^ THIS was the reason for which i suggested you to use red and green ..... so you can use, as example, green for tones and red for semitones, and have them disposed as in a keyboard (as example, keeping the 2 modules separated, so the beams comes out in two "fans" of beams, without need combining optics), and you have visual identification on-the-fly, about where the octaves are
BTW, if the board have difficult in reading the 2 "fans", you can use a dirty trick ..... two light sensors groups, one with a green filter (read only the green beams, for tones), and one with a red filter (read only the red beams, for semitones), also with two separated sound boards, just synchronized ..... you can call it a "super-professional laser harp", then )
I think the two color idea is great as well. As I was watching the video, I pictured a piano keyboard setup with the white keys as green and black keys as perhaps red.
Do you have a few links for building these? I'v seen a few good tutorials but lost the links.
^ there are some different ways for do that, the 2 more easy ones that came in mind are these ones:
different "fans" in this way:
but this can cause some problems, cause for the different inclinations, you have to displace your hands more, passing a semitone, and can "hit" involuntarily a beam different than the one you want.
Or, as alternative, combining the beams with a dichro, that gives you more different possibilities:
Green and yellow, red and green, or red and yellow beams, depending how you decide to drive the beams for the 2 combinations tones/semitones ..... other than this, all the beams remain on the same plane.
There is also a possible "cheap" way for change volume (or intensity, or flanging, or modulation, or whatever function you want to give it), using 2 or 3 light sensors with a linear diaphragm for have an indication (not precise, but still enough) of the distance of the hand, using this distance as supplementar control parameter, if you want to be a "bad boy" (no offenses, just a common word joke here )
It's all matter of how much work and programming you want to put in it ..... but, for sure, you can end with a machine that none of the commercial builders sells, actually :beer: