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We have been given a project at uni to create a multi touch display.

I've done some research into this and a lot of them call for special film on the glass or use a projector (meaning it needs a certain amount of darkness).

I want to make a multi touch screen that can be used in full daylight (outdoors) and not more than a few cm behind glass - has anyone come across such a project?

It needs to be about a 42" screen size - so not a small pre-made one.

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Most multi-touch displays have some form of an input unit, and a display.

The display can be a front-screen projector, a rear-screen projector, or a flat panel (LCD or plasma). These are all well understood technologies, and your choice will be driven by cost and how it interacts with the input unit.

The input unit can have more implementations. When I write 'light' understand that it can be visible light or infrared.

  • Rear-projected light, reflected by touch points, read by rear camera.
  • Front-projected light, interrupted by touch points, read by rear camera.
  • Front-projected light, reflected by the surface, interrupted by touch points, read by front camera.
  • Side-mounted LEDs and photo-transistors, with row/column scanning.
  • Touch-sensitive, capacitive grid.

That's just what I can think of off the top of my head. Any of the back-projection modes can use visible light; for front-projection you'll be better off using infrared.

For a more in-depth review, I suggest you do more research here:

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Using it in sunlight rules out pretty much anything that uses infrared for detecting the touch points. I used a DIY one and a surface and both are pretty useless as soon as sunlight comes even if it shines trough a window.

What does work even in sunlight is the detection of special markers (color, form, etc) if that is an option.

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  • \$\begingroup\$ Yeah, couldn't you just detect shadows on the screen instead? \$\endgroup\$ – endolith Dec 17 '09 at 17:24
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In the past, I've used a laminated piece of glass which has a frosty acetate middle layer, they're not too cheap unfortunately but they work well. I then used a projector to back project the screen on, and I had infra red LEDs lining the edge of the glass, then I used the IR camera on a Wiiremote to pick up the light reflected from the fingertips.

Mine works fine in any lighting, I once did a demo at a local pub, and the halogen lights above the pool tables kept setting it off, So I took an image of the room (on the IR camera) and subtracted it from the real time image, it worked fine after that.

It's true multi-touch using fTIR, and it's really smooth and responsive, if you experiment to remove the light related gremlins, it's more than worth it for the results, I wouldn't use any other method myself, SAW, multi-layer resistive and capacitive just don't compare

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The open-circuits wiki lists many multi-touch technologies and techniques:

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