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 MeadowApp()
{
    Console.WriteLine("Initializing...");

    capacitive = new Capacitive(
        analogPort: Device.CreateAnalogInputPort(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 => {
            // the first time through, old will be null.
            string oldValue = (result.Old is { } old) ? $"{old:n2}" : "n/a"; // C# 8 pattern matching
            Console.WriteLine($"Subscribed - " +
                $"new: {result.New}, " +
                $"old: {oldValue}");
        },
        filter: null
    );
    capacitive.Subscribe(consumer);

    // classical .NET events can also be used:
    capacitive.HumidityUpdated += (sender, result) =>
    {   // the first time through, old will be null.
        string oldValue = (result.Old is { } old) ? $"{old:n2}" : "n/a"; // C# 8 pattern matching
        Console.WriteLine($"Updated - New: {result.New}, Old: {oldValue}");
    };

    // Get an initial reading.
    ReadMoisture().Wait();

    // Spin up the sampling thread so that events are raised and IObservable notifications are sent.
    capacitive.StartUpdating(TimeSpan.FromSeconds(5));
}

protected async Task ReadMoisture()
{
    var moisture = await capacitive.Read();
    Console.WriteLine($"Moisture New Value { moisture }");            
}

Sample project(s) available on GitHub

Wiring Example

Characteristic	Locus
Inheritance	System.Object ObservableBase<System.Double> SensorBase<System.Double> > Capacitive
Implements	IMoistureSensor
Inherited Members	SensorBase<Double>.Updated SensorBase<Double>.samplingLock SensorBase<Double>.SamplingTokenSource SensorBase<Double>.Conditions SensorBase<Double>.IsSampling SensorBase<Double>.UpdateInterval SensorBase<Double>.RaiseEventsAndNotify(IChangeResult<>) SensorBase<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 : SensorBase<double>, IMoistureSensor

Constructors

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

Creates a Capacitive soil moisture sensor object with the specified analog pin and a IO device.

Declaration

public Capacitive(IAnalogInputController device, IPin analogPin, Voltage? minimumVoltageCalibration, Voltage? maximumVoltageCalibration, int sampleCount = 5, int sampleIntervalMs = 40)

Parameters

Type	Name	Description
IAnalogInputController	device	The IAnalogInputController to create the port on.
IPin	analogPin	Analog pin the temperature sensor is connected to.
System.Nullable<Voltage>	minimumVoltageCalibration
System.Nullable<Voltage>	maximumVoltageCalibration
System.Int32	sampleCount	How many samples to take during a given reading. These are automatically averaged to reduce noise.
System.Int32	sampleIntervalMs	The time, in milliseconds, to wait in between samples during a reading.

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

Creates a Capacitive soil moisture sensor object with the especified AnalogInputPort.

Declaration

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

Parameters

Type	Name	Description
IAnalogInputPort	analogPort
System.Nullable<Voltage>	minimumVoltageCalibration
System.Nullable<Voltage>	maximumVoltageCalibration

Properties

AnalogInputPort

Returns the analog input port

Declaration

public IAnalogInputPort AnalogInputPort { get; protected set; }

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

RaiseChangedAndNotify(IChangeResult<Double>)

Declaration

protected void RaiseChangedAndNotify(IChangeResult<double> changeResult)

Parameters

Type	Name	Description
IChangeResult<System.Double>	changeResult

ReadSensor()

Declaration

protected override Task<double> ReadSensor()

Returns

Type	Description
Task<System.Double>

Overrides

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

StartUpdating(TimeSpan)

Starts continuously sampling the sensor.

This method also starts raising Updated events and IObservable subscribers getting notified. Use the standbyDuration parameter to specify how often events and notifications are raised/sent.

Declaration

public void StartUpdating(TimeSpan updateInterval)

Parameters

Type	Name	Description
TimeSpan	updateInterval	A TimeSpan that specifies how long to wait between readings. This value influences how often *Updated events are raised and IObservable consumers are notified. The default is 5 seconds.

StopUpdating()

Stops sampling the sensor.

Declaration

public void StopUpdating()

VoltageToMoisture(Voltage)

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>>