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Break Beam Sensor

  1. Aug 4, 2007 #1
    Optics and bio research

    hi yall!

    im doing a neuroscience research on the circadian behavior of different species of fishes, and i need a device to measure activity levels of fish under different light conditions. one of the mostly used method is to have a light source (IR or something else) and a receiver and measure when the light beam breaks due to fish's movement. I have a couple questions as to the setup, and I need yall's help! the questions are:

    1. how should the setup be? any recommendations for type/brand of detector, etc?
    2. which is better, IR beam or any laser beam?
    3. is there a better way to detect the movement of fish?
    4. are there any computer programs available to take the data?

    i will really really appreciate your comments! thank you!!!
  2. jcsd
  3. Aug 5, 2007 #2


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    For circadian research, an IR beam would be preferable over a laser beam (I only know of equipment using IR beams though), I think (unless fish detect a very different light spectrum than mammals...you might want to check into this before making a final decision).

    One thing that comes to my mind as a potential problem is whether the equipment will work properly when the beam has to pass through water, or if you'll get artifacts from diffraction/motion of the water. You would want to contact the manufacturers about that. The other option would be something to tag the fish with that would measure their activity (do you need to know where they are traveling, or just how much/fast?)

    All of the equipment I've seen sold to monitor activity comes with the data analysis software. It's the software that's expensive, so think carefully about what analysis you intend to do and whose software best does it, and then compare the prices based on those criteria before buying.

    To use IR beam breaks, you'd have to set up a 3-D grid in an aquarium. With mammals, you just need to create a 2-D grid to monitor beam breaks because rats/mice/hamsters are staying on the ground in those cages. This sounds like it would be a very expensive set-up for anything but a very small aquarium.
  4. Aug 5, 2007 #3


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    Low light or IR video cameras might work and be simpler than seting up a 3D beam break grid.
    I don't have any details on analysis software or implementation.
  5. Oct 25, 2007 #4
    Basically I am going to install infrared emitter and receiver pairs across an aquarium so that everytime fish moves, the beam breaks and is recorded. The problem is that I have never made this before and I need some major help.

    I am going to need at least 5 sensors. The question is: do I mount all five sensons on one circuit board or do they have to be separate? If anyone can draw a circuit for me, I will worship you for my life.

    Also, I am going to somehow connect the signals to a computer/data logger. Does anybody know how that works?

    Thank you,


    << berkeman merged two threads >>
    Last edited by a moderator: Oct 25, 2007
  6. Oct 25, 2007 #5


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    There are several issues that you need to consider when doing a beam interruption across a distance like this. First, you will want to focus the emitted beam so that much of the energy lands on the sensor. You can use an LED emitter with a concave lens, for example. Second, you will need some noise rejection mechanism, to help you distinguish the light from your emitter versus all the other ambient light (especially the aquarium light with its 120Hz flicker, or worse if it's a flourescent light). The two most common ways to do this noise rejection are to use an IR source with an IR filter window at the receiver, and to modulate the source with some pattern that is demodulated/decoded at the receiver.
    Last edited: Oct 25, 2007
  7. Oct 25, 2007 #6


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    I think the bigest problem would be not being able to capture the activity from much of the volume of your tank with only 5 IR transmitter/sensors. And they are fairly directional giving you even smaller "eye balls".

    Would it be possible to put one large IR source on one side of the tank and a larger array of detectors (say a 5 X 5 or larger) on the other side?
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