Parts and where I found them

Okay, I was ready to find all the components needed for a LLP set up. Here's the list :

• A LCD with no FFC issue (I'll explain later)
• Clear, flat surface (Glass, Acrylic, Polycarbonate, Plexiglass, etc.) 
• Infrared Laser(s) x 4
• Line Generating Lens x 4
• Diffuser sheet
• Infrared Camera/Modified Webcam
• Few meters of electrical wire
• Some electrician stuff
• And of course the table.

The LCD Screen

I used for the prototype my old 17" LG 1730S. Chosing a LCD display for a MT Table is quite a challenge, as they can have the "FFC (Flat Flexible Cable) issue I've spoken earlier about. That problem can be sum up like this :

LCD screen are getting smaller and smaller, so are getting the cables and wires in them. FFC is a kind of flat wire (like tape actually) that are used in all LCDs to free some space. As you probably know, a LCD matrix is transparent and the light must go entirely though it. But sometimes, there is a FFC standing in front of the LCD matrix that you can't move (see picture below). In that case, a whole area of the screen won't be lightened when the LCD is disassemble and will be dark.

 Typical FFC Issue.

I've seen in the Lumenlab FFC database that this screen didn't have that problem, so I chose it.


Infrared Lasers

To be detected, your fingers must be lighted with IR light, in order for your camera to distinguish visible light from IR light. The common lasers used for that purpose are 780nm 25mW from Aizix.net. As I wanted to go for a 32" (82cm) LCD TV screen, I wanted the lasers to be powerful enough. For a smaller set up (17"), a 780nm 10mW would be ok.

A 780nm 25mW IR laser

The lasers must have a Line Generator in front of them, in order to create the laser plane. I chose the 89°, to waste less power from the laser, still from Aizix.net. A 120° would be ok too, and easier to calibrate (as it's quite a lot wider).


Infrared Camera

There are a quite a lot of solutions about the camera : the nuigroup.com community mainly bases its set ups with the PS3 Eye camera (Playstation 3), as it's quite cheap, has a good image quality and is VERY fast (60fps at 640*480). That was the way to go for me !


I bought one for 18€ at Fnac.com in France, and got it a couple of days later. Very cheap / fast.

The PS3 Eye Camera

But the camera isn't capable of seeing IR light without a couple of modifications :

• It has a IR light filter (that you'll want to remove as it's doing the opposite of what we want it to do)
• The lense is not bad, but for a smaller set up (table height) you'll want to go for a lower focal length
• Half of the PS3 Eyes (it seems to be quite random actually) have the IR filter you can't remove without destroying the whole lense. As everything's glued in it, you'll want to go for another lense mount.
• You need to add a IR bandpass filter to cut off the light noise from visible light

I'll explain later of to do all that and where to buy all the components.


Everything's ordered then, I can set up the main parts...