Ronald Niederhagen
rotary encoder with push button based on work I found elswhere.
Diff: QEI.h
- Revision:
- 0:ef2f1bbeb8e1
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/QEI.h Mon Dec 18 16:54:00 2017 +0000
@@ -0,0 +1,244 @@
+/**
+ * @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,
+ 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.
+ */
+
+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_;
+
+};
+
+#endif /* QEI_H */
+