File content as of revision 0:88e83d97a0ee:

#include 'mbed.h'

Ticker control_ticker;
PwmOut pwm_motor1(D4); //onderste motor
DigitalOut dir_motor1(D5);
AnalogIn potmeter1(A4);

// Sample time (motor1−timestep)
const double m1_Ts = 0.01;
// Controller gains (motor1−Kp,−Ki,...)
const double m1_Kp = 2.5, m1_Ki = 1.0, m1_Kd = 0.5;
double m1_err_int = 0, m1_prev_err = 0;
// Derivative filter coeicients (motor1−filter−b0,−b1,...)
const double m1_f_a1 = 1.0, m1_f_a2 = 2.0, m1_f_b0 = 1.0, m1_f_b1 = 3.0, m1_f_b2 = 4.0;
// Filter variables (motor1−filter−v1,−v2)
double m1_f_v1 = 0, m1_f_v2 = 0;

// Biquad filter (See slide 14)
double biquad( double u, double &v1, double &v2, const double a1, const double a2,
               const double b0, const double b1, const double b2 )
{
    double v = u − a1∗v1 − a2∗v2;
    double y = b0∗v + b1∗v1 + b2∗v2;
    v2 = v1;
    v1 = v;
    return y;
}

// Reusable PID controller with filter
double PID( double e, const double Kp, const double Ki, const double Kd, double Ts,
            double &e_int, double &e_prev, double &f_v1, double &f_v2, const double f_a1,
            const double f_a2, const double f_b0, const double f_b1, const double f_b3)
{
// Derivative
    double e_der = (e − e_prev)/Ts;
    e_der = biquad( e_der, f_v1, f_v2, f_a1, f_a2, f_b0, f_b1, f_b2 );
    e_prev = e;
// Integral
    e_int = e_int + Ts ∗ e;
// PID
    return Kp ∗ e + Ki ∗ e_int + Kd ∗ e_der;
}

void m1_Controller()
{
    double reference = potmeter1.read();
    double position = 0.002991∗encoder1.getPosition(); // Don’t use magic numbers!
    motor1 = PID( reference − position, m1_Kp, m1_Ki, m1_Kd, m1_Ts, m1_err_int,
                  m1_prev_err, m1_f_v1, m1_f_v2, m1_f_a1, m1_f_a2, m1_f_b0, m1_f_b1, m1_f_b2 );
    if(motor1 > 0)
        dir_motor1 = 0;
    else
        dir_motor1 = 1;

    pwm_motor1.write(abs(motor1));
} // Attach this function to a Ticker

int main()
{
    control_ticker.attach(m1_Controller, 0.01);

    while(1);
}