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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.

Related:

  • Non-Invasive washing machine cycle detector project (uses piezoelectric sensors) – Link.