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Need help with visible light photo detector circuit

Discussion in 'LEDs and Optoelectronics' started by Buzzed, Jan 13, 2012.

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  1. Buzzed

    Buzzed

    4
    0
    Jan 13, 2012
    Hi guys I’m a newbie residing in Ohio. I fly MikroKopters which is what brings up my question. Onboard my Hexa is a small GPS. The GPS uses a green LED that is normally on when powered up and starts to flash when 3D lock is achieved. Herein lies the problem, the LED is almost impossible to see in bright sunlight under the smoked dome of the MikroKopter and impossible to see when flying.

    What I would like to do is build a simple, lightweight, compact photo-detector that can see the LED and mimic the flash pattern. Then it can be used as a switch to power up a strip of flexible LEDs that will be mounted on one of the motor support arms that can easily be seen when flying.

    The target voltage is 12 – 14.8 volts dc which is the voltage of the flight pack and also the voltage for the flexible LED light strip.

    Any help you guys can afford would be greatly appreciated by me and the MikroKopter community.
     
  2. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    If you can get at the supply to the LED, then a single transistor could probably be used.
    If you go for a photo detector, you will have problems with ambient light. Photo transistors are small and light, you would want one with maximum sensitivty to the wavelengh of the LED.
     
  3. Buzzed

    Buzzed

    4
    0
    Jan 13, 2012
    I have a short length of the black tube sponge insulation that I am going to put the LED or CDS in to protect it from ambient light. It will be bonded over the existing green GPS LED and the top of the tube will be sealed with black silicone. Thoughts?
     
  4. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    A green LED gives an output at 565um, you will need a receiver sensitive around this wavelength. Either a transistor (not infra-red) or LDR (liight dependant resistor) should be suitable. Experiment with the chosen device will be necessary to get a matching circuit.
     
  5. Buzzed

    Buzzed

    4
    0
    Jan 13, 2012
    I wound up finding a nice assortment of CDS cells at Electronic Goldmine.
     
  6. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    OK. Measure the resistance of the cell with and without the led lit. It should then be possible to devise a circuit to switch your load.
     
  7. Buzzed

    Buzzed

    4
    0
    Jan 13, 2012
    Once the cells arrive I'll get back to you.
     
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