We’ve been learning a lot from the NUI Group, so we thought we’d give back a little by sharing a new technique: getting multi-touch blobs from infrared LED ribbons. We first tried to solder our own IR LED circuits. Although we got it to work, it was challenging, time consuming, and created many potential points of failure.
Because I was doing some other research involving lighting, I was familiar with flexible LED ribbons, and had a few of these ribbons/reels on hand in the visible light spectrum. We saw that many people were testing their blobs in IR right away, but that often required a dark room, an IR camera, etc. If you’re just trying to test the quality of your surface, this complicates the situation, as poor blobs could be the result of the camera, stray IR Light, the software, etc. So what we did was wrap one of the visible white light LED ribbons around the acrylic to see the FTIR effect first-hand, with our own eyes. By testing for blobs with visible light, you isolate the effects of the surface, can quickly see the results of different techniques (silicone of various types/thickness, Sulky Solvy, etc.) Not to mention it’s pretty cool to witness FTIR with your own eyes and watch your fingertips glow 
We were getting really good blobs with the white light LED ribbons, so we started to hunt around for LED ribbons in the infrared spectrum. We didn’t find a source online, but we had a contact at EnvironmentalLights.com from my prior lighting work. We spoke with him, convinced him of the value it would bring to the multi-touch field, and he actually created a new product for us: Infrared LED Ribbons. You can buy these by the foot or by the reel, and a bunch of accessories are available: wire connectors, power supplies and cables, aluminum channels, spacers, etc.
We did a quick test of the infrared LED ribbon, and it produced some really good blobs with direct touch of your fingertips. It also generated good blobs with test sheets of silicone and Sulky Solvy with a Rosco Grey screen on top. What’s great about the ribbon is that there are so many LEDs surrounding the acrylic, that it’s pretty much completely flooded with IR light, even if the sides are not super clear. And it saves so much time.
Earlier this week, we built our first multi-touch display using infrared LED ribbons, which worked quite well. We used a polished piece of acrylic from TAP Plastics, and an L-shaped strip of infrared LED ribbon with a soldered plug that attached to our power supply. This was placed inside aluminum channels (specifically sized for the LED ribbons) that were cut in the shape of a frame, with neoprene spacers to keep the LED lights the right distance away from the acrylic. We used Sulky Solvy for the compliant surface and Rosco Grey for the screen. Both of these were stretched over the acrylic to make them taught, and affixed using a perimeter of thin double-sided tape. Our IR camera was a modified Xbox Live camera, and we borrowed an Infocus DLP projector for this test.
Our next steps are to work on the housing that will hold the display, find a permanent projector, and start testing our blobs with the touchlib software. We’re using Macs, and ran into a few snags with touchlib on that platform. But we plan to make some tweaks to that (or maybe the new Mac tracker will be ready by then, fingers crossed!) Our ultimate goal is to investigate and document the human factors and usability of multi-touch interaction, which we’ll continue to share with the NUI Group community.
lol. It’d be nice to see some in the lower range as 940nm can be high for some cameras.
