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IR Phototransistor Emitter and Detector Questions

  1. Oct 19, 2007 #1
    I recently bought a phototransistor emitter and detector from radio shack: http://www.radioshack.com/sm-matched-infrared-emitter-and-phototransistor-detector--pi-2049723.html [Broken]. It didn't come with much instruction but i thought i could simply put a voltage accross the emitter and the detector would simply detect it and induce a voltage accross its leads. However, when i actualy do this it doesn't seem to work. I made sure i put the proper polarity accross the anode and cathode of the emitter but nothing happens. .... Any ideas? Does anyone have information or recomendation on IR remote controlls? This is not for any specific project, but i just want to learn how to use IR. I have tryed looking this up online but suprisingly i have not found much good information. If someone could direct me to a good resource i would appreciate it.
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Oct 19, 2007 #2


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    You bought a phototransistor detector rather than a solar cell, so it won't generate a voltage on its own. Bias the phototransistor as you would a regular transistor (collector positive with respect to emitter, assuming it's NPN). There is no base lead. Photons falling on the base region generate charge carriers through the photoelectric effect, and the base is so thin that they diffuse into the collector region and are swept into your circuit. What you should see is no current flowing when dark, and current proportional to the brightness when exposed to light.

    Make sure you put a resistor or load in series with the collector to limit the current.

    Good luck!
    Last edited by a moderator: May 3, 2017
  4. Oct 19, 2007 #3


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    The RS link you gave says the detector is a phototransistor.
    You will need a resistor and power supply for the detector.
    A 1000 ohm resistor and 9v battery should work.
    You measure the voltage change across the transistor or resistor.
    Be careful to use the correct battery polarity.
  5. Oct 20, 2007 #4


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    "It didn't come with much instruction but i thought i could simply put a voltage accross the emitter..."
    The emitter is a LED. The spec. is 2volts at 40mA so you will need a current limiting resistor. If you can't get an output from your detector transistor, then you may have "blown" the LED.
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