STM CircleOS forum / MEMS, acceleration values and filters?

kbe · 2008-05-23 15:24:31

Hello,

I am trying to get a precise instant acceleration value,
I tried to calculate the average acceleration value / sec, but I found an abnormal value!
The CircleOS calls the MEMS_Handler() through the TIM2_IRQHandler() which is configured by TIM_Configuration(); and it’s period is set to 256;
I tried to use the predefined filters, F4, F16, F64 and F256, but, the most appropriate filter was the F256 >>8 and did not give me very precise values…
I have established the filters’ formulas, but I did not find any idea about these choices yet!
I have explored the N_filtering variable of the mems.c, to sum up each 256 values, and to divide them by 256 (then, resetting the N_filtering to 0), but, these values are not very precise!
Have you any idea or comment?

Thanks

Last edited by kbe (2008-05-26 08:21:55)

Francis · 2008-05-26 10:47:34

When the handling of the MEMS had been implemented, we didn't have the good tools available now on this web site:
http://www.stm32circle.com/projects/project.php?id=39
http://www.stm32circle.com/projects/project.php?id=40
Therefore, the filtering is probably not well optimized. It has been tested only manually. If you have any suggestion to improve thishandling, they are very welcome.
You will find also on this forum some posts about some issue (noise) due to the electrical environment. I don't know how precise are the physical measurements.

halbstein · 2008-05-26 14:13:32

I used an digital ca. 50 Hz low pass for filtering
Together with the F256 Values it gave a quite stable reading

# 1 2008-05-23 15:24:31 MEMS, acceleration values and filters?

MEMS, acceleration values and filters?

# 2 2008-05-26 10:47:34 MEMS, acceleration values and filters?

Re: MEMS, acceleration values and filters?

# 3 2008-05-26 14:13:32 MEMS, acceleration values and filters?

Re: MEMS, acceleration values and filters?

Board footer