LIS3DH High pass filter doesn't work on z-Axis

alexanderpolleti9 · ‎2016-11-14

Posted on November 14, 2016 at 11:42

Hello everybody,

I am trying to apply the built in high pass filter of an LIS3DH to all 3 axis. For the x and y axis this works beautifully: When I rotate the board by 90� I see the peak in the data and flattening out again.

This seems not to work with the Z-Axis. I always get about 1g when I leave it lying on my desk z-axis towards earth...

I don't see any possibility to configure the axes that are used for high pass filtering...

I am using the lis3dh_driver from ST with the following settings:

/* enable the accelerometer */

LIS3DH_SetODR(LIS3DH_ODR_10Hz);

/* enable all axes */

LIS3DH_SetAxis(0x07);

/* full scale = 2g */

LIS3DH_SetFullScale(LIS3DH_FULLSCALE_2);

/* Enable block data update, so unread previous data will just be dismissed */

LIS3DH_SetBDU(MEMS_ENABLE);

/* big endian data selecten: LSB @ lower address */

LIS3DH_SetBLE(LIS3DH_BLE_LSB);

/* set fifo to stream mode and enable it */

LIS3DH_FIFOModeEnable(LIS3DH_FIFO_STREAM_MODE)

/* set low power mode and 8 bit resolution, start the measruements */

LIS3DH_SetMode(LIS3DH_LOW_POWER);

/* set high pass filter mode */

LIS3DH_SetHPFMode(LIS3DH_HPM_NORMAL_MODE);

LIS3DH_SetHPFCutOFF(LIS3DH_HPFCF_0);

LIS3DH_SetFilterDataSel(MEMS_ENABLE);

Any Idea how I could make the high pass filter work on the z-axis as well?

thanks for you replies

Alexander

#lis3dh-highpass

Miroslav BATEK · ‎2016-11-30

Posted on November 30, 2016 at 14:45

You can try to reset the HP filter by reading register 0x26h (according to application note AN3308).

Just to check, can you please explain what the following functions do?

LIS3DH_SetHPFMode(LIS3DH_HPM_NORMAL_MODE);

LIS3DH_SetFilterDataSel(MEMS_ENABLE);

Basically you should set the CTRL_REG2 (21h) to 0x08h to get high pass filtered data.

Best regards

Miroslav