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OPT3007: wrong lux measurements

marina cabezon
Prodigy 10 points
Part Number: OPT3007

I don't undestand OPT3007 lux measures. I am measuring in a daily indoor environment condition and the sensor measure very low lux values.

I configure the sensor with this value 0xC410 which means: automatic full-scale setting mode, 100ms conversion time, single shot.

For example: I measure with a digital light meter and the measure is around 400 lux but when I measure with OPT3007 I only measure 2.64 lux.

The value read from the result register (0x00h) is 0x108 and the conversion of the data is done as it is explained in datasheet:

//////////////////////////////////////////////////////////////////////////////////////////////////

rawData = 0x108  // Value read from RESULT REGISTER

mantisse= rawData & 0x0FFF;

exponent = (rawData & 0xF000) >> 12;
convertedLux = mantisse * (0.01 * exp2(exponent));
 
///////////////////////////////////////////////////////////////////////////////////////////////
The converted lux value is 2.64 lux which is very far from a valid result.
I don't know if the range of measurement is wrong but i'm configuring the sensor with the automatic scale mode.
  • 0
    TI__Expert 6800 points

    Hi Marina,

    According to your config register settings of 0xC410, bits 10:9 are 10, which will set the device to continuous mode. Have you made sure that the optical sensing area of the device is properly exposed to the ambient light? A picture of the device setup would help me understand the issue.

    Thank you,

    Brent Elliott

  • 0 in reply to Brent Elliott
    Prodigy 10 points

    Yes you are right. As you can see in the picture the sensor is bare so it is directly exposed to ambient light.

    .

    The OPT3007 (U430) is mounted on top layer where it is exposed to light as you can see in the picture above. There is neither hole nor clearance underneath the chip, so no light can enter from the bottom layer as youn can see in picture below.
  • 0 in reply to marina cabezon
    TI__Expert 6800 points

    Hi Marina,

    Since the optical sensing area of the OPT3007 is on the same side as the pins, you will need a PCB cutout in order to expose the sensing area. Since the cutout clearance for the sensor is limited due to the device pins being on the same side, it is recommended to mount this device on a flex-PCB since the board thickness will be smaller and more light will be able to be sensed.

    Thank you,

    Brent Elliott