Remarks

SHT31D
Status
Source code	GitHub
NuGet package

The SHT31D is a temperature and humidity sensor with a built in I2C interface. The sensor has a typical accuracy of +/- 2% relative humidity and +/- 0.3C.

Code Example

public class MeadowApp : App<F7Micro, MeadowApp>
{
    SHT31D sensor;

    public MeadowApp()
    {
        sensor = new SHT31D(Device.CreateI2cBus());
        sensor.Updated += Sensor_Updated;

        sensor.StartUpdating();
    }

    void Sensor_Updated(object sender, Meadow.Peripherals.Sensors.Atmospheric.AtmosphericConditionChangeResult e)
    {
        Console.WriteLine($"Temp: {e.New.Temperature}, Humidity: {e.New.Humidity}");
    }
}

Sample projects available on GitHub

Purchasing

The SHT31D temperature and humidity is available on a breakout board from Adafruit:

• SHT31D Temperature and Humidity Sensor

The SHT31D can operate in interrupt or polling mode. The default mode is interrupt mode.

Interrupt Mode

The application below generates and interrupt when the temperature or humidity changes by more than 0.1 °C. The sensor is checked every 100 milliseconds.

public class MeadowApp : App<F7Micro, MeadowApp>
{
    public MeadowApp()
    {
        // Create a new SHT31D object that will generate interrupts when
        // the temperature changes by more than +/- 0.1C or the humidity
        // changes by more than 1%.
        SHT31D sht31d = new SHT31D(temperatureChangeNotificationThreshold: 0.1F,
            humidityChangeNotificationThreshold: 1.0F);

        // Hook up the two interrupt handlers to display the changes in
        // temperature and humidity.
        sht31d.HumidityChanged += (s, e) =>
        {
            Console.WriteLine("Current humidity: " + e.CurrentValue.ToString("f2"));
        };

        sht31d.TemperatureChanged += (s, e) =>
        {
            Console.WriteLine("Current temperature: " + e.CurrentValue.ToString("f2"));
        };

        // Main program loop can now go to sleep as the work
        // is being performed by the interrupt handlers.
        Thread.Sleep(Timeout.Infinite);
    }
}

Polling Mode

The application below polls the sensor every 1000 milliseconds and displays the temperature and humidity on the debug console:

public class MeadowApp : App<F7Micro, MeadowApp>
{
    public MeadowApp()
    {
        SHT31D sht31d = new SHT31D(updateInterval: 0);

        Console.WriteLine("SHT31D Temperature / Humidity Test");

        while (true)
        {
            sht31d.Update();
            Console.WriteLine("Temperature: " + sht31d.Temperature.ToString("f2") + ", Humidity: " + sht31d.Humidity.ToString("f2"));
            Thread.Sleep(1000);
        }
    }
}

Wiring Example

The SHT31D breakout board from Adafruit is supplied with pull-up resistors installed on the SCL and SDA lines.

The ADR line is tied low giving and I2C address of 0x44. This address line can also be tied high and in this case the I2C address is 0x45.

Characteristic	Locus
Inheritance	System.Object > Sht31D
Implements	IAtmosphericSensor ITemperatureSensor IHumiditySensor
Namespace	Meadow.Foundation.Sensors.Atmospheric
Assembly	Sht31D.dll

Syntax

public class Sht31D : FilterableObservableBase<AtmosphericConditionChangeResult, AtmosphericConditions>, IAtmosphericSensor, ITemperatureSensor, IHumiditySensor

Constructors

Sht31D(II2cBus, Byte)

Create a new SHT31D object.

Declaration

public Sht31D(II2cBus i2cBus, byte address = 68)

Parameters

Type	Name	Description
II2cBus	i2cBus	I2cBus (0-1000 KHz).
System.Byte	address	Sensor address (should be 0x44 or 0x45).

Properties

Conditions

The AtmosphericConditions from the last reading.

Declaration

public AtmosphericConditions Conditions { get; protected set; }

Property Value

Type	Description
AtmosphericConditions

Humidity

The humidity, in percent relative humidity, from the last reading..

Declaration

public float Humidity { get; }

Property Value

Type	Description
System.Single

IsSampling

Gets a value indicating whether the analog input port is currently sampling the ADC. Call StartSampling() to spin up the sampling process.

Declaration

public bool IsSampling { get; protected set; }

Property Value

Type	Description
System.Boolean	true if sampling; otherwise, false.

Temperature

The temperature, in degrees celsius (°C), from the last reading.

Declaration

public float Temperature { get; }

Property Value

Type	Description
System.Single

Methods

RaiseChangedAndNotify(AtmosphericConditionChangeResult)

Declaration

protected void RaiseChangedAndNotify(AtmosphericConditionChangeResult changeResult)

Parameters

Type	Name	Description
AtmosphericConditionChangeResult	changeResult

Read()

Convenience method to get the current sensor readings. For frequent reads, use StartSampling() and StopSampling() in conjunction with the SampleBuffer.

Declaration

public Task<AtmosphericConditions> Read()

Returns

Type	Description
System.Threading.Tasks.Task<AtmosphericConditions>

StartUpdating(Int32)

Declaration

public void StartUpdating(int standbyDuration = 1000)

Parameters

Type	Name	Description
System.Int32	standbyDuration

StopUpdating()

Stops sampling the temperature.

Declaration

public void StopUpdating()

Update()

Get a reading from the sensor and set the Temperature and Humidity properties.

Declaration

public void Update()

Events

Updated

Declaration

public event EventHandler<AtmosphericConditionChangeResult> Updated

Event Type

Type	Description
System.EventHandler<AtmosphericConditionChangeResult>