Hey, I want to make a little setup like this work (I don’t know if it will work… ):

The Pen with LED looks like this, it lights up when you press it:
[See attachment]

Using light to trigger the camera at a point is a sure thing. But if you’re talking about picking this point out of the field of view of the camera which is also looking at projector output, you’ll want to go IR. One could conceivably get a red pass filter, but you’d still have to filter that color red out of your project (maybe software is enough, but I doubt it, may need a filter for the project which would get hot, I would think).

If you’re not going to be doing a projector in the same field of view, then you’re good. Computer vision looks for regions of interest, and I’m sure a bright red dot on an otherwise flat image counts as one. Would have to use a camera, though, and vision software like touchlib, or some other blob tracking.

... sorry the image didn’t load for me when i wrote the above but now I see it… yeah this could work, you’d need a red filter on the camera, and you’d probably also like to at least software tune-out the red on the screen, but otherwise it may work.

I would still think using infrared would be a more normal way of doing this, and people here would be more familiar with IR.

Ok, thanks very much, but what do you exactly mean with a “red pass filter”? Is it a infrared filter, or something else? By the way, I’m going to build this setup right now, so I can let you know if it works .

Thanks

just a filter that would pass red light only… you would have to figure out the exact ranges, talk to some photography friends maybe… might not be a cheap solution, but one could maybe fathom both a green filter and blue filter in tandem might do something towards your goal

This has turned Jonny lee’s Wiimote Whiteboard on its head!  I was trying to get a good calibration but my reflective screen made double blobs.  Having the pen the other way around makes it work perfectly! Simple ideas are always the best!