Hobby projects - Simple electronic circuits. Computer microphones Learn how to interface electret and dynamic microphones to the standard computer sound card. Metal detectors Theory of operation and schematics of the most common metal detectors used today: Very Low Frequency (VLF), Pulse Induction (PI) and Beat-Frequency Oscillator (BFO). Wireless microphone The wireless microphone transmitter can be built in an afternoon with simple, affordable and widely available parts.
Take care with transmitter circuits. It is illegal in most countries to operate radio transmitters without a license. Handbook of hardware pinouts, cables schemes and connectors layouts. Arduino Pong. Hack a Day. Mike's Electric Stuff.