Remarks
| Htu21d | |
|---|---|
| Status |  |
| Source code | GitHub |
| Datasheet(s) | 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
Htu21d? sensor;
public override Task Initialize()
{
Resolver.Log.Info("Initializing...");
sensor = new Htu21d(Device.CreateI2cBus());
var consumer = Htu21d.CreateObserver(
handler: result =>
{
Resolver.Log.Info($"Observer: Temp changed by threshold; new temp: {result.New.Temperature?.Celsius:N2}C, old: {result.Old?.Temperature?.Celsius:N2}C");
},
filter: result =>
{
//c# 8 pattern match syntax. checks for !null and assigns var.
if (result.Old?.Temperature is { } oldTemp &&
result.Old?.Humidity is { } oldHumidity &&
result.New.Temperature is { } newTemp &&
result.New.Humidity is { } newHumidity)
{
return ((newTemp - oldTemp).Abs().Celsius > 0.5 &&
(newHumidity - oldHumidity).Percent > 0.05);
}
return false;
}
);
sensor.Subscribe(consumer);
sensor.Updated += (sender, result) =>
{
Resolver.Log.Info($" Temperature: {result.New.Temperature?.Celsius:F1}C");
Resolver.Log.Info($" Relative Humidity: {result.New.Humidity?.Percent:F1}%");
};
return Task.CompletedTask;
}
public override async Task Run()
{
if (sensor == null) { return; }
var result = await sensor.Read();
Resolver.Log.Info("Initial Readings:");
Resolver.Log.Info($" Temperature: {result.Temperature?.Celsius:F1}C");
Resolver.Log.Info($" Relative Humidity: {result.Humidity:F1}%");
sensor.StartUpdating(TimeSpan.FromSeconds(1));
}
Sample project(s) 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:
Syntax
public class Htu21d : Htux1dBase, ISamplingSensor<(Units.Temperature? Temperature, RelativeHumidity? Humidity)>, ISamplingSensor<(Units.Temperature? Temperature, RelativeHumidity? Humidity)>, IDisposable, ITemperatureSensor, IHumiditySensorConstructors
Htu21d(II2cBus, Byte, Nullable<TimeSpan>)
Create a new Htu21d temperature and humidity sensor
Declaration
public Htu21d(II2cBus i2cBus, byte address = null, TimeSpan? updateInterval = null)Parameters
| Type | Name | Description |
|---|---|---|
| II2cBus | i2cBus | I2CBus (default to 100 KHz) |
| System.Byte | address | Sensor address (default to 0x40) |
| System.Nullable<TimeSpan> | updateInterval | Update interval, defaults to 1 sec if null |
Properties
FirmwareRevision
Firmware revision of the sensor.
Declaration
public byte FirmwareRevision { get; }Property Value
| Type | Description |
|---|---|
| System.Byte |
Methods
Heater(Boolean)
Turn the heater on or off
Declaration
public void Heater(bool heaterOn)Parameters
| Type | Name | Description |
|---|---|---|
| System.Boolean | heaterOn | Heater status, true = turn heater on, false = turn heater off. |
Initialize()
Initialize HTU21D
Declaration
protected void Initialize()ReadSensor()
Reads data from the sensor
Declaration
protected override Task<(Units.Temperature? Temperature, RelativeHumidity? Humidity)> ReadSensor()Returns
| Type | Description |
|---|---|
| Task<System.ValueTuple<System.Nullable<Units.Temperature>, System.Nullable<RelativeHumidity>>> | The latest sensor reading |
Overrides
Meadow.Foundation.SamplingSensorBase<System.ValueTuple<System.Nullable<Units.Temperature>, System.Nullable<RelativeHumidity>>>.ReadSensor()