AN4650 datasheet(65/102 Pages) STMICROELECTRONICS

65 / 102 page

DocID027415 Rev 1

65/102

AN4650

Mode 2 - sensor hub mode

102

6.4

Magnetometer hard-iron / soft-iron correction

The LSM6DS3 device supports the data acquisition of an external magnetometer with soft-

iron and hard-iron correction features. For this purpose, it is required to set the

MASTER_ON bit of the MASTER_CONFIG register to 1 to enable the sensor hub mode, to

associate the external magnetometer to slave 0 registers (SLV0_ADD, SLV0_SUBADD and

SLAVE0_CONFIG) and to set the Slave0_numop field of SLAVE0_CONFIG to 6.

The FUNC_EN bit of CTRL10_C register has to be set to 1 in order to enable the embedded

ironing functionalities. Then, distortion correction algorithms can be enabled as described in

Table 49: the IRON_EN bit of MASTER_CONFIG and the SOFT_EN bit of CTRL9_XL are

used to enable hard-iron correction only or both hard-iron and soft-iron corrections. In the

latter case, both calibrated (hard-iron & soft-iron) and uncalibrated (soft-iron only)

magnetometer data are available.

6.4.1

Hard-iron correction

Hard-iron distortion is normally generated by ferromagnetic material with permanent

magnetic fields that are part of the object (e.g. a tablet) in use; these materials could be

permanent magnets or magnetized iron or steel. They are time invariant and deform the

local geomagnetic field with different offset on different directions.

Generally, if the user performs many 3D rotations of the object in an ideal environment (no

hard-iron/soft-iron distortion) and plots the collected magnetic sensor raw data, the result

will be a perfect sphere with no offset. The hard-iron distortion effect is to offset the sphere

along the x, y and z axes; in the x-y plane, the hard-iron distortion is identified by an offset of

the origin of the ideal circle from (0, 0), as shown in Figure 20.

Figure 20. Hard-iron effect (X-Y 2D scatter plot)

Table 49. Ironing configuration

CTRL9_XL

SOFT bit

MASTER_CONFIG

IRON_EN bit

Ironing

configuration

No correction applied

Hard-iron only

Hard-iron + soft-iron corrections

AN4650 Datasheet(PDF) 65 Page - STMicroelectronics