Light Meter. How to Make an Proper Readout?

Discussion in 'The Projects Forum' started by MCU88, Mar 15, 2015.

  1. MCU88

    Thread Starter Member

    Mar 12, 2015
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    Hello...

    I have made an project that has an LDR and ten LEDs that respond accordingly to the level of light that the LDR sees. Q: How do I add some numbers, a scale to the LEDs so that they have an meaningful readout?


    [​IMG]

    [​IMG]
     
  2. DickCappels

    Moderator

    Aug 21, 2008
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    If you want to make something calibrated and that works with different light sources you would need a filter or set of filters to correct the response of the LDR to have a photopic response. This is approximately the same response as the "green" receptors in our eyes. An expensive solution.

    [​IMG]
    https://en.wikipedia.org/wiki/Photopic_vision

    If you consistently use it with the same kind or light (for example, same color temperature florescent or incandescent) then you can simply place a diffuser over the LDR (a ping pong ball cut in half works nicely) and then put it on the desk side-by-side with a borrowed illuminance meter (sometimes called a "Lux meter"), which is calibrated in Lux (for the originator of the until, Harrold Luxemberg) and calibrate your instrument for different amounts of incident light.
     
  3. bertus

    Administrator

    Apr 5, 2008
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  4. MCU88

    Thread Starter Member

    Mar 12, 2015
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    Sweet. So ...

    a. Ping pong ball cut in half
    b. Readout in Lux
    c. Calibrate to meter

    Cheers!
     
  5. MCU88

    Thread Starter Member

    Mar 12, 2015
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    How badly not linear? I mean like the rest of them it is an 'toy' worth 5-dollars.

    Other options for sensors instead of the LDR?
     
  6. bertus

    Administrator

    Apr 5, 2008
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  7. MCU88

    Thread Starter Member

    Mar 12, 2015
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    That's not too bad. A 45 degree line would denote 100% linear.

    I'll buy an lux meter and see if I can get away with it.
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have added some alternative sensors to mo other post.

    Bertus
     
  9. MCU88

    Thread Starter Member

    Mar 12, 2015
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    35
    Thanx Bertus. That's perfect ;)
     
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