Photodiode Signal Conditioning

Discussion in 'The Projects Forum' started by electronicsguy7810, Jan 7, 2016.

  1. electronicsguy7810

    Thread Starter New Member

    Jan 7, 2016
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    Hi,
    For a project, i'm wanting to use a photodiode and a microcontroller to log ambient light levels in my garden.
    I need an op-amp circuit that will output 5v to the microcontroller when ambient light is equivalent to 5mW/cm^2.
    The photodiode I have is TEMD6010FX01
    Below is what I have for a start
    photodiode.png
    Can anyone advise me on weather this is right, and if so how can I work out what C1 and R1 need to be

    Tim
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Need to know the output current of the photodiode at 5mW/cm^2 illumination.
    Do you have a data sheet for it?
     
  3. electronicsguy7810

    Thread Starter New Member

    Jan 7, 2016
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  4. crutschow

    Expert

    Mar 14, 2008
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    According to the data sheet the diode has a nominal sensitivity of 1μA per 1mW/cm^2 with a 5V reverse bias.
    It does not give the current with zero bias as your circuit shows.
    So if you apply a 5V reverse bias to the diode anode than a value of 1megΩ for R1 will give a nominal output of 5V for an illumination of 5 mW/cm^2.

    But note that the diode sensitivity tolerance is -25% to +225% so, if you need better accuracy then that, you will need to calibrate the circuit or get a diode with a better sensitivity tolerance.
     
    electronicsguy7810 and sailorjoe like this.
  5. electronicsguy7810

    Thread Starter New Member

    Jan 7, 2016
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    Thanks for the response!
    Is this what you mean?
    schemeit-project (1).png
     
  6. crutschow

    Expert

    Mar 14, 2008
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    That's forward biasing the diode.
    It needs to be -5V.
     
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