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ideas for detecting a laser spot

Discussion in 'Electronic Basics' started by Ahmed Samir, Feb 20, 2004.

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  1. Ahmed Samir

    Ahmed Samir Guest

    Hi everyone,
    i am looking for a way to detect a laser pointer spot on incident on an area
    of 0.25 square feet, the laser comes for ordinary laser pointers, from a
    disstance like 50 feet or something.
    any ideas??
    thanks
    ahmed samir
     
  2. Gary Lecomte

    Gary Lecomte Guest

    Go to my website at: http://www3.telus.net/chemelec/Projects/Projects.htm

    There is a Laser Alarm circuit there that has a detector.

    Take care.........Gary
     
  3. Detecting YOUR laser pointer? Or ANY laser pointer?

    Things become much easier if you chop the laser's power supply
    at a couple of kilohertz or so, so the light is modulated.
    Also, use very brief pulses with high power, maybe 50 uSec
    or so, so the average power remains low even though the pulses
    are very bright. These are well known tricks in the industrial
    photosensors industry.

    Second, if you know the laser wavelength, then you can put a
    narrow-band filter on your photosensor. This lets you reject
    all sorts of other light sources but without interfering
    with the desired laser signal. If the photosensor sees darkness
    with red laser spots, then you can crank the gain way up
    without it being overloaded by room light, etc.

    Of course if you're trying to detect laser pointers in general,
    then all of the above is useless, since normal laser pointers
    are DC, and normal laser pointers don't all have the same
    wavelength. (Perhaps a red bandpass filter on the sensor would
    help though. Just don't use an extremely narrow filter chosen
    to pass only a particular laser wavelength.)


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    Seattle, WA 206-789-0775 unusual phenomena, tesla coils, weird sci
     
  4. CFoley1064

    CFoley1064 Guest

    Subject: ideas for detecting a laser spot
    If it's a low power visible red laser like most pointers, you might want to try
    setting a photoresistor at the focal point of a fairly big lens, and measure
    the change in resistance. Photoresistors have a response curve similar to that
    of the eye, so if you can see it, you can probably get a response.

    Good luck
    Chris
     
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