multitouch phase 1

So I haven't been on here in a while, but I just read this article about multi touch DIY projects and discovered the NUI forums and have started a multi touch screen project using FTIR! The goal is to create a coffee table (18"-24") that has a 50" multi touch screen built in. That is a very short throw for that height table, but I think it is possible.

I decided I didn't want to buy my own LEDs and solder them all together. Recommended from the NUI forums is a company called environmental lights which sells ribbons of IR lights which are perfect for this application. They have 850 nm and 940 nm LEDs so I decided to purchase the IR LED Ribbon Delux Sample Kit to give it a test. As they mention on their site, the 850 have a slight reddish visible glow, but produces brighter IR from what I can tell. The red tint is faint when looking directly at the LEDs, and from along the acrylic it is almost impossible to see. I am leaning towards ordering a whole real of these LEDs in the 850 nm range.

I also stopped at Tap Plastics and picked up some random sized 3/8" and 1/2" acrylic sheets to test with. I didn't realize how many types of acrylic there are! Fortunately very few of them come in sizes over 1/4" so I just grabbed whatever was in the bargain bin. I also picked up an acrylic scraper as the first step to polish the acrylic edges. I also picked up some poly-urethane sheeting to test as a diffuse layer for the projection screen.

Last I hit up home depot and picked up some aluminum "C-channel" or "U-channel" and some sanding/buffing supplies. I noticed that people on the NUI forum (this thread, and this thread) had a hard time finding "C-channel" but there was a great section (in isle 19 hardware) at home depot which had good prototyping materials. I say good "prototyping" materials because the aluminum channels were a bit warped and blemished, but they worked well for my initial testing. In the kit from environmental lights there was some examples of the 1/2" and 3/8" channel which they sell and it was much nicer than anything I found at home depot. It also felt like it might have been anodized because it looked scratch resistant and more robust. Also, the LED strips fit nicely into the 1/2" channel from env lights where as the home depot 1/2" is just a bit small for the special connectors that came in the kit.

After getting home I spent some work cleaning the edges of the acrylic. I ran some tests with and without cleaning the edges and the polished edges produced better blobs. I drilled some of the C-channel to a wood board, I placed one of the LED strips in the channel and then the acrylic on top. After powering the LEDs, I used my video camera (web cam I ordered is still in the mail...) in night vision mode (IR band reject filter mostly removed) and then touched the acrylic. I had to press pretty hard, and you can see the blobs I was able to create below. (Yay for physics!)

I also tried spraying some acrylic frost on part of one, and scratching the surface (sand paper) to create different surfaces (diffuse layers). Both of them worked, but they scattered the light on any objects close to the surface. I'm going to have to see if this will work with the image detection software (touchlib) once the web cam arrives. I also want to see how I can reduce the amount of force needed on the screen to create the blobs.

I am currently waiting for the web cam and projector I won on eBay to arrive which should happen next week. Once they come in I'll hopefully be able to post some better images.

TODO:
Hook up the web cam and see if the software can recognize my blobs.
Determine where to place mirrors under the table to get the lowest profile table at 50" diagonal with the projector.
Determine a good touch surface to create a zero force effect.
Find a cool use for my new toy....

~cmos