Jesus Fausto / QEI

Quadrature encoder interface library with distance function

Dependents:   QEI_with_distance wheelchaircontrol wheelchaircontrolRos wheelchaircontrol ... more

Fork of QEI by Aaron Berk

QEI.cpp@4:dc96133b5129, 2018-10-27 (annotated)

Committer:
jvfausto
Date:
Sat Oct 27 10:09:39 2018 +0000
Revision:
4:dc96133b5129
Parent:
3:0035b165ecc4 
Not A lot has changed

Who changed what in which revision?

UserRevisionLine numberNew contents of line
aberk 0:5c2ad81551aa 1 /**
aberk 0:5c2ad81551aa 2 * @author Aaron Berk
aberk 0:5c2ad81551aa 3 *
aberk 0:5c2ad81551aa 4 * @section LICENSE
aberk 0:5c2ad81551aa 5 *
aberk 0:5c2ad81551aa 6 * Copyright (c) 2010 ARM Limited
aberk 0:5c2ad81551aa 7 *
aberk 0:5c2ad81551aa 8 * Permission is hereby granted, free of charge, to any person obtaining a copy
aberk 0:5c2ad81551aa 9 * of this software and associated documentation files (the "Software"), to deal
aberk 0:5c2ad81551aa 10 * in the Software without restriction, including without limitation the rights
aberk 0:5c2ad81551aa 11 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
aberk 0:5c2ad81551aa 12 * copies of the Software, and to permit persons to whom the Software is
aberk 0:5c2ad81551aa 13 * furnished to do so, subject to the following conditions:
aberk 0:5c2ad81551aa 14 *
aberk 0:5c2ad81551aa 15 * The above copyright notice and this permission notice shall be included in
aberk 0:5c2ad81551aa 16 * all copies or substantial portions of the Software.
aberk 0:5c2ad81551aa 17 *
aberk 0:5c2ad81551aa 18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
aberk 0:5c2ad81551aa 19 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
aberk 0:5c2ad81551aa 20 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
aberk 0:5c2ad81551aa 21 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
aberk 0:5c2ad81551aa 22 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
aberk 0:5c2ad81551aa 23 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
aberk 0:5c2ad81551aa 24 * THE SOFTWARE.
aberk 0:5c2ad81551aa 25 *
aberk 0:5c2ad81551aa 26 * @section DESCRIPTION
aberk 0:5c2ad81551aa 27 *
aberk 0:5c2ad81551aa 28 * Quadrature Encoder Interface.
aberk 0:5c2ad81551aa 29 *
aberk 0:5c2ad81551aa 30 * A quadrature encoder consists of two code tracks on a disc which are 90
aberk 0:5c2ad81551aa 31 * degrees out of phase. It can be used to determine how far a wheel has
aberk 0:5c2ad81551aa 32 * rotated, relative to a known starting position.
aberk 0:5c2ad81551aa 33 *
aberk 0:5c2ad81551aa 34 * Only one code track changes at a time leading to a more robust system than
aberk 0:5c2ad81551aa 35 * a single track, because any jitter around any edge won't cause a state
aberk 0:5c2ad81551aa 36 * change as the other track will remain constant.
aberk 0:5c2ad81551aa 37 *
aberk 0:5c2ad81551aa 38 * Encoders can be a homebrew affair, consisting of infrared emitters/receivers
aberk 0:5c2ad81551aa 39 * and paper code tracks consisting of alternating black and white sections;
aberk 0:5c2ad81551aa 40 * alternatively, complete disk and PCB emitter/receiver encoder systems can
aberk 0:5c2ad81551aa 41 * be bought, but the interface, regardless of implementation is the same.
aberk 0:5c2ad81551aa 42 *
aberk 0:5c2ad81551aa 43 * +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 44 * Channel A | ^ | | | | |
aberk 0:5c2ad81551aa 45 * ---+ ^ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 46 * ^ ^
aberk 0:5c2ad81551aa 47 * ^ +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 48 * Channel B ^ | | | | | |
aberk 0:5c2ad81551aa 49 * ------+ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 50 * ^ ^
aberk 0:5c2ad81551aa 51 * ^ ^
aberk 0:5c2ad81551aa 52 * 90deg
aberk 0:5c2ad81551aa 53 *
aberk 0:5c2ad81551aa 54 * The interface uses X2 encoding by default which calculates the pulse count
aberk 0:5c2ad81551aa 55 * based on reading the current state after each rising and falling edge of
aberk 0:5c2ad81551aa 56 * channel A.
aberk 0:5c2ad81551aa 57 *
aberk 0:5c2ad81551aa 58 * +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 59 * Channel A | | | | | |
aberk 0:5c2ad81551aa 60 * ---+ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 61 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 62 * ^ +-----+ ^ +-----+ ^ +-----+
aberk 0:5c2ad81551aa 63 * Channel B ^ | ^ | ^ | ^ | ^ | |
aberk 0:5c2ad81551aa 64 * ------+ ^ +-----+ ^ +-----+ +--
aberk 0:5c2ad81551aa 65 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 66 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 67 * Pulse count 0 1 2 3 4 5 ...
aberk 0:5c2ad81551aa 68 *
aberk 0:5c2ad81551aa 69 * This interface can also use X4 encoding which calculates the pulse count
aberk 0:5c2ad81551aa 70 * based on reading the current state after each rising and falling edge of
aberk 0:5c2ad81551aa 71 * either channel.
aberk 0:5c2ad81551aa 72 *
aberk 0:5c2ad81551aa 73 * +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 74 * Channel A | | | | | |
aberk 0:5c2ad81551aa 75 * ---+ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 76 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 77 * ^ +-----+ ^ +-----+ ^ +-----+
aberk 0:5c2ad81551aa 78 * Channel B ^ | ^ | ^ | ^ | ^ | |
aberk 0:5c2ad81551aa 79 * ------+ ^ +-----+ ^ +-----+ +--
aberk 0:5c2ad81551aa 80 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 81 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 82 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
aberk 0:5c2ad81551aa 83 *
aberk 0:5c2ad81551aa 84 * It defaults
aberk 0:5c2ad81551aa 85 *
aberk 0:5c2ad81551aa 86 * An optional index channel can be used which determines when a full
aberk 0:5c2ad81551aa 87 * revolution has occured.
aberk 0:5c2ad81551aa 88 *
aberk 0:5c2ad81551aa 89 * If a 4 pules per revolution encoder was used, with X4 encoding,
aberk 0:5c2ad81551aa 90 * the following would be observed.
aberk 0:5c2ad81551aa 91 *
aberk 0:5c2ad81551aa 92 * +-----+ +-----+ +-----+
aberk 0:5c2ad81551aa 93 * Channel A | | | | | |
aberk 0:5c2ad81551aa 94 * ---+ +-----+ +-----+ +-----
aberk 0:5c2ad81551aa 95 * ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 96 * ^ +-----+ ^ +-----+ ^ +-----+
aberk 0:5c2ad81551aa 97 * Channel B ^ | ^ | ^ | ^ | ^ | |
aberk 0:5c2ad81551aa 98 * ------+ ^ +-----+ ^ +-----+ +--
aberk 0:5c2ad81551aa 99 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 100 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 101 * ^ ^ ^ +--+ ^ ^ +--+ ^
aberk 0:5c2ad81551aa 102 * ^ ^ ^ | | ^ ^ | | ^
aberk 0:5c2ad81551aa 103 * Index ------------+ +--------+ +-----------
aberk 0:5c2ad81551aa 104 * ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
aberk 0:5c2ad81551aa 105 * Pulse count 0 1 2 3 4 5 6 7 8 9 ...
aberk 0:5c2ad81551aa 106 * Rev. count 0 1 2
aberk 0:5c2ad81551aa 107 *
aberk 0:5c2ad81551aa 108 * Rotational position in degrees can be calculated by:
aberk 0:5c2ad81551aa 109 *
aberk 0:5c2ad81551aa 110 * (pulse count / X * N) * 360
aberk 0:5c2ad81551aa 111 *
aberk 0:5c2ad81551aa 112 * Where X is the encoding type [e.g. X4 encoding => X=4], and N is the number
aberk 0:5c2ad81551aa 113 * of pulses per revolution.
aberk 0:5c2ad81551aa 114 *
aberk 0:5c2ad81551aa 115 * Linear position can be calculated by:
aberk 0:5c2ad81551aa 116 *
aberk 0:5c2ad81551aa 117 * (pulse count / X * N) * (1 / PPI)
aberk 0:5c2ad81551aa 118 *
aberk 0:5c2ad81551aa 119 * Where X is encoding type [e.g. X4 encoding => X=44], N is the number of
aberk 0:5c2ad81551aa 120 * pulses per revolution, and PPI is pulses per inch, or the equivalent for
aberk 0:5c2ad81551aa 121 * any other unit of displacement. PPI can be calculated by taking the
aberk 0:5c2ad81551aa 122 * circumference of the wheel or encoder disk and dividing it by the number
aberk 0:5c2ad81551aa 123 * of pulses per revolution.
aberk 0:5c2ad81551aa 124 */
aberk 0:5c2ad81551aa 125
aberk 0:5c2ad81551aa 126 /**
aberk 0:5c2ad81551aa 127 * Includes
aberk 0:5c2ad81551aa 128 */
aberk 0:5c2ad81551aa 129 #include "QEI.h"
aberk 0:5c2ad81551aa 130
aberk 0:5c2ad81551aa 131 QEI::QEI(PinName channelA,
aberk 0:5c2ad81551aa 132 PinName channelB,
aberk 0:5c2ad81551aa 133 PinName index,
aberk 0:5c2ad81551aa 134 int pulsesPerRev,
aberk 0:5c2ad81551aa 135 Encoding encoding) : channelA_(channelA), channelB_(channelB),
aberk 0:5c2ad81551aa 136 index_(index) {
aberk 0:5c2ad81551aa 137
aberk 0:5c2ad81551aa 138 pulses_ = 0;
aberk 0:5c2ad81551aa 139 revolutions_ = 0;
aberk 0:5c2ad81551aa 140 pulsesPerRev_ = pulsesPerRev;
aberk 0:5c2ad81551aa 141 encoding_ = encoding;
jvfausto 4:dc96133b5129 142
jvfausto 4:dc96133b5129 143 ti.start();
aberk 0:5c2ad81551aa 144 //Workout what the current state is.
aberk 0:5c2ad81551aa 145 int chanA = channelA_.read();
aberk 0:5c2ad81551aa 146 int chanB = channelB_.read();
aberk 0:5c2ad81551aa 147
aberk 0:5c2ad81551aa 148 //2-bit state.
aberk 0:5c2ad81551aa 149 currState_ = (chanA << 1) | (chanB);
aberk 0:5c2ad81551aa 150 prevState_ = currState_;
aberk 0:5c2ad81551aa 151
aberk 0:5c2ad81551aa 152 //X2 encoding uses interrupts on only channel A.
aberk 0:5c2ad81551aa 153 //X4 encoding uses interrupts on channel A,
aberk 0:5c2ad81551aa 154 //and on channel B.
aberk 0:5c2ad81551aa 155 channelA_.rise(this, &QEI::encode);
aberk 0:5c2ad81551aa 156 channelA_.fall(this, &QEI::encode);
aberk 0:5c2ad81551aa 157
aberk 0:5c2ad81551aa 158 //If we're using X4 encoding, then attach interrupts to channel B too.
aberk 0:5c2ad81551aa 159 if (encoding == X4_ENCODING) {
aberk 0:5c2ad81551aa 160 channelB_.rise(this, &QEI::encode);
aberk 0:5c2ad81551aa 161 channelB_.fall(this, &QEI::encode);
aberk 0:5c2ad81551aa 162 }
aberk 0:5c2ad81551aa 163 //Index is optional.
aberk 0:5c2ad81551aa 164 if (index != NC) {
aberk 0:5c2ad81551aa 165 index_.rise(this, &QEI::index);
aberk 0:5c2ad81551aa 166 }
aberk 0:5c2ad81551aa 167
aberk 0:5c2ad81551aa 168 }
aberk 0:5c2ad81551aa 169
aberk 0:5c2ad81551aa 170 void QEI::reset(void) {
aberk 0:5c2ad81551aa 171
aberk 0:5c2ad81551aa 172 pulses_ = 0;
aberk 0:5c2ad81551aa 173 revolutions_ = 0;
aberk 0:5c2ad81551aa 174
aberk 0:5c2ad81551aa 175 }
aberk 0:5c2ad81551aa 176
aberk 0:5c2ad81551aa 177 int QEI::getCurrentState(void) {
aberk 0:5c2ad81551aa 178
aberk 0:5c2ad81551aa 179 return currState_;
aberk 0:5c2ad81551aa 180
aberk 0:5c2ad81551aa 181 }
aberk 0:5c2ad81551aa 182
aberk 0:5c2ad81551aa 183 int QEI::getPulses(void) {
aberk 0:5c2ad81551aa 184
aberk 0:5c2ad81551aa 185 return pulses_;
aberk 0:5c2ad81551aa 186
aberk 0:5c2ad81551aa 187 }
aberk 0:5c2ad81551aa 188
aberk 0:5c2ad81551aa 189
aberk 0:5c2ad81551aa 190 // +-------------+
aberk 0:5c2ad81551aa 191 // | X2 Encoding |
aberk 0:5c2ad81551aa 192 // +-------------+
aberk 0:5c2ad81551aa 193 //
aberk 0:5c2ad81551aa 194 // When observing states two patterns will appear:
aberk 0:5c2ad81551aa 195 //
aberk 0:5c2ad81551aa 196 // Counter clockwise rotation:
aberk 0:5c2ad81551aa 197 //
aberk 0:5c2ad81551aa 198 // 10 -> 01 -> 10 -> 01 -> ...
aberk 0:5c2ad81551aa 199 //
aberk 0:5c2ad81551aa 200 // Clockwise rotation:
aberk 0:5c2ad81551aa 201 //
aberk 0:5c2ad81551aa 202 // 11 -> 00 -> 11 -> 00 -> ...
aberk 0:5c2ad81551aa 203 //
aberk 0:5c2ad81551aa 204 // We consider counter clockwise rotation to be "forward" and
aberk 0:5c2ad81551aa 205 // counter clockwise to be "backward". Therefore pulse count will increase
aberk 0:5c2ad81551aa 206 // during counter clockwise rotation and decrease during clockwise rotation.
aberk 0:5c2ad81551aa 207 //
aberk 0:5c2ad81551aa 208 // +-------------+
aberk 0:5c2ad81551aa 209 // | X4 Encoding |
aberk 0:5c2ad81551aa 210 // +-------------+
aberk 0:5c2ad81551aa 211 //
aberk 0:5c2ad81551aa 212 // There are four possible states for a quadrature encoder which correspond to
aberk 0:5c2ad81551aa 213 // 2-bit gray code.
aberk 0:5c2ad81551aa 214 //
aberk 0:5c2ad81551aa 215 // A state change is only valid if of only one bit has changed.
aberk 0:5c2ad81551aa 216 // A state change is invalid if both bits have changed.
aberk 0:5c2ad81551aa 217 //
aberk 0:5c2ad81551aa 218 // Clockwise Rotation ->
aberk 0:5c2ad81551aa 219 //
aberk 0:5c2ad81551aa 220 // 00 01 11 10 00
aberk 0:5c2ad81551aa 221 //
aberk 0:5c2ad81551aa 222 // <- Counter Clockwise Rotation
aberk 0:5c2ad81551aa 223 //
aberk 0:5c2ad81551aa 224 // If we observe any valid state changes going from left to right, we have
aberk 0:5c2ad81551aa 225 // moved one pulse clockwise [we will consider this "backward" or "negative"].
aberk 0:5c2ad81551aa 226 //
aberk 0:5c2ad81551aa 227 // If we observe any valid state changes going from right to left we have
aberk 0:5c2ad81551aa 228 // moved one pulse counter clockwise [we will consider this "forward" or
aberk 0:5c2ad81551aa 229 // "positive"].
aberk 0:5c2ad81551aa 230 //
aberk 0:5c2ad81551aa 231 // We might enter an invalid state for a number of reasons which are hard to
aberk 0:5c2ad81551aa 232 // predict - if this is the case, it is generally safe to ignore it, update
aberk 0:5c2ad81551aa 233 // the state and carry on, with the error correcting itself shortly after.
aberk 0:5c2ad81551aa 234 void QEI::encode(void) {
aberk 0:5c2ad81551aa 235
aberk 0:5c2ad81551aa 236 int change = 0;
aberk 0:5c2ad81551aa 237 int chanA = channelA_.read();
aberk 0:5c2ad81551aa 238 int chanB = channelB_.read();
jvfausto 3:0035b165ecc4 239 // printf("in here\r\n");
aberk 0:5c2ad81551aa 240 //2-bit state.
aberk 0:5c2ad81551aa 241 currState_ = (chanA << 1) | (chanB);
aberk 0:5c2ad81551aa 242
aberk 0:5c2ad81551aa 243 if (encoding_ == X2_ENCODING) {
aberk 0:5c2ad81551aa 244
aberk 0:5c2ad81551aa 245 //11->00->11->00 is counter clockwise rotation or "forward".
aberk 0:5c2ad81551aa 246 if ((prevState_ == 0x3 && currState_ == 0x0) ||
aberk 0:5c2ad81551aa 247 (prevState_ == 0x0 && currState_ == 0x3)) {
aberk 0:5c2ad81551aa 248
aberk 0:5c2ad81551aa 249 pulses_++;
aberk 0:5c2ad81551aa 250
aberk 0:5c2ad81551aa 251 }
aberk 0:5c2ad81551aa 252 //10->01->10->01 is clockwise rotation or "backward".
aberk 0:5c2ad81551aa 253 else if ((prevState_ == 0x2 && currState_ == 0x1) ||
aberk 0:5c2ad81551aa 254 (prevState_ == 0x1 && currState_ == 0x2)) {
aberk 0:5c2ad81551aa 255
aberk 0:5c2ad81551aa 256 pulses_--;
aberk 0:5c2ad81551aa 257
aberk 0:5c2ad81551aa 258 }
aberk 0:5c2ad81551aa 259
aberk 0:5c2ad81551aa 260 } else if (encoding_ == X4_ENCODING) {
aberk 0:5c2ad81551aa 261
aberk 0:5c2ad81551aa 262 //Entered a new valid state.
aberk 0:5c2ad81551aa 263 if (((currState_ ^ prevState_) != INVALID) && (currState_ != prevState_)) {
aberk 0:5c2ad81551aa 264 //2 bit state. Right hand bit of prev XOR left hand bit of current
aberk 0:5c2ad81551aa 265 //gives 0 if clockwise rotation and 1 if counter clockwise rotation.
aberk 0:5c2ad81551aa 266 change = (prevState_ & PREV_MASK) ^ ((currState_ & CURR_MASK) >> 1);
aberk 0:5c2ad81551aa 267
aberk 0:5c2ad81551aa 268 if (change == 0) {
aberk 0:5c2ad81551aa 269 change = -1;
aberk 0:5c2ad81551aa 270 }
aberk 0:5c2ad81551aa 271
aberk 0:5c2ad81551aa 272 pulses_ -= change;
aberk 0:5c2ad81551aa 273 }
aberk 0:5c2ad81551aa 274 }
aberk 0:5c2ad81551aa 275 prevState_ = currState_;
aberk 0:5c2ad81551aa 276 }
aberk 0:5c2ad81551aa 277
jvfausto 1:f57640259245 278 float QEI::getRevolutions(){
jvfausto 1:f57640259245 279 if (encoding_ == X2_ENCODING)
jvfausto 2:2a173fdae3ca 280 {
jvfausto 2:2a173fdae3ca 281 return (float)pulses_ / pulsesPerRev_;
jvfausto 2:2a173fdae3ca 282 }
jvfausto 1:f57640259245 283 else
jvfausto 2:2a173fdae3ca 284 return (float)pulses_ / (4 * pulsesPerRev_);
jvfausto 1:f57640259245 285 }
jvfausto 1:f57640259245 286
jvfausto 2:2a173fdae3ca 287 float QEI::getDistance(float diameter)
jvfausto 1:f57640259245 288 {
jvfausto 4:dc96133b5129 289 oldDistance_ = newDistance_;
jvfausto 4:dc96133b5129 290 newDistance_ = getRevolutions()*diameter*3.1415926;
jvfausto 4:dc96133b5129 291 return newDistance_;
jvfausto 1:f57640259245 292 }
jvfausto 1:f57640259245 293
aberk 0:5c2ad81551aa 294 void QEI::index(void) {
aberk 0:5c2ad81551aa 295
aberk 0:5c2ad81551aa 296 revolutions_++;
aberk 0:5c2ad81551aa 297 }
jvfausto 4:dc96133b5129 298 float QEI::getVelosity()
jvfausto 4:dc96133b5129 299 {
jvfausto 4:dc96133b5129 300 getDistance(53.975);
jvfausto 4:dc96133b5129 301 velosity_ = ti.read()*(newDistance_-oldDistance_);
jvfausto 4:dc96133b5129 302 ti.reset();
jvfausto 4:dc96133b5129 303 return velosity_;
jvfausto 4:dc96133b5129 304 }
jvfausto 4:dc96133b5129 305