How a FTIR Multi Touch Screen Works?

This is a relatively simple solution, that can be developed at home with a low cost. Jeff Han, an MIT researcher, was the first to use the total internal refraction (FTIR) in a multi-touch system, from that different building methods and experiments begin to emerge, a lot of that is documented in the NUI (Natural User Interface) group forum. The assembly that I’m developing here has a acrylic glass with infrared LEDs around it, translucent paper as a surface diffuser for the projected image, a câmera sensible only to infrared light and a projector. The infrared light keep reflecting inside the acrylic, here a snapshot form the camera below the glass shows only a black image. When you touch the acrylic, because of the frustrated total internal refraction, the LED beams get out straight down, the camera sees a white dot in the shape of the finger. A image analysis – made trough the TBeta software – transforms the white dots in cartesian coordinates that feeds my graphical software ‘Units’, through the TUIO protocol (some good libraries to read this protocol are availablehere). The result is projected back in real time on the surface been touched, the projection and the infrared don’t disturb one another because they work in different light spectrum’s.

Silicone is applied between the acrylic and the translucent paper, to better the touch sensibility, more on that later.

More info:
See the multi touch screen working, here.
How to transform a webcam to be sensible to infrared light, here.
An example of the graphical emergent software ‘Units_08′.