AnsweredAssumed Answered

LSM6DS33 how to filter accelerometer values even more (< 50Hz)

Question asked by Veselin Georgiev on Mar 8, 2018
Latest reply on Mar 12, 2018 by Miroslav B

Hi,

I'm trying to use the LSM6DS33 as an inertial navigation aid, participating in sensor fusion. The problem is that the application has large amount of vibrations and the accelerometer data is quite noisy. I need around 25 accelerometer samples per second, so to get a smoother signal I have enabled the analog low-pass filter at BW = 50Hz and the accelerometer ODR is 104 Hz; I average 4 samples manually whilst reading them to get equivalent ODR of 26 Hz with less aliasing.

 

This is better than before, but there's still some noise (around 0.1g random looking noise - measured on a vibrating platform) present in the resulting averaged samples. I verified that increasing the accelerometer ODR to 208 Hz decreases noise (aliasing) further. But that needs more I²C traffic and CPU time, so increasing the ODR even further will be prohibitive.

 

My question is: is it possible to set up the LSM6DS33 to sample the accelerometer at 833 Hz, average each 8 samples, and put the results in the FIFO (equivalent 104 ODR)? Or put in other way, to get an equivalent low-pass filtering BW lower than 50 Hz, ideally around 12 Hz?

 

For reference, my current config is:

CTRL1_XL = 0x4F; // acc setup -> 104 Hz, 8 g full scale, 50Hz bandwidth

CTRL2_G = 0x4C; // gyro setup -> 104 Hz, 2000 dps full scale

CTRL3_C = 0x44;  // set BDU (block data update) bit high
CTRL4_C = 0x81;  // enable FIFO length limit; XL_BW_SCAL_ODR=1

 

(and also some unrelated code for setting up the FIFO).

Outcomes