STM32 Smart Presence Detection VL53L8X

MikeReg · ‎2025-06-12

Hi,

Im currently testing the Smart Presence Detection Firmware for the VL53L8X and have some questions:
- When I start the ranging, the firmware triggers false positives (detecting someone when there isn't anyone) and after some seconds it stabilizes thus not detecting anyone unless a person approaches the sensor. Is this the normal behavior ?
- I would also like to know how direct sunlight affects the sensor. It makes more difficult to detect someone ? Trigger more false positive, however I believe it is only during few times along the day that we can "observe" 940 nm.

Thank you!

labussiy · ‎2025-06-16

Hello @MikeReg ,

The state machine of the solution is starting in "Presence Monitoring" state. We assume when we start the algo that a user is in front of the sensor, so we need few frames to analyze the scene and go to "Autonomous" in case there is no user.

Regarding the direct sunlight, the ToF technology is sensitive to the ambient light and it's impacting the max detection distance. You can compensate by increasing the integration time of the sensor, but it means you will increase the power consumption.

Thanks,

Yann

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MikeReg · ‎2025-06-17

Hi @labussiy ,

Thanks for clarifying some of the doubts!

In the SPD code Im seeing that the default integration time is SPD_AUTONOMOUS_INTEGRATION_TIME_L8 which is eqaul to 2 (I guess its ms). In the datasheet, I see a lot of reference to 5ms instead. Should I change to this value ? Also for the ranging period I have the spdAutonomousRangingPeriod which is 250, once again ms I guess. The

spdAutonomousRangingPeriod should be larger then the spdAutonomousIntegrationTime correct ?
And one last question, what for you would be a good integration time for a direct sunlight ? I think I will use a sensor to control bright level and change the integration time accordingly with that.

Thanks again!

labussiy · ‎2025-06-18

Hi @MikeReg ,

Before answering to your question, I advise you to use the page 37 of the User Guide. It's a summary of the default settings.

There are 2 sets of settings, for the "Autonomous mode" and for the "Tracking mode".

In Autonomous mode, we just want to detect small motions to wakeup the system and the algo, the power consumption is very low. The Integration time is 2 ms.

During the tracking, we need more accuracy so the integration time is increased to 10ms.

If the issue is the system stays in "Sleep" when a user in entering the scene, you can increase from 2ms to 5ms for example.

I hope it's clear enough.

Yann

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MikeReg · ‎2025-06-18

Hi @labussiy ,

Thanks again! So the tracking mode is after the Autonomous mode, where the algo detected something but is basically gathering more information to decide if its a user that pretends to use the device correct ?

I think that the issue I have seen, when in Autonomous mode and the sunlight is hitting the sensor it doesn't seem to wake. I will try to increase the integration time to check if i can have better results.

thank you!