Barometer

A barometer is a scientific instrument that is used to measure air pressure in a certain environment. The absolute barometric pressure sensor can measure pressure from 300 Pascal to 1100 hPa.

MetaWear RPro and Cpro, MMR, MMC, MTR, and MetaEnvironment boards come with a Bosch barometer.

The specific barometer model varies between the boards although both barometers are nearly identical save for a few settings. Bosch barometer functions are defined in the barometer_bosch.h header file where functions containing baro_bosch are barometer agnostic where as functions with baro_bmp280 and baro_bme280 are for those specific barometers.

Users can programatically determine which barometer is on their board with the mbl_mw_metawearboard_lookup_module function.

gyroType = mbl_mw_metawearboard_lookup_module(board, MBL_MW_MODULE_BAROMETER)
switch gyroType {
    case MODULE_BARO_TYPE_BMP280:
        break
    case MODULE_BARO_TYPE_BME280:
        break
    case MODULE_TYPE_NA:
        break
    default:
        break
}

Sensor Configuration

The Bosch barometers have 3 configurable parameters:

• Oversampling

• Infinite impulse filter (iir) coefficient

• Standby time

These operational parameters work in conjunction to control the noise, output resolution, and sampling rate. When you are done setting the configuration, call mbl_mw_baro_bosch_write_config to write the changes to the sensor.

# Set oversampling to low power mode
libmetawear.mbl_mw_baro_bosch_set_oversampling(board, BaroBoschOversampling.LOW_POWER)

# Set standby time to 500ms
libmetawear.mbl_mw_baro_bmp280_set_standby_time(board, BaroBmp280StandbyTime._500ms)

# Set iir filter coefficient
libmetawear.mbl_mw_baro_bosch_set_iir_filter(board, BaroBoschIirFilter.AVG_16)

# Write configuration to the sensor
libmetawear.mbl_mw_baro_bosch_write_config(board)

Pressure Sampling

Pressure data is represented as a float and is in units of Pascals. To receive pressure data, simply subscribe or log the pressure data signal and then start the sensor.

pa_data_signal = libmetawear.mbl_mw_baro_bosch_get_pressure_data_signal(board)
libmetawear.mbl_mw_datasignal_subscribe(pa_data_signal, None, sensor_data_handler)

Altitude Sampling

Altitude data is represented as a float and is in units of meters. To receive altitude data, simply subscribe or log the altitude data signal and then start the sensor.

def sensorDataHandler(self, context, data):
    data_ptr= cast(data.contents.value, POINTER(CartesianFloat))
    self.data_cartesian_float= copy.deepcopy(data_ptr.contents)
    self.data = self.data_cartesian_float

sensor_data_handler= FnVoid_VoidP_DataP(self.sensorDataHandler)

libmetawear.mbl_mw_baro_bosch_set_oversampling(board, BaroBoschOversampling.LOW_POWER)
libmetawear.mbl_mw_baro_bmp280_set_standby_time(board, BaroBmp280StandbyTime._500ms)
libmetawear.mbl_mw_baro_bosch_set_iir_filter(board, BaroBoschIirFilter.AVG_16)
libmetawear.mbl_mw_baro_bosch_write_config(board)

m_data_signal= self.libmetawear.mbl_mw_baro_bosch_get_altitude_data_signal(board)
libmetawear.mbl_mw_datasignal_subscribe(m_data_signal, None, sensor_data_handler)
libmetawear.mbl_mw_baro_bosch_start(board)