Build an Obstacle Avoiding Robot

Introduction

An obstacle-avoiding robot uses an ultrasonic sensor to detect objects in its path and autonomously navigates around them. This project combines distance sensing with motor control logic.

Components Required

• Arduino Uno
• HC-SR04 Ultrasonic Sensor
• L298N Motor Driver
• 2× DC Gear Motors (with wheels)
• SG90 Servo Motor (to scan left/right)
• Robot chassis
• 9V battery or 7.4V Li-Po
• Jumper wires

How It Works

1. The ultrasonic sensor continuously measures the distance ahead
2. If an obstacle is detected within 25cm, the robot stops
3. The servo sweeps the sensor left and right to scan both directions
4. The robot turns toward the direction with more clearance
5. It continues forward until the next obstacle

The Code

#include <Servo.h>

// Motor pins
const int ENA = 3, IN1 = 5, IN2 = 6;
const int ENB = 11, IN3 = 9, IN4 = 10;

// Ultrasonic
const int trigPin = 7, echoPin = 8;

Servo scanServo;
int speed = 180;

long getDistance() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  long duration = pulseIn(echoPin, HIGH, 30000);
  return duration * 0.034 / 2;
}

void moveForward() {
  analogWrite(ENA, speed); analogWrite(ENB, speed);
  digitalWrite(IN1, HIGH); digitalWrite(IN2, LOW);
  digitalWrite(IN3, HIGH); digitalWrite(IN4, LOW);
}

void turnLeft() {
  analogWrite(ENA, speed); analogWrite(ENB, speed);
  digitalWrite(IN1, LOW); digitalWrite(IN2, HIGH);
  digitalWrite(IN3, HIGH); digitalWrite(IN4, LOW);
}

void turnRight() {
  analogWrite(ENA, speed); analogWrite(ENB, speed);
  digitalWrite(IN1, HIGH); digitalWrite(IN2, LOW);
  digitalWrite(IN3, LOW); digitalWrite(IN4, HIGH);
}

void stopMotors() {
  analogWrite(ENA, 0); analogWrite(ENB, 0);
}

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(ENA, OUTPUT); pinMode(IN1, OUTPUT); pinMode(IN2, OUTPUT);
  pinMode(ENB, OUTPUT); pinMode(IN3, OUTPUT); pinMode(IN4, OUTPUT);
  scanServo.attach(12);
  scanServo.write(90); // center
  delay(1000);
}

void loop() {
  long dist = getDistance();

  if (dist > 25 || dist == 0) {
    moveForward();
  } else {
    stopMotors();
    delay(300);

    // Scan right
    scanServo.write(30);
    delay(500);
    long rightDist = getDistance();

    // Scan left
    scanServo.write(150);
    delay(500);
    long leftDist = getDistance();

    // Re-center
    scanServo.write(90);
    delay(300);

    if (rightDist > leftDist) {
      turnRight();
      delay(400);
    } else {
      turnLeft();
      delay(400);
    }
    stopMotors();
  }
  delay(50);
}

Testing & Calibration

• Adjust speed value (0-255) for your motors
• Modify the 25cm threshold based on your needs
• Tune the turn delay(400) to get approximately 90° turns