Remarks

LinearHallEffectTachometer
Status	Not Tested
Source code	GitHub
NuGet package

A Hall effect sensor is a device that is used to measure the magnitude of a magnetic field. Its output voltage is directly proportional to the magnetic field strength through it. These sensors are commonly used for proximity sensing, positioning, speed detection, and current sensing applications.

Frequently, a Hall sensor is combined with threshold detection so that it acts as and is called a switch. Commonly seen in industrial applications such as the pictured pneumatic cylinder, they are also used in consumer equipment; for example some computer printers use them to detect missing paper and open covers. They can also be used in computer keyboards, an application that requires ultra-high reliability.

Hall sensors are commonly used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing, tachometers and anti-lock braking systems. They are used in brushless DC electric motors to detect the position of the permanent magnet. In the pictured wheel with two equally spaced magnets, the voltage from the sensor will peak twice for each revolution. This arrangement is commonly used to regulate the speed of disk drives.

The following example instantiates a LinearHallEffectTachometer object, and registers the RPMsChanged event handler, and it outputs the RPMs in the output console. To trigger the event of the sensor, you can place a magnet on a rotating object like a small motor, or even a fidget spinner, and make sure that the magnet passes very close to the sensor in every rotation so it picks up the electromagnetic field and it will start measuring RPMs.

Code Example

The following example prints horizontal and vertical values ranging from -1 to 1, 0 being the center position:

public class MeadowApp : App<F7Micro, MeadowApp>
{
    public MeadowApp()
    {
        LinearHallEffectTachometer hallSensor;

        public MeadowApp()
        {
            Console.Write("Initializing...");

            hallSensor = new LinearHallEffectTachometer(
                inputPort: Device.CreateDigitalInputPort(Device.Pins.D02, Meadow.Hardware.InterruptMode.EdgeRising, Meadow.Hardware.ResistorMode.InternalPullUp, 0, 10),
                type: CircuitTerminationType.CommonGround,
                numberOfMagnets: 2,
                rpmChangeNotificationThreshold: 1);
            hallSensor.RPMsChanged += HallSensorRPMsChanged;

            Console.WriteLine("done");
        }

        void HallSensorRPMsChanged(object sender, ChangeResult<float> e)
        {
            Console.WriteLine($"RPM: {e.New}");
        }
    }
}

Sample projects available on GitHub

Wiring Example

Characteristic	Locus
Inheritance	System.Object > LinearHallEffectTachometer
Namespace	Meadow.Foundation.Sensors.HallEffect
Assembly	Meadow.Foundation.dll

Syntax

public class LinearHallEffectTachometer : object

Constructors

LinearHallEffectTachometer(IDigitalInputController, IPin, CircuitTerminationType, UInt16, Single)

LinearHallEffectTachometer driver

Declaration

public LinearHallEffectTachometer(IDigitalInputController device, IPin inputPin, CircuitTerminationType type = CircuitTerminationType.CommonGround, ushort numberOfMagnets = null, float rpmChangeNotificationThreshold = 1F)

Parameters

Type	Name	Description
IDigitalInputController	device	IDigitalInputController to create digital input port
IPin	inputPin
CircuitTerminationType	type
System.UInt16	numberOfMagnets
System.Single	rpmChangeNotificationThreshold

LinearHallEffectTachometer(IDigitalInputPort, CircuitTerminationType, UInt16, Single)

LinearHallEffectTachometer driver

Declaration

public LinearHallEffectTachometer(IDigitalInputPort inputPort, CircuitTerminationType type = CircuitTerminationType.CommonGround, ushort numberOfMagnets = null, float rpmChangeNotificationThreshold = 1F)

Parameters

Type	Name	Description
IDigitalInputPort	inputPort
CircuitTerminationType	type
System.UInt16	numberOfMagnets
System.Single	rpmChangeNotificationThreshold

Fields

lastNotifiedRPMs

Last notified RPM value

Declaration

protected float lastNotifiedRPMs

Field Value

Type	Description
System.Single

numberOfReads

Number of reads

Declaration

protected ushort numberOfReads

Field Value

Type	Description
System.UInt16

revolutionTimeStart

Revolution start time

Declaration

protected DateTime revolutionTimeStart

Field Value

Type	Description
DateTime

rpms

Revolutions pers minute

Declaration

protected float rpms

Field Value

Type	Description
System.Single

Properties

InputPort

Input port for the tachometer

Declaration

protected IDigitalInputPort InputPort { get; set; }

Property Value

Type	Description
IDigitalInputPort

NumberOfMagnets

Returns number of magnets of the sensor.

Declaration

public ushort NumberOfMagnets { get; }

Property Value

Type	Description
System.UInt16

RPMChangeNotificationThreshold

Any changes to the RPMs that are greater than the RPM change threshold will cause an event to be raised when the instance is set to update automatically.

Declaration

public float RPMChangeNotificationThreshold { get; set; }

Property Value

Type	Description
System.Single

RPMs

Returns number of revolutions per minute.

Declaration

public int RPMs { get; }

Property Value

Type	Description
System.Int32

Methods

OnRaiseRPMChanged()

Notify when RPMs change

Declaration

protected void OnRaiseRPMChanged()

Events

RPMsChanged

Event raised when the RPM change is greater than the RPMChangeNotificationThreshold value.

Declaration

public event EventHandler<ChangeResult<float>> RPMsChanged

Event Type

Type	Description
EventHandler<ChangeResult<System.Single>>