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OPT4060: Low light readings

Katy Stinton
Prodigy 10 points
Part Number: OPT4060

Tool/software:

Hello,

I am using the OTP4060 to measure the light in a display and I've noticed that when I set the display to the dimmest setting I can read very low counts (EXP = 0, MANTISSA ~28-48) when I set the conversion time to 200ms or faster.  Unfortunately the 400ms and 800ms conversion times are continuously reporting 0 (which surprises me, as these are supposed to be used in low light settings). 

This light source is PWMING at 0.19% (5/2667) duty cycle.  I have the range set to auto-range. I have noticed that although the interrupt signal is going low when expected (after 4 full conversion times), the counter for each color is not incrementing.

Can you please explain why the slowest conversion times are reporting all 0s?

  • 0
    TI__Expert 4300 points

    Hi Katy,

    Thank you for posting on the sensors forum!

    This behavior at these slower conversion times is strange - like you mentioned, slower conversion times are optimal for low light settings.

    I have a couple of questions based on your problem description:

    1. Could you please send me the configuration you are sending to the device through your processor to set the conversion time to 400ms and 800ms respectively? What are your writes to register 0xA and 0xB? Could you send whatever commands you are using and some scope shots of this transaction?

    2. You mentioned that the device is interrupting after 4 full conversions. What is the timing for each interrupt? Is it 1600ms for 400ms conversion time and 3200 for 800ms conversion time?

    3. Are registers 0x00 - 0x07 all reading 0? Is it just the Mantissa that is reading 0, or is all other bits (exponent, mantissa, CRC, counter) that are reading 0? Could you send an example of the register read? Could you send scope shots for this as well?

    4. Do you have a schematic you can share?

    Thanks,
    Daniel

  • 0 in reply to Daniel Balmaceda
    Prodigy 10 points

    Ah!  I was trying to gather more data for you and realized it was my fault!  I was timing out my state machine before the OPT4060 conversions could finish.  Thanks for your help and sorry for wasting time.