Laser Touch

Laser-Touch is a low-cost low-resolution touch sensor, that uses lasers for photo-based touch sensing as well as visual touch feedback. Here, I have built an electronic musical instrument using Laser Touch, that detects and highlights finger positions and plays corresponding notes.

Why I built this: For the final project of Stanford’s course MUSIC 250A (Physical Interaction Design for Music) I wanted to build a musical instrument with lasers, not the cliched “laser harp”—something more novel. After experimenting, I discovered that lasers could be used to sense touches, with functional and aesthetic advantages.

How it Works

A transparent panel is the touch surface, with laser beams above it, and photo-sensors below it.
When the surface is touched, the beam is obstructed and diffused at the touch-spot, which is picked up by the photodiode and the touch is mapped to the photo diode’s location.
While the laser beam is common, each photodiode is separated by a dividing wall such that the diffusion is not picked up by neighboring photo diodes much, to make the mapping more accurate.

This makes a great low-resolution but high-precision touch-sensing surface. On another note, the bright diffusion when the laser is obstructed gives instant visual feedback to the user of the spot touched.

Pros and Cons:

Pros:

Rugged: Sensing tech like capacitive and resistive can be fragile comparatively. Since the sensing element in laser touch is underneath and isolated from the touch surface, it can withstand high amounts of force and aberrations, making it much more effective in outdoor installations.
Fast and Precise Response: Compared to sensing tech like Camera-based touch recognition, laser-touch is faster and more precise—there is no processing of the signals, leaving no ambiguity in predicting the touch location.
Inexpensive: Since it uses cheap electrical components like laser diodes and photo diodes, making a large touch-sensing surface cheap to build.

Cons: