Autonomous Line-Following Robotic Vehicle with Dual IR Sensors

/*
 * Project: Autonomous Line Following Robot
 * Author: ElectronLab STEM Curriculum
 * Description: 2-Sensor High-Accuracy Line Tracker
 */

const int LEFT_SENSOR  = 2;
const int RIGHT_SENSOR = 3;

// Motor Driver Pins
const int IN1 = 5;
const int IN2 = 6;
const int IN3 = 9;
const int IN4 = 10;

void setup() {
  pinMode(LEFT_SENSOR, INPUT);
  pinMode(RIGHT_SENSOR, INPUT);
  
  pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);
  pinMode(IN3, OUTPUT);
  pinMode(IN4, OUTPUT);
}

void loop() {
  int leftVal  = digitalRead(LEFT_SENSOR);
  int rightVal = digitalRead(RIGHT_SENSOR);

  // Condition 1: Both sensors on white floor -> Drive straight forward
  if (leftVal == LOW && rightVal == LOW) {
    forward();
  }
  // Condition 2: Left sensor on black line -> Turn left to re-center
  else if (leftVal == HIGH && rightVal == LOW) {
    turnLeft();
  }
  // Condition 3: Right sensor on black line -> Turn right to re-center
  else if (leftVal == LOW && rightVal == HIGH) {
    turnRight();
  }
  // Condition 4: Both sensors on black line (Crossroad / Stop Line) -> Stop
  else if (leftVal == HIGH && rightVal == HIGH) {
    stopMotors();
  }
}

void forward() {
  digitalWrite(IN1, HIGH);
  digitalWrite(IN2, LOW);
  digitalWrite(IN3, HIGH);
  digitalWrite(IN4, LOW);
}

void turnLeft() {
  digitalWrite(IN1, LOW);
  digitalWrite(IN2, LOW);
  digitalWrite(IN3, HIGH);
  digitalWrite(IN4, LOW);
}

void turnRight() {
  digitalWrite(IN1, HIGH);
  digitalWrite(IN2, LOW);
  digitalWrite(IN3, LOW);
  digitalWrite(IN4, LOW);
}

void stopMotors() {
  digitalWrite(IN1, LOW);
  digitalWrite(IN2, LOW);
  digitalWrite(IN3, LOW);
  digitalWrite(IN4, LOW);
}