Arduino Hand-Following Robot Using IR and Ultrasonic Sensors

The motors are controlled via L298N motor driver logic, and speed is controlled using PWM pins. The logic supports:

• Forward motion when both IR sensors detect no obstacle and an object is in front.

• Turning left/right if one IR sensor detects an obstacle.

• Reversing when both IR sensors detect a wall or object.

• Stopping if the ultrasonic sensor detects the object is too close (<10cm).

  Hardware Used

• Arduino Uno

• HC-SR04 Ultrasonic Sensor

• 2 x IR Obstacle Sensors

• L298N Motor Driver Module

• 2 x DC Motors

• Battery Pack

Hand-Following Robot code using IR and ultrasonic sensors with DC motors:

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🔧 1. Library and Pin Configuration

#include <NewPing.h>

• Includes the NewPing library to handle ultrasonic sensor measurements with better timing and reliability.

#define IR_RIGHT A2
#define IR_LEFT A3

• IR sensor pins: A2 for right and A3 for left. These detect black/white surfaces or obstacles.

#define TRIGGER_PIN A1
#define ECHO_PIN A0
#define MAX_DISTANCE 100

• Defines HC-SR04 ultrasonic sensor pins and max distance in centimeters for sensing.

#define RIGHT_SPEED_PIN 10
#define LEFT_SPEED_PIN 11

• PWM pins connected to motor driver for controlling motor speed.

#define RIGHT_MOTOR_A 4
#define RIGHT_MOTOR_B 5
#define LEFT_MOTOR_A 6
#define LEFT_MOTOR_B 7

• Direction control pins for the motor driver. Two pins per motor (H-bridge logic).

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2. Constants for Speeds and Distance Thresholds

#define DEFAULT_SPEED 191
#define TURN_SPEED 127
#define MIN_DISTANCE 10
#define MAX_FOLLOW_DISTANCE 30 

• Speed values and distance thresholds to decide when to follow or stop.

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3. Ultrasonic Object Initialization

NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE);

• Creates a sonar object to interact with the ultrasonic sensor.

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4. Setup Function

void setup() {
Serial.begin(9600);
pinMode(IR_RIGHT, INPUT);
pinMode(IR_LEFT, INPUT);
pinMode(..., OUTPUT);
motor_stop();
} 

• Starts serial communication (useful for debugging).
• Sets IR pins as input and motor pins as output.
• Calls motor_stop() to keep robot still at start.

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5. Main Loop

void loop() {
delay(50);
unsigned int distance = sonar.ping_cm();
int rightIR = digitalRead(IR_RIGHT);
int leftIR = digitalRead(IR_LEFT); 

• Gets the distance to object in front.
• Reads IR sensor values (0 = obstacle, 1 = clear).

Then the control logic follows:

Move Forward

if (rightIR == 1 && leftIR == 1 && distance >= 10 && distance <= 30)

• If no obstacle detected on either side and object is within followable range → move forward.

Turn Right

else if (rightIR == 0 && leftIR == 1) 

• If obstacle on right → turn right.

Turn Left

else if (rightIR == 1 && leftIR == 0) 

• If obstacle on left → turn left.

Reverse

else if (rightIR == 0 && leftIR == 0) 

• If both sides are blocked → reverse to avoid collision.

Stop

else if (distance < 10 || (rightIR == 1 && leftIR == 1)) 

• If the object is too close or there's nothing to follow → stop.

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6. Movement Functions

Each motion control function does:

• analogWrite() sets motor speed using PWM.
• digitalWrite() sets motor direction using H-bridge logic.

For example:

void move_forward(int speed) {
analogWrite(...);
digitalWrite(...); // A = HIGH, B = LOW → forward direction
} 

Others like reverse(), turn_left(), and turn_right() follow similar structure but flip the direction control.

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motor_stop() Function

void motor_stop() {
analogWrite(..., 0); // Cut off speed
digitalWrite(..., LOW); // Stop motor movement
} 

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Summary of Behavior

Condition	Action
IR clear, object in range	Move forward
Obstacle right	Turn right
Obstacle left	Turn left
Obstacle both sides	Reverse
Too close or idle	Stop