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VL6180X Detecting Glass and Low Light Range Difference

Question asked by Steege.Michael on Apr 6, 2017
Latest reply on Apr 26, 2017 by Steege.Michael

Two questions.  I'm implementing the VL6180X sensor in a system that needs to detect presence of objects placed in a tray.   The objects are generally small glass vials with different colored caps.  


Question 1:  In ambient office lighting, the objects are detected at expected distances if the colored caps face the detector.  If the glass bottom of the vial faces the detector, it appears as if the detected distance is the cap on the other side of the vial.  It does not seem to detect the glass bottom of the vial.   What would cause that and what is the solution to detect the glass bottom (note: the vial may be as close as 15mm and as much as 70mm from the sensor- there is no cover glass on the sensor).


Question 2: After the object is placed and the distance detected, a cover door is closed which puts the object in the dark.   But in this low light condition, the detected range increases by as much as 30%.   (i.e. in low light at a distance of 45mm, the sensor returns a distance of about 60mm)  What causes the difference in range?   It seems that it would be highly accurate in low light conditions.  (note:  difference in ambient light vs low light was tested with a solid white object placed at a precise distance from the sensor - but it does the same with the glass vials).   (also note: I can detect the light levels and apply different range compensations if necessary)


The application needs to detect the object in both ambient and in low light conditions at a distance between 10mm and 90mm.


Any help, advice, or direction to application notes explaining this phenomenon is appreciated.   Also, it appears I cannot use the VL6180X SW API as I am am using a soc with limited ROM and including the api as is exceeds my ROM space when built. 


Thanks in advance,