QuadEnc.hpp

00001 /**
00002  * @class QuadEnc
00003  * @date June 2nd, 2016
00004  * @author Weimen Li
00005  * @brief Header file for a class which encapsulates a quadrature encoder.
00006  * @remark The algorith used to read from the encoder may be found at:
00007  * http://makeatronics.blogspot.com/2013/02/efficiently-reading-quadrature-with.html
00008  */
00009 
00010 #ifndef QUADENC_H_
00011 #define QUADENC_H_
00012 #include "mbed.h"
00013 
00014 class QuadEnc {
00015 public:
00016     /**
00017      * @brief Constructor for the QuadEnc object.
00018      * @param ChannelA The pin Channel A is connected to.
00019      * @param ChannelB The pin Channel B is connected to.
00020      * @param CPR The number of counts per revolution of the encoder.
00021      */
00022     QuadEnc(PinName ChannelA, PinName ChannelB, float CPR);
00023     virtual ~QuadEnc();
00024 
00025     /**
00026      * @brief Returns true when a new encoder count has been seen.
00027      * @returns Whether a new encoder count has been seen.
00028      * @remark Sets the hasNewCount flag to false after being called.
00029      */
00030     bool hasNewCount();
00031     /**
00032      * @brief Returns the current encoder count.
00033      * @returns The current encoder count.
00034      * @remark Declared to be inline for greater performance.
00035      */
00036     inline int32_t getCount() {
00037         // Generally, we would disable interrupts to avoid corruption here.
00038         // However, the returned value is the word size of the processor, so
00039         // It should be safe. Additionally, any corruption may only happen on the LSB.
00040         return count;
00041     }
00042     
00043     /**
00044      * @brief Returns the number of revolutions that have been counted.
00045      * @returns The number of revolutions that have been counted.
00046      */
00047     float getRevs();
00048 
00049     /**
00050      * @brief Resets the internal state variables of the encoder.
00051      * @returns void
00052      */
00053     void reset();
00054 private:
00055      /// The current encoder count since the program started.
00056     volatile int32_t count;
00057      /// Whether the encoder has a new count.
00058     volatile bool bHasNewCount;
00059     /// The number of counts per revolution.
00060     const float CPR;
00061     
00062     /// Digital Input for Channel A.
00063     DigitalIn ChannelAIn;
00064     /// Digital Input for Channel B.
00065     DigitalIn ChannelBIn;
00066     
00067     /// Interrupt Object for Channel A.
00068     InterruptIn ChannelAInter;
00069     /// Interrupt Object for Channel B.
00070     InterruptIn ChannelBInter;
00071 
00072     /// Member Function ISR to be called when a change is detected on the channel pins.
00073     void QuadEncISR();
00074 
00075     /// The previous encoder count.
00076     int32_t prevCount;
00077     /// The previous number of revolutions.
00078     float prevRevs;
00079     /// The raw encoder reading.
00080     uint8_t enc_val;
00081 };
00082 
00083 #endif /* QUADENC_H_ */