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AShmy.1
AShmy.1
Visitor II
May 10, 2021
Solved

SPAD zones in VL53L1X sensor

  • May 10, 2021
  • 1 reply
  • 996 views

Hello, I have series of questions related to the data implementations using SPAD zone settings. After reading of manuals i made conclusions how to use this feature of the sensor, but i'm not sure if my conclusions are correct.

1. I'm interested in accuracy of data returned by sensor in different zones. I tested all center zones started from 16x16 and reducing it to 4x4 size array. And each redusing gave me differense almost in 1.5cm, so the difference between value that retured in 16x16 case and 4x4 case equals 7-8cm! I had clear conditions of the experiment: sensor was fixed vertically in front of plane wall. I just wondered why the zones with the same center have such differents in output value.

2. The second quastions is about if there any possobility to define geometric locations of the zones. User manuals said that 16x16 array has 27 FoV, 8x8 -20 FoV, 4x4-15 FoV. So i'm really wondered how those zones geometricly exists, because the reducing of the FoV is not uniform (if it was uniform 4x4 would have near 6.5 FoV ).

I'm trying to get picture of object in front of the sensor using data from all possible zones. It mean i'm trying to scan FoV using 4x4 array, starting from the upper left angle of the 16x16 array and finishing with bottom right one. And data that i got in some zones realy confuse me, because i'm providing all tests in front of the plane.

I will be really greatful if you will explain more proporetly how to use SPAD multiplay zones to recieve as much data as possible (and also as accurate as it possible).

Thank You!

This topic has been closed for replies.
Best answer by John E KVAM

The only way to get really accurate measurements is to do an offset calibration for each FOV.

There are 2 things fighting you.

1) the light is not uniform. We tried, but size limitations mean the light does not go out in a completely uniform manner. Generally it doesn't matter much, but you are seeing the difference.

2) Lens blur. An ideal lens would be much farther from the sensor for the best focus. But we were forced put the sensor in a thin cell-phone. So the focus was a compromise. And lens blur is another issue. Any light that hits the lens light up the entire lens a bit. That's why the 4x4 region is not a 5 degree square as one would have expected.

But treat each zone as a separate calibration, and you will be much closer to what you want.

Just change the calibration at the same time you change your FOV and you will be much happier.

  • john

1 reply

John E KVAM
John E KVAMBest answer
ST Employee
May 27, 2021

The only way to get really accurate measurements is to do an offset calibration for each FOV.

There are 2 things fighting you.

1) the light is not uniform. We tried, but size limitations mean the light does not go out in a completely uniform manner. Generally it doesn't matter much, but you are seeing the difference.

2) Lens blur. An ideal lens would be much farther from the sensor for the best focus. But we were forced put the sensor in a thin cell-phone. So the focus was a compromise. And lens blur is another issue. Any light that hits the lens light up the entire lens a bit. That's why the 4x4 region is not a 5 degree square as one would have expected.

But treat each zone as a separate calibration, and you will be much closer to what you want.

Just change the calibration at the same time you change your FOV and you will be much happier.

  • john
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