Compliant surface and projection screen

To interrupt the IR light inside the plexi-glass, you have to push fairly hard, unless you have oily or wet fingers. This is where the compliant surface comes in. In some cases, the compliant surface can double as a projection screen. The compliant surface also helps keep the acrylic from getting scratches, provides consistant results instead of relying on how greasy or oily your hands are, and it makes the screen pressure sensitive (What is a compliant surface?).

When you dont use a compliant surface, you tend to get results like this:

When you use a compliant surface you get clearer results like this:

The projection surface, well, provides an area for the visual screen to be projected. Otherwise its just a touchscreen without any picture on it. That wouldn't be any fun, would it!? Materials often used for a projection surface are rosco grey, printer paper, vellum, and mylar. In my case, I will be using vellum coated with my compliant surface.

In my case, my compliant surface will be silicone rubber. I plan to use Tinkerman's method on applying the rubber. Though, I am fairly afraid of dust, so after I paint on the silicone, I'm going to cover it up with a bed-sheet.

I just bought xylol and silicone, so when I get vellum I will apply it.

The layers in the end will look something like this:

Works Cited:

"What is a compliant surface?" NUI Group Community Wiki. 29 Oct. 2009. Web.31 Dec. 2009. <http://wiki.nuigroup.com/What_is_a_compliant_surface%3F>.

The FTIR touch-screen concept

The refractive index of acrylic glass changes when you put you finer up against it, reflecting some of the IR light straight down. This will be detected by a modified webcam, that only detects IR light. When a finger, or any object, is placed on the glass, you get a 'blob' of IR light. This blob will eventually be recognized as a point of touch.

What is an FTIR

FTIR stands for Frustrated Total Internal Reflection.

This is a term used among the multi-touch community. There are many different types of multi-touch methods, including capacitance screens, resistance screens, back lit IR screens, color tracking, and more. I chose FTIR because it is best suited for what I want to do, and it seems to have the best results. FTIR was originally thought up by a guy named Jeff Han in 2005 (Han).

refractive index

A refractive index is how much the speed of light is reduced when inside a certain material. Water has a refractive index of 1.3330 (Laven), and the acrylic glass used for the FTIR has a refractive index of 1.50 (Reed). If the refractive index is lower on the material the light is trying to pass through, the light will be reflected. So, at a certain angle, all light is reflected off of the surface of water. This is how fiber optic cables work. All of FTIR in the multi-touch community is based around this concept: Getting the light to reflect inside the screen.

Works Cited:

Han, Jefferson Y. “Low Cost Multi-Touch Sensing through Frustrated Total Internal Reflection.” Symposium on User Interface Software and Technology: Proceedings of the 18th annual ACM symposium on User interface software and technology. Seattle,WA, USA, 2005. 115-118.

Laven, Philip. "Refractive index." Mie scattering. 16 Aug. 2009. Web. 30 Dec. 2009.<http://www.philiplaven.com/p20.html>.

Reed, Rick. "Refraction - Snell's Law." Refraction of light. 28 May 2009. Web. 30 Dec. 2009.<http://interactagram.com/physics/optics/refraction/>.