Touchscreen Progress 10

I got my screen back up and running again after juicing it up with 3x the LED's (old screen had 14 LEDs, new one has 42). This time I mounted my LEDs on a strip of plastic instead of sanding them and gluing them to the screen with UV Glue. Interestingly, when I first hooked it all up it wasn't any brighter (except at the edges) than using 14 LEDs. I figured that it must be that the light is not getting dispersed enough - my LEDs are a very tight angle (16 degrees). To fix this I sanded the heads flat which seemed to help a lot. Next thing I might try is making them concave with my dremel instead of flat which might help dispersion even more. The moral of the story - wider angle led's are better. Now that the LED's aren't glued to the screen it's a lot less fragile and easier to tear down and mess with.

I also ended up getting rid of my paper + plastidip surface and going back to the design outlined in Jeff Han's paper. I put a diffuser (I sanded a thin piece of plastic) to act as the screen. The diffuser helps reduce background noise and also eliminates one of the big problems I was having with the paper surface which was specular glare from the projector on the bottom of the acrylic screen. The other problems with the paper are that it gets wrinkly once the rubber is on it and it's not the nicest tactile surface for heavy use. Still, I think it might be possible to find a similar surface. A surface has to have the following properties:

• It has to be flexible enough to register individual finger presses and not be too hard to press
• Has to be rigid enough to keep it's shape (not too stretchy - esp if coated).
• It has to be usable as a rear projection surface
• Has to scatter IR (can't be IR transparent).
• has to feel good to touch and touch and drag

Any surface can be coated with the plasti-dip to ensure that it couples well with the acrylic screen.

Sensitivity is a lot better now for me, but it's still not up to the level that you can see in Han's multitouch video. Improving that will be my next priority. I have a new IR filter which should cut down on background noise. I'll also make some improvements to the blob detection code (detect more blobs but reject more based on criteria).