line finder robot

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line finder robot

Post by ashton87 » Wed Dec 13, 2017 9:17 am

hello everyone I have made a line follower robot using arduino onu with QTR-8 sensor, everything is okay so far it following the line perfectly,

but i want to add an operation that is the robot If got away from the line how can it search and get back to the line again automatically ?

Iv'e been searching for the code almost 1 month but i couldn't find or write it plz help me with the code

and this is my current code

#include <AFMotor.h>
#include <QTRSensors.h>

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 5 //experiment to determine this, slowly increase the speeds and adjust this value. ( Note: Kp < Kd)
#define M1_minumum_speed 150 //minimum speed of the Motor1
#define M2_minumum_speed 150 //minimum speed of the Motor2
#define M1_maksimum_speed 250 //max. speed of the Motor1
#define M2_maksimum_speed 250 //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()

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;

//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++)

if (DEBUG) {
for (int i = 0; i < NUM_SENSORS; i++)
Serial.print(' ');

for (int i = 0; i < NUM_SENSORS; i++)
Serial.print(' ');

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