Hello again… Thanks for all your feedback and interest in my project.
First of all fuz3 is right about the size of my setup. The glass size on top is about 32x24 inches.
I found cheap modular shelf that I picked up in the local Lowe’s store. I like it beacuse of its adjustable height and various sizes that are available.
Since many of you have questions about the laser, I thought I should clarify a few things.
First of all, Helza1 is right. Using a single laser to illuminate the table has a drawback of the shadow effect. Although in order for this to happen, your fingers must be completely in line with the laset light, which I found to be rare, it is possible to happen.
There are two ways I would go about this:
1. Use a mirror around the edges of the glass. The mirror is placed perpendicular to the surface and it extends only about 1mm from the surface.
2. Shine a second laser from the different angle.
3. Alternatively, use both 1 & 2.
Now, some of you asked about the laser spread. I don’t use any filter as such in front of the laser. In order to achieve the light spread, I used cylindrical lens in front of the laser collimated laser beam.
What this does is that it spreads the laser light in one dimenstion only - thus generating a line. The line formed with this method has a Gaussian intensity distribution. Meaning - the line appears bright in the center and fades away towards the edges. In my setup the light spread is 90 degrees. This is why Microsoft is using three laser beams spread apart so that when they overlap they generate somewhat uniform brightness across the surface.
I must note that there are some more sophisticated line lens solutions that don’t suffer from fading of the light towards the edges. These are of course more expensive but generate pretty uniform light line from end to end.
This whole thing brings me back a few months ago and how I found out that I could use this in the multitouch applications.
I was using one of those laser levelers to hang some pictures in my house. I realized that the laser in the leveler device forms a horizontal light plane that when it intersects with the walls of the house creates a straight line or light. Immediately I took the leveler and placed so that its light plane is right above the acrylic. I removed the IR filter from the camera (since the light from leveler is red) and when I touched the top of the glass I saw very bright spots that are easily detected.
If any one of you is interested in repeating this experiment, just get a cheap laser lever and try it for your self. You’ll see what kind of difference in light output does it make the distance of the laser light plane from the acrylic. The nice thing about this is that the laser light is visible and easier to adjust. You can also experiment with the camera placement both below and above the acrylic surface and see how this affects the detection accuracy. You could also shine a laser line into the acrylic at diferent incoming angles and see if you can cause FTIR effect. This, of course, will not work with projector setup since the laser leveler emits only visible light. To make it work with real MT setup you’ll need an IR emitting laser diode.
If anyone of you is interested, I could post some simple instructions on building your own low-cost IR laser line module that you can use in your MT setups.
Oh, one more thing, by simply adding a laser module you can modify the MTmini setup to use the IR laser light instead of the ambient light. This will make it usable in dark environments as well.
Hope this helps…
