Temperature

Temperature plays an import role in our every day life. We rely on it to monitor our health, food, and electronics to name a few examples. All MbientLab boards come with at least one temperature sensor, represented by the Sensor interface, and is acceesed through the Temperature interface.

import com.mbientlab.metawear.module.Temperature;

final Temperature temperature = board.getModule(Temperature.class);

Sensors

There are 4 types of temperature sensors on the MetaWear enumerated by the SensorType enum.

Sensor	Description
nRF SOC	Temperature sensor on the nRF SOC
External Thermistor	Separate thermistor that can be connected to the gpio pins
Bosch Env	Temperature sensor from either the BMP280 or BME280 devices
Preset Thermistor	Thermistor placed on the MetaWear board

All MbientLab boards, except MetaWear R, come with an NCP15XH103F03RC therimstor preset on the pcb and boards equipped with a Bosch Barometer can use the environmental unit to measure temperature as well. While the nRF SOC also has a temperature sensor, it is better use one of the other sensor types instead.

Available sensors are presented as an array returned by the sensors method. You can also find a specific sensor using findSensors.

import com.mbientlab.metawear.module.Temperature.SensorType;

// Does not work for MeteaWear R boards, use SensorType.NRF_SOC
final Temperature.Sensor tempSensor = temperature.findSensors(SensorType.PRESET_THERMISTOR)[0];

External Thermistor

Using the external thermistor requires some additional configuration before reading sensor data. After attaching the thermistor to the board, as outlined in our blog post, you need to tell the firmware which pins the thermistor is connected to and whether the thermistor is active high or low.

import com.mbientlab.metawear.module.Temperature.ExternalThermistor;

// Read data from pin 0, pulldown resistor is on pin 1, active low
((ExternalThermistor) temperature.findSensors(SensorType.EXT_THERMISTOR)[0])
            .configure((byte) 0, (byte) 1, false);

Bosch Env

There is no extra configuration needed for using the temperature sensors on the BMP280 and BME280; the only thing you need to do is start the the devices.

// only for RPro, CPro, Env, and Motion boards
board.getModule(BarometerBosch.class).start();
temperature.findSensors(SensorType.BOSCH_ENV)[0]).read();

Temperature Data

Temperature data is reported in Celsius and interepreted as a float value. It is represented as a forced data producer.

tempSensor.addRouteAsync(new RouteBuilder() {
    @Override
    public void configure(RouteComponent source) {
        source.stream(new Subscriber() {
            @Override
            public void apply(Data data, Object ... env) {
                Log.i("MainActivity", "Temperature (C) = "  data.value(Float.class));
            }
        });
    }
}).continueWith(new Continuation<Route, Void>() {
    @Override
    public Void then(Task<Route> task) throws Exception {
        tempSensor.read();
        return null;
    }
});