Build an Obstacle Avoiding Robot

This robot drives forward on its own, and when the ultrasonic sensor sees a wall it stops, looks left and right with a servo, and turns toward the clearer side. It is a classic science fair and university project.

1. Wiring

L298N Motor Driver:

• IN1, IN2, IN3, IN4 → Pins 5, 6, 9, 10
• OUT1/OUT2 → left motor, OUT3/OUT4 → right motor
• 12V → battery +, GND → battery − and Arduino GND
• 5V → Arduino VIN (keep the 5V jumper on)

Sensor and servo:

• HC-SR04 TRIG → A1, ECHO → A2, VCC → 5V, GND → GND
• Servo signal (orange) → Pin 3, red → 5V, brown → GND. Mount the HC-SR04 on the servo horn.

2. The Code

#include <Servo.h>
Servo head;
void drive(int a, int b, int c, int d) {
  digitalWrite(5, a); digitalWrite(6, b);
  digitalWrite(9, c); digitalWrite(10, d);
}
void forward() { drive(1,0,1,0); }
void back()    { drive(0,1,0,1); }
void left()    { drive(0,1,1,0); }
void right()   { drive(1,0,0,1); }
void stopCar() { drive(0,0,0,0); }

long distanceCm() {
  digitalWrite(A1, LOW); delayMicroseconds(2);
  digitalWrite(A1, HIGH); delayMicroseconds(10);
  digitalWrite(A1, LOW);
  long d = pulseIn(A2, HIGH, 30000) * 0.0343 / 2;
  return d == 0 ? 300 : d;
}

void setup() {
  for (int p : {5, 6, 9, 10, A1}) pinMode(p, OUTPUT);
  pinMode(A2, INPUT);
  head.attach(3); head.write(90);
}

void loop() {
  if (distanceCm() > 25) { forward(); delay(50); return; }
  stopCar(); back(); delay(300); stopCar();
  head.write(160); delay(400); long l = distanceCm();
  head.write(20);  delay(400); long r = distanceCm();
  head.write(90);  delay(200);
  if (l > r) left(); else right();
  delay(400); stopCar();
}

3. Tuning

Change 25 to stop closer or farther, and the turn delay(400) to make sharper or softer turns.