How to detect the Direction and Angle using XZ-accelerometer Sensor

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How to detect the Direction and Angle using XZ-accelerometer Sensor

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sakthivelkuland
Contributor III

Dear All,

I am using FXTH8719xxxx Family XZ axis Accelerometer Sensor. I need to find the direction as well how much angle turned by using X-axis ans Z Axis data. If any one can help me the possibility?

Each sensor Z-Axis have the different offset values, help me how to calibrate the Z-axis with the new sensor.

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sakthivelkuland
Contributor III

hi Anthony,

I have one points to clarify,

what is the values for Z0 - Z base values, How to find the Z base values?

Thanks,

Sakthivel K

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sakthivelkuland
Contributor III

Dear Anthony,

Thanks for your response. Your points are very helpful i'm collecting z-x axis data so i will apply your method if any points to clarify i get back to you.

Regards,

Sakthivel K

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anthonyduhamel
NXP Employee
NXP Employee

Hi Hulandaivel,

There are several methods to calibrate sensor offsets. The big limitation with an accelerometer is you need to do the calibration phase with quasi-static data. I mean: if you move the FXTH8719xxxx , you will add an acceleration vector on both axis (Z & X) and this will degrade/pervert the calibration... So you have to take care of the sensor rotation by doing very smooth motion (external acceleration should be very small compared to the 1g-force).

About calibration algorithms:

1. You can collect data/measurements around the circle in a buffer. When the full revolution is done, you compute the Z offset with an optimization method to minimize the standard deviation of the 1g vector on all measurements.

data.PNG

2. You can calculate the circle center with 3 points only. (Basic equations & resolution)

Capture.PNG

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The final angle can be calulated with the following equation:

Capture.PNG

-Z0 the Z bias

- Z current / X current  are the actual measurements.

Note that these equations are only valid in a static model and are using the 1g gravitational force as reference.

I hope it helps.

Thanks,

Anthony

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