New Scientist has an article on turning any surface into a touch screen using small piezoelectric sensors to sense surface vibrations -
“A series of acoustic sensors that turn any surface into a touch-sensitive computer interface have been developed by European researchers.
Two or more sensors are attached around the edges of the surface. These pinpoint the position of a finger, or another touching object, by tracking minute vibrations. This allows them to create a virtual touchpad, or keyboard, on any table or wall.” [via] – Link.
- Non-Invasive washing machine cycle detector project (uses piezoelectric sensors) – Link.