I use MMA8451Q to measure the tilt of the engine. How to use the built-in LP filter to remove vibration accelerations?

[mma8451q]

I use MMA8451Q to measure the tilt of the engine. How to use the built-in LP filter to remove vibration accelerations?

[reyes]

Hi Pavel,

The Low-Pass filter built-in the MMA8451 is not configurable, but it is enabled by setting bit4 of the HP_FILTER_CUTOFF Register (0x0F). It is important to mention that it is typically used for Pulse processing, so it could not work for your application purposes, but it could make sense to test it.

We have an application note that could result helpful to your application, “High-Pass Filtered Data and Transient Detection Using the MMA8451, 2, 3Q”: http://cache.freescale.com/files/sensors/doc/app_note/AN4071.pdf

Regards,

Jose

[danielgutierrez]

hi everyone!

I have one question regarding on LP filter...

In my applications, I need the acceleration data without filters. I have disable HP_FILTER_CUTOFF Register (0x0F) by clearing bit 4 in Register 0x0F. In this case, is there any filter active? anybody knows how I can remove both, HP filter and LP filter. In AN4076, section 6.1 the Information is un clear:

6.1 High-Pass Filtered Data or Low-Pass Filtered Data

Registers 0x01 through 0x06 are used to read the X, Y, Z data. The device can be configured to produce high-pass filtered

data or low-pass filtered data by setting or clearing the HPF_Out bit in the XYZ_Data_Cfg Register 0x0E. The following code

example shows how to set the HPF_Out bit.

Thank you in advance!!

[reyes]

Hi Daniel,

By clearing bit 4 (Pulse_LPF_EN) of register 0x0F (HP_FILTER CUTOFF) you are disabling LPF, and you would need to clear bit 4 (HPF_OUT) on register 0x0E (XYZ_DATA CFG) to disable the HPF.

Have a great day,
Jose Reyes

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