Page 172 - Hacking Roomba

Chapter 8 — Making Roomba Sing 153

give you a little shock similar to static electricity, however. This is how piezo crystals were first
discovered: Squeezing certain rocks generated sparks. In a less drastic application, a flexed
piezo can be used as a sensor to detect vibrations or even as a microphone to detect vibrations
in the air.

FIGURE 8-2: Piezo beeper inside Roomba

Piezo crystals are used in many consumer items besides beepers and microphones. Ceramic
record player cartridges use piezos to detect the grooves, piezo transducers vibrating at 2 MHz
are the basis of medical ultrasound imaging, and the igniters on fireplace lighters are piezos.
There’s research on turning piezo crystals into portable power sources. In the future, your
sneakers may contain little piezos that generate electricity to power your portable devices.

Other Sound Sources

Besides the beeper, Roomba has two other sources of noise: the vacuum motors and the drive
motors. These sound sources are less precise than the beeper and not melodic, but they do
make noise and so are fair game in Roomba musical compositions.
Vacuum Motors
The main vacuum motor produces the deepest bass sound due to the hollow dirt collection
chamber. The vacuum can be the bass drum or metronome, but the timing of it is tricky since
it takes a while to spin up.