Multitouch DIY for dummies

I've just realized that I am going to use the acronym FTIR a lot in this blog, and I should at least define it once.

The Multitouch DIY Scene deals mostly with techniques using Infra-Red (IR) cameras. Why? Because they are cheap and easy to find, and those techniques allow screens almost as big as you want. When you think about it, a digital camera is a lot of censors all wired up with the correct interface to easily connect them to your computer. The use of IR instead of standard camera is for the image of the screen not to mess with the image picked by the camera.

There are a few different techniques using IR, and I urge you to go there if you want to know more. Basically they all come down to this: there is a IR source somewhere, and when you touch the screen the IR light is reflected on your fingers and is picked up by the camera. Where you put the source is what differentiate the 4 main techniques.

In FTIR (Frustrated Total Internal Reflection), the IR light is beamed inside a plexiglass sheet (which actually is the screen). Then, when you touch the screen, some weird phenomenon creates a reflection that can be seen by the camera.

That is the technique I want to use for my table. Why? Because it doesn't use lasers, produce enough light to not need to be completely enclosed, and doesn't need a specific and expensive kind of acrylic sheet. Of course, it also have drawbacks, for example it cannot be used to detect fiducials. But I don't intend to use fiducials, so it's ok.

And now, you will know what I mean when I say that I want to build a FTIR table.