File content as of revision 3:f169c357a44d:

#include "mbed.h"
#include "QEI.h"  //QEI is a quadrature encoder library
#define pi  3.14159265358979323846


//create a new quadrature encoder object
QEI encoder(p25, p26, NC, 1200, QEI::X4_ENCODING);       //(encoder channel 1 pin, encoder channel 2 pin, index (n/a here), counts per revolution, mode (X4, X2))

//Ticker SampleFrequency;

//Values that will be used for the PID controller

int steps_per_rev = 1200; //Encoder CPR * gear ratio
float position = 0;
float error = 0;
float old_error = 0;
float goal_position = 0;
float p_gain = 1;
float d_gain = 0;
float sample_period = .01;
float command = 0;


PwmOut Motor[2] = {p21, p22};       //h-bridge pwm pins
DigitalOut dir1[2] = {p29, p15};    //h-bridge direction 1 pins
DigitalOut dir2[2] = {p30, p16}; 
//

float pulsesToRadians(float pulses) //Encoder steps to revolutions of output shaft in radians
{
    return ((pulses/steps_per_rev)*(2*pi));
}

void signal_to_hbridge( float signal, int motor)   //Input of -1 means full reverse, 1 means full forward
{                                       //An input of magnitude > 1 gets reduced to 1 (or -1) by the pwm.write function
    if (signal < 0) {
        dir1[motor].write(0);
        dir2[motor].write(1);
        Motor[motor].write(signal * -1);
    } 
    else if (signal > 0) {
        dir1[motor].write(1);
        dir2[motor].write(0);
        Motor[motor].write(signal);
    } 
    else {
        dir1[motor].write(0);
        dir2[motor].write(0);
    }
}
float updateCommand(void){
    
    position = pulsesToRadians(encoder.getPulses());        //use the getPulses functin to read encoder position, convert value to radians
    old_error = error;                                      
    error = position - goal_position;
    return p_gain*error + d_gain*(error-old_error)/sample_period;    //modify the command based on position feedback
    
}





int main() {
    Timer timer;
    timer.start();
    Motor[0].period(.00005);
    Motor[1].period(.00005);
    //SampleFrequency.attach(&updateCommand, sample_period);        //Encoder will be sampled at 2.5 kHz
    while(1) {
    
           if (timer.read() > .0004){
                command = updateCommand();
                timer.reset();

           }
           signal_to_hbridge(command, 0);
     
        }
    }