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jeanot, yes..ish. Not a very clear explanation. My sketch is with a motor rotating three mirrors in a triangle so that as soon as the reflected beam has exited at one extreme a new beam starts at the beginning again. The beam would then be reflected up using the prism and show as a red dot on the inside of the edge. Rather than get some feedback or control of the motor; one or two of the sensors could be used to signal 'beam starting' and 'beam ending'. Obviously there would be trigonometry to figure out exactly where on the perimeter the dot should be at an intermediate time!It's rather complicated to implement - just a brain-storming type idea.PS I've not figured out the issue with the pi3d events multiple key presses at the same time!
You might be able to do something with a laser and a rotating mirror. The laser spot would be projected as a red dot on the edge which would have to be a kind of frosted glass or plastic. The timing would be done relative to first and last illumination of sensors positioned so they couldn't be occluded.You could do a two dimensional version with laser shining onto the W and N sides and sensors on the E and S sides.Of course this system would be better with the laser bean not hitting the sides at too oblique an angle which would require the rotating mirrors to be well away from the side of the screen. Alternatively the laser could pass under the volume interceptable by fingers, a bit like this!
Jeanot, I may not be entirely objective (as I say on the Raspberry Pi forum) but I truly think this is an exceptional project and write-up.
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