Build a robot that follows a line with Arduino.

// Line Follower  reads two IR sensors, steers two motors

const int Left_A = 8, Left_B = 9, SpeedA = 6;
const int Right_A = 10, Right_B = 11, SpeedB = 5;
const int irSensorLeft = 4;
const int irSensorRight = 7;
const int RUNSPEED = 190;

void forward() {
  digitalWrite(Left_A, LOW);  digitalWrite(Left_B, HIGH);
  digitalWrite(Right_A, LOW); digitalWrite(Right_B, HIGH);
}
void turnleft() {
  digitalWrite(Left_A, HIGH); digitalWrite(Left_B, HIGH);
  digitalWrite(Right_A, LOW); digitalWrite(Right_B, HIGH);
}
void turnright() {
  digitalWrite(Left_A, LOW);  digitalWrite(Left_B, HIGH);
  digitalWrite(Right_A, HIGH);digitalWrite(Right_B, HIGH);
}
void stopmoving() {
  digitalWrite(Left_A, HIGH); digitalWrite(Left_B, HIGH);
  digitalWrite(Right_A, HIGH);digitalWrite(Right_B, HIGH);
}

void setupsetup()Configures every pin's direction once, then sets the motors spinning at a fixed base speed before the loop takes over steering.() {
  pinMode(Left_A, OUTPUT); pinMode(Left_B, OUTPUT); pinMode(SpeedA, OUTPUT);
  pinMode(Right_A, OUTPUT); pinMode(Right_B, OUTPUT); pinMode(SpeedB, OUTPUT);
  pinMode(irSensorLeft, INPUTINPUTBoth sensors are read, not driven  this tells the pin to listen rather than send voltage.);
  pinMode(irSensorRight, INPUT);
  analogWrite(SpeedA, RUNSPEED);
  analogWrite(SpeedB, RUNSPEED);
  forward();
}

void looploop()Runs continuously  every pass re-reads both sensors and picks one of four actions based on what they see.() {
  int left  = digitalReaddigitalRead(pin)Returns HIGH or LOW. LOW means that sensor is still over the black line; HIGH means it has slid onto the lighter surface.(irSensorLeft);
  int right = digitalRead(irSensorRight);

  ifif / else if / elseExactly one of these four branches runs each pass  this is the entire "brain" of the robot. (left == LOW && right == LOW) {
    forward();               // both still on the line
  } elseelse ifChecked only when the first condition was false. if (left == HIGH && right == LOW) {
    turnleft();               // left sensor slid off  steer left
  } else if (left == LOW && right == HIGH) {
    turnright();              // right sensor slid off  steer right
  } else {
    stopmoving();              // both lost the line  halt
  }
}