Quadrature encoder interface library.
Dependents: SimpleRover PIDRover IMURover PID_VelocityExample ... more
QEI.h
00001 /** 00002 * @author Aaron Berk 00003 * 00004 * @section LICENSE 00005 * 00006 * Copyright (c) 2010 ARM Limited 00007 * 00008 * Permission is hereby granted, free of charge, to any person obtaining a copy 00009 * of this software and associated documentation files (the "Software"), to deal 00010 * in the Software without restriction, including without limitation the rights 00011 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 00012 * copies of the Software, and to permit persons to whom the Software is 00013 * furnished to do so, subject to the following conditions: 00014 * 00015 * The above copyright notice and this permission notice shall be included in 00016 * all copies or substantial portions of the Software. 00017 * 00018 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 00019 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 00020 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 00021 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 00022 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 00023 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 00024 * THE SOFTWARE. 00025 * 00026 * @section DESCRIPTION 00027 * 00028 * Quadrature Encoder Interface. 00029 * 00030 * A quadrature encoder consists of two code tracks on a disc which are 90 00031 * degrees out of phase. It can be used to determine how far a wheel has 00032 * rotated, relative to a known starting position. 00033 * 00034 * Only one code track changes at a time leading to a more robust system than 00035 * a single track, because any jitter around any edge won't cause a state 00036 * change as the other track will remain constant. 00037 * 00038 * Encoders can be a homebrew affair, consisting of infrared emitters/receivers 00039 * and paper code tracks consisting of alternating black and white sections; 00040 * alternatively, complete disk and PCB emitter/receiver encoder systems can 00041 * be bought, but the interface, regardless of implementation is the same. 00042 * 00043 * +-----+ +-----+ +-----+ 00044 * Channel A | ^ | | | | | 00045 * ---+ ^ +-----+ +-----+ +----- 00046 * ^ ^ 00047 * ^ +-----+ +-----+ +-----+ 00048 * Channel B ^ | | | | | | 00049 * ------+ +-----+ +-----+ +----- 00050 * ^ ^ 00051 * ^ ^ 00052 * 90deg 00053 * 00054 * The interface uses X2 encoding by default which calculates the pulse count 00055 * based on reading the current state after each rising and falling edge of 00056 * channel A. 00057 * 00058 * +-----+ +-----+ +-----+ 00059 * Channel A | | | | | | 00060 * ---+ +-----+ +-----+ +----- 00061 * ^ ^ ^ ^ ^ 00062 * ^ +-----+ ^ +-----+ ^ +-----+ 00063 * Channel B ^ | ^ | ^ | ^ | ^ | | 00064 * ------+ ^ +-----+ ^ +-----+ +-- 00065 * ^ ^ ^ ^ ^ 00066 * ^ ^ ^ ^ ^ 00067 * Pulse count 0 1 2 3 4 5 ... 00068 * 00069 * This interface can also use X4 encoding which calculates the pulse count 00070 * based on reading the current state after each rising and falling edge of 00071 * either channel. 00072 * 00073 * +-----+ +-----+ +-----+ 00074 * Channel A | | | | | | 00075 * ---+ +-----+ +-----+ +----- 00076 * ^ ^ ^ ^ ^ 00077 * ^ +-----+ ^ +-----+ ^ +-----+ 00078 * Channel B ^ | ^ | ^ | ^ | ^ | | 00079 * ------+ ^ +-----+ ^ +-----+ +-- 00080 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 00081 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 00082 * Pulse count 0 1 2 3 4 5 6 7 8 9 ... 00083 * 00084 * It defaults 00085 * 00086 * An optional index channel can be used which determines when a full 00087 * revolution has occured. 00088 * 00089 * If a 4 pules per revolution encoder was used, with X4 encoding, 00090 * the following would be observed. 00091 * 00092 * +-----+ +-----+ +-----+ 00093 * Channel A | | | | | | 00094 * ---+ +-----+ +-----+ +----- 00095 * ^ ^ ^ ^ ^ 00096 * ^ +-----+ ^ +-----+ ^ +-----+ 00097 * Channel B ^ | ^ | ^ | ^ | ^ | | 00098 * ------+ ^ +-----+ ^ +-----+ +-- 00099 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 00100 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 00101 * ^ ^ ^ +--+ ^ ^ +--+ ^ 00102 * ^ ^ ^ | | ^ ^ | | ^ 00103 * Index ------------+ +--------+ +----------- 00104 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 00105 * Pulse count 0 1 2 3 4 5 6 7 8 9 ... 00106 * Rev. count 0 1 2 00107 * 00108 * Rotational position in degrees can be calculated by: 00109 * 00110 * (pulse count / X * N) * 360 00111 * 00112 * Where X is the encoding type [e.g. X4 encoding => X=4], and N is the number 00113 * of pulses per revolution. 00114 * 00115 * Linear position can be calculated by: 00116 * 00117 * (pulse count / X * N) * (1 / PPI) 00118 * 00119 * Where X is encoding type [e.g. X4 encoding => X=44], N is the number of 00120 * pulses per revolution, and PPI is pulses per inch, or the equivalent for 00121 * any other unit of displacement. PPI can be calculated by taking the 00122 * circumference of the wheel or encoder disk and dividing it by the number 00123 * of pulses per revolution. 00124 */ 00125 00126 #ifndef QEI_H 00127 #define QEI_H 00128 00129 /** 00130 * Includes 00131 */ 00132 #include "mbed.h" 00133 00134 /** 00135 * Defines 00136 */ 00137 #define PREV_MASK 0x1 //Mask for the previous state in determining direction 00138 //of rotation. 00139 #define CURR_MASK 0x2 //Mask for the current state in determining direction 00140 //of rotation. 00141 #define INVALID 0x3 //XORing two states where both bits have changed. 00142 00143 /** 00144 * Quadrature Encoder Interface. 00145 */ 00146 class QEI { 00147 00148 public: 00149 00150 typedef enum Encoding { 00151 00152 X2_ENCODING, 00153 X4_ENCODING 00154 00155 } Encoding; 00156 00157 /** 00158 * Constructor. 00159 * 00160 * Reads the current values on channel A and channel B to determine the 00161 * initial state. 00162 * 00163 * Attaches the encode function to the rise/fall interrupt edges of 00164 * channels A and B to perform X4 encoding. 00165 * 00166 * Attaches the index function to the rise interrupt edge of channel index 00167 * (if it is used) to count revolutions. 00168 * 00169 * @param channelA mbed pin for channel A input. 00170 * @param channelB mbed pin for channel B input. 00171 * @param index mbed pin for optional index channel input, 00172 * (pass NC if not needed). 00173 * @param pulsesPerRev Number of pulses in one revolution. 00174 * @param encoding The encoding to use. Uses X2 encoding by default. X2 00175 * encoding uses interrupts on the rising and falling edges 00176 * of only channel A where as X4 uses them on both 00177 * channels. 00178 */ 00179 QEI(PinName channelA, PinName channelB, PinName index, int pulsesPerRev, Encoding encoding = X2_ENCODING); 00180 00181 /** 00182 * Reset the encoder. 00183 * 00184 * Sets the pulses and revolutions count to zero. 00185 */ 00186 void reset(void); 00187 00188 /** 00189 * Read the state of the encoder. 00190 * 00191 * @return The current state of the encoder as a 2-bit number, where: 00192 * bit 1 = The reading from channel B 00193 * bit 2 = The reading from channel A 00194 */ 00195 int getCurrentState(void); 00196 00197 /** 00198 * Read the number of pulses recorded by the encoder. 00199 * 00200 * @return Number of pulses which have occured. 00201 */ 00202 int getPulses(void); 00203 00204 /** 00205 * Read the number of revolutions recorded by the encoder on the index channel. 00206 * 00207 * @return Number of revolutions which have occured on the index channel. 00208 */ 00209 int getRevolutions(void); 00210 00211 private: 00212 00213 /** 00214 * Update the pulse count. 00215 * 00216 * Called on every rising/falling edge of channels A/B. 00217 * 00218 * Reads the state of the channels and determines whether a pulse forward 00219 * or backward has occured, updating the count appropriately. 00220 */ 00221 void encode(void); 00222 00223 /** 00224 * Called on every rising edge of channel index to update revolution 00225 * count by one. 00226 */ 00227 void index(void); 00228 00229 Encoding encoding_; 00230 00231 InterruptIn channelA_; 00232 InterruptIn channelB_; 00233 InterruptIn index_; 00234 00235 int pulsesPerRev_; 00236 int prevState_; 00237 int currState_; 00238 00239 volatile int pulses_; 00240 volatile int revolutions_; 00241 00242 }; 00243 00244 #endif /* QEI_H */
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