Here’s an interesting project by Caleb Coppock:
Graphite conducts electricity. Two wires brush against the surface of a paper disk as it spins. The wires are connected to a simple electronic tone generator. When a line of graphite is drawn across the disk, connecting two wires, a tone is heard. The quality of the line affects the sound. For example, if the line is thick, allowing more current to pass over it, the pitch changes to a lower tone.