On Tue, 2006-02-14 at 21:31 +1300, Russell McMahon wrote:
> Uses force sensing to detect multiple simultaneous touch surface
> contacts.
> Useful for eg 'chording and bi-manual applications'.

Actually Russell, they're using FTIR and not force. So you have to keep
the screen clean!

When I used to work at SRI, we developed a flat panel display prototype
based on the principle of FTIR. The pixels were a huge array of
piezo-electric actuators that when driven would touch the screen and
"frustrate" the "totally internally reflected" beams of light shone
through the edges. To achieve decent sized displays we had to use acrylic
with little optical attenuation in the visible range. But we could also
measure the effect that this author describes. For example, if you shine
light into one edge and measure its intensity at the opposite edge, then
the intensity would drop as more pixels touched the screen. Those closer
to the light source would cause more attenuation (and were slightly
brighter) than those those further away. In our case, this was a nuisance
and not a feature and so we went through great lengths to minimize its
effect.

Now that I work for Synaptics, I'm biased that the best way to detect
touch is capacitively. And while we haven't made any product the size of
this user's display, I have read about one that Sony prototyped a few
years ago.

Scott

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