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Rotating Laser Lever Receiver / Detector

Discussion in 'LEDs and Optoelectronics' started by Dug, Feb 9, 2012.

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  1. Dug

    Dug

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    Feb 9, 2012
    Hi.
    I'm chasing a circuit to make a laser level receiver please.
    It'll be about a foot high, with maybe 50 vertical LEDs. I'd like ONE of those LEDs to light up when the photo-diode(?) beside it detects the laser beam, thus showing me where on the detector the laser is striking. The laser rotates at about 500rpm, I assume the detector circuit will have to detect this faint laser pulsing differentiating it form ambient light readings? I'm not too bright, but keen for some help please?
    Thanks.
     
  2. BobK

    BobK

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    Jan 5, 2010
    I presume you cannot see the laser on a white target in this environment, or else you would not need the detectors / LEDs.

    If that is the case, it is pretty challenging, because the ambient light is going to overwhelm the detectors.

    The first thing I would try is putting the detectors at the end of black tubes that are pointed towared the laser source to eliminate as much ambient light as possible. Also a filter the color of the laser would help.

    You probably also need to get an AC signal from the detectors, which would be at 8.33 Hz based on 500 RPM / 60. You could then make a highly selective amplifier for this frequency. This is how IR remotes work, but at 40000Hz.

    I don't think you want to build 50 of this circuit, so you would also want to multiplex all of the 50 photodiodes to the amp / detector. But that brings up another problem. At 8.33 Hz, the response time of the detector is going to be long, at least 1/8 of a second since it needs to see at least one cycle, and if multiplext 50 times, then you are talking about at least 6 seconds for a fulll scan.

    Bob
     
    Last edited: Feb 9, 2012
  3. davenn

    davenn Moderator

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    I work with laser levels for surveying, generally they are quite bright, even in daytime.
    At 500 rpm or even much much slower than that, they are going to paint a continuous line that will easily be picked up by diode detectors.
    The diode detector strips I see are generally ~ 20 to 30 diodes high. Good diodes, spect'ed and filtered for red light should NOT pose too much of a problem


    Dave

    Thanks Steve will learn to type one day ;)
     
    Last edited: Feb 11, 2012
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Should NOT pose too much of a problem, I presume.
     
  5. Dug

    Dug

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    Feb 9, 2012
    Thanks for the help so far.
    My laser level, and 4 others I have used in the last 10 years, do not show a visible beam.
    I do believe you can now buy ones you can slow to see the beam, if I have to buy one of them to help solve my problem, I will, but the thing that interests me is that, my idea is not new science. There have been detectors for this type of rotating laser for 15 years and more. They detect the beam, but then only offer 3 lights to represent where the beam as struck. High, Level, Low. I was just hoping I could find somewhere that would know how this detection was done, (no shadow tubes), but I'm not having much luck sorry.
    Again, thanks for the assistance, I welcome more, but it seems I was naïve in thinking there was a solution simple to the electronics community.
     
  6. BobK

    BobK

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    Jan 5, 2010
    Wow, I guess I was way off on this one :eek:

    I guess it makes sense that you could not see the line when it is going by that fast, but the pulse would be plenty strong to be picked up by a photo-diode which would respond much faster than they eye. Always good to learn something new.

    Bob
     
  7. Dug

    Dug

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    Feb 9, 2012
    Thanks everyone. Any circuit diagrams please?
     
  8. davenn

    davenn Moderator

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    Sep 5, 2009
    sorry Dug

    cant help you on a multi diode detector system

    D
     
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