LIS2DTW12 wake up filter

[RStra]

Hello,

I want to monitor signals in range 0.5 - 80 Hz to wake up a microcontroller on INT1 pin when acceleration is above a certain threshold.

My setup is :

ODR = 200Hz

FS = 2G

MODE = Low power mode 4, Low Noise

BW_FILT = 00 --> ODR/2 --> 100Hz

WK_THS = 1 --> 31.25 mg

FDS = 0 --> LP Filter

interrupts_enable = 1 --> ENABLE INTERRUPT

int1_wu = 1 --> Route wake up on INT1

In this configuration I have a LP filter, ODR is 200 Hz so BW according with BW_FILT is 100 Hz.

The wake up interrupt is routed to INT 1 and enabled and the threshold is 31.25 mg.

If no acceleration is applied I have 1G on z axis due to the gravity, acceleration on x and y axis are below 31.25mg.

My question is why with a LP filter I do not have a wake up interrupt due to the gravity ?

I was expected to have continuous triggers on INT1 due to the gravity.

Reagards,

Riccardo

[DSull.3]

Hi Riccardo, you don't have continuous wake up triggers on INT1 since the interrupt rises when the 31.25 mg threshold is down to up crossed (for a specific duration), as shown in the picture:

See the app note https://www.st.com/resource/en/application_note/an5038-lis2dw12-alwayson-3d-accelerometer-stmicroelectronics.pdf

You might apply the HP filter if you want to rule out the 1g gravity constant acceleration.

\Dk

[RStra · Accepted solution]

Hello,

thank you for the app note, it was very useful.

I didn't have continuous WK interrupt because USR_OFF_ON_WU was set to 0 so the filter path for the wake up function was high pass even if FDS was 0.

Thanks for the support.

Regards,

Riccardo

[Eleon BORLINI]

Thank you Riccardo @RStra​ for having shared the solution to the Community!

-Eleon