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This is an experiment based on “frustrated total internal reflection” aka FTIR.
This is a very basic demo and we did it just to see how it work and it took us just 4 days!
The most difficult part is seting-up the hardware, in the following list you can see what we used:
* 1 panel of plexiglass 8mm thickness
* 2 strips of IR LEDs (18 LED per strip)
* 2 sheets of tracing paper
* 1 projector
* 1 mirror
* 1 analog camera sensitive to IR light
* 1 IR filter for the camera
* 1 computer
in this video you can see how it work what i did.
here you can see some photos of the setup
the two LED strips its must be placed on the edges of the plexiglass panel (more strips and more LEDs is, of course, better).
here you can see what happen inside the panel when you touch it (FTIR) :
Image credit Jeff Huan
http://www.cs.nyu.edu/~jhan/ftirsense/ftirschematic.gif
When you are done with this part most of the work is done!
Place the camera underneath the table, the camera must be IR sensible (almost all digital cameras, including webcams, are but they are usually fitted with an IR filter that cuts all the IR light. We must open the camera and remove it!).
Put a visible light filter in front of the camera (one of the best is just the black tail end of developed slide films).
Put the projector underneath the table with a mirror reflecting the image on the projection surface. This is needed just to be able to place the projector in a comfortable horizontal position and to gain a bit of image size.
ok have you done it?
connect all to the computer and vvvvenjoy...