. Besides the wall transformer, the relay is most expensive component, costing me about 3 dollars. Conservatively, the components cost 15 dollars total. Supply is 9V, although I do not think it matters whether it uses 12V or 7.5V. I should have used a circuit board variable resistor, since those are cheaper. Perhaps you can see the electrical tape. I did not think they are necessary, but some of those connections are pretty close together, and they have a 120VAC difference.