HA! the "surface" is little more than....

A cardboard box!.

This is quite cool :)
Make your own multitouch pad: http://uk.youtube.com/watch?v=pQpr3W-YmcQ

Not sure how you would combine it with an lcd though :P

Bummer, I wanted to see the screen on the pad as well. :/

But other than that, it was cool. Must try it out someday. Think I have a spare webcam somewhere...

A LCD screen is lit from the back with a lamp, I bet when you touch the LCD screen with your fingers, then the fingertips are also visible from the back, so a camera could detect them the same way.

LCD Panels are very dark and thick: you need a powerful halogen lamp in order to see the fingers through the panel, and eventually fans to dissipate the heat in the box.

better build this ..
http://www.tomshardware.com/de/Beamer-Eigenbau-TFT-Panel,testberichte-952.html
http://www.tomshardware.com/de/Beamer-Eigenbau-Projektor-Monitore,testberichte-975-6.html

It doesnt need to be that bright to see the actual image itself though, without the back cover on you can just hold them up to a normal strip light and you can see the image fine.
It could possibly be done with a 'cool' backlight for the screen, (like white UBLEDs, or a normal striplight with the box painted white)
but in addition to the lighting, use an INFRA-red camera/filter for detecting the fingers.

Sweet.

someone's comment
LOL.

Man. I can remember back when I first discovered Afrotechmods I thought it was a joke. Apparently some people took it way too seriously.

I actually already tried in the past for different reasons: a portable halogen lamp at 20 centimeters keeps everything pitch black. By bringing the lamp closer you can light no more than a small circle with the actual pixels visible. You need a lot of lumen to see through a standard LCD panel.

I tried it, didn't work like it did in the video.. My whole hand was casting a shadow, so it couldn't really find my fingertips very well (tried with a lot of different lights).

@dorion, are you sure you didnt have the thick white plastic coverplate over the back of it ? Most laptop LCD screens come sealed with this on and it cannot be removed (easily). These screens are not designed to pass light through (as the normal backlight is internal so gets reflected/diffused by it, rather than passng through it).

However, when i worked with LCDs a few years ago, we had bare ones you could see through when the thick plastic backplate/mirror is not present.
Just holding it up to a kitchen light, the image was completely visible. You could even put one on an old fasioned OHP (like you used to get in schools) and as well as just lighting up the image, it would project it on the wall!

Saw some site once that showed how to build your own projector using a laptop LCD screen. Looked cool. :)

Hmmm, might try that.

Sure, it didn't have the antireflection screen.


Of course, but the lamp of the OHP actually produces between 2000 and 4000 lumens depending on the model.

A LCD panel usually blocks about 90% of the light if not a bit more. I guess you would need at least 1000 lumens to see your fingers through it. The point is, if you want to replicate the microsoft surface using that technique you should use a poweful lamp, and the resulting surface could also be a bit too hot on touch. You should also put a protective UV screen between the lamp and the panel or the panel would discolorize during years.

Lol. I think we got our wires crossed there :), I wasn't talking about being able seeing fingers through it (which agreed, would need a LOT, if its even possible!).

I wasnt saying that though, i was simply saying not a lot of light (not projector bulbs anyway) is needed to see the image on the screen, just a suitably bright polarized white light (that runs cool ie UBLEDS or strip lighting). I realise now you were talking about shining a light through the pixels in their darkened state (eg. black), which of course dont allow much light through at all.

However, I was originally talking about trying to use an infra red/heat imaging camera to detect the fingers with a normal or heat improvised backlighting solution.