BMM150 Trim Values & Z repetitions

[Vinod]

I am working with Arduino Nano BLE33_Sense Rev. 2 MCU.  This MCU has built-in sensors, BMI270, BMM150, etc.  I am writing app for BMM150 to determine heading.  I have extracted the trim data from the trim registers.  These data are partially in agreement with the trim data shown in one of your data sheet, shown below:

                                             BOSCH Data                      Data from

                                                                                          Arduino MCU

dig_X1                         0                                                  0

dig_Y1                          0                                                  0

dig_X2                         26                                               25                         different

dig_Y2                          26                                               25                         different

dig_xy1                        29                                               29

dig_xy2                        -3                                                -3

dig_z1                          22752                                        21463                  different

dig_z2                          737                                             770                       different

dig_z3                          -1035                                         0                            different

dig_z4                          0                                                  0

dig_xyz1                      6753                                           7019                     different

I am not sure what to make of the difference.  Please help me if the difference is due to Arduino with built-in sensors or I am making some mistake in extracting the data.  By the way, one the app supplied by Arduino for BMM150 also reproduced the same data as mine.

A second question I have is regarding preset values for REPZ repetitions (register 0x52).  According to the definition input value should be 14 (15 -1) for BMM150_REPZ_REGULAR preset.  Please help me, if my interpretation is flawed. What is the significance of the repetitions?

Thanks, Vinod

[BSTRobin]

Hi Vinod,

You could refer BMM150 official sensor API and example code to get sensor data, by call bmm150_read_mag_data() to get compensated x, y, z mag data.
https://github.com/boschsensortec/BMM150-Sensor-API/tree/master/examples/generic

In BMM150 sensor API, z_rep was set according different preset mode.

/*!
* @brief This API is used to set the preset mode of the sensor.
*/
int8_t bmm150_set_presetmode(struct bmm150_settings *settings, struct bmm150_dev *dev)
{
int8_t rslt;
uint8_t preset_mode;

/* Check for null pointer in the device structure */
rslt = null_ptr_check(dev);

/* Proceed if null check is fine */
if (rslt == BMM150_OK)
{
preset_mode = settings->preset_mode;

switch (preset_mode)
{
case BMM150_PRESETMODE_LOWPOWER:

/* Set the data rate x,y,z repetition
* for Low Power mode
*/
settings->data_rate = BMM150_DATA_RATE_10HZ;
settings->xy_rep = BMM150_REPXY_LOWPOWER;
settings->z_rep = BMM150_REPZ_LOWPOWER;
rslt = set_odr_xyz_rep(settings, dev);
break;
case BMM150_PRESETMODE_REGULAR:

/* Set the data rate x,y,z repetition
* for Regular mode
*/
settings->data_rate = BMM150_DATA_RATE_10HZ;
settings->xy_rep = BMM150_REPXY_REGULAR;
settings->z_rep = BMM150_REPZ_REGULAR;
rslt = set_odr_xyz_rep(settings, dev);
break;
case BMM150_PRESETMODE_HIGHACCURACY:

/* Set the data rate x,y,z repetition
* for High Accuracy mode *
*/
settings->data_rate = BMM150_DATA_RATE_20HZ;
settings->xy_rep = BMM150_REPXY_HIGHACCURACY;
settings->z_rep = BMM150_REPZ_HIGHACCURACY;
rslt = set_odr_xyz_rep(settings, dev);
break;
case BMM150_PRESETMODE_ENHANCED:

/* Set the data rate x,y,z repetition
* for Enhanced Accuracy mode
*/
settings->data_rate = BMM150_DATA_RATE_10HZ;
settings->xy_rep = BMM150_REPXY_ENHANCED;
settings->z_rep = BMM150_REPZ_ENHANCED;
rslt = set_odr_xyz_rep(settings, dev);
break;
default:
rslt = BMM150_E_INVALID_CONFIG;
break;
}
}

return rslt;
}