Thursday, December 23, 2010


It will be a little while before I have the necessary components for this project all cobbled together.  My hope is that I will have it finished by the time that I am doing my second course of programming in the fall of 2011 so that I can write an OS for multi-touch. 

This particular project is going to require some fairly in-depth research.  I will be posting all related research as I find it.

Saturday, December 11, 2010

Materials for FTIR Project

The materials that I've managed to scrounge up so far are 40 IR LEDs, a PS3 Eye, an old LCD monitor, and some other assorted bits and pieces.

The big things that I need now are a bigger/newer LCD monitor and the Acrylic sheet.

Friday, December 10, 2010

Project "Hello World" (FTIR and a Multi-touch Computer)

For my first project I'll be doing a Multi-touch computer.

--Here's the Theory-- (Mostly courtesy of NUI Group and a couple of other websites like them)

There are many different ways of capturing multi-touch, but the two that I am considering are Frustrated Total Internal Reflection (FTIR) and Diffused Illumination (DI).  Both of these technologies rely on infrared light to detect objects on an acrylic/polycarbonate/plexiglass sheet.  The areas in which they differ are as follows:

FTIR uses infrared LED's positioned around the edges of the acrylic sheet, to light up the entire sheet.  Due to a rather interesting physical property of the acrylic, the light will stay inside the sheet, hence the Total Internal Reflection.  It does this because the light rays are almost parallel to the surface of the sheet, and as they reach the upper surface they bounce down to the bottom of the sheet and so on.  Where the light gets frustrated is when an object is placed on the acrylic sheet.  This causes some of the light rays to be reflected straight down and out of the acrylic to a camera which has a filter so that it only senses infrared light.  The blob of light is then transported to a computer where it is computed as a touch point.

I plan on starting with FTIR and then exploring DI because the acrylic sheet for FTIR is much less expensive than the specialized one required for DI.  The reason that DI requires a special type of acrylic is so that it can sense objects that are slightly above the surface of the sheet.  FTIR cannot do this because the object has to touch the acrylic in order for the light to be reflected.  DI works in a similar fashion to FTIR but with a little twist.  It uses the same type of infrared LED array that FTIR does in terms of their placement, but DI uses an acrylic sheet impregnated with a substance that acts like tiny mirrors and reflect some of the infrared light up and out the the acrylic sheet.  When an object is placed over the sheet it reflects some of the infrared light downwards to be picked up by the camera.  The farther away the object the dimmer it appears, so with the right program you can compute just how far it is from the surface.