Obstacle Avoiding Robot using Arduino

How an obstacle avoiding robot works

The robot repeats three steps many times every second:

Components required

Wiring: pin connections

Use these pins so the code below works without changes. Keep the two jumper caps on the ENA and ENB pins of the L298N so the motors run at full speed.

HC-SR04 to Arduino

L298N to Arduino

Motors and battery

Always connect the Arduino GND to the L298N GND. Without a common ground the robot will behave randomly. Wiring problems cause most failures, so see wrong sensor connections and incorrect power supply if something does not work.

Step-by-step assembly

Arduino code

Open the Arduino IDE, paste the code, select your board and port, and click Upload. No extra library is needed.

const int trigPin = 7;
const int echoPin = 8;
const int in1 = 5;   // left motor
const int in2 = 6;
const int in3 = 9;   // right motor
const int in4 = 10;
const int safeDistance = 20;  // cm

long readDistanceCm() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  long duration = pulseIn(echoPin, HIGH, 30000);
  if (duration == 0) return 400;      // no echo: path is clear
  return duration * 0.034 / 2;        // convert time to cm
}

void forward() {
  digitalWrite(in1, HIGH); digitalWrite(in2, LOW);
  digitalWrite(in3, HIGH); digitalWrite(in4, LOW);
}

void backward() {
  digitalWrite(in1, LOW);  digitalWrite(in2, HIGH);
  digitalWrite(in3, LOW);  digitalWrite(in4, HIGH);
}

void turnRight() {
  digitalWrite(in1, HIGH); digitalWrite(in2, LOW);
  digitalWrite(in3, LOW);  digitalWrite(in4, HIGH);
}

void stopMotors() {
  digitalWrite(in1, LOW); digitalWrite(in2, LOW);
  digitalWrite(in3, LOW); digitalWrite(in4, LOW);
}

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(in1, OUTPUT);
  pinMode(in2, OUTPUT);
  pinMode(in3, OUTPUT);
  pinMode(in4, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  long distance = readDistanceCm();
  Serial.println(distance);

  if (distance > safeDistance) {
    forward();
  } else {
    stopMotors();
    delay(200);
    backward();
    delay(400);
    turnRight();
    delay(500);
    stopMotors();
    delay(100);
  }
}

How the code works

• readDistanceCm() sends a 10 microsecond pulse and times the echo with pulseIn().
• forward(), backward(), turnRight(), stopMotors() set the L298N inputs to spin the motors in the right directions.
• loop() drives forward while the path is clear. When something is closer than 20 cm, the robot stops, reverses, turns right and checks again.
• Serial.println(distance) prints the distance so you can check the sensor in the Serial Monitor at 9600 baud.

This code uses short delay() calls for the turning moves. That is fine here, but for smoother behaviour read about using delay() too much and switch to millis().

Test and tune your robot

Troubleshooting

Upgrade ideas

More ideas: see our Top 20 STEM projects and 20 Arduino mini projects.

Robotics learning with Robopro.in

At Robopro.in, students and makers can find Arduino boards, sensors, motor drivers, motors and robotics kits for building practical projects.