Did you have to use resistors for the lasers? The ones I’ve ordered are rated at 3.7v I think, and I don’t want to overdrive them.

Do you recon this method would be sufficient to make something similiar to the unit in this video.

http://www.youtube.com/watch?v=OVD_Lvv4UOI

Can you comment about the thickness of the acrylic sheet you used? Does it bend when you press hard at the middle of the screen?
I used 1/4 inch acrylic and yes it does bend slightly in the middle, but never enough that drastically effected performance. For later builds, I did use thicker acrylic and built a frame on all four sides.

What is the angle of the lens on your laser modules?
Unfortunately it wasn’t an exact science for this particular build, hence the use of the putty. What I did to tune it, was place a white sheet of paper off all the edges of the screen and using the web camera adjust the lasers to shoot directly into the light guard to ensure that it was as close to the acyclic surface as possible.

Does the system perform well in a room with bright sunlight (not facing directly then window though)?
I’ve had success running the system in conference room with mid day sun light. If sun light does become a problem, I suggest enclosing the space between the camera and the screen. In later builds, I a completely enclosed the system similar to the Microsoft surface which worked better in daytime situations.

Thanks for the comment!

I purchased my lasers from another forum member on nuigroup.com. It’s been almost a year since I bought them, but you can message him if you like:

http://nuigroup.com/forums/member/1652/

eBay is also a great source for laser modules, just remember to get one with the line generating lens. In regards to powering the laser, my modules were rated at 5v, so I powered them off a usb port for testing. For my final install, I bought a 5v dc power supply from radio shack and built a custom switch.

Thanks!

Thanks for the comment! I would say that the main advantage of using lasers is that they scale up easily. The lack of a necessary compliant layer used in FTIR setups allows for a quick build time and larger scalable surfaces. With two lasers I would stick to a size near my setup of 36″x24″ to avoid shadows, but if you bump up to 4 or even 6 lasers, I’ve seen clean setups of around an 100″ diagonal.

In regards to cost, excluding the computer and the projector, overall it was around $450. The availability of the lasers is much easier with the growth of the DIY multi-touch community so I would estimate a savings of about $150 if I where to build the table again today.

Hope this helps!

Thanks for the comment! I cut the 1/4″ acrylic screen to 36″x24″. In regards to 2 vs 4 lasers it just comes down to the size of the screen. There is some fade in the upper corners due to the angle of the laser line is not wide enough and only one laser will illuminate fingers. This is in the extreme corners. I’ve never had more than a few people interacting with my setup, but in theory I would have some problems with illumination with a high number of fingers on the screen at once (more than 3 people). My advice is if you plan on a larger screen than mine or plan on high number of users, go with 4 lasers. Hope this helps!