You might be able to just use one laser module- with the lens that creates a line (available for as little as $8 USD) . Then an array of phototransistors st when any one is shaded an object is detected. But if this is safety-related, I suggest an tested and approved commercial solution.
Best regards, Spehro Pefhany
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I've got a bit of a crazy idea to try and build one of those 'invisible' MIDI harps (I think Jean Michel Jarre once used them). Essentially there would be a bunch of light beam sensors of some sort (I'd probably only do an octave), in the ceiling, shining *directly* onto light sensors in the floor. As soon as the light is broken, the sensor triggers and results in a MIDI signal being sent.
OK, so from that description, I've clearly little idea what I'm doing and what the best way to go about this would be. I'm not adverse to actually buying a little MIDI keyboard and pulling it apart to provide me with some sort of latch-MIDI implementation. The trickiest bit, I'd imagine, would be to get a system where the sensors aren't affected by light from the adjacent bulbs - the lights would have to shine
*directly* down into the sensors and not spread at all. Or is visible light not the way to go - should I use infra-red of some sort?Given all that, is there any advise anyone can give me please?! Anyone seen this project done anywhere?
Thanks
andyt
I read in sci.electronics.design that Andy Turner wrote (in ) about 'Ideas for light sensor trigger/switch?', on Mon, 14 Feb 2005:
Visible red laser pointers will do quite well. Low-power ones.
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You can place the fototransistor at the bottom of a tube, giving it a bit of 'tunnel' vision. For the emitters you can use leds with a narrow angle. If you use visible light, it is easier to align them. Blue leds are nice, or perhaps a rainbow of color. This give a nice effect when blowing smoke through the curtain, preferrably from smoking some good marihuana. I don't think it is neccesairy, but you could use modulated light, at 10Khz or so, and only amplify/rectify the AC signal from the fototransistors, using a simple high pass filter. That would certainly make it insensitive to other ambient lights.
Nice project BTW.
-- Thanks, Frank. (remove 'q' and 'invalid' when replying by email)
Multiplex LED emitters and synchronously detect with the receivers.
That eliminates crosstalk between the 'strings' and the synchronous detection can be arranged to more or less ignore ambient light.
You can afford to drive the emitters much harder with the low duty cycle which helps your signal to noise ratio on the receivers.
It will just work better all round unless you want to use lasers so the strings are 'visible'.
That would prevent two or more "strings" from triggering the MIDI synth simultaneously.
Well if you are going to be pedantic about it, midi is a serial data stream which can't 'trigger' two notes simultaneously anyway.
stream
I'm thinking more like N-key roll over on serial keyboards...
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