Obstacle-Avoiding Car

What You'll Build

Here you build a real robot. Two motors drive the wheels, an ultrasonic sensor on a servo looks ahead, and the Arduino decides where to go. Put it on the floor and it will explore your room by itself, backing up and turning whenever something blocks the way.

What You Need

• ✓Arduino Uno
• ✓L298N motor driver
• ✓2 × DC gear motor
• ✓HC-SR04
• ✓SG90 servo
• ✓6×AA rechargeable battery pack
• ✓Chassis

How It Works

The Arduino cannot power motors directly — its pins are far too weak. The L298N driver sits in between: the Arduino sends small control signals, and the driver switches the big battery current to the motors. The robot repeats a simple think-loop: measure the distance ahead; if the path is clear, drive forward; if not, stop, look left and right, and turn toward whichever side has more space.

Before You Wire It

Wiring

Step-by-Step Instructions

1. 1

   Choose the right battery

   Use 6 rechargeable AA cells (about 7.2 V) as the safer first choice, and ask an adult to confirm they suit your exact motors and driver. Do not use a small rectangular 9V PP3 battery: it cannot reliably supply the high startup current these motors need. LiPo packs can catch fire if damaged, shorted, over-discharged, or charged incorrectly, so only an adult experienced with LiPo safety may select, charge, store, and connect one.

2. 2

   Build the chassis

   Bolt the motors and wheels on, then add the caster wheel at the back. Keep the battery low and central so the car does not tip while turning.

3. 3

   Wire power in the right order

   Battery to the L298N first, then the shared ground, then the signal pins last. Add an on/off switch in the battery's + wire so you can stop a runaway robot instantly, and unplug the battery whenever you rewire.

4. 4

   Wire the driver

   Double-check the shared ground. A robot with two separate power supplies and no common ground behaves randomly, and it is the single most common robot bug.

5. 5

   Test each motor alone

   Raise the wheels off the floor, keep fingers, hair and clothing clear, and have an adult nearby. Run each motor for two seconds. Disconnect power before swapping a motor's two screw-terminal wires.

6. 6

   Add the scanner

   Mount the servo at the front with the ultrasonic sensor on top. Centre the servo at 90° before you glue anything.

7. 7

   Upload the brain

   Now put it together: sense, decide, drive. Start with a generous 30 cm safety distance and lower it once you trust the robot.

8. 8

   Tune the behaviour

   Change the turn duration to make the robot more or less curious, and adjust speed so it does not crash before it can react.

Arduino Code

#include <Servo.h>

Servo look;
const int TRIG = 12, ECHO = 13;
const int IN1 = 5, IN2 = 6, IN3 = 7, IN4 = 8;
const int ENA = 9, ENB = 10;
const int SPEED = 150;
const int SAFE_CM = 30;

int distance() {
  digitalWrite(TRIG, LOW);  delayMicroseconds(2);
  digitalWrite(TRIG, HIGH); delayMicroseconds(10);
  digitalWrite(TRIG, LOW);
  return pulseIn(ECHO, HIGH) * 0.034 / 2;
}

void drive(int a, int b, int c, int d) {
  digitalWrite(IN1, a); digitalWrite(IN2, b);
  digitalWrite(IN3, c); digitalWrite(IN4, d);
  analogWrite(ENA, SPEED); analogWrite(ENB, SPEED);
}

void forward() { drive(HIGH, LOW, HIGH, LOW); }
void back()    { drive(LOW, HIGH, LOW, HIGH); }
void left()    { drive(LOW, HIGH, HIGH, LOW); }
void right()   { drive(HIGH, LOW, LOW, HIGH); }
void stopCar() { analogWrite(ENA, 0); analogWrite(ENB, 0); }

void setup() {
  for (int p = 5; p <= 10; p++) pinMode(p, OUTPUT);
  pinMode(TRIG, OUTPUT); pinMode(ECHO, INPUT);
  look.attach(11);
  look.write(90);
}

void loop() {
  if (distance() > SAFE_CM) {
    forward();
  } else {
    stopCar();  delay(200);
    back();     delay(400);
    stopCar();

    look.write(160); delay(400);
    int leftSpace = distance();
    look.write(20);  delay(600);
    int rightSpace = distance();
    look.write(90);  delay(400);

    if (leftSpace > rightSpace) left(); else right();
    delay(450);
    stopCar();
  }
}

Understanding the Code

Challenges & Upgrades

Troubleshooting

Helpful Resources