encoder.cpp

00001 #include "encoder.h"
00002 
00003 // Represents a quadrature motor encoder. Modified from mbed QEI 
00004 Encoder::Encoder(PinName channelA, PinName channelB) : 
00005     channelA_(channelA), 
00006     channelB_(channelB){
00007     pulses = 0;
00008 
00009     //Workout what the current state is.
00010     int chanA = channelA_.read();
00011     int chanB = channelB_.read();
00012 
00013     //2-bit state.
00014     currState_ = (chanA << 1) | (chanB);
00015     prevState_ = currState_;
00016 
00017     channelA_.rise(this, &Encoder::encode);
00018     channelA_.fall(this, &Encoder::encode);
00019 }
00020 
00021 //Internally updates the pulse count for the encoder.
00022 void Encoder::encode(void) {
00023     int chanA  = channelA_.read();
00024     int chanB  = channelB_.read();
00025 
00026     //2-bit state.
00027     currState_ = (chanA << 1) | (chanB);
00028 
00029     //11->00->11->00 is counter clockwise rotation or "forward".
00030     if ((prevState_ == 0x3 && currState_ == 0x0) ||
00031             (prevState_ == 0x0 && currState_ == 0x3)) {
00032         pulses+=2;
00033     }
00034     //10->01->10->01 is clockwise rotation or "backward".
00035     else if ((prevState_ == 0x2 && currState_ == 0x1) ||
00036              (prevState_ == 0x1 && currState_ == 0x2)) {
00037         pulses-=2;
00038     }
00039     
00040     prevState_ = currState_;
00041 }
00042 
00043 //Resets the encoder
00044 void Encoder::reset(void) {
00045     pulses = 0;
00046 }
00047 
00048 // Reset both encoders
00049 void Encoder:: resetEncoders(){
00050     leftEncoder.reset();
00051     rightEncoder.reset();
00052 }
00053 
00054 // Returns the average number of pulses across both encoders since last reset. Unit is encoder pulses; intended for straight driving only.
00055 int Encoder:: getEncoderDistance(bool left){
00056     
00057     return (left == 1) ? leftEncoder : rightEncoder;
00058 }