FtEncoder.h

00001 #ifndef FTENCODER_H
00002 #define FTENCODER_H
00003 
00004 #include "InterruptIn.h"
00005 #include "us_ticker_api.h"
00006 #include "FunctionPointer.h"
00007 #include "TimeoutTweaked.h"
00008 
00009 using namespace mbed;
00010 
00011 /// Simple Interface for the simple encoder of the red fischertechnik motors.
00012 /// The interface counts both, rising and falling edges, resulting in 150 counts per revolution.
00013 /// The interface also provides a speed measurement updated with each edge. 
00014 /// @note Connect the green wire to GND, the red one to +3.3V and the 
00015 /// black signal line to any of mbed numbered pins. Additionally connect the signal line
00016 /// via a pullup resitor to +3.3V. A 10K resistor works fine.
00017 /// 
00018 class FtEncoder
00019 {
00020     static const float c_speedFactor = 1e6/75.0; /// 1/(µs * 150/2) edges per revolution)
00021     static const int c_nTmStmps = 1<<2; /// size of ringbuffer: Has to be 2^x
00022 
00023     InterruptIn m_encIRQ;
00024     TimeoutTweaked m_tmOut;
00025 
00026     volatile unsigned int m_cnt; /// edge counter
00027     unsigned int m_standStillTimeout; 
00028     volatile unsigned int m_cursor;  /// ringbuffer cursor
00029     volatile uint32_t m_timeStamps[c_nTmStmps]; /// ringbuffer of edge timestamps 
00030 
00031     FunctionPointer m_callBack;
00032 
00033     /// ISR called on rising and falling encoder edges
00034     void encoderISR();
00035     /// ISR called on edge timeout i.e. standstill
00036     void timeoutISR();
00037 
00038 public:
00039 
00040     /// create a simple interface to the encoder connected to the given pin
00041     /// @param name of the pin the black encoder signal wire is connected to
00042     /// @param standStillTimeout After this time [µs] without any encoder edge getSpeed() returns zero
00043     FtEncoder(PinName pwm, unsigned int standStillTimeout=50000);
00044 
00045     /// get number of falling and rising encoder edges
00046     inline unsigned int getCounter() const {
00047         return m_cnt;
00048     };
00049 
00050     /// reset the encoder edge counter to the given value (default is 0)
00051     inline void resetCounter(unsigned int cnt=0) {
00052         m_cnt=cnt;
00053     };
00054 
00055     /// get period [µs] between the two latest edges of same direction (rising or falling)
00056     /// @note Returns standStillTimeout if motor stands still or no edges have been detected yet
00057     unsigned int getLastPeriod() const;
00058 
00059     /// get time stamp [µs] of last update i.e. encoder edge or timeout
00060     unsigned int getTimeStampOfLastUpdate() const {
00061         return m_timeStamps[m_cursor];
00062     };
00063 
00064     /// returns current time stamp [µs]
00065     /// @note simply calls us_ticker_read() from mbed's C-API (capi/us_ticker_api.h)
00066     inline unsigned int  getCurrentTimeStamp() const {
00067         return us_ticker_read();
00068     }
00069 
00070     /// get speed in revolutions per second (Hz)
00071     float getSpeed() const;
00072 
00073     /// hook in a call back to the encoder ISR e.g. for sending a RTOS signal
00074     void setCallBack(FunctionPointer callBack) {
00075         m_callBack=callBack;
00076     };
00077 };
00078 
00079 #endif