Drawdio is in IEEE Spectrum’s “If You Build It, Santa Will Come” – thx Erico!

This is part of IEEE Spectrum’s Special Report on IEEE SPECTRUM’S 2009 Holiday Gift Guide. What better way to introduce a young person to the joys of engineering than by giving a gift that you construct together? I tested four suitable kits. Two are for unusual electronic musical instruments, and two are for dabbling in radio.

The Drawdio turns a pencil—or a pencil sketch—into a musical instrument that sounds something like a kazoo. The kit, available from Adafruit Industries, costs just US $17.50, takes only an hour or so to assemble, and includes everything you need but the AAA battery. If you have any experience soldering components to a printed-circuit board, assembly will be a snap. The hardest step is pushing a thumbtack (included) into the end of a pencil (also included) to make electrical contact with the graphite that runs down its center.

Drawdio is simply an oscillator whose frequency is controlled by the resistance of the circuit path connecting the part of the pencil you grip with the attached thumbtack. You can make sounds by grabbing the pencil in one hand and touching the tack with the other, but that’s not the fun way to use it. Instead, draw a heavy line, laying down a lot of conductive graphite as you go. Then press on one end of the line with the forefinger of your free hand while holding the tip of the pencil on the other end of the pencil line. Apply adequate pressure, and Drawdio will emit a low buzz. Moving the tip of the pencil closer to your finger reduces the resistance of the frequency-control path, shifting the sound to a higher pitch. So it’s not hard at all to generate a simple tune. If you have trouble hitting the right notes consistently, just mark their positions on the line.