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HPras
Visitor II
August 6, 2020
Solved

LIS3DH High Resolution Threshold

  • August 6, 2020
  • 1 reply
  • 2958 views

Hi Community,

I am using Lis3dh sensor in 50HZ ODR, High Pass filter enabled with cut-off frequency 0.1 HZ with full scale range 8G and FIFO is enabled and set FIFO-to-Stream Mode.

Case 1:

I get interrupts for small events Normal Mode(HR bit is not set) for the same threshold and when i see the x,y,z axis value is more than the threshold.

Case 2:

With HR Bit enabled , I am not getting the interrupt for the same small event for the same threshold which means that event didn't cross the threshold.

I am sure both time same events only happened.

As per Datasheet and Application note, that Output value only will be in 12-bit in High resolution mode.

Is there HR bit anyway related to do with Threshold?

Please help me .

Thanks,

Hari

    This topic has been closed for replies.
    Best answer by niccolò

    Hi @Community member​ ,

    thank you for confirming that the issue was not in the initialization.

    I think that the problem could be that the trigger is at a frequency that is not seen from the sensor.

    Let me explain myself: as stated in page 16 of the datasheet the HR mode make you use a reduced bandwidth that is ODR/9 (in your case it is 5.5Hz), opposed to the BW in Normal mode that is ODR/2 (25Hz in your case).

    So, if the trigger has a frequency between 5.5Hz and 25Hz it can get lost between samples.

    Can this be the issue?

    (It is to be noted that the HR mode was meant to be used to enhance resolution in DC component, not in high frequency vibrations)

    1 reply

    N
    niccolò
    ST Employee
    August 10, 2020

    Hi @Community member​ ,

    no, the threshold value is related only to the FS value.

    Are you sure that the rest of the configuration is the same in both your work cases?

    maybe you can check the registers after both start ups, with a whole reading to check for differences.

    H
    HPrasAuthor
    Visitor II
    August 29, 2020

    Hi @niccolo.ruffini​,

    tried reading all the register after the initialisation with and without High resolution bit enabled. I not seeing any other register value changing except output register OUTXH,OUTYH,OUTZH,OUTXL,OUTYL,OUTZL in either of the cases.

    Thanks,

    Hari Prasath

    N
    niccolòAnswer
    ST Employee
    August 31, 2020

    Hi @Community member​ ,

    thank you for confirming that the issue was not in the initialization.

    I think that the problem could be that the trigger is at a frequency that is not seen from the sensor.

    Let me explain myself: as stated in page 16 of the datasheet the HR mode make you use a reduced bandwidth that is ODR/9 (in your case it is 5.5Hz), opposed to the BW in Normal mode that is ODR/2 (25Hz in your case).

    So, if the trigger has a frequency between 5.5Hz and 25Hz it can get lost between samples.

    Can this be the issue?

    (It is to be noted that the HR mode was meant to be used to enhance resolution in DC component, not in high frequency vibrations)

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