Simon Ford
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LabVIEW_PID
Simple PID example for LabVIEW
Diff: QEI.h
- Revision:
- 0:e3b759ab4b5c
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/QEI.h Mon Aug 02 18:53:02 2010 +0000 @@ -0,0 +1,205 @@ +//****************************************************************************/ +//@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 disk 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 +// +// This interface uses 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 ... +// +// An optional index channel can be used which determines when a full +// revolution has occured. +// +// If a 4 pules per revolution encoder was used, 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 [in our case 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 [in our case X=4], 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: + + /** + * 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. + */ + QEI(PinName channelA, PinName channelB, PinName index, int pulsesPerRev); + + /** + * 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); + +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); + + InterruptIn* channelA_; + InterruptIn* channelB_; + InterruptIn* index_; + + int pulsesPerRev_; + int revolutions_; + int prevState_; + int currState_; + + volatile int pulses_; + +}; + +#endif /* QEI_H */