Page 213 - Hacking Roomba

194 Part II — Fun Things to Do

FIGURE 10-3: A drawing made with RoombaSketch

Using Roomba as a Theremin

The theremin is a strange and unique musical instrument. It’s played without even touching it;
placing your hands in front of it in particular ways adjusts its pitch and loudness. The Beach
Boys song “Good Vibrations,” old Star Trek episodes, and countless horror movies have used
the theremin to good effect, so you have undoubtedly heard it. It produces a clear pure sine
wave tone that glides between notes and sounds vaguely human-like.
Invented in 1919 by Leon Theremin, the theremin was the result of research into electrostatic
proximity sensors. Figure 10-4 shows the inventor playing his instrument. The theremin con-
sists of two antennae, one for controlling pitch and one for controlling volume.The pitch antenna
is usually vertical and on the right-hand side of the player. The circuitry inside the theremin
measures the varying capacitance between the player’s body and the antennae and adjusts the
loudness and pitch accordingly. If you’ve ever used your body to get better reception on your
TV, you’ve experienced how the theremin works.

Making a Theremin Out of Roomba

The two Roomba dirt sensors are apparently capacitive-based and thus a likely candidate to use
as a theremin input. Unfortunately, they do not seem to be tuned to picking up human-sized
variations. But the other downward-facing sensors offer an alternative for the pitch control. By