detecting specific color of light

Discussion in 'General Electronics Chat' started by Tobias, Jan 27, 2009.

  1. Tobias

    Thread Starter Active Member

    May 19, 2008
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    Thanks for the help with the op-amp question earlier. My dad wants me to make an application for him to detect a yellow warning light turning on. The light might be around 30-40ft away. Can anyone recommend a place to start to find a device that will detect the light?
    Thanks
    Toby
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    A photodiode or a phototransistor with the proper wavelength of maximum sensitivity can do the work.
     
  3. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    These sensitivity ranges are quite broad, however. For a specific color, the best way is to use a color filter or gel. (Of course this should fall inside the sensitivity bandwidth of the diode in use!)

    eric
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    As ambient light could cause false detections, I would recommend adding some sort of reference signal. It can be from an unfiltered signal or signal from a different filter. Basically, you would look for a change in the ratio of your yellow light detector to the reference signal.

    John
     
  5. thingmaker3

    Retired Moderator

    May 16, 2005
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    I may be out in left field here, but could one use a 30 - 40 ft cable & use the light's voltage to trigger a second indicator?
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    And for a really weird idea, a photo detector in a black tube (think telescope), with a prism in front. The prism will bend light according to color, the black tube will filter ambient out. A mechanical approach.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    If the light is in a static situation - not a traffic light, for instance, then any detector close to the lamp will work just fine. Shield it from ambient, and the only light it can respond to is that warning lamp.
     
  8. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I assumed it must work day or night. The yellow part of the spectrum is pretty prevalent in daylight. Any sort of single-beam detector, whether it uses a gel filter, prism, or grating, will be affected by that. John

    Edit: The reference beam also is a type of failsafe, should something obstruct the shielding tube, such as a bee or wasp hive, large truck, etc .
     
    Last edited: Jan 27, 2009
  9. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Does this imply that you have control of the warning light?

    If so can you mount a small detector immediately in front of it, shielded so that it only sees the light (or abscence of it) from the lamp?

    Upon activation the detector could then transmit a signal by various means.
     
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