AppMEMS#5b: The X-CUBE-MEMS1 libraries in detail - MotionAC functions

[Eleon BORLINI]

--- More detail on MotionAC library ---

The library acquires data from the accelerometer and calculates the offset and scale factor coefficients together with the calibration quality value. Calibration can be done in two ways: dynamic calibration and 6-point calibration. The offset and scale factor coefficients are then used to compensate raw data coming from accelerometer. In particular, it features:

1. offset compensation up to 0.2 g;
2. scale factor compensation, in range from 0.8 to 1.2 in every direction;
3. update frequency from 20 to 100 Hz.

The central function that performs the calibration is this one:

void MotionAC_Update (MAC_input_t *data_in, uint8_t *is_calibrated)

*data_in parameter is a pointer to a structure with input data + timestamp, while *is_calibrated parameter is a pointer to a value which returns 1 if calibration is done.

See below the detailed calibration process to make your app with the MotionAC effective! �?�

[Eleon BORLINI]

This calibration algorithm uses the normal motion of the three orthogonal axes of a stationary accelerometer sensor exposed to Earth’s gravitation field.

Step 1. Hold the device firmly as shown in position 1.

Step 2. Gently rotate the device by 180° around the YZ plane such that in position 4, the device is flipped to its back side.

Step 3. Rotate the device by 180° in a clockwise fashion around the XZ plane to reach position 1.