Page 112 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

wire
Steel, Copper, or Aluminum Foil

Conductive Hook-up
Foam

Aluminum
Foil
Pressure
Changes VOM
Resistance

Side View
5.38 Conductive foam touch sensor

packed in to prevent static damage. The foam has a nominal con-
ductivity that changes as the material is compressed. 91

It is important to use low-density (soft) conductive foam, because
it is soft and spongy. As pressure is applied, the foam compresses,
which changes the nominal resistance between the conductors.
Figure 5.38 illustrates a simple touch sensor. The conductive plates
may be made from printed circuit flexible board (PCB), aluminum
foil, or something similar. Higher-fidelity touch and pressure sensors
are reviewed a little later in this chapter.

Piezoelectric material

There are a great many piezoelectric sensors. Piezoelectric sensors
can detect vibration, impact, and thermal radiation. Pennwall
Company makes a unique product called piezoelectric film. This is
an aluminized plastic that’s been manufactured in such a way as to
render the plastic piezoelectric.
The material is sensitive enough to detect the thermal radiation of a
person passing in front of it. Many commercial light sentries sold in
hardware stores use piezoelectric film behind a Fresnel lens to detect
the thermal radiation of a person. This type of light sentry auto-
matically turns on a light when someone walks into its field of view.

Team LRN Sensors