Line Following Robot

Project Overview

Our line-following robot uses infrared sensors to detect and follow a black line on a white surface. This project taught us fundamental concepts in robotics: sensor input, decision-making logic, and motor control.

Design Goals

1. Follow a line with 90%+ accuracy
2. Handle sharp turns and intersections
3. Maintain smooth, consistent speed
4. Complete a test course in under 60 seconds

Hardware Components

Main Controller

• Arduino Uno: The brain of our robot
• 9V Battery: Powers the Arduino and sensors
• 12V Battery Pack: Powers the motors

Sensors

• 2x IR Sensors: Detect the line (black vs white)
• Positioned 3cm apart for optimal line detection

Motors & Chassis

• 2x DC Motors: Provide movement
• L298N Motor Driver: Controls motor speed and direction
• Acrylic Chassis: Lightweight and easy to modify

The Code

Here’s our core line-following logic:

const int leftSensor = 2;
const int rightSensor = 3;
const int leftMotorForward = 5;
const int leftMotorBackward = 6;
const int rightMotorForward = 9;
const int rightMotorBackward = 10;

void setup() {
  pinMode(leftSensor, INPUT);
  pinMode(rightSensor, INPUT);
  pinMode(leftMotorForward, OUTPUT);
  pinMode(leftMotorBackward, OUTPUT);
  pinMode(rightMotorForward, OUTPUT);
  pinMode(rightMotorBackward, OUTPUT);
}

void loop() {
  int left = digitalRead(leftSensor);
  int right = digitalRead(rightSensor);

  if (left == LOW && right == LOW) {
    // Both sensors on line: move forward
    moveForward();
  } else if (left == LOW && right == HIGH) {
    // Line drifting right: turn right
    turnRight();
  } else if (left == HIGH && right == LOW) {
    // Line drifting left: turn left
    turnLeft();
  } else {
    // Lost the line: stop
    stopMotors();
  }
}

void moveForward() {
  digitalWrite(leftMotorForward, HIGH);
  digitalWrite(rightMotorForward, HIGH);
  digitalWrite(leftMotorBackward, LOW);
  digitalWrite(rightMotorBackward, LOW);
}

void turnRight() {
  digitalWrite(leftMotorForward, HIGH);
  digitalWrite(rightMotorForward, LOW);
  digitalWrite(leftMotorBackward, LOW);
  digitalWrite(rightMotorBackward, LOW);
}

void turnLeft() {
  digitalWrite(leftMotorForward, LOW);
  digitalWrite(rightMotorForward, HIGH);
  digitalWrite(leftMotorBackward, LOW);
  digitalWrite(rightMotorBackward, LOW);
}

void stopMotors() {
  digitalWrite(leftMotorForward, LOW);
  digitalWrite(rightMotorForward, LOW);
  digitalWrite(leftMotorBackward, LOW);
  digitalWrite(rightMotorBackward, LOW);
}

Challenges We Faced

1. Sensor Calibration

Problem: Sensors were too sensitive to ambient light.

Solution: Added a small shield around each sensor and calibrated the threshold for our specific environment.

2. Oscillation

Problem: The robot wobbled back and forth while following the line.

Solution: Implemented PWM speed control to make gentler turns instead of full-power corrections.

3. Sharp Corners

Problem: Robot would overshoot tight 90-degree turns.

Solution: Added a third sensor in the middle to detect when the robot completely loses the line, then execute a search pattern.

Results

After testing and tuning:

• ✅ 95% line-following accuracy
• ✅ Handles 90-degree turns
• ✅ Average speed: 0.5 m/s
• ✅ Course completion: 48 seconds

Lessons Learned

1. Sensor Placement Matters: The 3cm spacing between sensors was optimal for our line width
2. Test Early, Test Often: We spent 60% of project time testing and tuning
3. Simple is Better: Our initial PID control was overkill; simpler logic worked great
4. Documentation Helps: Keeping a test log helped us track what changes improved performance

Next Steps

Future improvements we’re considering:

• Add speed control for straightaways vs turns
• Implement PID control for smoother motion
• Add obstacle detection
• Create a race mode for competition

Want to Build Your Own?

Check out our full build guide and code on GitHub: github.com/robotics-club/line-follower