Class PwmLed | Meadow.Foundation API website

Remarks

PwmLed
Status
Source code	GitHub
NuGet package

*PwmLed represents an LED whose voltage (and brightness) is controlled by the duty-cycle of a PWM signal. It can be used both with Leds that have been current limited with in-series resistors, or Leds without resistors.

Controlling an LED via a PWM signal is more power efficient than using a current-limiting resistor. It also provides more control, allowing multiple grades of brightness.

To use PwmLed without a resistor, pass in the forward voltage (voltage drop) of the LED to the forwardVoltage constructor parameter, and the class will limit its output to the maximum forward voltage rating of the LED.

To use with an LED that has a resistor in series, pass 0.0 or TypicalForwardVoltage.ResistorLimited for the forwardVoltage parameter.

Code Example

PwmLedBarGraph pwmLedBarGraph;

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

    // Using an array of Pins that support PWM (D02 - D13)
    IPin[] pins =
    {
         Device.Pins.D11,
         Device.Pins.D10,
         Device.Pins.D09,
         Device.Pins.D08,
         Device.Pins.D07,
         Device.Pins.D06,
         Device.Pins.D05,
         Device.Pins.D04,
         Device.Pins.D03,
         Device.Pins.D02
    };

    pwmLedBarGraph = new PwmLedBarGraph(pins, new Voltage(2.2));

    return Task.CompletedTask;
}

public override async Task Run()
{
    Resolver.Log.Info("TestLedBarGraph...");

    float percentage = 0;

    while (true)
    {
        Resolver.Log.Info("Turning them on and off for 200ms using SetLed...");
        for (int i = 0; i < pwmLedBarGraph.Count; i++)
        {
            pwmLedBarGraph.SetLed(i, true);
            await Task.Delay(100);
            pwmLedBarGraph.SetLed(i, false);
        }

        await Task.Delay(1000);

        Resolver.Log.Info("Turning them on using Percentage...");
        while (percentage < 1)
        {
            percentage += 0.01f;
            pwmLedBarGraph.Percentage = Math.Min(1.0f, percentage);
            await Task.Delay(100);
        }

        await Task.Delay(1000);

        Resolver.Log.Info("Turning them off using Percentage...");
        while (percentage > 0)
        {
            percentage -= 0.01f;
            pwmLedBarGraph.Percentage = Math.Max(0.0f, percentage);
            await Task.Delay(100);
        }

        await Task.Delay(1000);

        Resolver.Log.Info("Blinking for 5 seconds at 500ms on/off...");
        pwmLedBarGraph.StartBlink();
        await Task.Delay(5000);
        pwmLedBarGraph.Stop();

        await Task.Delay(1000);

        Resolver.Log.Info("Bar blinking with high and low brightness for 5 seconds...");
        pwmLedBarGraph.StartBlink(TimeSpan.FromMilliseconds(200), TimeSpan.FromMilliseconds(200), 0.75f, 0.25f);
        await Task.Delay(5000);
        pwmLedBarGraph.Stop();

        await Task.Delay(1000);

        Resolver.Log.Info("Bar pulsing for 5 seconds...");
        pwmLedBarGraph.StartPulse();
        await Task.Delay(5000);
        pwmLedBarGraph.Stop();

        await Task.Delay(1000);
    }
}

Sample project(s) available on GitHub

Wiring Example

<img src="../../API_Assets/Meadow.Foundation.Leds.PwmLed/PwmLed_Fritzing.svg"

Characteristic	Locus
Inheritance	System.Object > PwmLed
Implements	IDisposable
Namespace	Meadow.Foundation.Leds
Assembly	Meadow.Foundation.dll

Syntax

public class PwmLed : IPwmLed, IDisposable

Constructors

PwmLed(IPin, Voltage, CircuitTerminationType)

Initializes a new instance PwmLed class

Declaration

public PwmLed(IPin pin, Voltage forwardVoltage, CircuitTerminationType terminationType = CircuitTerminationType.CommonGround)

Parameters

Type	Name	Description
IPin	pin	Pin
Voltage	forwardVoltage	Forward voltage
CircuitTerminationType	terminationType	Whether the other end of the LED is hooked to ground or High. Typically used for RGB Leds which can have either a common cathode, or common anode. But can also enable an LED to be reversed by inverting the PWM signal.

PwmLed(IPwmPort, Voltage, CircuitTerminationType)

Creates a new PwmLed on the specified PWM pin and limited to the appropriate voltage based on the passed forwardVoltage. Typical LED forward voltages can be found in the TypicalForwardVoltage class.

Declaration

public PwmLed(IPwmPort pwmPort, Voltage forwardVoltage, CircuitTerminationType terminationType = CircuitTerminationType.CommonGround)

Parameters

Type	Name	Description
IPwmPort	pwmPort	Port to control
Voltage	forwardVoltage	Forward voltage of led
CircuitTerminationType	terminationType	Termination type of LED

Properties

Brightness

Gets the brightness of the LED, controlled by a PWM signal, and limited by the calculated maximum voltage. Valid values are from 0 to 1, inclusive.

Declaration

public float Brightness { get; set; }

Property Value

Type	Description
System.Single

ForwardVoltage

Gets the forward voltage value

Declaration

public Voltage ForwardVoltage { get; protected set; }

Property Value

Type	Description
Voltage

IsDisposed

Is the object disposed

Declaration

public bool IsDisposed { get; }

Property Value

Type	Description
System.Boolean

IsOn

Gets or Sets the state of the LED

Declaration

public bool IsOn { get; set; }

Property Value

Type	Description
System.Boolean

Port

Gets the PwmPort

Declaration

protected IPwmPort Port { get; set; }

Property Value

Type	Description
IPwmPort

Methods

Dispose()

Dispose of the object

Declaration

public void Dispose()

Dispose(Boolean)

Dispose of the object

Declaration

protected virtual void Dispose(bool disposing)

Parameters

Type	Name	Description
System.Boolean	disposing	Is disposing

SetBrightness(Single)

Sets the LED to a specific brightness.

Declaration

public void SetBrightness(float brightness)

Parameters

Type	Name	Description
System.Single	brightness	Valid values are from 0 to 1, inclusive

StartBlink(Single, Single)

Start a Blink animation which sets the brightness of the LED alternating between a low and high brightness setting.

Declaration

public void StartBlink(float highBrightness = 1F, float lowBrightness = 0F)

Parameters

Type	Name	Description
System.Single	highBrightness
System.Single	lowBrightness

StartBlink(TimeSpan, TimeSpan, Single, Single)

Start the Blink animation which sets the brightness of the LED alternating between a low and high brightness setting, using the durations provided.

Declaration

public void StartBlink(TimeSpan onDuration, TimeSpan offDuration, float highBrightness = 1F, float lowBrightness = 0F)

Parameters

Type	Name	Description
TimeSpan	onDuration
TimeSpan	offDuration
System.Single	highBrightness
System.Single	lowBrightness

StartBlinkAsync(TimeSpan, TimeSpan, Single, Single, CancellationToken)

Start blinking the LED

Declaration

protected Task StartBlinkAsync(TimeSpan onDuration, TimeSpan offDuration, float highBrightness, float lowBrightness, CancellationToken cancellationToken)

Parameters

Type	Name	Description
TimeSpan	onDuration	on duration in ms
TimeSpan	offDuration	off duration in ms
System.Single	highBrightness	maximum brightness
System.Single	lowBrightness	minimum brightness
CancellationToken	cancellationToken	token for cancellation

Returns

Type	Description
Task

StartPulse(Single, Single)

Start the Pulse animation which gradually alternates the brightness of the LED between a low and high brightness setting.

Declaration

public void StartPulse(float highBrightness = null, float lowBrightness = 0.15F)

Parameters

Type	Name	Description
System.Single	highBrightness
System.Single	lowBrightness

StartPulse(TimeSpan, Single, Single)

Start the Pulse animation which gradually alternates the brightness of the LED between a low and high brightness setting, using the durations provided.

Declaration

public void StartPulse(TimeSpan pulseDuration, float highBrightness = null, float lowBrightness = 0.15F)

Parameters

Type	Name	Description
TimeSpan	pulseDuration
System.Single	highBrightness
System.Single	lowBrightness

StartPulseAsync(TimeSpan, Single, Single, CancellationToken)

Start pulsing the led

Declaration

protected Task StartPulseAsync(TimeSpan pulseDuration, float highBrightness, float lowBrightness, CancellationToken cancellationToken)

Parameters

Type	Name	Description
TimeSpan	pulseDuration	duration in ms
System.Single	highBrightness	maximum brightness
System.Single	lowBrightness	minimum brightness
CancellationToken	cancellationToken	token used to cancel pulse

Returns

Type	Description
Task

Stop()

Stops any running animations.

Declaration

public void Stop()