I built a multi-touch screen using an LCD display (not finished). I used a Benq 22” FP222WA as the LCD, a Philips SPC1000NC as the camera and I don’t know what kind of LEDs I’m using only that they are 5mm in size (the guy at the electronics store didn’t know either). The setup is very similar to this one: http://nuigroup.com/forums/viewthread/1040/ but I’m still using the acrylic for protection. I tried FTIR but my blobs are quite weak (i should polish the acrylic better). So I’m using this type of front illumination (probably side illumination is a better name). I used 48 LEDs arranged along all 4 sides and I think it’s overkill. But i still have a problem, my LEDs have a narrow angle and this means that along the sides in between the LEDs there’s no IR light while in the middle of the screen my blobs are very bright, so I need to place the LEDs farther from the screen. I also used a pen with an LED for the mouse drive because it’s much easier to click a small icon with a pen than a finger.

http://www.youtube.com/watch?v=Xvzn2ZJBMA0

Nice setup, be sure not the damage the sides of the lcd panel...I know someone who can talk about that

Hey congrats ! It’s good to see a working multitouch lcd. Maybe I’m off topic but I’d like to know if you did something special for the backlight (and what is you setup) ? because it looks really great.

I did absolutely nothing to the backlight, there are 2 long flourescent lights along the top and bottom edge of the backlight acrylic. After removing the white reflective layer behind the backlight the screen is not as bright as it was before, but as you ca see it’s still usable(it will probably be brighter if I make a case around the whole thing to reflect some of the light). I also removed the fresnel and one difuser (the screen had 2 difusers).All of this + the LCD panel was and still is sandwitched between a metal frame and a plastic frame(picture below), so everything stays in it’s place.

And when you have a completely white picture is it white or grey (admitting your screen is in a box, because I think that you can see a little through the screen so it’s not really white) ? (once again I’m sorry to disturb you with this)

Compared with a sheet of paper it’s a little grey, but if you just look at it it’s quite white (I’ve seen whorse on old LCDs), and that is whithout a case. The LCD is not that transparent to normal light, for example you can’t se your hand behind the screen if it’s more than 5cm form the backlighit; if you hold your hand behind the screen and touching the backlight , you can see a shadow on the screen (at least that’s how my LCD is).

Ok ! Thanks a lot ! I guess there is a different render for each screen… I hope you’ll construct a box soon, I can’t wait to see a finished project

I took o few pictures, hope they help. The first three are with the reflective layer, the next two do not have the layer and the last is my hand up against the backlight. A white case should solve the problem.

Great job！ I would like to try later, The LCD setup seems much more promising than projecters

looking good !!!  Very impressive results !!
LCD definaly gonna be my next testbed !