Get Firefox!

FTIR Multi-Touch Surface
Matthew Hagerty, Jun 2006 (
Work in Progress.


Building the touch surface. More text to come, but for now here are the pictures.

45 Degree Edge

I cut the edge (using a table saw) at 45 degrees to optimize the coupling of light into the acrylic. I sanded and polised the edges with buffing compound and a buffing wheel.

45 Degree Edge Close Up

Close up (it is really hard photograph a clear object!)

45 Degree Edge Straight On

Front view of the 45 degree edge.

45 Degree Edge Profile

Side profile of the 45 degree edge.

Acrylic In Waiting

Edges cut and polished, just waiting for the frame.

Basic Frame

I made a simple frame from MDF. I really don't like it, but it will do for now.


I need to hold the LEDs at 45 degrees to the acrylic and these fit the bill.

Modified Supports

I had to cut the tab off the support so the acrylic could sit flush to the face.

LED Boards

I cut a prototyping board into strips to mount the LEDs on.

LED Module

Each LED module will have three LEDs and connect together to accomodate the size of the acrylic.

LED Module Placement

Checking to see how the boards fit on the supports.

LED Module Placement

It will take about 4.5 LED modules for this 28 inch acrylic.

LED Module Back

Back of completed LED module.

LED Module Front

Front of completed LED module.

Mounted LED Modules

LED modules mounted. The wire retainer clips I had laying around work surprisingly well!

Mount Profile

Note how the LED is perpendicular to the 45 degree edge. This allows the maximum amount of IR light to enter the acrylic.

Mounted Modules

I still need one more module to complete the row, but I got too excited to try out the surface so I'll have to finish it later.

Completed Surface

With the baffle in place and a few quick mirror retaining clips, the surface is ready for testing!

Baffle Profile

One last shot of the mounted modules with the baffle in place.


Now that's a lot of IR light! Look at the top edge, glowing very bright.

Bottom Front

The baffle keeps the user from being lit with IR light.

Unfiltered Camera View

This is how the camera sees the surface without a filter.


Check out those nice bright spots courtesy of my niece.

More Spots

Looking at the whole surface with an IR camera.

Unfiltered Camera Spots

What the video camera sees without a filter.

Make-Shift Screen

I needed a screen so I quickly taped a piece of white tissue paper to the non-compliant surface (the back).

Read View of Screen

Projecting on to the screen.

Camera with Filter

The filter (currently 3 layers of negative exposed color film) cuts all the visible projected light.

Filtered Camera View

How the camera sees the screen with a filter.

Tracking with VVVV

My 4-year-old daughter exclaimed "I made a clue!" This is a very basic VVVV patch to track the blobs and produce spheres at the tracked locations. What you see is the contours node preview, the DX window is on the second screen which is the projector