How to use a photodiode or photoresistor? Can I still use fibre optics from lamp?

Discussion in 'The Projects Forum' started by kulazt, Jan 31, 2009.

  1. kulazt

    Thread Starter New Member

    Jan 31, 2009
    I am currently in university and have been assigned a project where i have to build a sensor. To narrow and simplify the question down, i basically have to measure the light emitted from an optical fibre using a photo diode or a photo transistor. As i don't have a very good basic knowledge in electric circuits can anyone tell me how i would connect a voltmeter or something to measure the change in light intensity received by the photo diode or phototransistor? Is all i need just the actual photodiode or photo transistor and the voltmeter or do i need any other extra components?

    Also, if i cut off the fibre optics from a fibre optic lamp, will they still be able to work, i.e. i will still be able to use them to transmit light and receive light?
  2. mik3

    Senior Member

    Feb 4, 2008
    Is the light intensity out of the fibre constant or does it vary?
  3. kulazt

    Thread Starter New Member

    Jan 31, 2009
    yep the light intensity varies. A transmitting fibre carries light from a light source such as a LED, it then reflects off a mirror. The mirror is able to bend which means different amount of light will be reflected off each time. The reflected light is then picked up by the receiving fibre (optical fibre) and it is the light from this fibre which i want to measure the change in intensity.
  4. bertus


    Apr 5, 2008
  5. beenthere

    Retired Moderator

    Apr 20, 2004
  6. AdamM

    Active Member

    Mar 7, 2009
    I'm not an electronics expert by any means, but I have done some projects recently using photo diodes. Depending on the input light intensity I think you should be able to use just the photo diode and an ohmmeter (or impedance setting on a multi meter) to detect changes in light intensity.

    I would suggest hooking it up so the ohmmeter applies forward bias to the photo diode (in other words, the positive lead on the meter to the positive lead on the diode). You should get a measurable change in resistance through the diode as light levels change. Will this fit the criteria for your assignment?

    Perhaps the more experienced folks on the forum could correct any mistakes in my suggestion :)