Remarks

RotaryEncoder
Status
Source code GitHub
NuGet package

Rotary encoders are similar in form factor to potentiometers, but instead of modifying a voltage output, they send a digital signal encoded using Gray Code when rotated that can be decoded to ascertain the direction of turn.

Rotary encoders have several advantages over potentiometers as input devices, namely:

  • They’re more power efficient; they only use power when actuated.
  • They’re not rotation-bound; they spin infinitely in either direction.
  • Many rotary encoders also have a built-in pushbutton.

Rotary encoders are used almost exclusively on things like volume knobs on stereos.

And because they’re not rotation bound, they are especially useful in the case in which a device might have multiple inputs to control the same parameter. For instance, a stereo’s volume might be controlled via a knob and a remote control. If a potentiometer were used for the volume knob, then the actual volume could get out of synch with the apparent value on the potentiometer when the volume was changed via the remote.

For this reason, rotary encoders are particularly useful in connected things, in which parameters might be controlled remotely.

Two-bit Gray Code

This rotary encoder driver works with most rotary encoders which return a two-bit Gray Code which is the minimum number of bits necessary to describe direction. Most common rotary encoders use two-bit Gray Code, so this driver should work with most common rotary encoders.

The following example uses a rotary encoder to adjust the brightness of a PwmLed.

public class MeadowApp : App<F7Micro, MeadowApp>
{
    protected RotaryEncoder _rotary = null;
    protected PwmLed _led = null;
    // how much to change the brightness per rotation step. 
    // 0.05 = 20 clicks to 100%
    protected float _brightnessStepChange = 0.05F; 

    public MeadowApp()
    {
        // instantiate our peripherals
        _rotary = new RotaryEncoder(Device.Pins.D07, Device.Pins.D09);
        _rotary.Rotated += RotaryRotated;

        _led = new PwmLed(Device.Pins.D12, TypicalForwardVoltage.Red);
    }

    protected void RotaryRotated(object sender, RotaryTurnedEventArgs e)
    {
        // if clockwise, turn it up! clamp to 1, so we don't go over.
        if (e.Direction == RotationDirection.Clockwise)
        {
            if(_led.Brightness >= 1) 
            {
                return;
            } 
            else 
            {
                _led.SetBrightness((_led.Brightness + 
                    _brightnessStepChange).Clamp(0,1));
            }
        } 
        else // otherwise, turn it down. clamp to 0 so we don't go below. 
        { 
            if (_led.Brightness <= 0) 
            {
                return;
            } 
            else 
            {
                _led.SetBrightness((_led.Brightness - 
                    _brightnessStepChange).Clamp(0,1));
            }
        }
    }
}

Sample projects available on GitHub

Wiring Example

Note, depending on your encoder, it may have a common/ground (gnd) or (-) leg in addition to the positive (+) leg. If it does, make sure to wire it to ground.

The a-phase pin may be labeled (A), (CLK) or other. If the Rotated event is indicating the wrong direction, simply switch the a-phase and b-phase pins.

Characteristic Locus
Inheritance System.Object > RotaryEncoder > RotaryEncoderWithButton
Namespace Meadow.Foundation.Sensors.Rotary
Assembly Meadow.Foundation.dll

Syntax

public class RotaryEncoder : IRotaryEncoder

Constructors

RotaryEncoder(IDigitalInputPort, IDigitalInputPort)

Instantiate a new RotaryEncoder on the specified ports

Declaration
public RotaryEncoder(IDigitalInputPort aPhasePort, IDigitalInputPort bPhasePort)

Parameters

Type Name Description
IDigitalInputPort aPhasePort
IDigitalInputPort bPhasePort

RotaryEncoder(IIODevice, IPin, IPin)

Instantiate a new RotaryEncoder on the specified pins.

Declaration
public RotaryEncoder(IIODevice device, IPin aPhasePin, IPin bPhasePin)

Parameters

Type Name Description
IIODevice device
IPin aPhasePin
IPin bPhasePin

Fields

_aTriggered

Signals that the aPhase has triggered an event

Declaration
protected bool _aTriggered

Field Value

Type Description
System.Boolean

_processing

Whether or not we're processing the gray code (encoding of rotational information)

Declaration
protected bool _processing

Field Value

Type Description
System.Boolean

_results

Two sets of gray code results to determine direction of rotation. Note that this is no longer used in the seperate event logic

Declaration
protected TwoBitGrayCode[] _results

Field Value

Type Description
TwoBitGrayCode[]

Properties

APhasePort

Returns the pin connected to the A-phase output on the rotary encoder.

Declaration
public IDigitalInputPort APhasePort { get; }

Property Value

Type Description
IDigitalInputPort

BPhasePort

Returns the pin connected to the B-phase output on the rotary encoder.

Declaration
public IDigitalInputPort BPhasePort { get; }

Property Value

Type Description
IDigitalInputPort

Methods

OnRaiseRotationEvent(RotationDirection)

Invokes the RotaryTurnedEventHandler, passing the direction in the RotaryTurnedEventArgs

Declaration
protected void OnRaiseRotationEvent(RotationDirection direction)

Parameters

Type Name Description
RotationDirection direction

ProcessRotationResults()

Determines the direction of rotation when the PhasePinChanged event is triggered

Declaration
protected void ProcessRotationResults()

Events

Rotated

Raised when the rotary encoder is rotated and returns a RotaryTurnedEventArgs object which describes the direction of rotation.

Declaration
public event RotaryTurnedEventHandler Rotated

Event Type

Type Description
RotaryTurnedEventHandler