How to calibrate VL53L0x

[zhy]

Hi，

     1》In the dark，Place the white target 140mm from the sensor

          call function

         Status = VL53L0X_perform_offset_calibration(&vl53l0x_dev,0x8c0000,&pOffsetMicroMeter);

     2》In indoor environments ，Place the black target  600mm from sensor

         call function

         Status = VL53L0X_perform_xtalk_calibration(&vl53l0x_dev, 0x2580000, &pXTalkCompensationRateMegaCps);

    3》in main function       

        Status = VL53L0X_set_offset_calibration_data_micro_meter(&vl53l0x_dev,&pOffsetMicroMeter);  

        Status = VL53L0X_SetXTalkCompensationRateMegaCps(&vl53l0x_dev,pXTalkCompensationRateMegaCps); 

    Is the above process correct?  

       But

       

     Status = VL53L0X_set_offset_calibration_data_micro_meter(&vl53l0x_dev,11300);              //设置offset

     Status = VL53L0X_get_offset_calibration_data_micro_meter(&vl53l0x_dev,&pOffsetMicroMeter);   //读取offset

         pOffsetMicroMeter = 11250   

    if ony call 

          Status = VL53L0X_get_offset_calibration_data_micro_meter(&vl53l0x_dev,&pOffsetMicroMeter);   //读取offset

          pOffsetMicroMeter = 32150        

   it seem :

           dtat not be write NVM

                                                      best wish

                                                                      thank you

[zhy]

   Hi, 

   

    PALDevDataSet(Dev, LinearityCorrectiveGain, 1000);        //How to adjust it if I have a cover plate?

    PALDevDataSet(Dev, DmaxCalRangeMilliMeter, 400);        //  Only 400mm can be measured  ？

    PALDevDataSet(Dev, DmaxCalSignalRateRtnMegaCps,

        (FixPoint1616_t)((0x00016B85))); /* 1.42 No Cover Glass*/   //Do I need to adjust it if I have a cover plate?

[John_Kvam]

With no coverglass, there should be no crosstalk. (There can be some if you have part of your structure near the sensor, but that's a mechanical issue to be avoided.)

But when you put on the coverglass you get the photons bouncing back from this glass and that's crosstalk.

The algo is trying to figure out how many photons are from the target and how many are from the glass. 

So with a target at some distance - that you supply - the algo has Number of photons, the correct distance and the measured distance. With those 3, it works out what percentage of photons come from the coverglass. 

But to do this it needs help. 

YOU have to experiment and find a target reflectivity and a distance where you are under-ranging by 10 or 20 percent. Just picking 600mm isn't going to do it. 

So find a dark target (I use matte finish black spray paint). And start ranging. If you've done the offset cal, you should be reasonably spot on  if the target is near, and it should get worse as you increase the distance. 

Once you find a spot where you under-range by 10 to 20%, use that target and location in your production. 

The correct distance depends on the quality of your glass. Very thin, clear, closely mounted and clean glasses will need a longer distance than thick, hazy, dirty ones with a large air gap between the sensor and the glass. 

In production I suggest making a range set up where the sensor is pointed at the crosstalk target, a white flap can be installed that when folded down, you can do the offset, fold away the offset target and do the crosstalk. 

- john 

[Zhiyuan.Han · Accepted solution]

Hi     

About your concern, it is reasonable. 

     Status = VL53L0X_set_offset_calibration_data_micro_meter(&vl53l0x_dev,11300);              //设置offset

     Status = VL53L0X_get_offset_calibration_data_micro_meter(&vl53l0x_dev,&pOffsetMicroMeter);   //读取offset

         pOffsetMicroMeter = 11250   

The register format is 10.2 fixed-point with units in mm:

• 10 bits for the integer part
• 2 bits for the fractional part
  The fractional bits represent $1/4$ mm = 250 µm.

OffsetCalibrationDataMicroMeter = 11300; // µm

encodedOffsetVal = 11300 / 250 = 45 // exact division, remainder 50 is discarded, This is integer division, so it truncates toward zero (it is not rounding):

What actually gets written into the register is “45 steps of 250 µm.”, that's why you read out value is 11250.

And if you don't set the offset value, or you rebooted the device after you setting the offset value, the read value will be the NVM offset value. 

Br

Zhiyuan.Han

[zhy]

I want to reduce power consumption, but there's an error. Could you advise how to configure XSHUNT for the next measurement after lowering it?

[zhy]

Hi,Han

Does lowering the XSHUT really save power? I'm using a battery!

                                         thank you

[Zhiyuan.Han]

Hi 

Pulling down XSHUT will help to set the sensor to HW standby status, and it helps to save 1uA standby current from 6uA to 5uA.

to save battery power, I suggest you disabling the power supply directly, this will be the best case. 

Br

Zhiyuan.Han 

[Zhiyuan.Han]

Hi 

You need to pull-high the XSHUT again, and re-initialize the sensor, then perform the ranging test.

Br

Zhiyuan.Han