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.

let gyroType = MetaWear.mbl_mw_metawearboard_lookup_module(device.board, MBL_MW_MODULE_BAROMETER);
switch (gyroType) {
    case MBL_MW_MODULE_BARO_TYPE_BMP280:
        console.log("BMP280 barometer")
        break;
    case MBL_MW_MODULE_BARO_TYPE_BME280:
        console.log("BME280 barometer")
        break;
    case UInt8(MBL_MW_MODULE_TYPE_NA):
        console.log("no barometer")
        break;
    default:
        console.log("unknown barometer")
        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 ultra high resolution
MetaWear.mbl_mw_baro_bosch_set_oversampling(device.board, MBL_MW_BARO_BOSCH_OVERSAMPLE_ULTRA_HIGH);

// Set standby time to 62.5ms or closest valid value
MetaWear.mbl_mw_baro_bosch_set_standby_time(device.board, 62.5);

// Set iir filter coefficient
MetaWear.mbl_mw_baro_bosch_set_iir_filter(device.board, MBL_MW_BARO_BOSCH_IIR_FILTER_AVG_4);

// Write configuration to the sensor
MetaWear.mbl_mw_baro_bosch_write_config(device.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.

console.log('Get barometer.')
let baro = MetaWear.mbl_mw_baro_bosch_get_pressure_data_signal(device.board);

console.log('Set up stream.')
MetaWear.mbl_mw_datasignal_subscribe(baro, ref.NULL, MetaWear.FnVoid_VoidP_DataP.toPointer((ctx, pointer) => {
    var data = pointer.deref();
    var value = data.parseValue();
    console.log('epoch: ' + data.epoch + ' pressure: ' + value);
}))

console.log('Start barometer.');
MetaWear.mbl_mw_baro_bosch_start(device.board);

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.

console.log('Setup barometer.')
MetaWear.mbl_mw_baro_bosch_set_oversampling(device.board, MBL_MW_BARO_BOSCH_OVERSAMPLING_ULTRA_LOW_POWER);
MetaWear.mbl_mw_baro_bosch_set_iir_filter(device.board, MBL_MW_BARO_BOSCH_IIR_FILTER_OFF);
MetaWear.mbl_mw_baro_bmp280_set_standby_time(device.board, MBL_MW_BARO_BMP280_STANDBY_TIME_0_5ms);
MetaWear.mbl_mw_baro_bosch_write_config(device.board);

console.log('Get barometer.')
let baro = MetaWear.mbl_mw_baro_bosch_get_altitude_data_signal(device.board);

console.log('Set up stream.')
MetaWear.mbl_mw_datasignal_subscribe(baro, ref.NULL, MetaWear.FnVoid_VoidP_DataP.toPointer((ctx, pointer) => {
    var data = pointer.deref();
    var value = data.parseValue();
    console.log('epoch: ' + data.epoch + ' pressure: ' + value);
}))

console.log('Start barometer.');
MetaWear.mbl_mw_baro_bosch_start(device.board);