Bug/pot

Source/Meadow.Foundation.Core/Sensors/Potentiometer/Potentiometer.cs

@@ -10,9 +10,7 @@
 /// </summary>
 public class Potentiometer : IPotentiometer, IDisposable
 {
-    /// <inheritdoc/>
-    public event EventHandler<IChangeResult<Resistance>>? Changed;
-
+    private EventHandler<IChangeResult<Resistance>>? changedEvent;
     private IAnalogInputPort inputPort;
     private Voltage referenceVoltage;
     private bool portCreated = false;
@@ -33,7 +31,7 @@
     /// </summary>
     /// <param name="inputPort">The input port to read the potentiometer value from.</param>
     /// <param name="maxResistance">The maximum resistance value of the potentiometer.</param>
     public Potentiometer(IAnalogInputPort inputPort, Resistance maxResistance)
     {
         Initialize(inputPort, maxResistance, inputPort.ReferenceVoltage);
         portCreated = false;
@@ -66,19 +64,40 @@
         portCreated = true;
     }
 
+    /// <inheritdoc/>
+    public event EventHandler<IChangeResult<Resistance>>? Changed
+    {
+        add
+        {
+            if (changedEvent == null || changedEvent?.GetInvocationList().Length == 0)
+            {
+                inputPort.Updated += OnInputPortUpdated;
+                inputPort.StartUpdating();
+            }
+            changedEvent += value;
+        }
+        remove
+        {
+            changedEvent -= value;
+            if (changedEvent?.GetInvocationList().Length == 0)
+            {
+                inputPort.StopUpdating();
+                inputPort.Updated -= OnInputPortUpdated;
+            }
+        }
+    }
+
     private void Initialize(IAnalogInputPort inputPort, Resistance maxResistance, Voltage refereceVoltage)
     {
         this.inputPort = inputPort;
         MaxResistance = maxResistance;
         referenceVoltage = inputPort.ReferenceVoltage;
-
-        inputPort.Updated += OnInputPortUpdated;
     }
 
     private void OnInputPortUpdated(object sender, IChangeResult<Voltage> e)
     {
         var newValue = new Resistance(MaxResistance.Ohms * e.New.Volts / referenceVoltage.Volts);
-        Changed?.Invoke(this, new ChangeResult<Resistance>(newValue, oldValue));
+        changedEvent?.Invoke(this, new ChangeResult<Resistance>(newValue, oldValue));
         oldValue = newValue;
     }
 

Source/Meadow.Foundation.Peripherals/Sensors.Flow.HallEffect/Driver/Drivers/YfB10.cs

@@ -7,17 +7,20 @@ namespace Meadow.Peripherals.Sensors.Flow;
 /// </summary>
 /// <remarks>
 /// Configures the sensor with its factory calibration values:
-/// - Scale factor: 7.5 Hz per L/min
+/// - Scale factor: 8.0 Hz per L/min
 /// - Offset: 4 Hz
+/// Note: Different data sheets differ on what the scale is on this device.  Adjust the constructor parameters if required.
 /// </remarks>
 public class YfB10 : HallEffectBase
 {
     /// <summary>
     /// Initializes a new instance of the YF-B10 flow sensor.
     /// </summary>
     /// <param name="pin">The digital input pin connected to the sensor's signal line.</param>
-    public YfB10(IPin pin)
-        : base(pin, 7.5, 4)
+    /// <param name="scale">The scale factor used to calculate flow. Defaults to 8.0 Hz per L/min.</param>
+    /// <param name="offset">The offset used to calculate flow.  Defaults to 4hz</param>
+    public YfB10(IPin pin, double scale = 8.0, double offset = 4)
+        : base(pin, scale, offset)
     {
     }
 }

Source/Meadow.Foundation.Peripherals/Sensors.Flow.HallEffect/Driver/HallEffectBase.cs

@@ -62,6 +62,11 @@ private VolumetricFlow CalculateFlow(Frequency frequency, double scale, double o
         // First solve for Q (L/min): F = (S * Q - O)
         // F + O = S * Q
         // Q = (F + O) / S
+        if (frequency.Hertz == 0)
+        {
+            return VolumetricFlow.Zero;
+        }
+
         double litersPerMinute = (frequency.Hertz + offset) / scale;
 
         return new VolumetricFlow(litersPerMinute, VolumetricFlow.UnitType.LitersPerMinute);