AN4650 datasheet(68/102 Pages) STMICROELECTRONICS

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Mode 2 - sensor hub mode

AN4650

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DocID027415 Rev 1

6.4.4

Ironing example

The following example demonstrates how to define the values to be assigned to hard-iron

and soft-iron correction registers starting from the calculated hard-iron vector and soft-iron

rotation matrix. This example refers to the usage of the LIS3MDL magnetometer sensor with

4 gauss of configured full-scale (sensitivity = 6842 LSB/gauss).



Hard-iron (X,Y,Z) offset values vector (gauss):

These three offset values must be multiplied by the LIS3MDL sensitivity value (6842

LSB/gauss for full-scale = 4 gauss) in order the get the LSB values to be written in the hard-

iron correction registers (Table 50):



Soft-iron rotation matrix:

These soft-iron matrix elements must be multiplied by 8 in order to get the LSB values to be

written in the soft-iron correction registers (Table 51):

Table 50. Hard-iron register values

Offset values [LSB]

-2296 (F708h)

MAG_OFFX_H = F7h

MAG_OFFX_L = 08h

+865 (0361h)

MAG_OFFY_H = 03h

MAG_OFFY_L = 61h

-785 (FCEFh)

MAG_OFFZ_H = FCh

MAG_OFFZ_L = EFh

Table 51. Soft-iron register values

Soft-iron matrix elements

+1.229006

MAG_SI_XX = 0Ah

+0.173917

MAG_SI_XY = 01h

+0.052327

MAG_SI_XZ = 00h

+0.173917

MAG_SI_YX = 01h

+1.033307

MAG_SI_YY = 08h

HI 3x1



0.335605

–

0.126487

0.114722

–

SI 3x3



1.229006 0.173917 0.052327

0.173917 1.033307

0.130089

–

0.052327 0.130089

–

1.243645

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