Multitouch Table

I saw this post from Maximum PC on the consctruction of a multitouch surface so I decided I'd try my hand at it. So far, I'm $70 in and hoping to keep the entire project under $150. I'm more than pleased with the results as of right now and hoping it will stay this good once I get my hands on a projector.

You can read the article on the specifics of how it works. Basically tons of infrared LEDs (I used 5mm 940nm LEDs from BestHongKong, at $.08 a piece they're the best I could find) shine into the side of a plexiglass sheet and when it's touched the IR light is diffused which allows a modified webcam to see it. The image is then run through touchlib and interpreted as touch points.

Hand Touching Surface

The first part of this project I tackled was the webcam. Maximum PC used a PS3 Eye since it has a pretty high framerate at a reasonable resolution, plus it's cheap, so I decided if it was good enough for them it was good enough for me. Taking it apart was the most difficult thing I've done with this project. It has screws on the back but there's also little plastic latches around the outside of the case, most of which I broke off. Once it was apart I removed the lens assembly and broke/dug out the IR filter. I then cut two squares from a floppy disk to filter out visible light and put them in place. Once I assembled it and tested it out, this is what it sees when I shine the LEDs into it (note that this light is invisible to the human eye).

IR LEDs Into Webcam

The construction was time consuming and repititive, but can be completed in a lazy weekend. I took an 24"x18"x.22" piece of plexiglass and polished the edges so light could shine in easier. Then I constructed the LED arrays. I planned on running them off a modified power supply since the LEDs pull about 2.2amps, which is more than a run-of-the-mill AC to DC power brick can supply. I placed the LEDs every 3/4" and put them in cluster of eight to run them off the 12v rails on the power supply. I found that if you took a piece of wood and drilled holes at the desired distance. It made soldering infinitely easier.

Soldering LED Clusters

I ended up making 14 LED clusters and wired them up around the outside of the plexiglass. I used hot glue to hold them in place. They're not held on very good but it won't matter once I build a wooden frame around the screen.

LED clusters Around Screen

This is all you need to make a multitouch sensitive surface. The next thing I plan on doing is putting in a projector to make it a touchscreen. The only bad thing here is that I need to get my hands on a cheap projector. What I'll probably end up doing is looking around on Ebay for a broken projector that I can repair. For questions or comments, feel free to post them on my blog