Make Subscriber Dave Vondle let us know about this great project he just posted. He started with a rear projection TV, turned it into a laser light plane-based multi-touch screen, and wrote it up on the IDEO Labs Blog:

Continuing our multi-touch research, we’ve been working on turning an off-the-shelf rear projection TV into a multi-touch display. This screen has the best width-to-depth ratio of any multitouch system (67″ diagonal viewing area and only 16″ deep). This is also the first example of hacking a multi-touch system into an off-the-shelf television. The system we settled on uses very few additional components and could potentially be applied to any rear-projection TV.

The system has four IR lasers mounted in the corners. Each laser has a line generator on it (line generators are put on laser-levels to create a line of laser light). The four lasers produce a plane of infrared light across the entire surface of the screen. When a finger intersects this plane of light, the light illuminates it. We have two cameras inside the TV that look at the interior of the screen from the inside. These cameras have filters on them that only allow infrared light through. The cameras see the “blobs” of infrared light and track these points.

IDEO Labs: Rear-Projection TV Turned into a Multi-touch Display