The Drawdio is a simple musical synthesizer that uses the conductive properties of pencil graphite to create different sounds. It was designed by Jay Silver and makes use of the famous 555 timer integrated circuit.
It is now a popular beginner electronics kit. The kit costs $19 — however, the circuit was released under the Creative Commons license, and the plans are freely available: Why not build one from scratch?
I built the one in the photos in under an hour, and because I salvaged everything other than the 555 Timer chip and the transistor, it cost less than a dollar.
For many science and electronics projects, the resources I find on the web are unclear or incomplete. The Drawdio is an exception to this, as there are quite adequate instructions already available online; a full build tutorial is therefor unnecessary, and I will just point you to the resources that I used.
I built the prototype from Make Projects’ excellent tutorial video:
Here is a (slapdash) schematic for the circuit. It uses the original 5v 555 chip, and also corrects a mistake I found in Make’s schematic, which had the battery symbol backwards!