edu.wpi.first.wpilibj

Class Encoder

java.lang.Object

edu.wpi.first.wpilibj.SensorBase

edu.wpi.first.wpilibj.Encoder

All Implemented Interfaces:

CounterBase, LiveWindowSendable, PIDSource, Sendable

public class Encoder
extends SensorBase
implements CounterBase, PIDSource, LiveWindowSendable

Class to read quad encoders. Quadrature encoders are devices that count shaft rotation and can sense direction. The output of the QuadEncoder class is an integer that can count either up or down, and can go negative for reverse direction counting. When creating QuadEncoders, a direction is supplied that changes 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 to allow the FPGA to do 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, kPDPChannels, kPDPModules, kPwmChannels, kRelayChannels, kSolenoidChannels, kSolenoidModules, kSystemClockTicksPerMicrosecond

Constructor Summary

Constructors

Constructor and Description
Encoder(DigitalSource aSource, DigitalSource bSource) Encoder constructor.
Encoder(DigitalSource aSource, DigitalSource bSource, boolean reverseDirection) Encoder constructor.
Encoder(DigitalSource aSource, DigitalSource bSource, boolean reverseDirection, CounterBase.EncodingType encodingType) Encoder constructor.
Encoder(DigitalSource aSource, DigitalSource bSource, DigitalSource indexSource) Encoder constructor.
Encoder(DigitalSource aSource, DigitalSource bSource, DigitalSource indexSource, boolean reverseDirection) Encoder constructor.
Encoder(int aChannel, int bChannel) Encoder constructor.
Encoder(int aChannel, int bChannel, boolean reverseDirection) Encoder constructor.
Encoder(int aChannel, int bChannel, boolean reverseDirection, CounterBase.EncodingType encodingType) Encoder constructor.
Encoder(int aChannel, int bChannel, int indexChannel) Encoder constructor.
Encoder(int aChannel, int bChannel, 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.
int	getEncodingScale()
int	getFPGAIndex()
double	getPeriod() Deprecated. Use getRate() in favor of this method. This returns unscaled periods and getRate() scales using value from setDistancePerPulse().
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.
java.lang.String	getSmartDashboardType()
boolean	getStopped() Determine if the encoder is stopped.
ITable	getTable()
void	initTable(ITable subtable) Initializes a table for 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.
void	startLiveWindowMode() Start having this sendable object automatically respond to value changes reflect the value on the table.
void	stopLiveWindowMode() Stop having this sendable object automatically respond to value changes.
void	updateTable() Update the table for this sendable object with the latest values.

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

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

Methods inherited from class java.lang.Object

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

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 aChannel,
               int bChannel,
               boolean reverseDirection)

Encoder constructor. Construct a Encoder given a and b channels. The encoder will start counting immediately.

Parameters:

aChannel - The a channel DIO channel. 0-9 are on-board, 10-25 are on the MXP port

bChannel - 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 aChannel,
               int bChannel)

Encoder constructor. Construct a Encoder given a and b channels. The encoder will start counting immediately.

Parameters:

aChannel - The a channel digital input channel.

bChannel - The b channel digital input channel.

Encoder

public Encoder(int aChannel,
               int bChannel,
               boolean reverseDirection,
               CounterBase.EncodingType encodingType)

Encoder constructor. Construct a Encoder given a and b channels. The encoder will start counting immediately.

Parameters:

aChannel - The a channel digital input channel.

bChannel - 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 aChannel,
               int bChannel,
               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:

aChannel - The a channel digital input channel.

bChannel - 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 aChannel,
               int bChannel,
               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:

aChannel - The a channel digital input channel.

bChannel - The b channel digital input channel.

indexChannel - The index channel digital input channel.

Encoder

public Encoder(DigitalSource aSource,
               DigitalSource bSource,
               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:

aSource - The source that should be used for the a channel.

bSource - 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 aSource,
               DigitalSource bSource)

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:

aSource - The source that should be used for the a channel.

bSource - the source that should be used for the b channel.

Encoder

public Encoder(DigitalSource aSource,
               DigitalSource bSource,
               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:

aSource - The source that should be used for the a channel.

bSource - 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 aSource,
               DigitalSource bSource,
               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:

aSource - The source that should be used for the a channel.

bSource - 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 aSource,
               DigitalSource bSource,
               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:

aSource - The source that should be used for the a channel.

bSource - 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()

Returns:

the Encoder's FPGA index

getEncodingScale

public int getEncodingScale()

Returns:

the encoding scale factor 1x, 2x, or 4x, per the requested encodingType. Used to divide raw edge counts down to spec'd counts.

free

public void free()

Description copied from class: SensorBase

Free the resources used by this object

Overrides:

free in class SensorBase

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

public double getPeriod()

Deprecated. Use getRate() in favor of this method. This returns unscaled periods and getRate() scales using value from setDistancePerPulse().

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.

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.

Returns:

The distance driven since the last reset as scaled by the value from setDistancePerPulse().

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.

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. TODO: Should this throw a checked exception, so that the user has to deal with giving an incorrect value?

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()

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,
                           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(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,
                           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

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

getSmartDashboardType

public java.lang.String getSmartDashboardType()

Specified by:

getSmartDashboardType in interface Sendable

Returns:

the string representation of the named data type that will be used by the smart dashboard for this sendable

initTable

public void initTable(ITable subtable)

Initializes a table for this sendable object. $

Specified by:

initTable in interface Sendable

Parameters:

subtable - The table to put the values in.

getTable

public ITable getTable()

Specified by:

getTable in interface Sendable

Returns:

the table that is currently associated with the sendable

updateTable

public void updateTable()

Update the table for this sendable object with the latest values.

Specified by:

updateTable in interface LiveWindowSendable

startLiveWindowMode

public void startLiveWindowMode()

Start having this sendable object automatically respond to value changes reflect the value on the table.

Specified by:

startLiveWindowMode in interface LiveWindowSendable

stopLiveWindowMode

public void stopLiveWindowMode()

Stop having this sendable object automatically respond to value changes.

Specified by:

stopLiveWindowMode in interface LiveWindowSendable