Patrick Wensing / QEI_pmw

QEI library with velocity implementation based on time difference between successive encoder counts.

Dependents:   Bezier_Trajectory_Follower Dolphin 2_131TEST Jerby ... more

QEI.h@3:d998cfe55eac, 2015-08-13 (annotated)

Committer:
pwensing
Date:
Thu Aug 13 20:20:48 2015 +0000
Revision:
3:d998cfe55eac
Parent:
2:6b96b8a96492 
documentation

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pwensing 1:6c5b94eeb0a0 1 /*
pwensing 0:43b9eeecccc7 2 * @author Aaron Berk
pwensing 0:43b9eeecccc7 3 *
pwensing 0:43b9eeecccc7 4 * @section LICENSE
pwensing 0:43b9eeecccc7 5 *
pwensing 0:43b9eeecccc7 6 * Copyright (c) 2010 ARM Limited
pwensing 0:43b9eeecccc7 7 *
pwensing 0:43b9eeecccc7 8 * Permission is hereby granted, free of charge, to any person obtaining a copy
pwensing 0:43b9eeecccc7 9 * of this software and associated documentation files (the "Software"), to deal
pwensing 0:43b9eeecccc7 10 * in the Software without restriction, including without limitation the rights
pwensing 0:43b9eeecccc7 11 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
pwensing 0:43b9eeecccc7 12 * copies of the Software, and to permit persons to whom the Software is
pwensing 0:43b9eeecccc7 13 * furnished to do so, subject to the following conditions:
pwensing 0:43b9eeecccc7 14 *
pwensing 0:43b9eeecccc7 15 * The above copyright notice and this permission notice shall be included in
pwensing 0:43b9eeecccc7 16 * all copies or substantial portions of the Software.
pwensing 0:43b9eeecccc7 17 *
pwensing 0:43b9eeecccc7 18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
pwensing 0:43b9eeecccc7 19 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
pwensing 0:43b9eeecccc7 20 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
pwensing 0:43b9eeecccc7 21 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
pwensing 0:43b9eeecccc7 22 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
pwensing 0:43b9eeecccc7 23 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
pwensing 0:43b9eeecccc7 24 * THE SOFTWARE.
pwensing 0:43b9eeecccc7 25 *
pwensing 0:43b9eeecccc7 26 * @section DESCRIPTION
pwensing 0:43b9eeecccc7 27 *
pwensing 0:43b9eeecccc7 28 * Quadrature Encoder Interface.
pwensing 0:43b9eeecccc7 29 *
pwensing 0:43b9eeecccc7 30 * A quadrature encoder consists of two code tracks on a disc which are 90
pwensing 0:43b9eeecccc7 31 * degrees out of phase. It can be used to determine how far a wheel has
pwensing 0:43b9eeecccc7 32 * rotated, relative to a known starting position.
pwensing 0:43b9eeecccc7 33 *
pwensing 0:43b9eeecccc7 34 * Only one code track changes at a time leading to a more robust system than
pwensing 0:43b9eeecccc7 35 * a single track, because any jitter around any edge won't cause a state
pwensing 0:43b9eeecccc7 36 * change as the other track will remain constant.
pwensing 0:43b9eeecccc7 37 *
pwensing 0:43b9eeecccc7 38 * Encoders can be a homebrew affair, consisting of infrared emitters/receivers
pwensing 0:43b9eeecccc7 39 * and paper code tracks consisting of alternating black and white sections;
pwensing 0:43b9eeecccc7 40 * alternatively, complete disk and PCB emitter/receiver encoder systems can
pwensing 0:43b9eeecccc7 41 * be bought, but the interface, regardless of implementation is the same.
pwensing 0:43b9eeecccc7 42 *
pwensing 0:43b9eeecccc7 43 * +-----+ +-----+ +-----+
pwensing 0:43b9eeecccc7 44 * Channel A | ^ | | | | |
pwensing 0:43b9eeecccc7 45 * ---+ ^ +-----+ +-----+ +-----
pwensing 0:43b9eeecccc7 46 * ^ ^
pwensing 0:43b9eeecccc7 47 * ^ +-----+ +-----+ +-----+
pwensing 0:43b9eeecccc7 48 * Channel B ^ | | | | | |
pwensing 0:43b9eeecccc7 49 * ------+ +-----+ +-----+ +-----
pwensing 0:43b9eeecccc7 50 * ^ ^
pwensing 0:43b9eeecccc7 51 * ^ ^
pwensing 0:43b9eeecccc7 52 * 90deg
pwensing 0:43b9eeecccc7 53 *
pwensing 0:43b9eeecccc7 54 * The interface uses X2 encoding by default which calculates the pulse count
pwensing 0:43b9eeecccc7 55 * based on reading the current state after each rising and falling edge of
pwensing 0:43b9eeecccc7 56 * channel A.
pwensing 0:43b9eeecccc7 57 *
pwensing 0:43b9eeecccc7 58 * +-----+ +-----+ +-----+
pwensing 0:43b9eeecccc7 59 * Channel A | | | | | |
pwensing 0:43b9eeecccc7 60 * ---+ +-----+ +-----+ +-----
pwensing 0:43b9eeecccc7 61 * ^ ^ ^ ^ ^
pwensing 0:43b9eeecccc7 62 * ^ +-----+ ^ +-----+ ^ +-----+
pwensing 0:43b9eeecccc7 63 * Channel B ^ | ^ | ^ | ^ | ^ | |
pwensing 0:43b9eeecccc7 64 * ------+ ^ +-----+ ^ +-----+ +--
pwensing 0:43b9eeecccc7 65 * ^ ^ ^ ^ ^
pwensing 0:43b9eeecccc7 66 * ^ ^ ^ ^ ^
pwensing 0:43b9eeecccc7 67 * Pulse count 0 1 2 3 4 5 ...
pwensing 0:43b9eeecccc7 68 *
pwensing 0:43b9eeecccc7 69 * This interface can also use X4 encoding which calculates the pulse count
pwensing 0:43b9eeecccc7 70 * based on reading the current state after each rising and falling edge of
pwensing 0:43b9eeecccc7 71 * either channel.
pwensing 0:43b9eeecccc7 72 *
pwensing 0:43b9eeecccc7 73 * +-----+ +-----+ +-----+
pwensing 0:43b9eeecccc7 74 * Channel A | | | | | |
pwensing 0:43b9eeecccc7 75 * ---+ +-----+ +-----+ +-----
pwensing 0:43b9eeecccc7 76 * ^ ^ ^ ^ ^
pwensing 0:43b9eeecccc7 77 * ^ +-----+ ^ +-----+ ^ +-----+
pwensing 0:43b9eeecccc7 78 * Channel B ^ | ^ | ^ | ^ | ^ | |
pwensing 0:43b9eeecccc7 79 * ------+ ^ +-----+ ^ +-----+ +--
pwensing 0:43b9eeecccc7 80 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
pwensing 0:43b9eeecccc7 81 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
pwensing 0:43b9eeecccc7 82 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
pwensing 0:43b9eeecccc7 83 *
pwensing 0:43b9eeecccc7 84 * It defaults
pwensing 0:43b9eeecccc7 85 *
pwensing 0:43b9eeecccc7 86 * An optional index channel can be used which determines when a full
pwensing 0:43b9eeecccc7 87 * revolution has occured.
pwensing 0:43b9eeecccc7 88 *
pwensing 0:43b9eeecccc7 89 * If a 4 pules per revolution encoder was used, with X4 encoding,
pwensing 0:43b9eeecccc7 90 * the following would be observed.
pwensing 0:43b9eeecccc7 91 *
pwensing 0:43b9eeecccc7 92 * +-----+ +-----+ +-----+
pwensing 0:43b9eeecccc7 93 * Channel A | | | | | |
pwensing 0:43b9eeecccc7 94 * ---+ +-----+ +-----+ +-----
pwensing 0:43b9eeecccc7 95 * ^ ^ ^ ^ ^
pwensing 0:43b9eeecccc7 96 * ^ +-----+ ^ +-----+ ^ +-----+
pwensing 0:43b9eeecccc7 97 * Channel B ^ | ^ | ^ | ^ | ^ | |
pwensing 0:43b9eeecccc7 98 * ------+ ^ +-----+ ^ +-----+ +--
pwensing 0:43b9eeecccc7 99 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
pwensing 0:43b9eeecccc7 100 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
pwensing 0:43b9eeecccc7 101 * ^ ^ ^ +--+ ^ ^ +--+ ^
pwensing 0:43b9eeecccc7 102 * ^ ^ ^ | | ^ ^ | | ^
pwensing 0:43b9eeecccc7 103 * Index ------------+ +--------+ +-----------
pwensing 0:43b9eeecccc7 104 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
pwensing 0:43b9eeecccc7 105 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
pwensing 0:43b9eeecccc7 106 * Rev. count 0 1 2
pwensing 0:43b9eeecccc7 107 *
pwensing 0:43b9eeecccc7 108 * Rotational position in degrees can be calculated by:
pwensing 0:43b9eeecccc7 109 *
pwensing 0:43b9eeecccc7 110 * (pulse count / X * N) * 360
pwensing 0:43b9eeecccc7 111 *
pwensing 0:43b9eeecccc7 112 * Where X is the encoding type [e.g. X4 encoding => X=4], and N is the number
pwensing 0:43b9eeecccc7 113 * of pulses per revolution.
pwensing 0:43b9eeecccc7 114 *
pwensing 0:43b9eeecccc7 115 * Linear position can be calculated by:
pwensing 0:43b9eeecccc7 116 *
pwensing 0:43b9eeecccc7 117 * (pulse count / X * N) * (1 / PPI)
pwensing 0:43b9eeecccc7 118 *
pwensing 0:43b9eeecccc7 119 * Where X is encoding type [e.g. X4 encoding => X=44], N is the number of
pwensing 0:43b9eeecccc7 120 * pulses per revolution, and PPI is pulses per inch, or the equivalent for
pwensing 0:43b9eeecccc7 121 * any other unit of displacement. PPI can be calculated by taking the
pwensing 0:43b9eeecccc7 122 * circumference of the wheel or encoder disk and dividing it by the number
pwensing 0:43b9eeecccc7 123 * of pulses per revolution.
pwensing 0:43b9eeecccc7 124 */
pwensing 0:43b9eeecccc7 125
pwensing 0:43b9eeecccc7 126 #ifndef QEI_H
pwensing 0:43b9eeecccc7 127 #define QEI_H
pwensing 0:43b9eeecccc7 128
pwensing 2:6b96b8a96492 129 /*
pwensing 0:43b9eeecccc7 130 * Includes
pwensing 0:43b9eeecccc7 131 */
pwensing 0:43b9eeecccc7 132 #include "mbed.h"
pwensing 0:43b9eeecccc7 133
pwensing 0:43b9eeecccc7 134 /**
pwensing 0:43b9eeecccc7 135 * Defines
pwensing 0:43b9eeecccc7 136 */
pwensing 0:43b9eeecccc7 137 #define PREV_MASK 0x1 //Mask for the previous state in determining direction
pwensing 0:43b9eeecccc7 138 //of rotation.
pwensing 0:43b9eeecccc7 139 #define CURR_MASK 0x2 //Mask for the current state in determining direction
pwensing 0:43b9eeecccc7 140 //of rotation.
pwensing 0:43b9eeecccc7 141 #define INVALID 0x3 //XORing two states where both bits have changed.
pwensing 0:43b9eeecccc7 142
pwensing 0:43b9eeecccc7 143 /**
pwensing 0:43b9eeecccc7 144 * Quadrature Encoder Interface.
pwensing 0:43b9eeecccc7 145 */
pwensing 0:43b9eeecccc7 146 class QEI {
pwensing 0:43b9eeecccc7 147
pwensing 0:43b9eeecccc7 148 public:
pwensing 0:43b9eeecccc7 149
pwensing 0:43b9eeecccc7 150 typedef enum Encoding {
pwensing 0:43b9eeecccc7 151
pwensing 0:43b9eeecccc7 152 X2_ENCODING,
pwensing 0:43b9eeecccc7 153 X4_ENCODING
pwensing 0:43b9eeecccc7 154
pwensing 0:43b9eeecccc7 155 } Encoding;
pwensing 0:43b9eeecccc7 156
pwensing 0:43b9eeecccc7 157 /**
pwensing 0:43b9eeecccc7 158 * Constructor.
pwensing 0:43b9eeecccc7 159 *
pwensing 0:43b9eeecccc7 160 * @param channelA mbed pin for channel A input.
pwensing 0:43b9eeecccc7 161 * @param channelB mbed pin for channel B input.
pwensing 0:43b9eeecccc7 162 * @param index mbed pin for optional index channel input,
pwensing 0:43b9eeecccc7 163 * (pass NC if not needed).
pwensing 0:43b9eeecccc7 164 * @param pulsesPerRev Number of pulses in one revolution.
pwensing 0:43b9eeecccc7 165 * @param encoding The encoding to use. Uses X2 encoding by default. X2
pwensing 0:43b9eeecccc7 166 * encoding uses interrupts on the rising and falling edges
pwensing 0:43b9eeecccc7 167 * of only channel A where as X4 uses them on both
pwensing 0:43b9eeecccc7 168 * channels.
pwensing 0:43b9eeecccc7 169 */
pwensing 0:43b9eeecccc7 170 QEI(PinName channelA, PinName channelB, PinName index, int pulsesPerRev, Encoding encoding = X2_ENCODING);
pwensing 0:43b9eeecccc7 171
pwensing 0:43b9eeecccc7 172 /**
pwensing 0:43b9eeecccc7 173 * Reset the encoder.
pwensing 0:43b9eeecccc7 174 *
pwensing 0:43b9eeecccc7 175 * Sets the pulses and revolutions count to zero.
pwensing 0:43b9eeecccc7 176 */
pwensing 0:43b9eeecccc7 177 void reset(void);
pwensing 0:43b9eeecccc7 178
pwensing 0:43b9eeecccc7 179 /**
pwensing 0:43b9eeecccc7 180 * Read the state of the encoder.
pwensing 0:43b9eeecccc7 181 *
pwensing 0:43b9eeecccc7 182 * @return The current state of the encoder as a 2-bit number, where:
pwensing 0:43b9eeecccc7 183 * bit 1 = The reading from channel B
pwensing 0:43b9eeecccc7 184 * bit 2 = The reading from channel A
pwensing 0:43b9eeecccc7 185 */
pwensing 0:43b9eeecccc7 186 int getCurrentState(void);
pwensing 0:43b9eeecccc7 187
pwensing 0:43b9eeecccc7 188 /**
pwensing 0:43b9eeecccc7 189 * Read the number of pulses recorded by the encoder.
pwensing 0:43b9eeecccc7 190 *
pwensing 0:43b9eeecccc7 191 * @return Number of pulses which have occured.
pwensing 0:43b9eeecccc7 192 */
pwensing 0:43b9eeecccc7 193 int getPulses(void);
pwensing 0:43b9eeecccc7 194
pwensing 0:43b9eeecccc7 195 /**
pwensing 0:43b9eeecccc7 196 * Read the number of revolutions recorded by the encoder on the index channel.
pwensing 0:43b9eeecccc7 197 *
pwensing 0:43b9eeecccc7 198 * @return Number of revolutions which have occured on the index channel.
pwensing 0:43b9eeecccc7 199 */
pwensing 0:43b9eeecccc7 200 int getRevolutions(void);
pwensing 0:43b9eeecccc7 201
pwensing 0:43b9eeecccc7 202 /**
pwensing 0:43b9eeecccc7 203 * Read the number of counts per second as measured by the time between
pwensing 0:43b9eeecccc7 204 * successive encoder counts
pwensing 0:43b9eeecccc7 205 *
pwensing 0:43b9eeecccc7 206 * @return Number of counts per second as a float.
pwensing 0:43b9eeecccc7 207 */
pwensing 0:43b9eeecccc7 208 float getVelocity(void);
pwensing 0:43b9eeecccc7 209
pwensing 0:43b9eeecccc7 210 private:
pwensing 0:43b9eeecccc7 211
pwensing 0:43b9eeecccc7 212 /**
pwensing 0:43b9eeecccc7 213 * Update the pulse count.
pwensing 0:43b9eeecccc7 214 *
pwensing 0:43b9eeecccc7 215 * Called on every rising/falling edge of channels A/B.
pwensing 0:43b9eeecccc7 216 *
pwensing 0:43b9eeecccc7 217 * Reads the state of the channels and determines whether a pulse forward
pwensing 0:43b9eeecccc7 218 * or backward has occured, updating the count appropriately.
pwensing 0:43b9eeecccc7 219 */
pwensing 0:43b9eeecccc7 220 void encode(void);
pwensing 0:43b9eeecccc7 221
pwensing 0:43b9eeecccc7 222 /**
pwensing 0:43b9eeecccc7 223 * Called on every rising edge of channel index to update revolution
pwensing 0:43b9eeecccc7 224 * count by one.
pwensing 0:43b9eeecccc7 225 */
pwensing 0:43b9eeecccc7 226 void index(void);
pwensing 0:43b9eeecccc7 227
pwensing 0:43b9eeecccc7 228 Encoding encoding_;
pwensing 0:43b9eeecccc7 229
pwensing 0:43b9eeecccc7 230 InterruptIn channelA_;
pwensing 0:43b9eeecccc7 231 InterruptIn channelB_;
pwensing 0:43b9eeecccc7 232 InterruptIn index_;
pwensing 0:43b9eeecccc7 233
pwensing 0:43b9eeecccc7 234 int pulsesPerRev_;
pwensing 0:43b9eeecccc7 235 int prevState_;
pwensing 0:43b9eeecccc7 236 int currState_;
pwensing 0:43b9eeecccc7 237
pwensing 0:43b9eeecccc7 238 int currTime_;
pwensing 0:43b9eeecccc7 239 int prevTime_;
pwensing 0:43b9eeecccc7 240 int currDirection_;
pwensing 0:43b9eeecccc7 241 int prevDirection_;
pwensing 0:43b9eeecccc7 242
pwensing 0:43b9eeecccc7 243 Timer timer;
pwensing 0:43b9eeecccc7 244
pwensing 0:43b9eeecccc7 245 volatile int pulses_;
pwensing 0:43b9eeecccc7 246 volatile int revolutions_;
pwensing 0:43b9eeecccc7 247
pwensing 0:43b9eeecccc7 248 };
pwensing 0:43b9eeecccc7 249
pwensing 0:43b9eeecccc7 250 #endif /* QEI_H */