We created a fully assembled multi-touch surface for the first time the other day. It looks rather nice, and produces good blobs! We believe there are a number of innovations in this process, which really simplified the construction time and cost:
- Use of infrared LED ribbons as our IR Light source
- Use of LED ribbon channel with neoprene spacers for the display frame
- Double-sided taped perimeter for applying Sulky Solvy and Rosco Grey
We captured the process on video and with photos. The photos are numbered and walk you through the whole process step-by-step, assuming you’ve ordered a few supplies first.
[Note: The idea of using IR light with plexiglass (FTIR) is from a paper by Jeff Han (http://www.cs.nyu.edu/~jhan/ftirsense/index.html). If you are planning to sell something based on this you should probably check with him to make sure it is ok.]
Photos
View the photos with step-by-step instructions.
Video
August 13th, 2008 at 10:31 am
How hard are you having to press to get a good blog while dragging your finger? This is a primary concern of mine.
The surface looks nicely done.
August 13th, 2008 at 11:00 am
I’d say we’re pressing anywhere in the 2-4 range on a scale of 1-10, with 1 being a feather-light touch, and 10 being full pressure. The Rosco Grey is such a nice surface, it makes it very easy to slide your finger around. Also, the Rosco on top of the Sulky Solvy actually creates a kind of cushion that’s thicker and softer than pure acrylic. You can see this effect in the video clip (4:25 mark), where I notice that if you press hard and drag, the material gives a little, creating a ripple. But we don’t press that hard in normal use. We’ll have to see how it responds once we have the software working with the blobs we’re getting.
November 12th, 2008 at 4:53 pm
I noticed that you only cover the left side and the top with the IR ribbon. This means as you move diagonal down the screen, the IR becomes less bright. I imagine that since there are so many LEDs that this is not an issue, but without software testing no one will know. If two IR ribbons were placed, one at the top, one at the bottom, this would solve the problem, if presented.
I am planning on building a multi-touch board and am wondering how this setup performs with software.
Thanks,
Alex
November 12th, 2008 at 7:46 pm
Hi Alex, we started to setup the software, but had to put this on hold while we finish some other research projects. We may be able to resume this soon. I think if the camera and software are calibrated right, it should work fine. The blobs appear strong in all parts of the surface when viewed with an IR webcam. For the LED ribbons, we used an “L” shape instead of two parallel strips “| |” for simplicity in the wiring connections. There’s definitely a lot of IR light bouncing around in there with that many LEDs
December 4th, 2008 at 11:46 pm
Jim,
I’m curious what you used to make your visible light filter?
December 5th, 2008 at 12:20 am
Hi Alex, we cut up a piece of processed 35mm film negative. We cut 2 small squares out of the dark black part (it’s at the end of the reel, and does not have any photo exposed on it). We opened up the Xbox Live camera following a guide online, removed the IR filter, and replaced it with 2 pieces of the negative material (cut to the same size). It seemed to work pretty well!