FXOS8700CQ low pass filter for tilt sensor?

[tedhuntington1]

Hi,

I am using the FXOS8700CQ strictly for tilt detection. I find that I am getting some high acceleration readings though.

I see that I can set the CTRL_REG1 LNOISE bit.

Does the HP_FILTER_CUTOFF setting LPF=1 and HPF=1 work as a low pass filter for regular sampling or only for pulse detection?

What is the best way to configure this device for reading just the acceleration due to the earth's gravity?

Thanks,

Ted

[tedhuntington1]

Adding that- is a good strategy to lower the sample rate if only concerned about acceleration from the earth's gravity? Will that affect the quality of the sample at all?

[TomasVaverka · Accepted solution]

Hi Ted,

The low pass filter can be enabled for the pulse detection by setting the pulse_lpf_en bit in the HP_FILTER_CUTOFF register. It is always enabled for all the other functions (landscape/portrait, transient, freefall/motion…). The low pass filter is a simple 1st order decimation filter, i.e. a moving average filter followed by a down-sampling. Its cut-off frequency depends on ODR and MODS settings.

The best way to configure the FXOS8700CQ for tilt sensing is using the lowest possible ODR (ideally 1.56 Hz), High Resolution mode (MODS[0:1] = 0b10) with the lnoise bit set. 

I hope it helps.

Regards,

Tomas

PS: If my answer helps to solve your question, please mark it as "Correct". Thank you.