That youtube video actually uses back EMF from the LED’s themselfs and no photo diodes. Back EMF is where some voltage is induced in the opposite direction, in the LED’s case by catching some of it’s reflected light. Though, you would need sensitive equipment and some decent electronics knowledge + expensive gear like an oscilloscope to even think about making one.

I really like the capacitive touch idea also. If you could make and sell various sized grids for use in LCD’s, so long as they support the values of which this multitouch community is all about, it could be a good thing.

Also, I think that cameras and IR light is the only way to go if you want to scale up past a certain point. But for everyone who is happy to build somthing which is LCD sized, it’s a great idea.

Please let us know how your progress goes!

I found an interesting link elsewhere in the forum:

http://www.integritouch.com/

Seems like it would be possible, with a better understanding of LCD technology, to use the LCD itself for capacitive touch. OR to use a second LCD layer as a capacitive layer behind the visual LCD layer. I am not positive, but there must be some kind of wiring inside the LCD for it to set certain pixels on/off. Doing more research into this idea as I type.

EDIT: As I understand LCD technology, there are three main layers that make up the actual LCD layer. (1) Vertical “wires”, (2) Liquid Crystal substrate, (3) Horizontal “wires”. If you were to keep the (2) LC layer dormant constantly, and use the control wires in layers (1) and (3), you could setup capacitive touch. The hardware required probably would be rather expensive/difficult. However, a multi-touch display that is little more than the thickness of an LCD is quite attractive. Couple that with a powerful laptop, and you could have a total Multi-Touch setup that is less than 2” thick!

I’m actually going to build that capacitive grid system some day, but I really don’t know how to design the control circuit.

Here is a document where is a quite good explanation of the principle of capasitive sensing. Only that there is ground marker on the hand. I wonder does it mean that you have to be grounded before it works?

No, you are ground for the most part anyways (at least in terms of the power applied to the capacitors). I’ve spent most of the night researching capacitive systems (thus I can now spell capacitive). I’ve posted in a few other places where I believe I might be able to bring some information in. Pretty soon here I will probably open a new topic in the Hardware section on Capacitive+LCD Technology, that way it is a little easier for others to find. When I do, I will add it here.

Here are two purposed designs of the iPhone’s capacitance system:

http://img233.imageshack.us/my.php?image=iphone8c39ee15sy1.jpg
http://img225.imageshack.us/img225/6287/iphone9c3a840ctb8.jpg

EDIT:
New Topic for Capacitive Discussion:

http://nuigroup.com/forums/viewthread/777/

You can also take a look here, some of the thing has allready been talked about: http://nuigroup.com/forums/viewthread/441/

hey:
did anyone successfully build a multitouch surface using an LCD display?

I really want to get off projected based systems, so I’m giving a go with LCD monitors, and hopefully transfer my work onto monitors.

So i ordered in a new LCD monitor, 19 “ widescreen, i’ll be recycling a leftover cheap webcam, ordered a new ir filter, etc....

Been reading about the back-lighting issue with LCD’s. 

Has anyone tried to illuminate the screen with a powerful light source, but then place a Visible Pass/ IR Block filter on top of the lamp?

I believe GE plastics, makes a polycarbonate (Lexan) that absorbs NIR and IR light.  I’ll try to get a sample from a sales rep in the next few days when I get time to talk to someone at GE.

What are other issue’s people are encountering?

I’m surprised no one encountered any problems with the way LCD monitors are packaged, what with their folded up circuitry and all.  Are people ordering ribbon-cable extenders to move the circuit board off the back?

-n

Please have a look at:

http://www.pcadvisor.co.uk/news/index.cfm?newsid=10894

Sharp LCD has built-in scanner
Novel display offers touchscreen alternative

best regards

---------- Finger
---------- LCD Panel
---------- Black visible light filter (for more clarity with the LCD)

---------- Light source and camera

As mentioned, the VGA controller would probably get in the way.

stickyb - 03 August 2007 04:26 AM

Ok, i’ve done the following yesterday:

Disassembled a Dell 2707 WFP LCD Screen ( Full 1080p HD resolution )
and used only the panel with the corresponding electronics (no backlight).

Here is the setup:

________________________ acryl (very thin, just for protecting the panel)
________________________ lcd panel

Patterns/Raster (for smooth/even lighting)

\o/ \o/
(ir SMD led (white SMD led
with lens with lens,
and diffusor diffusor and
pre-mounted ir cut out filter
on strips) pre-mounted on
strips)


|O|
(ir camera fire-i
with bandpass filter)

it works just great! blobs are visible very clear and sharp.

i talked with the guys from unibrain. if you use a 1.9 fisheye lens
you have only a minimum object distance of 10mm.

so the plan is to use 4 fire-i cameras with 1.9mm lenses and a
distance to the lcd panel of 160mm. doing it this way it
will be possible to reach a depth of max. 200mm of the complete
multi touch display with all needed parts (without computers
for processing the blobs etc.).

i think it is possible. and it would even be thin enough to be wall
mountable.

the only bad thing is:
approximately 2500 EUR (3425 USD) building costs.
fortunately i’ve found a sponsor!

sorry for my bad english.

Very good, very good! Please post pictures or video soon. Your setup seems to be successful and we would all like to see how you did it.