Hi, I am developing a solution using IIS3DWB, I want to change the ODR from 26667hz to 13000hz, how can I do this? I am unable to find anything in the datasheet. Request support from the community. Regards, Aman

[ABham.1]

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[Eleon BORLINI]

Hi Aman @ABham.1​ ,

please consider that for the IIS3DWB the ODR is fixed at 26667hz and it is not possible to change it in the configuration registers. With this ODR, the maximum detectable acceleration frequency by Nyquist theorem is 13kHz. However, please note also that the MEMS mechanical cutoff frequency is 7kHz (datasheet p.19), so this is actually the maximum detectable acceleration frequency at full sensitivity. Of course, running the device up to 26.667kHz allow a noise reduction coming from oversampling.

If you are interested in reducing the ODR for a bandwidth reason, you can use the second Low Pass filter (digital LPF2, datasheet p.20) to adjust the band according to your preferences (up to 5.4kHz). Which is your target application?

On the other side, if you want to reduce the power consumption of the device (by reducing the ODR frequency), you can think to not to enable the system permanently, or to run the SPI at a lower frequency (for example 13kHz) so that you can reduce the number of clock and data edge commutations per second. In this way you will loose samples and so reduce the band (and maybe loss a little in the noise figure), but you'll reduce the operating power consumption. 

If my reply answered your question, please click on Select as Best at the bottom of this post. This will help other users with the same issue to find the answer faster.

-Eleon

[ABham.1]

Hi Eleon,

Thanks a lot for the reply. The problem is if the ODR is not configurable we need to send complete 26667 samples to the Cloud from our sensor and do the spectrum analysis. We cannot compromise in the resolution of the spectrum, we need atleast 1Hz. Increasing the number of samples means a bigger json file, lot of IoT platforms have a limit on the MQTT size. So I guess we will have to look for compression options now if we cannot change the ODR.

Regards,

Aman

[du00000001]

Receive the data @ 26667 SPS and pass them through a simple sliding average filter. Following this filter, you can "pick" every 2nd value for transmission. This might introduce a bit of aliasing error if the frequencies measured include frequencies beyond 6.5 kHz. If so, you may consider Eleon's suggestion to configure the sensor's LPF2 to 5.4 kHz.

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BTW: frequency resolution per FFT is not linear (it's DC to Nyquist with nsamples values), so what's that "at least 1 Hz resolution" requirement nonsense ?