Line Follower Robot — Competition-Ready (Arduino + PID)

An autonomous robot that follows a black line on a white track using infrared reflectance sensors and differential drive. This repo contains two control approaches:

• Basic 2-sensor bang-bang controller: main.ino (quick start)
• Advanced 5-sensor PID controller: main_pid.ino (smooth, fast, handles sharp turns and gaps)

How it works

Infrared sensors emit IR light and measure reflectance from the surface. White reflects more, black reflects less. The controller estimates the line position and adjusts motor speeds to keep the robot centered.

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Hardware

• MCU: Arduino Uno (ATmega328P) or Nano
• Motor driver: L298N (or L293D; wiring identical PWM/IN logic)
• Motors: 2× TT/DC gear motors with wheels
• Sensors:
  • Basic: 2× digital IR line sensors (left/right)
  • Advanced: 5× analog IR reflectance sensors (array)
• Power: 2S Li-ion/LiPo (7.4V) or 6×AA pack; separate motor/logic rails recommended
• Chassis: lightweight acrylic or 3D-printed; ball caster
• Misc: jumpers, spacers, switch, battery holder

Tip: For competitions, prefer a 5–8 sensor analog array and a rigid, light chassis.

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Wiring

Motors and driver (both sketches)

• ENABLE_LEFT_MOTOR → L298N ENA (PWM) → Arduino D5
• LEFT_MOTOR_PIN1/PIN2 → L298N IN1/IN2 → Arduino D9/D10
• ENABLE_RIGHT_MOTOR → L298N ENB (PWM) → Arduino D6
• RIGHT_MOTOR_PIN1/PIN2 → L298N IN3/IN4 → Arduino D7/D8
• Motor outputs: L298N OUT1–OUT2 → left motor, OUT3–OUT4 → right motor
• Power: Motor VIN (battery), +5V logic to Arduino 5V, common GND

Sensors

• Basic (digital):
  • Right sensor DO → Arduino D11 (IR_SENSOR_RIGHT)
  • Left sensor DO → Arduino D12 (IR_SENSOR_LEFT)
  • VCC 5V, GND common; trim pots adjust thresholds
• Advanced (analog 5×):
  • S0..S4 → Arduino A0..A4 (SENSOR_0..SENSOR_4)
  • VCC 5V, GND common

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Firmware

1) Basic two-sensor control (bang-bang)

File: main.ino

Behavior:

• Both white → drive straight
• Right sees black → steer right
• Left sees black → steer left
• Both black → stop (e.g., junction/finish)

Tweak MOTOR_SPEED to set base speed.

2) Advanced five-sensor PID control

File: main_pid.ino

Features:

• Automatic sensor calibration on startup (3s)
• Weighted average line position (0..4000)
• PID correction for smooth, fast tracking
• Line-loss handling that steers back towards last seen direction

Key parameters:

• BASE_SPEED (default 150), MAX_SPEED (255)
• PID gains: Kp, Ki, Kd
• CALIBRATION_TIME_MS (default 3000)

Upload either sketch as-is depending on your hardware.

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PID Tuning (quick guide)

1. Start with Ki = 0, moderate BASE_SPEED (120–160).
2. Increase Kp until it oscillates, then back off ~20%.
3. Raise Kd to damp oscillations and improve cornering.
4. Add small Ki only if there’s consistent bias/drift.

Symptoms:

• Wobble → decrease Kp or increase Kd
• Slow response → increase Kp
• Corner overshoot → increase Kd or reduce BASE_SPEED

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Build and Run

1. Assemble hardware per wiring above.
2. Place robot over the track; ensure strong contrast (matte black line on matte white).
3. Upload main.ino for a quick test, then main_pid.ino for competition performance.
4. With PID sketch, on power-up it calibrates for ~3s. Slowly move the robot across the line during this period.
5. Adjust gains and BASE_SPEED to your track.

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Repository Structure

• main.ino — basic digital 2-sensor controller
• main_pid.ino — advanced analog 5-sensor PID controller
• README.md — documentation, wiring, tuning

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Troubleshooting

• Robot veers consistently: check sensor heights (2–3 mm), parallelism, and add Ki slightly.
• Random jitter: ensure clean power, common ground, decouple with 100 µF near driver.
• Misses sharp turns: increase Kd, or raise BASE_SPEED slightly for better angular authority.
• Loses line on gaps: ensure line contrast; the sketch biases towards last known direction.

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License

MIT