Can offset registers on LIS2MDL compensate strong magnetic field?

[MHo]

Hi,

I'm working on a prototype device. It is very compact, battery powered and has a motor inside. I want to know if the offset can be set (during production) to compensate a very strong magnetic field and still be able to detect earth magnetic field for heading. Is there any other way/sensor can achieve this?

Thank you,

Min-Ching Ho

[Eleon BORLINI]

Hi @Community member​ , it depends on how strong is the sensed magnetic field. From the absolute maximum ratings of the datasheet p.14, the Maximum exposed field is 10000 gauss (and I believe you won't exceed this field intensity...). The magnetic sensor full scale is however well below this value, at +-50 gauss. Supposing the case of a full hard iron compensation, the procedure is described in the AN5069 p.19 and allows a maximum compensation per axis is of the order of magnitude of FS/2, acting of registers from OFFSET_X_REG_L (45h) to OFFSET_Z_REG_H (4Ah). Unfortunately, the magnetometer with maximum FS in ST portfolio is the LIS2MDL, and it is not possible to compensate background static magnetic field greater than 50 gauss. Regards

[MHo]

Hi @Eleon BORLINI​ ,

Sorry for late reply. I found some hard-iron calibration method on line. But, I don't know which method works. Does ST have any document describe how to perform a proper hard-iron calibration (on production line)?

Thank you,

Min-Ching Ho

[Eleon BORLINI]

Hi Min-Ching Ho, sure, you can refer to the UM2192: MotionMC magnetometer calibration library in X-CUBE-MEMS1 expansion for STM32Cube.

/* Magnetometer calibration algorithm update */
MotionMC_Update(&data_in);
/* Get the magnetometer calibration coefficients */
MotionMC_GetCalParams(&data_out);
/* Apply calibration coefficients */
mag_cal_x = (int)((data_in.Mag[0] - data_out.HI_Bias[0]) * SF_Matrix[0][0]
 + (data_in.Mag[1] - data_out.HI_Bias[1]) * SF_Matrix[0][1]
 + (data_in.Mag[2] - data_out.HI_Bias[2]) * SF_Matrix[0][2]);
mag_cal_y = (int)((data_in.Mag[0] - data_out.HI_Bias[0]) * SF_Matrix[1][0]
 + (data_in.Mag[1] - data_out.HI_Bias[1]) * SF_Matrix[1][1]
 + (data_in.Mag[2] - data_out.HI_Bias[2]) * SF_Matrix[1][2]);
mag_cal_z = (int)((data_in.Mag[0] - data_out.HI_Bias[0]) * SF_Matrix[2][0]
 + (data_in.Mag[1] - data_out.HI_Bias[1]) * SF_Matrix[2][1]
 + (data_in.Mag[2] - data_out.HI_Bias[2]) * SF_Matrix[2][2]);
}

The algorithm between data in and data out is ST proprietary, but you can find some more details in the design tip document DT0059: Ellipsoid or sphere fitting for sensor calibration. Regards

[MHo]

Thank you, @Eleon BORLINI​ . I'll check those documents.

Min-Ching Ho

[MHo]

Hi @Eleon BORLINI​ ,

I tried to integrate MotionMC library into my test code. I was able to build it on a different platform, nRF52840. When the code calls MotionMC_Initialize(), it always crashed. Can you help on this?

The test call looks like this:

char MotionMC_LoadCalFromNVM(unsigned short int datasize, unsigned int *data)
{
 return (char)1; /* FAILURE: Read from NVM not implemented. */
}
 
char MotionMC_SaveCalInNVM(unsigned short int datasize, unsigned int *data)
{
 return (char)1; /* FAILURE: Write to NVM not implemented. */
}
 
static void _CalibrationHandler( nrf_cli_t const * inCLI, size_t argc, char **argv )
{
 char lib_version[36] = {0};
 
 MotionMC_Initialize( 20, 1 ); // system crashes when this is called.
 MotionMC_GetLibVersion(lib_version);
 
 nrf_cli_fprintf( inCLI, NRF_CLI_NORMAL, "MotionMC lib ver %s\r\n", lib_version );
}

Another question, do you have MotionMC library built with "-mfloat-abi=hard"?

Thank you,

Min-Ching Ho

[MHo]

I have found the answer. It seems your library can only run on STM32 chips.

[Eleon BORLINI]

Hi Min-Ching Ho, of course the libraries "as-they-are" shall run on STM32 MCU. However, regarding your question "Another question, do you have MotionMC library built with "-mfloat-abi=hard"?" , the X-CUBE-MEMS1 package can be compiled to run on all ARM-based MCUs and with the soft, but since the the release of STM proprietary libraries is subject to signature of a License User Agreement (LUA), you should contact an STMicroelectronics sales office and representatives for further information.

Please also check this discussion if it can be of your help --> https://community.st.com/s/question/0D50X0000Bvk9coSQA/source-code-for-stcoms-xcubemems1-available

"Go to project properties and try to find the settings there,

I don't have Attolic TrueStudio but in STM32CubeIDE it looks like in the attached screenshot.

"

Regards

[MHo]

@Eleon BORLINI​ ,

Thank you for the info. I checked your MotionMC library. I found it is using some HW modules, e.g. RAM ECC. We are using a SoC from another vendor. If we contact with your representatives, will we be able to get a library that could run on a different SoC? If we can get one, will the performance be significantly lower?

Thank you,

Min-Ching Ho

[Slong.1]

Hello, can you use these libraries on nrf52840?

[MHo]

Yes. I was able to make it work.