Remarks

HTU21D
Status
Source code	GitHub
NuGet package

The HTU21D is a low-cost, easy to use, highly accurate, digital humidity and temperature sensor controlled via the I2C bus.

Code Example

public class MeadowApp : App<F7Micro, MeadowApp>
{
    Htu21d sensor;

    public MeadowApp()
    {
        sensor = new Htu21d(Device.CreateI2cBus(400));

        sensor.Updated += Sensor_Updated;

        sensor.StartUpdating(1000);
    }

    private 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

Wiring Example

To wire a HTU21D to your Meadow board, connect the following:

HTU21D	Meadow Pin
GND	GND
SCL	D08 (SCL)
SDA	D07 (SDA)
VCC	3V3

It should look like the following diagram:

Characteristic	Locus
Inheritance	System.Object > Htu21d
Implements	IAtmosphericSensor ITemperatureSensor IHumiditySensor
Namespace	Meadow.Foundation.Sensors.Atmospheric
Assembly	Htu21d.dll

Syntax

public class Htu21d : FilterableChangeObservableBase<AtmosphericConditionChangeResult, AtmosphericConditions>, IAtmosphericSensor, ITemperatureSensor, IHumiditySensor

Constructors

Htu21d(II2cBus, Byte)

Create a new Htu21d temperature and humidity sensor.

Declaration

public Htu21d(II2cBus i2cBus, byte address = 64)

Parameters

Type	Name	Description
II2cBus	i2cBus	I2CBus (default to 100 KHz).
System.Byte	address	Sensor address (default to 0x40).

Fields

htu21d

HTD21D(F) is an I2C device.

Declaration

protected readonly II2cPeripheral htu21d

Field Value

Type	Description
II2cPeripheral

Properties

Conditions

The AtmosphericConditions from the last reading.

Declaration

public AtmosphericConditions Conditions { get; protected set; }

Property Value

Type	Description
AtmosphericConditions

DEFAULT_SPEED

Declaration

public int DEFAULT_SPEED { get; }

Property Value

Type	Description
System.Int32

FirmwareRevision

Firmware revision of the sensor.

Declaration

public byte FirmwareRevision { get; }

Property Value

Type	Description
System.Byte

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 sensor is currently in a sampling loop. 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.

SerialNumber

Serial number of the device.

Declaration

public ulong SerialNumber { get; }

Property Value

Type	Description
System.UInt64

Temperature

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

Declaration

public float Temperature { get; }

Property Value

Type	Description
System.Single

Methods

Heater(Boolean)

Turn the heater on or off.

Declaration

public void Heater(bool onOrOff)

Parameters

Type	Name	Description
System.Boolean	onOrOff	Heater status, true = turn heater on, false = turn heater off.

Initialize()

Declaration

protected void Initialize()

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>

ReadSensor()

Declaration

protected Task<AtmosphericConditions> ReadSensor()

Returns

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

Reset()

Reset the sensor and take a fresh reading.

Declaration

public void Reset()

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()

Events

Updated

Declaration

public event EventHandler<AtmosphericConditionChangeResult> Updated

Event Type

Type	Description
System.EventHandler<AtmosphericConditionChangeResult>