QEI - | Mbed

Users » farbodjam » Code » QEI

QEI.h@0:fc0482177a6d, 2011-08-27 (annotated)

Committer:: farbodjam
Date:: Sat Aug 27 12:47:06 2011 +0000
Revision:: 0:fc0482177a6d

Who changed what in which revision?

User	Revision	Line number	New contents of line
farbodjam	0:fc0482177a6d	1	/**
farbodjam	0:fc0482177a6d	2	* @author Aaron Berk
farbodjam	0:fc0482177a6d	3	*
farbodjam	0:fc0482177a6d	4	* @section LICENSE
farbodjam	0:fc0482177a6d	5	*
farbodjam	0:fc0482177a6d	6	* Copyright (c) 2010 ARM Limited
farbodjam	0:fc0482177a6d	7	*
farbodjam	0:fc0482177a6d	8	* Permission is hereby granted, free of charge, to any person obtaining a copy
farbodjam	0:fc0482177a6d	9	* of this software and associated documentation files (the "Software"), to deal
farbodjam	0:fc0482177a6d	10	* in the Software without restriction, including without limitation the rights
farbodjam	0:fc0482177a6d	11	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
farbodjam	0:fc0482177a6d	12	* copies of the Software, and to permit persons to whom the Software is
farbodjam	0:fc0482177a6d	13	* furnished to do so, subject to the following conditions:
farbodjam	0:fc0482177a6d	14	*
farbodjam	0:fc0482177a6d	15	* The above copyright notice and this permission notice shall be included in
farbodjam	0:fc0482177a6d	16	* all copies or substantial portions of the Software.
farbodjam	0:fc0482177a6d	17	*
farbodjam	0:fc0482177a6d	18	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
farbodjam	0:fc0482177a6d	19	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
farbodjam	0:fc0482177a6d	20	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
farbodjam	0:fc0482177a6d	21	* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
farbodjam	0:fc0482177a6d	22	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
farbodjam	0:fc0482177a6d	23	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
farbodjam	0:fc0482177a6d	24	* THE SOFTWARE.
farbodjam	0:fc0482177a6d	25	*
farbodjam	0:fc0482177a6d	26	* @section DESCRIPTION
farbodjam	0:fc0482177a6d	27	*
farbodjam	0:fc0482177a6d	28	* Quadrature Encoder Interface.
farbodjam	0:fc0482177a6d	29	*
farbodjam	0:fc0482177a6d	30	* A quadrature encoder consists of two code tracks on a disc which are 90
farbodjam	0:fc0482177a6d	31	* degrees out of phase. It can be used to determine how far a wheel has
farbodjam	0:fc0482177a6d	32	* rotated, relative to a known starting position.
farbodjam	0:fc0482177a6d	33	*
farbodjam	0:fc0482177a6d	34	* Only one code track changes at a time leading to a more robust system than
farbodjam	0:fc0482177a6d	35	* a single track, because any jitter around any edge won't cause a state
farbodjam	0:fc0482177a6d	36	* change as the other track will remain constant.
farbodjam	0:fc0482177a6d	37	*
farbodjam	0:fc0482177a6d	38	* Encoders can be a homebrew affair, consisting of infrared emitters/receivers
farbodjam	0:fc0482177a6d	39	* and paper code tracks consisting of alternating black and white sections;
farbodjam	0:fc0482177a6d	40	* alternatively, complete disk and PCB emitter/receiver encoder systems can
farbodjam	0:fc0482177a6d	41	* be bought, but the interface, regardless of implementation is the same.
farbodjam	0:fc0482177a6d	42	*
farbodjam	0:fc0482177a6d	43	* +-----+ +-----+ +-----+
farbodjam	0:fc0482177a6d	44	* Channel A \| ^ \| \| \| \| \|
farbodjam	0:fc0482177a6d	45	* ---+ ^ +-----+ +-----+ +-----
farbodjam	0:fc0482177a6d	46	* ^ ^
farbodjam	0:fc0482177a6d	47	* ^ +-----+ +-----+ +-----+
farbodjam	0:fc0482177a6d	48	* Channel B ^ \| \| \| \| \| \|
farbodjam	0:fc0482177a6d	49	* ------+ +-----+ +-----+ +-----
farbodjam	0:fc0482177a6d	50	* ^ ^
farbodjam	0:fc0482177a6d	51	* ^ ^
farbodjam	0:fc0482177a6d	52	* 90deg
farbodjam	0:fc0482177a6d	53	*
farbodjam	0:fc0482177a6d	54	* The interface uses X2 encoding by default which calculates the pulse count
farbodjam	0:fc0482177a6d	55	* based on reading the current state after each rising and falling edge of
farbodjam	0:fc0482177a6d	56	* channel A.
farbodjam	0:fc0482177a6d	57	*
farbodjam	0:fc0482177a6d	58	* +-----+ +-----+ +-----+
farbodjam	0:fc0482177a6d	59	* Channel A \| \| \| \| \| \|
farbodjam	0:fc0482177a6d	60	* ---+ +-----+ +-----+ +-----
farbodjam	0:fc0482177a6d	61	* ^ ^ ^ ^ ^
farbodjam	0:fc0482177a6d	62	* ^ +-----+ ^ +-----+ ^ +-----+
farbodjam	0:fc0482177a6d	63	* Channel B ^ \| ^ \| ^ \| ^ \| ^ \| \|
farbodjam	0:fc0482177a6d	64	* ------+ ^ +-----+ ^ +-----+ +--
farbodjam	0:fc0482177a6d	65	* ^ ^ ^ ^ ^
farbodjam	0:fc0482177a6d	66	* ^ ^ ^ ^ ^
farbodjam	0:fc0482177a6d	67	* Pulse count 0 1 2 3 4 5 ...
farbodjam	0:fc0482177a6d	68	*
farbodjam	0:fc0482177a6d	69	* This interface can also use X4 encoding which calculates the pulse count
farbodjam	0:fc0482177a6d	70	* based on reading the current state after each rising and falling edge of
farbodjam	0:fc0482177a6d	71	* either channel.
farbodjam	0:fc0482177a6d	72	*
farbodjam	0:fc0482177a6d	73	* +-----+ +-----+ +-----+
farbodjam	0:fc0482177a6d	74	* Channel A \| \| \| \| \| \|
farbodjam	0:fc0482177a6d	75	* ---+ +-----+ +-----+ +-----
farbodjam	0:fc0482177a6d	76	* ^ ^ ^ ^ ^
farbodjam	0:fc0482177a6d	77	* ^ +-----+ ^ +-----+ ^ +-----+
farbodjam	0:fc0482177a6d	78	* Channel B ^ \| ^ \| ^ \| ^ \| ^ \| \|
farbodjam	0:fc0482177a6d	79	* ------+ ^ +-----+ ^ +-----+ +--
farbodjam	0:fc0482177a6d	80	* ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
farbodjam	0:fc0482177a6d	81	* ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
farbodjam	0:fc0482177a6d	82	* Pulse count 0 1 2 3 4 5 6 7 8 9 ...
farbodjam	0:fc0482177a6d	83	*
farbodjam	0:fc0482177a6d	84	* It defaults
farbodjam	0:fc0482177a6d	85	*
farbodjam	0:fc0482177a6d	86	* An optional index channel can be used which determines when a full
farbodjam	0:fc0482177a6d	87	* revolution has occured.
farbodjam	0:fc0482177a6d	88	*
farbodjam	0:fc0482177a6d	89	* If a 4 pules per revolution encoder was used, with X4 encoding,
farbodjam	0:fc0482177a6d	90	* the following would be observed.
farbodjam	0:fc0482177a6d	91	*
farbodjam	0:fc0482177a6d	92	* +-----+ +-----+ +-----+
farbodjam	0:fc0482177a6d	93	* Channel A \| \| \| \| \| \|
farbodjam	0:fc0482177a6d	94	* ---+ +-----+ +-----+ +-----
farbodjam	0:fc0482177a6d	95	* ^ ^ ^ ^ ^
farbodjam	0:fc0482177a6d	96	* ^ +-----+ ^ +-----+ ^ +-----+
farbodjam	0:fc0482177a6d	97	* Channel B ^ \| ^ \| ^ \| ^ \| ^ \| \|
farbodjam	0:fc0482177a6d	98	* ------+ ^ +-----+ ^ +-----+ +--
farbodjam	0:fc0482177a6d	99	* ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
farbodjam	0:fc0482177a6d	100	* ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
farbodjam	0:fc0482177a6d	101	* ^ ^ ^ +--+ ^ ^ +--+ ^
farbodjam	0:fc0482177a6d	102	* ^ ^ ^ \| \| ^ ^ \| \| ^
farbodjam	0:fc0482177a6d	103	* Index ------------+ +--------+ +-----------
farbodjam	0:fc0482177a6d	104	* ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
farbodjam	0:fc0482177a6d	105	* Pulse count 0 1 2 3 4 5 6 7 8 9 ...
farbodjam	0:fc0482177a6d	106	* Rev. count 0 1 2
farbodjam	0:fc0482177a6d	107	*
farbodjam	0:fc0482177a6d	108	* Rotational position in degrees can be calculated by:
farbodjam	0:fc0482177a6d	109	*
farbodjam	0:fc0482177a6d	110	* (pulse count / X * N) * 360
farbodjam	0:fc0482177a6d	111	*
farbodjam	0:fc0482177a6d	112	* Where X is the encoding type [e.g. X4 encoding => X=4], and N is the number
farbodjam	0:fc0482177a6d	113	* of pulses per revolution.
farbodjam	0:fc0482177a6d	114	*
farbodjam	0:fc0482177a6d	115	* Linear position can be calculated by:
farbodjam	0:fc0482177a6d	116	*
farbodjam	0:fc0482177a6d	117	* (pulse count / X * N) * (1 / PPI)
farbodjam	0:fc0482177a6d	118	*
farbodjam	0:fc0482177a6d	119	* Where X is encoding type [e.g. X4 encoding => X=44], N is the number of
farbodjam	0:fc0482177a6d	120	* pulses per revolution, and PPI is pulses per inch, or the equivalent for
farbodjam	0:fc0482177a6d	121	* any other unit of displacement. PPI can be calculated by taking the
farbodjam	0:fc0482177a6d	122	* circumference of the wheel or encoder disk and dividing it by the number
farbodjam	0:fc0482177a6d	123	* of pulses per revolution.
farbodjam	0:fc0482177a6d	124	*/
farbodjam	0:fc0482177a6d	125
farbodjam	0:fc0482177a6d	126	#ifndef QEI_H
farbodjam	0:fc0482177a6d	127	#define QEI_H
farbodjam	0:fc0482177a6d	128
farbodjam	0:fc0482177a6d	129	/**
farbodjam	0:fc0482177a6d	130	* Includes
farbodjam	0:fc0482177a6d	131	*/
farbodjam	0:fc0482177a6d	132	#include "mbed.h"
farbodjam	0:fc0482177a6d	133
farbodjam	0:fc0482177a6d	134	/**
farbodjam	0:fc0482177a6d	135	* Defines
farbodjam	0:fc0482177a6d	136	*/
farbodjam	0:fc0482177a6d	137	#define PREV_MASK 0x1 //Mask for the previous state in determining direction
farbodjam	0:fc0482177a6d	138	//of rotation.
farbodjam	0:fc0482177a6d	139	#define CURR_MASK 0x2 //Mask for the current state in determining direction
farbodjam	0:fc0482177a6d	140	//of rotation.
farbodjam	0:fc0482177a6d	141	#define INVALID 0x3 //XORing two states where both bits have changed.
farbodjam	0:fc0482177a6d	142
farbodjam	0:fc0482177a6d	143	/**
farbodjam	0:fc0482177a6d	144	* Quadrature Encoder Interface.
farbodjam	0:fc0482177a6d	145	*/
farbodjam	0:fc0482177a6d	146	class QEI {
farbodjam	0:fc0482177a6d	147
farbodjam	0:fc0482177a6d	148	public:
farbodjam	0:fc0482177a6d	149
farbodjam	0:fc0482177a6d	150	typedef enum Encoding {
farbodjam	0:fc0482177a6d	151
farbodjam	0:fc0482177a6d	152	X2_ENCODING,
farbodjam	0:fc0482177a6d	153	X4_ENCODING
farbodjam	0:fc0482177a6d	154
farbodjam	0:fc0482177a6d	155	} Encoding;
farbodjam	0:fc0482177a6d	156
farbodjam	0:fc0482177a6d	157	/**
farbodjam	0:fc0482177a6d	158	* Constructor.
farbodjam	0:fc0482177a6d	159	*
farbodjam	0:fc0482177a6d	160	* Reads the current values on channel A and channel B to determine the
farbodjam	0:fc0482177a6d	161	* initial state.
farbodjam	0:fc0482177a6d	162	*
farbodjam	0:fc0482177a6d	163	* Attaches the encode function to the rise/fall interrupt edges of
farbodjam	0:fc0482177a6d	164	* channels A and B to perform X4 encoding.
farbodjam	0:fc0482177a6d	165	*
farbodjam	0:fc0482177a6d	166	* Attaches the index function to the rise interrupt edge of channel index
farbodjam	0:fc0482177a6d	167	* (if it is used) to count revolutions.
farbodjam	0:fc0482177a6d	168	*
farbodjam	0:fc0482177a6d	169	* @param channelA mbed pin for channel A input.
farbodjam	0:fc0482177a6d	170	* @param channelB mbed pin for channel B input.
farbodjam	0:fc0482177a6d	171	* @param index mbed pin for optional index channel input,
farbodjam	0:fc0482177a6d	172	* (pass NC if not needed).
farbodjam	0:fc0482177a6d	173	* @param pulsesPerRev Number of pulses in one revolution.
farbodjam	0:fc0482177a6d	174	* @param encoding The encoding to use. Uses X2 encoding by default. X2
farbodjam	0:fc0482177a6d	175	* encoding uses interrupts on the rising and falling edges
farbodjam	0:fc0482177a6d	176	* of only channel A where as X4 uses them on both
farbodjam	0:fc0482177a6d	177	* channels.
farbodjam	0:fc0482177a6d	178	*/
farbodjam	0:fc0482177a6d	179	QEI(PinName channelA, PinName channelB, PinName index, int pulsesPerRev, Encoding encoding = X2_ENCODING);
farbodjam	0:fc0482177a6d	180
farbodjam	0:fc0482177a6d	181	/**
farbodjam	0:fc0482177a6d	182	* Reset the encoder.
farbodjam	0:fc0482177a6d	183	*
farbodjam	0:fc0482177a6d	184	* Sets the pulses and revolutions count to zero.
farbodjam	0:fc0482177a6d	185	*/
farbodjam	0:fc0482177a6d	186	void reset(void);
farbodjam	0:fc0482177a6d	187
farbodjam	0:fc0482177a6d	188	/**
farbodjam	0:fc0482177a6d	189	* Read the state of the encoder.
farbodjam	0:fc0482177a6d	190	*
farbodjam	0:fc0482177a6d	191	* @return The current state of the encoder as a 2-bit number, where:
farbodjam	0:fc0482177a6d	192	* bit 1 = The reading from channel B
farbodjam	0:fc0482177a6d	193	* bit 2 = The reading from channel A
farbodjam	0:fc0482177a6d	194	*/
farbodjam	0:fc0482177a6d	195	int getCurrentState(void);
farbodjam	0:fc0482177a6d	196
farbodjam	0:fc0482177a6d	197	/**
farbodjam	0:fc0482177a6d	198	* Read the number of pulses recorded by the encoder.
farbodjam	0:fc0482177a6d	199	*
farbodjam	0:fc0482177a6d	200	* @return Number of pulses which have occured.
farbodjam	0:fc0482177a6d	201	*/
farbodjam	0:fc0482177a6d	202	int getPulses(void);
farbodjam	0:fc0482177a6d	203
farbodjam	0:fc0482177a6d	204	/**
farbodjam	0:fc0482177a6d	205	* Read the number of revolutions recorded by the encoder on the index channel.
farbodjam	0:fc0482177a6d	206	*
farbodjam	0:fc0482177a6d	207	* @return Number of revolutions which have occured on the index channel.
farbodjam	0:fc0482177a6d	208	*/
farbodjam	0:fc0482177a6d	209	int getRevolutions(void);
farbodjam	0:fc0482177a6d	210
farbodjam	0:fc0482177a6d	211	private:
farbodjam	0:fc0482177a6d	212
farbodjam	0:fc0482177a6d	213	/**
farbodjam	0:fc0482177a6d	214	* Update the pulse count.
farbodjam	0:fc0482177a6d	215	*
farbodjam	0:fc0482177a6d	216	* Called on every rising/falling edge of channels A/B.
farbodjam	0:fc0482177a6d	217	*
farbodjam	0:fc0482177a6d	218	* Reads the state of the channels and determines whether a pulse forward
farbodjam	0:fc0482177a6d	219	* or backward has occured, updating the count appropriately.
farbodjam	0:fc0482177a6d	220	*/
farbodjam	0:fc0482177a6d	221	void encode(void);
farbodjam	0:fc0482177a6d	222
farbodjam	0:fc0482177a6d	223	/**
farbodjam	0:fc0482177a6d	224	* Called on every rising edge of channel index to update revolution
farbodjam	0:fc0482177a6d	225	* count by one.
farbodjam	0:fc0482177a6d	226	*/
farbodjam	0:fc0482177a6d	227	void index(void);
farbodjam	0:fc0482177a6d	228
farbodjam	0:fc0482177a6d	229	Encoding encoding_;
farbodjam	0:fc0482177a6d	230
farbodjam	0:fc0482177a6d	231	InterruptIn channelA_;
farbodjam	0:fc0482177a6d	232	InterruptIn channelB_;
farbodjam	0:fc0482177a6d	233	InterruptIn index_;
farbodjam	0:fc0482177a6d	234
farbodjam	0:fc0482177a6d	235	int pulsesPerRev_;
farbodjam	0:fc0482177a6d	236	int prevState_;
farbodjam	0:fc0482177a6d	237	int currState_;
farbodjam	0:fc0482177a6d	238
farbodjam	0:fc0482177a6d	239	volatile int pulses_;
farbodjam	0:fc0482177a6d	240	volatile int revolutions_;
farbodjam	0:fc0482177a6d	241
farbodjam	0:fc0482177a6d	242	};
farbodjam	0:fc0482177a6d	243
farbodjam	0:fc0482177a6d	244	#endif /* QEI_H */

Repository toolbox

Export to desktop IDE

Build repository

Repository details

Type:	Program
Created:	27 Aug 2011
Imports:	250
Forks:	0
Commits:	1
Dependents:	1
Dependencies:	0
Followers:	4

QEI.h@0:fc0482177a6d, 2011-08-27 (annotated)

Who changed what in which revision?

Repository toolbox

Repository details

Important Information for this Arm website

Access Warning