Mario Marchese of Nyack, NY, built this neat drawing machine:

This is “The Audio Portrait Artist (TAPA).” It is made from recycled DC motors, cigar boxes, pieces from a broken multimeter, roof shingles, wine corks, and old radio knobs. TAPA works similar to a CNC machine, but instead of cutting things, it draws. There are four microphones which are each individually filtered to sense a certain range of sound. Starting from very low deep sounds to high pitches, TAPA draws in a specific direction based on the pitch it hears. There are four control knobs on top to control the sensitivity of each mic. Each microphone is individually amplified using LM386N IC chips, and a ULN2003A IC chip bring both DC motors together. There are two relays that control the direction for both motors. The analog gauge is wired together with the circuit to show the intensity of sound it receives.

You can watch videos of the machine at work on the maker’s blog, but I couldn’t embed them. By the way Mario has tons of cool projects on the blog.