Ramvik Touch: How it Works
I’ll be chronicling the whole process of building my touchscreen table, and this second post will explain just how one of these things works.
Essentially, there are 5 things required for one of these setups. There are different methods of setting it all up, but these things are the same:
1. A display, usually from a projector (an LCD can also be used but is more complicated and limited in size)
2. A diffusion surface, for the image to shine onto and to capture the “bumps” of your fingers (more on this later)
3. An infrared light source
4. A camera, modified to capture only infrared light
5. A computer with software to capture and process the bumps registered on your touch surface.
Rear DI surface setup.
The picture above helps put everything together here. We’ve got the projector beaming an image onto the diffusion surface, using a mirror to extend the throw of the image (I’ll discuss the projector specifics in a future post). The infrared light source can be done in several ways, but in my table I’ll be using infrared LED spotlights, located under the surface of the table. These lights flood the inside of the box with infrared light, invisible to the human eye. When my fingers come into contact with the surface of the screen, they bounce light down back towards the bottom of the table, as shown here:
Down at the bottom of the table, a webcam is pointed up at the underside of our screen surface. However, this camera is modified to only register infrared light, rather than the visible light filters normally equipped on webcams. When you look at this image on the computer, the infrared reflections your fingers make on the glass look like this:
Now, using free, open-source software on our computer, we can interpret the location of the bumps which the webcam is registering, and turn them into multitouch actions on our Windows 7 system.
In the next Ramvik Touch blog post, I’ll talk about projectors, and what kind of specs I’ll need to build this specific table.
If you think this is a really cool idea, you should really check out this thread on the NUI forums. In fact, you should check out that whole forum, as it is pretty much the definitive resource on building and discussing these things.
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by Joel (Daabears)
On April 8, 2010 at 9:20 am
This is fantastic. I’ve been doing some research into doing something very similar. Yea for multi-touch!