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Notes on construction of a internal reflection infrared rear projection touch table.

Infrared LEDs

Using the technique from TouchFactors Lab. They have a nice flickr stream on constructing the touch surface.

We are trying the IR LEDs from Environmental Lights.

Projection/Touch Surface

Top view schematic of the edge for measurement
Edge view schematic of the edge for measurement

The touch surface consists of a rectangular sheet of 3/8" plexiglas or acrylic, with a touch-compliant surface laid on top.

Start off with a 4:3 aspect ratio so we can use a regular XVGA projector (1028x768).

In order to rest inside a "deep" aluminum channel that also holds the LED strips, we need to add a 0.5" edge to the plexiglas top.

In order to adhere the compliant surface to the plexiglas top , we need a margin of 1" (e.g. for attaching with a strip of double-sided tape?). (One inch may be too much, but we can always trim the surface down.

Thus, the horizontal and vertical dimensions of the plexigas must be extended by 2 x (1.5") = 3" to accomodate the aluminum channel and margin.

A small table would have a projection area of 32" x 24", laid on a 35" x 27" plexiglas top.

A larger table would have a projection area of 48" x 36", laid on a 51" x 39" plexiglas top.

A long informative thread on the use of silicone coated vellum as a touch-compliant surface. We are going to try the technique of Tinkerman (aka dinomaui, in which a 50:50 mixture of xylene and GE Silicone I is applied with a textured roller to the back of the vellum.

Table Frame Design

Could use a drafting table.

This drafting table would look neat as a touch table!

Multi-Touch Software

Touche Cocoa Framework

"Touché is a free, open-source tracking environment for optical multitouch tables. It has been written for MacOS X Leopard and uses many of its core technologies, such as QuickTime, Core Animation, Core Image and the Accelerate framework, but also high-quality open-source libraries such as libdc1394 and OpenCV, in order to achieve good tracking performance." Licensed under LGPLv3.


"MultiTouch.framework is a native Cocoa multi-touch framework for Mac OS X. It uses the default event handling system and the responder chain of the operating system, providing a familiar application programming interface to Mac OS X developers. It is built upon a modular low-level architecture that unifies all touch events, with input units for different multi-touch input devices including FTIR, DI, iPhone/iPod touch, as well as any TUIO-based devices. Thus, as a developer, you do not need to care about the actual input device being used. One of the great advantages of this toolkit is that you can develop and test your multi-touch application on your standard desktop Mac, using your iPhone as multi-touch input device, without having to work at an FTIR table all the time."

There is a video at:

Parts List

Narrow Dimmable LED Ribbon Flex (InfraRed 940 nm)

Regular Ribbon Flex (0.375 in. glass) Aluminum DEEP Channel, 98 in. long, Brushed Nickel

Clear Acrylic Pane (27" x 35", 3/8" thick, polished on edges with bumped corners.

Quali-Tech's "ROLLER Foam" paint roller.

Progress Report

Day 1 (2009-05-03)

Cut aluminum channels with beveled ends to fit acrylic pane. Notched end of one channel to allow LED ribbon power cord to enter.

IMG 1746.jpg

Adhered LED ribbon inside the four aluminum channels (arranged in a long line on the floor) and placed bumpers at regular intervals.

Lifted channels and place them around pane. This took a few tries because the bumpers would easily fall out. Maybe use some mild adhesive on the bumpers next time.


Milestone: After powering up LED ribbon, we were able to see bright fingertip blobs using an infrared sensitive webcam in a darkened room. Yeah!


Other data points:

  • Apple iSight (both builtin and free-standing) must have infrared filters, since they cannot see blobs.
  • "Etched Glass" window film will not make a good surface, since when attached smoothly and firmly, it disrupts internal reflection too much.

Day 3

Close-up video of finger-tips on Silicone-coated vellum

Random Links

FTIR Multitouch and Display Device - A Guide to build your own - Experiments with Processing, OSC

"hello dear reader. on this site you will find some notes and tips on building your own FTIR (Frustrated Total Internal Reflection) input device that is actually working! i've searched the net quite some time finding all infos to get it up and running. the other part is pure software and the possibilities to create funny and also useful things are immense."


"touch screen interfaces are generally hard and flat. impress tries to break from that tradition by making the display flexible. allowing you to feel more like you are interacting with the display." Via hackaday

RENCI Vis Group Multi-Touch Blog Description of the Duke Multi-Touch Wall

TouchFactors Lab

Peau Productions

Nortd Touchkit