Build a multi-touch display for an exhibit piece that tracks people’s finger movements across a surface and translates them into a projected visuals. This project is simpler than your usual multi-touch surfaces, as the projection is not onto the surface, but set towards the exhibit in front of the user. I chose to experiment with [...]]]> Project

Build a multi-touch display for an exhibit piece that tracks people’s finger movements across a surface and translates them into a projected visuals. This project is simpler than your usual multi-touch surfaces, as the projection is not onto the surface, but set towards the exhibit in front of the user. I chose to experiment with a method called ‘frustrated total internal reflection‘. This brings me way back to High School physics class, taking advantage of the basic characteristic of light as it breaks within and between different materials. When directed into glass at a certain angle, light will

Above is the *simple* initial prototype I put together with a piece of plexi, some LEDs and good ol’ Duck tape. The blue superbright LEDs give it a nice feel. The camera is placed behind the surface, capturing a user’s finger movement across the surface.

Parts

• sheet of clear plexiglass
• 4 superbright LEDs – connected in series.
• 12V power supply
• Logitech webcam – behind the surface.
• processing applet – I wrote a very simple application which takes video as input, goes over all pixels and highlights the brightest areas.

above: The tips of my fingers as seen through the processing application

Next Step – use IR LEDs

I experimented with a variety of IR LEDs but suspect they were too directional and probably not strong enough. I’ve placed an order for the Osram SFH485 880nm IR LEDs which will hopefully solve this problem. They are also recommended by Jeff Han in his DIY multi-touch presentation.

References

Sasha Harris-Cronin put together an informative page on DIY multitouch screens.

tinker.it multitouch table experiment.

encryptio.com – great DIY multitouch tutorial

[tags] multitouch, DIY, electronics, plexi, processing, LED, infrared, sensor [/tags]