VL53L1X detect wrong with black object

[HHo.4]

Hi,

I'm building a project that uses 20 VL53L1x sensors to detect any people or objects that go in the danger zone of a machine.

The sensor will detect any objects or people below 2 meters distance. We set up the sensor 30cm above the ground.

The measure configure of sensor :

 - Timing Budget MicroSeconds: 30ms.

 - Inter measurement period MilliSeconds: 70ms.

 - Do not use the glass cover.

I tested the reliability of the sensor and the result like below:

 - People with blue, white pants are reliably detected.

 - People with black khaki can not be detected by the sensor.

 - People with black jeans can not be detected by the sensor.

I tested indoor.​

I try​ to calibration. And I success to calibration RefSPAD, but I fails Offset and Crosstalk. It return error.

I called function in API:

1.VL53L1_WaitDeviceBooted

2.VL53L1_DataInit

3.VL53L1_StaticInit

4.VL53L1_PerformRefSpadManagement

5.VL53L1_SetMeasurementTimingBudgetMicroSeconds // I setting 30000

6.VL53L1_SetInterMeasurementPeriodMilliSeconds // I setting 40

7.VL53L1_PerformOffsetSimpleCalibration //I setting 140mm

8.VL53L1_PerformSingleTargetXTalkCalibration //I setting 140mm

9.VL53L1_GetCalibrationData

​

Please help me to explain this issue. Do you have any advice for me to detect reliability for all objects with all colors and materials?

​

[John E KVAM]

in order to get a measurement you need to get some photons back. The number of photons we get back does not depend on the color, but it does depend on size and reflectivity. I'm going to guess that you are not getting enough photons because cotton is not as reflective as other materials - (like wool, polyester, or nylon). What color your material is dyed does not matter.

So the things you can do are:

1) longer integration time - allows more time to accumulate more photons.

2) lower the signal threshold - this threshold warns you when you don't get enough photons .

But it's imperative that you get the calibration right.

The trick to crosstalk calibration is to find a place where you are under-ranging by 10 or 20%. Do this by simply running the sensor. Make sure your target diameter is 1/2 that of your distance. (I.e. if a 50 cm distance, you need a 25 cm diameter target.)

With this setup you can run your crosstalk.

• john