LSM6DSV16BX: use QVar to detect the presence of a human on a surfboard.

[NicolasGoualard]

Hello ST Forum,

I am currently working on a project that aims to help surfers analyse their surfing sessions. The goal is to use a LSM6DSV16BX attached to a surfboard, using the IMU to analyse the board's movement, and one of the QVar channel to detect whether the board is put in water.

I was wondering about how to use the second QVar channel. In particular I was wondering if it could be used to detect the presence of the surfer on the board without contact.

In the August 2022 revision of AN5755, the document states that using a single electrode is recommended for presence detection, especially in cases where powerline noise is weak, which seems to be my use case. However, the surfer and his/her surfboard will be immerged in seawater. Do you know if it is possible to detect human presence in these conditions ?
Additionnaly, since QVar channels seem designed to be used differentially, do you know if I can use one channel to detect if the device is in water, and the other channel to detect a human presence around ?

In order to detect if the device is put in water I used conductive 3d printable filament to make two electrodes, which seems to work fine in my small amount of testing. Do you have any tips on how to design the human presence electrode and/or the needed circuitry ?

Finally, the August 2022 revision of the 5755 application note described how to use the QVar channels for human detection, however in the August 2024 revision of the same AN the human detection part has been removed. Does that mean that it is not recommended anymore for this application ?

I am happy to provide more information if needed.

Thanks in advance for your help.

Best regards,
Nicolas Goualard

[Federica Bossi]

Hi @NicolasGoualard ,

The AN5575 was modified removing the presence detection since we no longer recommend the application. This feature depends on boundary conditions/variables, often not controllable, that affects the normal functioning.

 

Anyway, if you want to use it together with water leakage detection, you have to use the 2 inputs in single ended mode multiplexing in time: when you use the input dedicated to water detection, you have to disable the other input and vice versa.