Remarks

Capacitive
Status
Source code	GitHub
NuGet package

Capacitive Soil Moisture sensor is a simple breakout for measuring the moisture in soil and similar materials. This sensor measures moisture levels by capacitive sensing, rather then resistive sensing like other types of moisture sensor such as the FC-28.

Capacitive sensing means measuring the dielectrum that is formed by the soil and the water is the most important factor that forms the dielectrum. Even though this kind of sensor might be a little pricier, it is made of corrosion resistant material giving it a longer service of life than a resistive sensor.

The following example shows how read the soil moisture every second:

public class MeadowApp : App<F7Micro, MeadowApp>
{
    Capacitive _Capacitive;

    public MeadowApp()
    {
        // create a new Capacitive sensor object connected to analog pin A01
        _Capacitive = new Capacitive(Device.Pins.A01);

        Run();
    }

    async Task Run()
    {
        while (true)
        {
            float moisture = await _Capacitive.Read();
            Console.WriteLine($"Moisture: {0}", moisture);
            Thread.Sleep(1000);
        }
    }
}

Sample projects available on GitHub

Code Example

Capacitive capacitive;

public override Task Initialize()
{
    Resolver.Log.Info("Initialize...");

    capacitive = new Capacitive(
        Device.Pins.A00,
        minimumVoltageCalibration: new Voltage(2.84f),
        maximumVoltageCalibration: new Voltage(1.63f)
    );

    // Example that uses an IObservable subscription to only be notified when the humidity changes by filter defined.
    var consumer = Capacitive.CreateObserver(
        handler: result =>
        {
            string oldValue = (result.Old is { } old) ? $"{old:n2}" : "n/a"; // C# 8 pattern matching
            Resolver.Log.Info($"Subscribed - " +
                $"new: {result.New}, " +
                $"old: {oldValue}");
        },
        filter: null
    );
    capacitive.Subscribe(consumer);

    // classical .NET events can also be used:
    capacitive.HumidityUpdated += (sender, result) =>
    {
        string oldValue = (result.Old is { } old) ? $"{old:n2}" : "n/a"; // C# 8 pattern matching
        Resolver.Log.Info($"Updated - New: {result.New}, Old: {oldValue}");
    };

    //==== One-off reading use case/pattern
    ReadSensor().Wait();

    capacitive.StartUpdating(TimeSpan.FromMilliseconds(1000));

    return Task.CompletedTask;
}

protected async Task ReadSensor()
{
    var humidity = await capacitive.Read();
    Resolver.Log.Info($"Initial humidity: {humidity:N2}C");
}

Sample project(s) available on GitHub

Wiring Example

Characteristic	Locus
Inheritance	System.Object ObservableBase<System.Double> SamplingSensorBase<System.Double> > Capacitive
Implements	ISamplingSensor<System.Double> IMoistureSensor
Inherited Members	SamplingSensorBase<Double>.samplingLock SamplingSensorBase<Double>.Updated SamplingSensorBase<Double>.SamplingTokenSource SamplingSensorBase<Double>.Conditions SamplingSensorBase<Double>.IsSampling SamplingSensorBase<Double>.UpdateInterval SamplingSensorBase<Double>.RaiseEventsAndNotify(IChangeResult<>) SamplingSensorBase<Double>.Read() ObservableBase<Double>.observers ObservableBase<Double>.NotifyObservers(IChangeResult<>) Meadow.Foundation.ObservableBase<System.Double>.Subscribe(IObserver<>) Meadow.Foundation.ObservableBase<System.Double>.CreateObserver(Action<>, System.Nullable<Predicate<IChangeResult<UNIT>>>)
Namespace	Meadow.Foundation.Sensors.Moisture
Assembly	Capacitive.dll

Syntax

public class Capacitive : SamplingSensorBase<double>, ISamplingSensor<double>, IMoistureSensor

Constructors

Capacitive(IAnalogInputPort, Nullable<Voltage>, Nullable<Voltage>)

Creates a Capacitive soil moisture sensor object with the especified AnalogInputPort

Declaration

public Capacitive(IAnalogInputPort analogInputPort, Voltage? minimumVoltageCalibration, Voltage? maximumVoltageCalibration)

Parameters

Type	Name	Description
IAnalogInputPort	analogInputPort	The port for the analog input pin
System.Nullable<Voltage>	minimumVoltageCalibration	Minimum calibration voltage
System.Nullable<Voltage>	maximumVoltageCalibration	Maximum calibration voltage

Capacitive(IPin, Nullable<Voltage>, Nullable<Voltage>, Int32, Nullable<TimeSpan>)

Declaration

public Capacitive(IPin analogInputPin, Voltage? minimumVoltageCalibration, Voltage? maximumVoltageCalibration, int sampleCount = 5, TimeSpan? sampleInterval = null)

Parameters

Type	Name	Description
IPin	analogInputPin
System.Nullable<Voltage>	minimumVoltageCalibration
System.Nullable<Voltage>	maximumVoltageCalibration
System.Int32	sampleCount
System.Nullable<TimeSpan>	sampleInterval

Properties

AnalogInputPort

Returns the analog input port

Declaration

protected IAnalogInputPort AnalogInputPort { get; }

Property Value

Type	Description
IAnalogInputPort

MaximumVoltageCalibration

Voltage value of most moist soil. Default of 3.3V.

Declaration

public Voltage MaximumVoltageCalibration { get; set; }

Property Value

Type	Description
Voltage

MinimumVoltageCalibration

Voltage value of most dry soil. Default of 0V.

Declaration

public Voltage MinimumVoltageCalibration { get; set; }

Property Value

Type	Description
Voltage

Moisture

Last value read from the moisture sensor.

Declaration

public double? Moisture { get; protected set; }

Property Value

Type	Description
System.Nullable<System.Double>

Methods

RaiseEventsAndNotify(IChangeResult<Double>)

Raise change events for subscribers

Declaration

protected override void RaiseEventsAndNotify(IChangeResult<double> changeResult)

Parameters

Type	Name	Description
IChangeResult<System.Double>	changeResult	The change result with the current sensor data

ReadSensor()

Reads data from the sensor

Declaration

protected override Task<double> ReadSensor()

Returns

Type	Description
Task<System.Double>	The latest sensor reading

Overrides

Meadow.Foundation.SamplingSensorBase<System.Double>.ReadSensor()

StartUpdating(Nullable<TimeSpan>)

Starts continuously sampling the sensor

Declaration

public override void StartUpdating(TimeSpan? updateInterval)

Parameters

Type	Name	Description
System.Nullable<TimeSpan>	updateInterval

StopUpdating()

Stops sampling the sensor

Declaration

public override void StopUpdating()

Overrides

Meadow.Foundation.SamplingSensorBase<System.Double>.StopUpdating()

VoltageToMoisture(Voltage)

Converts voltage to moisture value, ranging from 0 (most dry) to 1 (most wet)

Declaration

protected double VoltageToMoisture(Voltage voltage)

Parameters

Type	Name	Description
Voltage	voltage

Returns

Type	Description
System.Double

Events

HumidityUpdated

Raised when a new sensor reading has been made. To enable, call StartUpdating().

Declaration

public event EventHandler<IChangeResult<double>> HumidityUpdated

Event Type

Type	Description
EventHandler<IChangeResult<System.Double>>