Quadrature encoder interface library.
QEI.h
- Committer:
- aberk
- Date:
- 2010-09-02
- Revision:
- 0:5c2ad81551aa
- Child:
- 1:ce2f5a0d50b6
File content as of revision 0:5c2ad81551aa:
/** * @author Aaron Berk * * @section LICENSE * * Copyright (c) 2010 ARM Limited * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN * THE SOFTWARE. * * @section DESCRIPTION * * Quadrature Encoder Interface. * * A quadrature encoder consists of two code tracks on a disc which are 90 * degrees out of phase. It can be used to determine how far a wheel has * rotated, relative to a known starting position. * * Only one code track changes at a time leading to a more robust system than * a single track, because any jitter around any edge won't cause a state * change as the other track will remain constant. * * Encoders can be a homebrew affair, consisting of infrared emitters/receivers * and paper code tracks consisting of alternating black and white sections; * alternatively, complete disk and PCB emitter/receiver encoder systems can * be bought, but the interface, regardless of implementation is the same. * * +-----+ +-----+ +-----+ * Channel A | ^ | | | | | * ---+ ^ +-----+ +-----+ +----- * ^ ^ * ^ +-----+ +-----+ +-----+ * Channel B ^ | | | | | | * ------+ +-----+ +-----+ +----- * ^ ^ * ^ ^ * 90deg * * The interface uses X2 encoding by default which calculates the pulse count * based on reading the current state after each rising and falling edge of * channel A. * * +-----+ +-----+ +-----+ * Channel A | | | | | | * ---+ +-----+ +-----+ +----- * ^ ^ ^ ^ ^ * ^ +-----+ ^ +-----+ ^ +-----+ * Channel B ^ | ^ | ^ | ^ | ^ | | * ------+ ^ +-----+ ^ +-----+ +-- * ^ ^ ^ ^ ^ * ^ ^ ^ ^ ^ * Pulse count 0 1 2 3 4 5 ... * * This interface can also use X4 encoding which calculates the pulse count * based on reading the current state after each rising and falling edge of * either channel. * * +-----+ +-----+ +-----+ * Channel A | | | | | | * ---+ +-----+ +-----+ +----- * ^ ^ ^ ^ ^ * ^ +-----+ ^ +-----+ ^ +-----+ * Channel B ^ | ^ | ^ | ^ | ^ | | * ------+ ^ +-----+ ^ +-----+ +-- * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ * Pulse count 0 1 2 3 4 5 6 7 8 9 ... * * It defaults * * An optional index channel can be used which determines when a full * revolution has occured. * * If a 4 pules per revolution encoder was used, with X4 encoding, * the following would be observed. * * +-----+ +-----+ +-----+ * Channel A | | | | | | * ---+ +-----+ +-----+ +----- * ^ ^ ^ ^ ^ * ^ +-----+ ^ +-----+ ^ +-----+ * Channel B ^ | ^ | ^ | ^ | ^ | | * ------+ ^ +-----+ ^ +-----+ +-- * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ * ^ ^ ^ +--+ ^ ^ +--+ ^ * ^ ^ ^ | | ^ ^ | | ^ * Index ------------+ +--------+ +----------- * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ * Pulse count 0 1 2 3 4 5 6 7 8 9 ... * Rev. count 0 1 2 * * Rotational position in degrees can be calculated by: * * (pulse count / X * N) * 360 * * Where X is the encoding type [e.g. X4 encoding => X=4], and N is the number * of pulses per revolution. * * Linear position can be calculated by: * * (pulse count / X * N) * (1 / PPI) * * Where X is encoding type [e.g. X4 encoding => X=44], N is the number of * pulses per revolution, and PPI is pulses per inch, or the equivalent for * any other unit of displacement. PPI can be calculated by taking the * circumference of the wheel or encoder disk and dividing it by the number * of pulses per revolution. */ #ifndef QEI_H #define QEI_H /** * Includes */ #include "mbed.h" /** * Defines */ #define PREV_MASK 0x1 //Mask for the previous state in determining direction //of rotation. #define CURR_MASK 0x2 //Mask for the current state in determining direction //of rotation. #define INVALID 0x3 //XORing two states where both bits have changed. /** * Quadrature Encoder Interface. */ class QEI { public: typedef enum Encoding { X2_ENCODING, X4_ENCODING } Encoding; /** * Constructor. * * Reads the current values on channel A and channel B to determine the * initial state. * * Attaches the encode function to the rise/fall interrupt edges of * channels A and B to perform X4 encoding. * * Attaches the index function to the rise interrupt edge of channel index * (if it is used) to count revolutions. * * @param channelA mbed pin for channel A input. * @param channelB mbed pin for channel B input. * @param index mbed pin for optional index channel input, * (pass NC if not needed). * @param pulsesPerRev Number of pulses in one revolution. * @param encoding The encoding to use. Uses X2 encoding by default. X2 * encoding uses interrupts on the rising and falling edges * of only channel A where as X4 uses them on both * channels. */ QEI(PinName channelA, PinName channelB, PinName index, int pulsesPerRev, Encoding encoding = X2_ENCODING); /** * Reset the encoder. * * Sets the pulses and revolutions count to zero. */ void reset(void); /** * Read the state of the encoder. * * @return The current state of the encoder as a 2-bit number, where: * bit 1 = The reading from channel B * bit 2 = The reading from channel A */ int getCurrentState(void); /** * Read the number of pulses recorded by the encoder. * * @return Number of pulses which have occured. */ int getPulses(void); /** * Read the number of revolutions recorded by the encoder on the index channel. * * @return Number of revolutions which have occured on the index channel. */ int getRevolutions(void); private: /** * Update the pulse count. * * Called on every rising/falling edge of channels A/B. * * Reads the state of the channels and determines whether a pulse forward * or backward has occured, updating the count appropriately. */ void encode(void); /** * Called on every rising edge of channel index to update revolution * count by one. */ void index(void); Encoding encoding_; InterruptIn channelA_; InterruptIn channelB_; InterruptIn index_; int pulsesPerRev_; int prevState_; int currState_; volatile int pulses_; volatile int revolutions_; }; #endif /* QEI_H */