The Graphite Sequencer is an art piece that explores turning a record player into a tangible interface for sequencing music:
Disc are coded with graphite, which conducts electricity. Two wires touch the paper discs as they spin.
The wires are connected to a simple tone generator.
When a line is drawn across the disk, connecting the two wires, a tone is heard. The quality of the line affects te sound. For example, if the line is thick, more current can pass over it, creating a lower tone.