Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Photodetector circuit set up

  1. Aug 30, 2006 #1
    How would one set up a circuit where a photodetector closes a switch in a circuit once it detects light?
     
  2. jcsd
  3. Aug 30, 2006 #2

    berkeman

    User Avatar

    Staff: Mentor

    Depending on the photodector, you would probably bias it up and do a current-to-voltage converter circuit. Then take that output voltage and amplify it a bit to get enough power to close your switch (like a relay?).
     
  4. Aug 30, 2006 #3
    Hey berkeman. How are you? I am only in my second week of my first circuits course, so could you explain what you just said in slightly more detail.
     
  5. Aug 30, 2006 #4
    I would probably want to use a PhotoConductor, huh?
     
  6. Aug 30, 2006 #5

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    A photodiode is what you want to use.

    Is this coursework?
     
  7. Aug 30, 2006 #6
    No, just curious.
     
  8. Aug 30, 2006 #7
    A photodiode you say? So let me know if I am correct. A photodiode detects when photons are entering it. When it detects enough photons it starts doing its job. Am I right so far?
    The job that it does is it allows current to flow in the circuit (but only in one direction).
    Is that right?
     
  9. Aug 31, 2006 #8
    If I am right then wouldn't the photodiode act just like a switch only it "opens/closes" by the detection of light?
     
  10. Aug 31, 2006 #9

    berkeman

    User Avatar

    Staff: Mentor

    Hi 000, I forget if I recommended this book to you already, but "The Art of Electronics" by Horowitz and Hill is a good book to get to augment your early studies. It explains all about photodiodes and current-to-voltage conversion using opamps. Here's wikipedia's entry on photodiodes:

    http://en.wikipedia.org/wiki/Photodiode
     
  11. Aug 31, 2006 #10
    Thanks berkeman. I will pick up that book. And I read wikipedia's entry on photodiodes. I have extracted from that article that a photodiode would act just like a switch. The switch is open when no light is detected, and it closes when it detects light. Am I right?
    Because that's what I want to do. I want to close a circuit when it detects light, and open it when it is dark.
     
  12. Aug 31, 2006 #11

    berkeman

    User Avatar

    Staff: Mentor

    No. When light hits a photodiode, a reverse photocurrent is generated. This photocurrent is small, so you need amplification to do anything with it.
     
  13. Aug 31, 2006 #12
    So would this apply to a photodiode as the photodetector?
     
  14. Aug 31, 2006 #13
    Nothing: Check into a phototransistor. It behaves more like what you originally assumed. If I remember correctly, the ones I have used are 2 leaded devices.
     
  15. Aug 31, 2006 #14

    dlgoff

    User Avatar
    Science Advisor
    Gold Member

    I don't want to get ahead of your learning curve but this photo detector link gives some circuits using various detectors as suggested by Beckeman and Averagesupernova.

    Regards
     
  16. Aug 31, 2006 #15
    Kick butt. Thanks dlgoff.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Photodetector circuit set up
Loading...