PID based Line Follower Robot

/* 
*  www.nishanchettri.com
*  github.com/nishanchettri
*  admin@nishanchettri.com
*/

#include <AFMotor.h>    //Adafruit Motor Shield Library. First you must download and install AFMotor library
#include <QTRSensors.h> //Pololu QTR Sensor Library. First you must download and install QTRSensors library
  
AF_DCMotor motor1(1, MOTOR12_1KHZ ); //create motor #1 using M1 output on Motor Drive Shield, set to 1kHz PWM frequency
AF_DCMotor motor2(2, MOTOR12_1KHZ ); //create motor #2 using M2 output on Motor Drive Shield, set to 1kHz PWM frequency


#define KP 2 //experiment to determine this, start by something small that just makes your bot follow the line at a slow speed
#define KD 4 //experiment to determine this, slowly increase the speeds and adjust this value. ( Note: Kp < Kd) 
#define M1_minumum_speed 50  //minimum speed of the Motor1
#define M2_minumum_speed 50  //minimum speed of the Motor2
#define M1_maksimum_speed 150 //max. speed of the Motor1
#define M2_maksimum_speed 150 //max. speed of the Motor2
#define MIDDLE_SENSOR 4       //number of middle sensor used
#define NUM_SENSORS 5         //number of sensors used
#define TIMEOUT 2500          //waits for 2500 us for sensor outputs to go low
#define EMITTER_PIN 2         //emitterPin is the Arduino digital pin that controls whether the IR LEDs are on or off. Emitter is controlled by digital pin 2
#define DEBUG 0

//sensors 0 through 5 are connected to analog inputs 0 through 5, respectively
QTRSensorsRC qtrrc((unsigned char[]) {A4,A3,A2,A1,A0} ,NUM_SENSORS, TIMEOUT, EMITTER_PIN);
  
unsigned int sensorValues[NUM_SENSORS];
  
void setup()
{

manual_calibration();

set_motors(0,0);
}
  
int lastError = 0;
int last_proportional = 0;
int integral = 0;
  
void loop()
{
unsigned int sensors[5];
int position = qtrrc.readLine(sensors); //get calibrated readings along with the line position, refer to the QTR Sensors Arduino Library for more details on line position.
int error = position - 2000;

  
int motorSpeed = KP * error + KD * (error - lastError);
lastError = error;
  
int leftMotorSpeed = M1_minumum_speed + motorSpeed;
int rightMotorSpeed = M2_minumum_speed - motorSpeed;
  
// set motor speeds using the two motor speed variables above
set_motors(leftMotorSpeed, rightMotorSpeed);
}
  
void set_motors(int motor1speed, int motor2speed)
{
if (motor1speed > M1_maksimum_speed ) motor1speed = M1_maksimum_speed;
if (motor2speed > M2_maksimum_speed ) motor2speed = M2_maksimum_speed;
if (motor1speed < 0) motor1speed = 0; 
if (motor2speed < 0) motor2speed = 0; 
motor1.setSpeed(motor1speed); 
motor2.setSpeed(motor2speed);

motor1.run(FORWARD); 
motor2.run(FORWARD);
}

//calibrate for sometime by sliding the sensors across the line, or you may use auto-calibration instead
void manual_calibration() {
  
int i;
for (i = 0; i < 250; i++)
{
 
qtrrc.calibrate(QTR_EMITTERS_ON);
delay(20);
}
  
if (DEBUG) {
Serial.begin(9600);
for (int i = 0; i < NUM_SENSORS; i++)
{
Serial.print(qtrrc.calibratedMinimumOn[i]);
Serial.print(' ');
}
Serial.println();
  
for (int i = 0; i < NUM_SENSORS; i++)
{
Serial.print(qtrrc.calibratedMaximumOn[i]);
Serial.print(' ');
}
Serial.println();
Serial.println();
}
}