Line-Following Robot with Remote Control

Arduino-based line-following robot with dual operating modes: autonomous line tracking using PD control with a 5-sensor array and manual control via ESP32 wireless gamepad.

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Features

• Dual Operating Modes:

  • Auto Mode: PD-controlled line following with 5-sensor array for precise tracking
  • Manual Mode: Joystick control via wireless gamepad

• Dynamic Speed Control:

  • Adjustable base speed via controller buttons (L1/R1)
  • Automatic speed reduction on sharp turns
  • Speed range: 60-255 (PWM)

• Advanced Line Following:

  • 5-sensor weighted position calculation
  • PD (Proportional-Derivative) control algorithm
  • Line memory when sensors lose track
  • Adaptive speed for curves

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Hardware Requirements

Microcontrollers

• Arduino board (Uno/Nano recommended)
• ESP32 (for wireless controller communication)

Components

• Motor Driver: Dual H-Bridge motor driver (L298N, TB6612FNG, or similar)
• Motors: 2x DC motors with wheels
• Sensors: 5x IR line sensors (digital output)
• Communication: SoftwareSerial connection between Arduino and ESP32
• Power Supply: Battery packs for motors and Arduino

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Wiring & Pinout

Motor Pins

Motor	Pin Function	Arduino Pin	Notes
Left Motor	PWM (Speed)	5 (Lpwm_pin)	PWM capable pin
	Direction 1 (Forward)	4 (pinLF)	Digital I/O
	Direction 2 (Backward)	3 (pinLB)	Digital I/O
Right Motor	PWM (Speed)	6 (Rpwm_pin)	PWM capable pin
	Direction 1 (Forward)	8 (pinRF)	Digital I/O
	Direction 2 (Backward)	7 (pinRB)	Digital I/O

Sensor Pins (5-Sensor Array)

Sensor Position	Arduino Pin	Notes
Far Left (FL)	A1 (SENSOR_LEFT)	Analog pin as Digital Input
Middle Left (ML)	A3 (SENSOR_MIDDLE_LEFT)	Analog pin as Digital Input
Center (M)	A5 (SENSOR_MIDDLE)	Analog pin as Digital Input
Middle Right (MR)	A2 (SENSOR_MIDDLE_RIGHT)	Analog pin as Digital Input
Far Right (FR)	A0 (SENSOR_RIGHT)	Analog pin as Digital Input

Communication Pins

Function	Arduino Pin	Connection
ESP32 RX	10	Connect to ESP32 TX
ESP32 TX	11	Connect to ESP32 RX

Note: Ensure common ground (GND) connection between Arduino, Motor Driver, Sensors, and ESP32.

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Communication Protocol

The Arduino receives data from ESP32 in a comma-separated format enclosed in angle brackets:

<Y,X,Cross,Circle,L1,R1>

Data Packet Format

Variable	Type	Range	Description
Y	int	-127 to 127	Joystick Y-axis (Throttle/Forward-Backward)
X	int	-127 to 127	Joystick X-axis (Steering/Left-Right)
Cross	int	0 or 1	Button State (Enable Auto Mode)
Circle	int	0 or 1	Button State (Enable Manual Mode)
L1	int	0 or 1	Button State (Decrease Speed)
R1	int	0 or 1	Button State (Increase Speed)

Example: <50,-30,0,0,0,1> means joystick at Y=50, X=-30, R1 pressed

Serial Configuration:

• Arduino: 115200 baud (USB Serial Monitor)
• ESP32: 9600 baud (SoftwareSerial)

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Control Guide

Controller Mapping

Button/Input	Function
Cross (X)	Switch to Auto Mode (line following)
Circle (O)	Switch to Manual Mode (stop + manual control)
L1	Decrease base speed by 25
R1	Increase base speed by 25
Left Joystick	Manual driving (Y=forward/back, X=steering)

Operating Modes

Auto Mode (Line Following)

• Robot autonomously follows a dark line on light surface
• Uses PD control for smooth tracking
• Automatically slows down on sharp curves
• Maintains line even if temporarily lost

Manual Mode

• Direct joystick control
• Y-axis: Forward/backward throttle
• X-axis: Left/right steering
• Deadzone of ±15 to prevent drift

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Tuning Parameters

PD Controller

float Kp = 25;  // Proportional gain (responsiveness)
float Kd = 15;  // Derivative gain (damping/smoothness)

Speed Settings

int BASE_SPEED = 150;      // Default straight-line speed
int MAX_SPEED = 255;       // Maximum motor speed
int MIN_SPEED = 60;        // Minimum to prevent stalling
int SPEED_INCREMENT = 25;  // Speed change per button press
int SPEED_DROP = 50;       // Speed reduction on curves

Tuning Tips

• Increase Kp: More aggressive corrections, faster response
• Decrease Kp: Gentler corrections, may be slower
• Increase Kd: More damping, reduces oscillation
• Decrease Kd: Less damping, may oscillate
• Increase SPEED_DROP: Slower on curves (more stable)
• Decrease SPEED_DROP: Faster on curves (may overshoot)

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How It Works

Line Following Algorithm (PD Control)

1. Sensor Reading

• Read 5 digital sensors (0=white, 1=black line)

2. Position Calculation

• Calculate weighted position error:

  Weights: FL=-2000, ML=-1000, M=0, MR=+1000, FR=+2000
  Error = Sum(sensor × weight) / Active sensors
  

3. PD Control

• Calculate correction based on error:

  P = error
  D = error - lastError
  correction = (Kp × P) + (Kd × D)
  

4. Speed Adjustment

• Slow down on sharp turns:

  if |error| > 1000:
      currentSpeed = BASE_SPEED - SPEED_DROP
  

5. Motor Control

• Apply correction to motors:

  leftSpeed = currentSpeed + correction
  rightSpeed = currentSpeed - correction
  

Sensor Logic

The sensors are configured for Active-HIGH (digital):

• 1 (HIGH) = Black Line Detected
• 0 (LOW) = White Surface Detected

Manual Control

Tank-style mixing of throttle and steering:

leftMotorSpeed = throttle - steering
rightMotorSpeed = throttle + steering

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Setup Instructions

1. Hardware Assembly

• Connect motors to motor driver
• Wire 5 sensors in array with equal spacing
• Connect motor driver to Arduino pins
• Set up SoftwareSerial between Arduino and ESP32
• Ensure common ground connection

2. Software Upload

• Install Arduino IDE
• Install SoftwareSerial library (if not included)
• Upload goodcode.ino to Arduino
• Configure ESP32 with gamepad receiver code (separate project)

3. Calibration

• Place robot on track
• Adjust sensor height (3-5mm from surface recommended)
• Test sensor readings via Serial Monitor (115200 baud)
• Tune Kp/Kd values for your specific track

4. Testing

• Open Serial Monitor (115200 baud)
• Verify controller data reception: Arduino Ready. Waiting for <Y,X,Cross,Circle,L1,R1>...
• Test Manual Mode first using joystick
• Switch to Auto Mode on line
• Adjust speed using L1/R1 buttons

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Troubleshooting

Issue	Solution
Robot doesn't move	Check motor connections and power supply
Oscillates on line	Decrease Kp or increase Kd
Loses line on curves	Increase SPEED_DROP or decrease BASE_SPEED
Slow response	Increase Kp
No controller data	Check ESP32 serial connection (pins 10/11) and baud rate
Motors run backwards	Swap forward/backward pins in code
Sensors not detecting	Check sensor height and verify digital output
Speed won't change	Verify L1/R1 button signals in Serial Monitor

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Code Structure

goodcode.ino
├── Pin Definitions & Tuning Parameters
├── Global Variables
├── setup()
│   ├── Pin initialization
│   └── Serial initialization
├── loop()
│   ├── recvWithStartEndMarkers()  // Receive data from ESP32
│   ├── parseData()                // Parse controller input
│   ├── adjustSpeed()              // Handle L1/R1 speed changes
│   └── handleState()              // Switch between modes
├── Control Functions
│   ├── runPDLineFollower()        // Advanced PD line following
│   └── driveRobot()               // Manual joystick control
└── Motor Helpers
    ├── setLeftMotor()
    ├── setRightMotor()
    ├── rotate_left()
    ├── rotate_right()
    └── stopRobot()

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Usage Instructions

1. Upload: Upload goodcode.ino to your Arduino board
2. Power On: Power on the robot and ESP32/Controller setup
3. Start-up: Arduino displays: Arduino Ready. Waiting for <Y,X,Cross,Circle,L1,R1>...
4. Mode Select:
   • Press Cross button → Activate Auto Mode (line following)
   • Press Circle button → Activate Manual Mode (stop + manual control)
5. Speed Control:
   • Press R1 → Increase base speed by 25
   • Press L1 → Decrease base speed by 25
   • Speed changes are displayed in Serial Monitor
6. Operation:
   • Manual: Use controller joystick to drive
   • Auto: Place robot on black line track - it will follow until mode is switched

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License

Open source - feel free to modify and adapt for your projects.

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Credits

Developed for Arduino-based line-following robot with ESP32 wireless control integration.