Package edu.wpi.first.wpilibj

Class Encoder

java.lang.Object
edu.wpi.first.wpilibj.Encoder
All Implemented Interfaces:
Sendable, CounterBase, AutoCloseable
public class Encoder
extends Object
implements CounterBase, Sendable, AutoCloseable
Class to read quadrature encoders.

Quadrature encoders are devices that count shaft rotation and can sense direction. The output of the Encoder class is an integer that can count either up or down, and can go negative for reverse direction counting. When creating Encoders, a direction can be supplied that inverts the sense of the output to make code more readable if the encoder is mounted such that forward movement generates negative values. Quadrature encoders have two digital outputs, an A Channel and a B Channel, that are out of phase with each other for direction sensing.

All encoders will immediately start counting - reset() them if you need them to be zeroed before use.

  • Field Details

  • Constructor Details

    • Encoder

      public Encoder​(int channelA, int channelB, boolean reverseDirection)
      Encoder constructor. Construct a Encoder given a and b channels.

      The encoder will start counting immediately.

      Parameters:
      channelA - The 'a' channel DIO channel. 0-9 are on-board, 10-25 are on the MXP port
      channelB - The 'b' channel DIO channel. 0-9 are on-board, 10-25 are on the MXP port
      reverseDirection - represents the orientation of the encoder and inverts the output values if necessary so forward represents positive values.

    • Encoder

      public Encoder​(int channelA, int channelB)
      Encoder constructor. Construct an Encoder given a and b channels.

      The encoder will start counting immediately.

      Parameters:
      channelA - The a channel digital input channel.
      channelB - The b channel digital input channel.

    • Encoder

      public Encoder​(int channelA, int channelB, boolean reverseDirection, CounterBase.EncodingType encodingType)
      Encoder constructor. Construct an Encoder given a and b channels.

      The encoder will start counting immediately.

      Parameters:
      channelA - The a channel digital input channel.
      channelB - The b channel digital input channel.
      reverseDirection - represents the orientation of the encoder and inverts the output values if necessary so forward represents positive values.
      encodingType - either k1X, k2X, or k4X to indicate 1X, 2X or 4X decoding. If 4X is selected, then an encoder FPGA object is used and the returned counts will be 4x the encoder spec'd value since all rising and falling edges are counted. If 1X or 2X are selected, then a counter object will be used and the returned value will either exactly match the spec'd count or be double (2x) the spec'd count.

    • Encoder

      public Encoder​(int channelA, int channelB, int indexChannel, boolean reverseDirection)
      Encoder constructor. Construct an Encoder given a and b channels. Using an index pulse forces 4x encoding

      The encoder will start counting immediately.

      Parameters:
      channelA - The a channel digital input channel.
      channelB - The b channel digital input channel.
      indexChannel - The index channel digital input channel.
      reverseDirection - represents the orientation of the encoder and inverts the output values if necessary so forward represents positive values.

    • Encoder

      public Encoder​(int channelA, int channelB, int indexChannel)
      Encoder constructor. Construct an Encoder given a and b channels. Using an index pulse forces 4x encoding

      The encoder will start counting immediately.

      Parameters:
      channelA - The a channel digital input channel.
      channelB - The b channel digital input channel.
      indexChannel - The index channel digital input channel.

    • Encoder

      public Encoder​(DigitalSource sourceA, DigitalSource sourceB, boolean reverseDirection)
      Encoder constructor. Construct an Encoder given a and b channels as digital inputs. This is used in the case where the digital inputs are shared. The Encoder class will not allocate the digital inputs and assume that they already are counted.

      The encoder will start counting immediately.

      Parameters:
      sourceA - The source that should be used for the 'a' channel.
      sourceB - the source that should be used for the 'b' channel.
      reverseDirection - represents the orientation of the encoder and inverts the output values if necessary so forward represents positive values.

    • Encoder

      public Encoder​(DigitalSource sourceA, DigitalSource sourceB)
      Encoder constructor. Construct an Encoder given a and b channels as digital inputs. This is used in the case where the digital inputs are shared. The Encoder class will not allocate the digital inputs and assume that they already are counted.

      The encoder will start counting immediately.

      Parameters:
      sourceA - The source that should be used for the 'a' channel.
      sourceB - the source that should be used for the 'b' channel.

    • Encoder

      public Encoder​(DigitalSource sourceA, DigitalSource sourceB, boolean reverseDirection, CounterBase.EncodingType encodingType)
      Encoder constructor. Construct an Encoder given a and b channels as digital inputs. This is used in the case where the digital inputs are shared. The Encoder class will not allocate the digital inputs and assume that they already are counted.

      The encoder will start counting immediately.

      Parameters:
      sourceA - The source that should be used for the 'a' channel.
      sourceB - the source that should be used for the 'b' channel.
      reverseDirection - represents the orientation of the encoder and inverts the output values if necessary so forward represents positive values.
      encodingType - either k1X, k2X, or k4X to indicate 1X, 2X or 4X decoding. If 4X is selected, then an encoder FPGA object is used and the returned counts will be 4x the encoder spec'd value since all rising and falling edges are counted. If 1X or 2X are selected then a counter object will be used and the returned value will either exactly match the spec'd count or be double (2x) the spec'd count.

    • Encoder

      public Encoder​(DigitalSource sourceA, DigitalSource sourceB, DigitalSource indexSource, boolean reverseDirection)
      Encoder constructor. Construct an Encoder given a, b and index channels as digital inputs. This is used in the case where the digital inputs are shared. The Encoder class will not allocate the digital inputs and assume that they already are counted.

      The encoder will start counting immediately.

      Parameters:
      sourceA - The source that should be used for the 'a' channel.
      sourceB - the source that should be used for the 'b' channel.
      indexSource - the source that should be used for the index channel.
      reverseDirection - represents the orientation of the encoder and inverts the output values if necessary so forward represents positive values.

    • Encoder

      public Encoder​(DigitalSource sourceA, DigitalSource sourceB, DigitalSource indexSource)
      Encoder constructor. Construct an Encoder given a, b and index channels as digital inputs. This is used in the case where the digital inputs are shared. The Encoder class will not allocate the digital inputs and assume that they already are counted.

      The encoder will start counting immediately.

      Parameters:
      sourceA - The source that should be used for the 'a' channel.
      sourceB - the source that should be used for the 'b' channel.
      indexSource - the source that should be used for the index channel.

  • Method Details

    • getFPGAIndex

      public int getFPGAIndex()
      Get the FPGA index of the encoder.
      Returns:
      The Encoder's FPGA index.

    • getEncodingScale

      public int getEncodingScale()
      Used to divide raw edge counts down to spec'd counts.
      Returns:
      The encoding scale factor 1x, 2x, or 4x, per the requested encoding type.

    • close

      public void close()
      Specified by:
      close in interface AutoCloseable

    • getRaw

      public int getRaw()
      Gets the raw value from the encoder. The raw value is the actual count unscaled by the 1x, 2x, or 4x scale factor.
      Returns:
      Current raw count from the encoder

    • get

      public int get()
      Gets the current count. Returns the current count on the Encoder. This method compensates for the decoding type.
      Specified by:
      get in interface CounterBase
      Returns:
      Current count from the Encoder adjusted for the 1x, 2x, or 4x scale factor.

    • reset

      public void reset()
      Reset the Encoder distance to zero. Resets the current count to zero on the encoder.
      Specified by:
      reset in interface CounterBase

    • getPeriod

      @Deprecated public double getPeriod()
      Deprecated.
      Use getRate() in favor of this method.
      Returns the period of the most recent pulse. Returns the period of the most recent Encoder pulse in seconds. This method compensates for the decoding type.

      Warning: This returns unscaled periods. Use getRate() for rates that are scaled using the value from setDistancePerPulse().

      Specified by:
      getPeriod in interface CounterBase
      Returns:
      Period in seconds of the most recent pulse.

    • setMaxPeriod

      @Deprecated public void setMaxPeriod​(double maxPeriod)
      Deprecated.
      Use setMinRate() in favor of this method. This takes unscaled periods and setMinRate() scales using value from setDistancePerPulse().
      Sets the maximum period for stopped detection. Sets the value that represents the maximum period of the Encoder before it will assume that the attached device is stopped. This timeout allows users to determine if the wheels or other shaft has stopped rotating. This method compensates for the decoding type.
      Specified by:
      setMaxPeriod in interface CounterBase
      Parameters:
      maxPeriod - The maximum time between rising and falling edges before the FPGA will report the device stopped. This is expressed in seconds.

    • getStopped

      public boolean getStopped()
      Determine if the encoder is stopped. Using the MaxPeriod value, a boolean is returned that is true if the encoder is considered stopped and false if it is still moving. A stopped encoder is one where the most recent pulse width exceeds the MaxPeriod.
      Specified by:
      getStopped in interface CounterBase
      Returns:
      True if the encoder is considered stopped.

    • getDirection

      public boolean getDirection()
      The last direction the encoder value changed.
      Specified by:
      getDirection in interface CounterBase
      Returns:
      The last direction the encoder value changed.

    • getDistance

      public double getDistance()
      Get the distance the robot has driven since the last reset as scaled by the value from setDistancePerPulse(double).
      Returns:
      The distance driven since the last reset

    • getRate

      public double getRate()
      Get the current rate of the encoder. Units are distance per second as scaled by the value from setDistancePerPulse().
      Returns:
      The current rate of the encoder.

    • setMinRate

      public void setMinRate​(double minRate)
      Set the minimum rate of the device before the hardware reports it stopped.
      Parameters:
      minRate - The minimum rate. The units are in distance per second as scaled by the value from setDistancePerPulse().

    • setDistancePerPulse

      public void setDistancePerPulse​(double distancePerPulse)
      Set the distance per pulse for this encoder. This sets the multiplier used to determine the distance driven based on the count value from the encoder. Do not include the decoding type in this scale. The library already compensates for the decoding type. Set this value based on the encoder's rated Pulses per Revolution and factor in gearing reductions following the encoder shaft. This distance can be in any units you like, linear or angular.
      Parameters:
      distancePerPulse - The scale factor that will be used to convert pulses to useful units.

    • getDistancePerPulse

      public double getDistancePerPulse()
      Get the distance per pulse for this encoder.
      Returns:
      The scale factor that will be used to convert pulses to useful units.

    • setReverseDirection

      public void setReverseDirection​(boolean reverseDirection)
      Set the direction sensing for this encoder. This sets the direction sensing on the encoder so that it could count in the correct software direction regardless of the mounting.
      Parameters:
      reverseDirection - true if the encoder direction should be reversed

    • setSamplesToAverage

      public void setSamplesToAverage​(int samplesToAverage)
      Set the Samples to Average which specifies the number of samples of the timer to average when calculating the period. Perform averaging to account for mechanical imperfections or as oversampling to increase resolution.
      Parameters:
      samplesToAverage - The number of samples to average from 1 to 127.

    • getSamplesToAverage

      public int getSamplesToAverage()
      Get the Samples to Average which specifies the number of samples of the timer to average when calculating the period. Perform averaging to account for mechanical imperfections or as oversampling to increase resolution.
      Returns:
      SamplesToAverage The number of samples being averaged (from 1 to 127)

    • setIndexSource

      public final void setIndexSource​(int channel)
      Set the index source for the encoder. When this source is activated, the encoder count automatically resets.
      Parameters:
      channel - A DIO channel to set as the encoder index

    • setIndexSource

      public final void setIndexSource​(DigitalSource source)
      Set the index source for the encoder. When this source is activated, the encoder count automatically resets.
      Parameters:
      source - A digital source to set as the encoder index

    • setIndexSource

      public final void setIndexSource​(int channel, Encoder.IndexingType type)
      Set the index source for the encoder. When this source rises, the encoder count automatically resets.
      Parameters:
      channel - A DIO channel to set as the encoder index
      type - The state that will cause the encoder to reset

    • setIndexSource

      public final void setIndexSource​(DigitalSource source, Encoder.IndexingType type)
      Set the index source for the encoder. When this source rises, the encoder count automatically resets.
      Parameters:
      source - A digital source to set as the encoder index
      type - The state that will cause the encoder to reset

    • setSimDevice

      public void setSimDevice​(SimDevice device)
      Indicates this input is used by a simulated device.
      Parameters:
      device - simulated device handle

    • getDecodingScaleFactor

      public double getDecodingScaleFactor()
      Gets the decoding scale factor for scaling raw values to full counts.
      Returns:
      decoding scale factor

    • initSendable

      public void initSendable​(SendableBuilder builder)
      Description copied from interface: Sendable
      Initializes this Sendable object.
      Specified by:
      initSendable in interface Sendable
      Parameters:
      builder - sendable builder