File content as of revision 6:ea3b3f50c893:

#include "mbed.h"
#include "MODSERIAL.h"
#include "FastPWM.h"
#include "QEI.h"
#include <math.h>
#include "BiQuad.h"

DigitalIn button1(D12);
AnalogIn pot2(A0);
Ticker motor; //ticker to call motor values
DigitalOut motor1Direction(D7); // is a boolean
FastPWM motor1Velocity(D6);
MODSERIAL pc(USBTX, USBRX);
QEI Encoder(D8,D9,NC,8400);
volatile double frequency = 17000.0;
volatile double period_signal = 1.0/frequency;
float vel = 0.0f;
float referencevelocity;
float motorvalue2;
int counts;
float position1 = 0;
float position2;
float position11;
float position22;
float timeinterval = 0.001f;
float measuredvelocity;
double Kp = 5;
double Ki = 0.1;
double Kd = 1;
float motorvalue;
float desiredposition; 
float measuredposition;
float referenceposition;



// --------------------   README ------------------------------------
// positive referenceposition corresponds to a counterclockwise motion
// negative referenceposition corresponds to a clockwise motion 

//PID control implementation (BiQuead)
double PID_controller(double error)
{
    static double error_integral = 0;
    static double error_prev = error;
    static BiQuad LowPassFilter(0.0640, 0.1279, 0.0640, -1.1683, 0.4241);
    
    //Proportional part:
    double u_k = Kp * error;
    
    // Integreal part
    error_integral = error_integral + error * timeinterval;
    double u_i = Ki*error_integral;
    
    // Derivate part
    double error_derivative = (error - error_prev)/timeinterval;
    double filtered_error_derivative = LowPassFilter.step(error_derivative);
    double u_d = Kd * filtered_error_derivative;
    error_prev = error;
    
    //sum all parts and return it
    return u_k + u_i + u_d;
}

//get the measured position
double getmeasuredposition()
{   
    counts = Encoder.getPulses();
    counts = counts % 8400;
    measuredposition = ((float)counts) / 8400.0f * 2.0f;
    
    return measuredposition;
}

//get the reference of the velocity
double getreferenceposition()
{
    referenceposition = 1; //this determines the amount of spins
    return referenceposition;
}   

//send value to motor
void sendtomotor(float motorvalue)
{   
    motorvalue2 = motorvalue;
    vel = fabs(motorvalue);
    vel = vel > 1.0f ? 1.0f : vel;   //if velocity is greater than 1, reduce to 1, otherwise remain vel
    motor1Velocity = vel;

    motor1Direction = (motorvalue > 0.0f); //boolean output: true gives counterclockwise direction, false gives clockwise direction
}

// function to call reference velocity, measured velocity and controls motor with feedback
void measureandcontrol(void)
{
    float referenceposition = getreferenceposition();
    measuredposition = getmeasuredposition();
    motorvalue = PID_controller(referenceposition - measuredposition);
    sendtomotor(motorvalue);
}
int main()
{
    pc.baud(115200);
    pc.printf("Starting...\r\n");
    motor1Velocity.period(period_signal);
    motor.attach(measureandcontrol, timeinterval); 
    while(true)
    {
        wait(0.5);
        //pc.printf("velocity = %f\r\n", vel);
        //pc.printf("motor1Direction = %i\r\n", (int)motor1Direction);
        //pc.printf("motorvalue2 = %f\r\n", motorvalue2);
        pc.printf("number of counts %i\r\n", counts);
        pc.printf("measured position is %f\r\n", measuredposition);
        //pc.printf("position1 = %f\r\n",position11);
        //pc.printf("position2 = %f\r\n",position22);
        pc.printf("motorvalue is %f\r\n", motorvalue);
        
        char c = pc.getcNb();
        
        if (c == 'c')
        {
            pc.printf("Programm stops running");
            motorvalue = 0;
            sendtomotor(motorvalue);
            return -1;
        }
    }
}