SparkFun Forums

[alberto2000]

I am thinking of an art project where I want to have a laser beam going from the floor straight up to the ceiling, where a photoresistor/transistor catches the beam. I am aware that the alignment will be difficult to make as it has to be very exact. The idea is simple: when the beam is interrupted, I want to make a noise. I want to use Arduino for controlling and give out midi signals into an analog synthesizer. The best would be, if the sensor could read also if the beam is only interrupted a little, so that i can get an analog value of beam interruption and generate noise based on "how much" the beam is interrupted. The project will be exhibited in a dark room with fog, so the beam can be seen by eye. Can anyone help me out with suggestions or ideas how to approach this project? Is it the right thing to use a photoresistor/transistor for that? Any help is greatly appreciated!

[jremington]

I googled "arduino laser photoresistor" and got 85,000 results.

[alberto2000]

Nice! I googled "happy cat" and got about 206,000,000 results!

[coderxtreme]

Hi, I recently did such a project.

Laser: http://www.ebay.com/itm/1PC-Laser-Trans ... 5d4d61d7c1

Receiver: http://www.ebay.com/itm/Hot-Products-La ... 417e4b810d

Demo: https://www.youtube.com/watch?v=-E-KkOK ... e=youtu.be
Processing Source Code: http://pastebin.com/uMMA5yES

The microcontroller is arduino running firmata. A PC is being used running Processing.org and connecting to the arduino to through serial.

[Mee_n_Mac]

IIRC one of the SF guys did a similar broken IR beam music project for a museum and documented it in a tutorial. Perhaps a search of the tutorials or projects would find it. I think an important lesson learned was to use modulated IR, like your TV remotes do, to avoid interference from ambient light. Whatever you use for a light source, the receiver should be sensitive to that wavelength and have a response time quick enough for your usage.

EDIT : FWIW here's a link to the project I mentioned above.
https://www.sparkfun.com/tutorials/282

[alberto2000]

Thanks a lot, this is a very nice tutorial and has some good tips on basic project approaching too.

My scenario differs in that I need the beam (only one beam, so its kind of a one-string-laser-harp) to be visible, so I will exhibit it in a dark room filled with artificial haze/fog. The biggest problem as far as I see is the alignment of the laser to precisely hit the photoresistor on the ceiling - I am wondering how to simplify that, like, maybe diffusing/defocussing the beam into a blob of light and measuring that instead of the direct beam...

[lyndon]

I would not recommend a photocell. Not that it won't work, but photocells have decreased sensitivity after you hit them with very bright light. They take a while to recover from that, sometimes hours. So I'd test it out, but be prepared to use something else if it stops working properly after a while. Then again, a filter in front of the photocell might take care of that.

If it doesn't, well, some time ago I designed a laser target with about 1" area. I used a handful of 10mm square photodiodes and the guy I did it for didn't care about the small dead area between the diodes. Digikey has this which is a photodiode with a 15mm sq. area that should be fairly easy to hit with a laser. If it's too expensive ($14) then perhaps an inexpensive photodiode with a large lens in front of it would work for you.

[Mee_n_Mac]

FYI ... saw over @ HaD.
http://www.elecfreaks.com/7079.html

[russp]

Use a dollar store magnifying glass as a light collector for your photodetector. Putting the detector at the focal length distance (a few inches) behind the glass will give you a target width equal to the diameter of the magnifier.