Obstacle Avoiding Robot with Servo Scanning

365 viewsMarch 8, 2026

ArduinoRobotHC-SR04ServoL298NAutonomous

An autonomous robot that navigates around obstacles using an ultrasonic sensor mounted on a servo for 180° scanning. The robot looks left and right when an obstacle is detected and chooses the clearest path to continue.

Components & Supplies

×1Arduino Uno R3

×1HC-SR04 Ultrasonic Sensor

×1SG90 Servo Motor

×1L298N Motor Driver Module

×2DC Gear Motor (3-6V)

×1Robot Chassis Kit (2WD)

×14x AA Battery Holder

Circuit Connections

Component	Pin		Pin	Component
Arduino	A0	→	TRIG	HC-SR04
Arduino	A1	→	ECHO	HC-SR04
Arduino	5V	→	VCC	HC-SR04
Arduino	GND	→	GND	HC-SR04
Arduino	D3 (PWM)	→	Signal	Servo
Arduino	D5 (PWM)	→	ENA	L298N
Arduino	D6	→	IN1	L298N
Arduino	D7	→	IN2	L298N
Arduino	D8	→	IN3	L298N
Arduino	D9	→	IN4	L298N
Arduino	D10 (PWM)	→	ENB	L298N

How It Works

Unlike simple obstacle avoidance robots that only detect obstacles straight ahead, this robot has an HC-SR04 sensor mounted on a servo. When an obstacle is detected within 25cm, the robot stops and the servo sweeps the sensor left and right to measure distances in both directions. The robot then turns toward the direction with the most clearance.

This creates more intelligent navigation behavior and reduces getting stuck in corners.

arduino— Obstacle Avoidance Sketch

#include <Servo.h>

Servo scanServo;
const int trigPin = A0;
const int echoPin = A1;
const int enA = 5, in1 = 6, in2 = 7;
const int enB = 10, in3 = 8, in4 = 9;
const int spd = 160;

float getDistance() {
  digitalWrite(trigPin, LOW); delayMicroseconds(2);
  digitalWrite(trigPin, HIGH); delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  return (pulseIn(echoPin, HIGH) * 0.0343) / 2.0;
}

void forward() {
  analogWrite(enA, spd); analogWrite(enB, spd);
  digitalWrite(in1, HIGH); digitalWrite(in2, LOW);
  digitalWrite(in3, HIGH); digitalWrite(in4, LOW);
}
void stopBot() { analogWrite(enA, 0); analogWrite(enB, 0); }
void turnLeft() {
  analogWrite(enA, spd); analogWrite(enB, spd);
  digitalWrite(in1, LOW); digitalWrite(in2, HIGH);
  digitalWrite(in3, HIGH); digitalWrite(in4, LOW);
}
void turnRight() {
  analogWrite(enA, spd); analogWrite(enB, spd);
  digitalWrite(in1, HIGH); digitalWrite(in2, LOW);
  digitalWrite(in3, LOW); digitalWrite(in4, HIGH);
}

void setup() {
  Serial.begin(9600);
  scanServo.attach(3);
  scanServo.write(90);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(enA, OUTPUT); pinMode(in1, OUTPUT); pinMode(in2, OUTPUT);
  pinMode(enB, OUTPUT); pinMode(in3, OUTPUT); pinMode(in4, OUTPUT);
  delay(2000);
}

void loop() {
  scanServo.write(90);
  delay(200);
  float frontDist = getDistance();

  if (frontDist > 25) {
    forward();
  } else {
    stopBot();
    delay(300);

    scanServo.write(180);
    delay(500);
    float leftDist = getDistance();

    scanServo.write(0);
    delay(500);
    float rightDist = getDistance();

    scanServo.write(90);

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