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AJura.1
Visitor II
March 22, 2021
Solved

How to use the high pass filter in LIS3DHTR?

  • March 22, 2021
  • 3 replies
  • 1418 views

Hi, I'm using the LIS3DHTR and I read the applications note and the datasheet, but after that I'm still no understanding how to use the high pass filter, so I have some questions.

1-The purpose of the high pass filter is to filter de DC component?

2-I read that 2 modes exits, but in the application note AN3308 explains that there are 4 modes. Could you explain exactly what each mode do and how to use them? I do not understand if I need to reed the reference register each ODR or only at the beggining and the differences between each mode.

¡Thanks !

    This topic has been closed for replies.
    Best answer by Eleon BORLINI

    Hi @AJura.1​ ,

    they are the same normal mode.

    The REFERENCE (26h) register is just recommended to be read when the device operating mode is switched from high-resolution configuration (HR) to power-down mode (PD); this operation resets the filtering block before switching to normal/high-performance mode again (app note, p.11).

    Moreover, it is used when you to want to high-pass filtering your dataout, instantly deleting the DC component of the acceleration (app note, p.18).

    -Eleon

    3 replies

    E
    Eleon BORLINI
    ST Employee
    March 23, 2021

    Hi @AJura.1​ ,

    1-The purpose of the high pass filter is to filter de DC component?

    Basically yes, it is intended to remove the DC components, and in particular the Earth gravity vector. If you want to go deeper in the HP filter use, you can check the C code on Github lis3dh_wake_up.c, that shows the simplest way to detect wake-up from sensor and how to use HP filter.

    2-Could you explain exactly what each mode do and how to use them?

    You are right, the modes are 4, probably the 2 (super)modes are Low power and normal mode. They are described in the application note AN3308 you reported, together with the meaning and the definitions for each operating mode. They are listed by increasing power consumption, and also decreasing accuracy and resolution.

    0693W000008xeJwQAI.png 

    If my reply answered --at least partially- your question, please click on Select as Best at the bottom of this post. This will help other users with the same issue to find the answer faster. 

    -Eleon

    A
    AJura.1Author
    Visitor II
    March 23, 2021

    Hi @Eleon BORLINI​ ,

    Thanks fot your reply but, I don't understand the difference between the normal mode (reset by reading REFERENCE) and the normal mode which is activated with the bits (10).

    E
    Eleon BORLINIAnswer
    ST Employee
    March 25, 2021

    Hi @AJura.1​ ,

    they are the same normal mode.

    The REFERENCE (26h) register is just recommended to be read when the device operating mode is switched from high-resolution configuration (HR) to power-down mode (PD); this operation resets the filtering block before switching to normal/high-performance mode again (app note, p.11).

    Moreover, it is used when you to want to high-pass filtering your dataout, instantly deleting the DC component of the acceleration (app note, p.18).

    -Eleon

    A
    AJura.1Author
    Visitor II
    March 29, 2021

    Hi @Eleon BORLINI​ ,

    Ok, I understand It has been very helpful. Thanks!

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