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I am a novice / hobbyist and I have a project in mind that involves detecting where a laser is aimed at on a relatively large scale (300+ sensors). I've found circuits that would work on a small scale such as a phototransistor or a comparator IC to compare resistances, but I have absolutely no idea how to scale this up in a cost effective manor. This will be used to then output digital logic signals to a microprocessor. Any ideas?

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    \$\begingroup\$ It depends on your operation really. If I were to do this in an array kind of formation (think trying to find the laser on a relatively flat surface) I would be more likely to use an IR laser, an IR camera and some video processing instead of a ton of photo-anythings. Smaller form factor, much more portable, and it shouldn't be hard to find a single dot given enough contrast. Could probably be done for ~$40, too. \$\endgroup\$ – ambitiose_sed_ineptum Dec 14 '16 at 18:09
  • \$\begingroup\$ You should give much more details about your project, or narrow down the question. How large is the area, what is the beam shape (a laser point), ambient illumination intensity relative to a laser intensity. These are just things to start with. \$\endgroup\$ – Nazar Dec 14 '16 at 18:10
  • \$\begingroup\$ Sorry about that, yes the goal is to find where a laser dot hits on a flat surface, utilizing a laser pointer of some kind. I will look into the video processing approach. Thanks ambitiose! \$\endgroup\$ – Shaun Adams Dec 14 '16 at 18:14
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    \$\begingroup\$ I agree with ambitiose, I'd use image processing here. To simplify the image processing problem, if you know the wavelength of the laser you can put an optical bandpass filter in the camera's light path which would let you isolate light from the laser. \$\endgroup\$ – Peter Dec 14 '16 at 19:22
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you could assemble a photo-resistor array, if you're looking for a cheap, small, precise measurement of the location of a dot. You will need a number of Input equal to the number of rows + the number of columns, wired up like so:

enter image description here
instead of LEDs, use photoresistors. wire all 'R' wires to a 5k pullup, and all 'C' Wires to a 5k pulldown

You can buy a hundred of these for about 10 cents a piece, probably less, and make a 10x10 matrix for 10 USD.

if you don't need that sort of precision, I agree with ambitoise, and check out some image recognition solutions.

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