Humidity

A humidity sensor senses relative humidity. This means that it measures both air temperature and moisture. Relative humidity, expressed as a percent, is the ratio of actual moisture in the air to the highest amount of moisture air at that temperature can hold.

MetaEnvironment and MTR boards have a Bosch BME280 integrated environmental unit.

Humidity functionality of that sensor are controlled by the functions in the humidity.h header file.

Oversampling

The humidity sensing portion of the BME280 chip only has 1 configurable parameter which is the oversampling mode. This is set by calling mbl_mw_humidity_bme280_set_oversampling. Unlike other configuration functions, this function will immediately write the change to the sensor.

MetaWear.mbl_mw_humidity_bme280_set_oversampling(board, MBL_MW_HUMIDITY_BME280_OVERSAMPLING_16X);

Humidity Measurement

Measuring humidity is manually triggered by calling mbl_mw_datasignal_read with a humidity data signal. Humidity data is percetange from 0 to 100 represented as a float.

// Setup barometer
MetaWear.mbl_mw_humidity_bme280_set_oversampling(device.board, MBL_MW_HUMIDITY_BME280_OVERSAMPLING_1X);

// Get humidity signal
var hum = MetaWear.mbl_mw_humidity_bme280_get_percentage_data_signal(device.board);

// Subscribe to it
console.log('Subscribe');
MetaWear.mbl_mw_datasignal_subscribe(hum, ref.NULL, MetaWear.FnVoid_VoidP_DataP.toPointer((ctx, pointer) => {
  var data = pointer.deref();
  var value = data.parseValue();
  console.log('epoch: ' + data.epoch + ' humidity: ' + value);
}));

// Read
MetaWear.mbl_mw_datasignal_read(hum);