edu.wpi.first.wpilibj

Class Encoder

java.lang.Object

edu.wpi.first.wpilibj.SendableBase

edu.wpi.first.wpilibj.SensorBase

edu.wpi.first.wpilibj.Encoder

All Implemented Interfaces:

CounterBase, PIDSource, Sendable

public class Encoder
extends SensorBase
implements CounterBase, PIDSource, Sendable

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.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Encoder.IndexingType

Nested classes/interfaces inherited from interface edu.wpi.first.wpilibj.CounterBase

CounterBase.EncodingType

Field Summary

Fields

Modifier and Type	Field and Description
protected DigitalSource	m_aSource The a source.
protected DigitalSource	m_bSource The b source.
protected DigitalSource	m_indexSource The index source.

Fields inherited from class edu.wpi.first.wpilibj.SensorBase

kAnalogInputChannels, kAnalogOutputChannels, kDigitalChannels, kPCMModules, kPDPChannels, kPDPModules, kPwmChannels, kRelayChannels, kSolenoidChannels, kSystemClockTicksPerMicrosecond

Constructor Summary

Constructors

Constructor and Description
Encoder(DigitalSource sourceA, DigitalSource sourceB) Encoder constructor.
Encoder(DigitalSource sourceA, DigitalSource sourceB, boolean reverseDirection) Encoder constructor.
Encoder(DigitalSource sourceA, DigitalSource sourceB, boolean reverseDirection, CounterBase.EncodingType encodingType) Encoder constructor.
Encoder(DigitalSource sourceA, DigitalSource sourceB, DigitalSource indexSource) Encoder constructor.
Encoder(DigitalSource sourceA, DigitalSource sourceB, DigitalSource indexSource, boolean reverseDirection) Encoder constructor.
Encoder(int channelA, int channelB) Encoder constructor.
Encoder(int channelA, int channelB, boolean reverseDirection) Encoder constructor.
Encoder(int channelA, int channelB, boolean reverseDirection, CounterBase.EncodingType encodingType) Encoder constructor.
Encoder(int channelA, int channelB, int indexChannel) Encoder constructor.
Encoder(int channelA, int channelB, int indexChannel, boolean reverseDirection) Encoder constructor.

Method Summary

Modifier and Type	Method and Description
void	free() Free the resources used by this object.
int	get() Gets the current count.
boolean	getDirection() The last direction the encoder value changed.
double	getDistance() Get the distance the robot has driven since the last reset as scaled by the value from setDistancePerPulse(double).
double	getDistancePerPulse() Get the distance per pulse for this encoder.
int	getEncodingScale() Used to divide raw edge counts down to spec'd counts.
int	getFPGAIndex() Get the FPGA index of the encoder.
double	getPeriod() Deprecated. Use getRate() in favor of this method.
PIDSourceType	getPIDSourceType() Get which parameter of the device you are using as a process control variable.
double	getRate() Get the current rate of the encoder.
int	getRaw() Gets the raw value from the encoder.
int	getSamplesToAverage() Get the Samples to Average which specifies the number of samples of the timer to average when calculating the period.
boolean	getStopped() Determine if the encoder is stopped.
void	initSendable(SendableBuilder builder) Initializes this Sendable object.
double	pidGet() Implement the PIDSource interface.
void	reset() Reset the Encoder distance to zero.
void	setDistancePerPulse(double distancePerPulse) Set the distance per pulse for this encoder.
void	setIndexSource(DigitalSource source) Set the index source for the encoder.
void	setIndexSource(DigitalSource source, Encoder.IndexingType type) Set the index source for the encoder.
void	setIndexSource(int channel) Set the index source for the encoder.
void	setIndexSource(int channel, Encoder.IndexingType type) Set the index source for the encoder.
void	setMaxPeriod(double maxPeriod) Sets the maximum period for stopped detection.
void	setMinRate(double minRate) Set the minimum rate of the device before the hardware reports it stopped.
void	setPIDSourceType(PIDSourceType pidSource) Set which parameter of the encoder you are using as a process control variable.
void	setReverseDirection(boolean reverseDirection) Set the direction sensing for this encoder.
void	setSamplesToAverage(int samplesToAverage) Set the Samples to Average which specifies the number of samples of the timer to average when calculating the period.

Methods inherited from class edu.wpi.first.wpilibj.SensorBase

checkAnalogInputChannel, checkAnalogOutputChannel, checkDigitalChannel, checkPDPChannel, checkPDPModule, checkPWMChannel, checkRelayChannel, checkSolenoidChannel, checkSolenoidModule, getDefaultSolenoidModule, setDefaultSolenoidModule

Methods inherited from class edu.wpi.first.wpilibj.SendableBase

addChild, getName, getSubsystem, setName, setName, setName, setSubsystem

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface edu.wpi.first.wpilibj.Sendable

getName, getSubsystem, setName, setName, setSubsystem

Field Detail

m_aSource

protected DigitalSource m_aSource

The a source.

m_bSource

protected DigitalSource m_bSource

The b source.

m_indexSource

protected DigitalSource m_indexSource

The index source.

Constructor Detail

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 a 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 a 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 m_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 a 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 a 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 a 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 a 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 a 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 m_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 a 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 a 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 Detail

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.

free

public void free()

Free the resources used by this object.

Overrides:

free in class SendableBase

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

public void setMaxPeriod(double maxPeriod)

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)

setPIDSourceType

public void setPIDSourceType(PIDSourceType pidSource)

Set which parameter of the encoder you are using as a process control variable. The encoder class supports the rate and distance parameters.

Specified by:

setPIDSourceType in interface PIDSource

Parameters:

pidSource - An enum to select the parameter.

getPIDSourceType

public PIDSourceType getPIDSourceType()

Description copied from interface: PIDSource

Get which parameter of the device you are using as a process control variable.

Specified by:

getPIDSourceType in interface PIDSource

Returns:

the currently selected PID source parameter

pidGet

public double pidGet()

Implement the PIDSource interface.

Specified by:

pidGet in interface PIDSource

Returns:

The current value of the selected source parameter.

setIndexSource

public 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 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 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 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

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