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Wanted: Simple Light Detector Circuit

Discussion in 'Electronic Basics' started by Radio Man, Oct 8, 2004.

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  1. Radio Man

    Radio Man Guest

    I need a sensitive light detector that i can place in front of the eyepiece
    of
    a binocular. This detector should sound a "beep" whenever it detects light.
    I would also like it to be powered by 6 vdc or less.
     
  2. What amount of light? A star bright star in view? Headlights 50 feet
    away shining directly on the binoculars? Sunlight? That covers a
    range of millions to one, I think.
     
  3. Radio Man

    Radio Man Guest

    I should have been specific....."Starlight" is what i want to detect.
     
  4. The basic photo diode amplifier is shown on page 6 of this opamp
    reference:
    http://www.national.com/an/AN/AN-20.pdf

    If you connect a second opamp as a comparator you can drive a small
    piezo buzzer directly from the second opamp. Since opamps amplify the
    difference between their two inputs, you connect the output of the
    first amplifier to one of the second one's inputs and connect the
    other input to a trim pot connected as a supply voltage divider that
    can produce any voltage between the positive and negative supply
    rails. I think I would start with a pair of 9 volt batteries
    connected in series as the supply, (18 volts total) with the junction
    between them as the signal ground. An LM358 dual opamp might be good
    enough and is very common.

    Here are the data sheets for some photo diodes sold through Digikey.
    http://rocky.digikey.com/WebLib/Sharp/Web Data/bs520.pdf
    http://www.photonicdetectors.com/pdf/pdbc107.pdf
    http://www.photonicdetectors.com/pdf/pdbc113.pdf
    http://www.photonicdetectors.com/pdf/pdbc140.pdf
    http://rocky.digikey.com/WebLib/Photonic Detectors/Web Data/pdbc135.pdf

    Here is an example of a piezo buzzer that an opamp can drive:
    http://rocky.digikey.com/WebLib/CUI Inc/Web data/CEP-2260A.pdf

    You may need an additional lens to form an image of the star on the
    detector like your eye's lens does for your retina.
     
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