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Interfacing OPT101 with ADC

Adi Ghosh
Prodigy 30 points
Other Parts Discussed in Thread: OPT101, TL082, OPT3001

Hi all, I am trying to interface OPT101 for measuring ambient light in terms of lux.....Now what Vcc shall I put? I am interfacing it to an ADC of MCU. Can I go upto 30 volts and use an extra opamp to get OPT101 output down within 0 to 5 volts?

  • 0
    TI__Genius 14825 points

    Adi,

    The OPT101 data sheet specs the device from Vs = 2.7V to 36V.  On page 3 in the spec table, the output is driven typically up to (Vs)-1.15, so for your design, you could power the OPT101 with a 5V supply and get up to 3.85V output.  This would be within your 5V ADC input limit, though it may not afford you the range of lights you need to measure.

    Without knowing more about your circuit design, I would say that you can likely use an extra op amp to scale down the output of the OPT101 to match the limited range of the ADC on your MCU.  You may wish to add some clamping diodes or zeners on the ADC inputs to prevent accidental overvoltage damage on the inputs from the Op Amp.

    Please feel free to provide additional information about your application and we'll be able to investigate further.  In the mean time, I hope this helps.

    -Jason Bridgmon

  • 0 in reply to Jason Bridgmon
    Prodigy 30 points

    I am trying to develop a precise ambient light intensity controller by driving LEDs by PWM. I want to sense light by OPT101. But since light within the intensity will give high output thus I have to give voltage up to 30 volts or more for opt101. But I need to scale down it to 0 to 5 volts as you have stated too. Do I need series resistance with the zener for zener protection? Which opamp shall I use for scaling down voltage? I have TL082 and LM356 with me.

  • 0 in reply to Adi Ghosh
    TI__Expert 6930 points

    Hi,

    Are you using the internal 1M Ohm resistor?  If so then to get 30V output you are anticipating 30uA of photocurrent...Figure 4 in the data sheet has information regarding changing the transimpedance with an external resistor...in your case you will want to reduce the transimpedance...the table in Figure 4 should help you to determine the correct configuration.  Have you already connected the OPT101 and see that you are getting 30V output from your light source?  May I ask what end equipment is this light intensity controller going into?

  • 0 in reply to Edward Mullins
    Prodigy 30 points

    my plan is...OPT101 to Scale down Opamp then to ADC with 5v ref then to MCU for PWM control then to LED driver and to LEDs. I am using internal 1M resistance which is closest...I may use external less resistance for response with less slope....

  • 0 in reply to Adi Ghosh
    Prodigy 20 points

    i am using opt101 to measure lux. i am using 5V supply voltage and i am getting output voltage in the range of 2.5 to 3.5 volt in normal room condition. how could i convert voltage to lux.

  • 0 in reply to vairamani
    TI__Expert 6930 points

    Hi, please visit www.ti.com and search for a new product, OPT3001.  The output of OPT3001 is measured directly in lux.