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Obstacle avoiding robot simulator: build, wire and code it in 3D

Teach a robot to see a wall, and turn before it hits it.

Build an obstacle avoider from its parts: an HC-SR04 ultrasonic sensor on the front, an L298N motor driver and an Arduino Uno. Write the rule that decides what it does when something is in the way, and drive it round the room in 3D.

Open the Obstacle Avoider labAll robots

Free with a free account · Runs in the browser · Class 8 to 10

How the obstacle avoider works

The HC-SR04 sends a short burst of ultrasound and listens for the echo. The time the echo takes gives the distance: distance = time × 0.034 ÷ 2 centimetres (sound travels about 0.034 cm per microsecond, and the pulse goes there and back). The Arduino checks it again and again:

Parts you build it from

Wiring

These are the connections the lab checks before it lets the obstacle avoider run.

The code

This is the code the lab starts with. STOP_DIST decides how close is too close; DRIVE_SPEED and TURN_SPEED set how it moves.

// --- PIN DEFINITIONS (must match your wiring!) ---
#define TRIG_PIN  A0   // HC-SR04 TRIG -> Arduino A0
#define ECHO_PIN  A1   // HC-SR04 ECHO -> Arduino A1
#define IN1       3    // L298N IN1 -> D3  (Left motor forward)
#define IN2       4    // L298N IN2 -> D4  (Left motor reverse)
#define IN3       5    // L298N IN3 -> D5  (Right motor forward)
#define IN4       6    // L298N IN4 -> D6  (Right motor reverse)

// --- CHANGE THIS VALUE to control obstacle distance ---
#define STOP_DIST 25     // Stop & turn when < 25 cm (try: 15, 30, 40)
#define DRIVE_SPEED 180  // Straight-line speed (0-255)
#define TURN_SPEED  200  // Speed while spinning (0-255)

long getDistance() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  long dur = pulseIn(ECHO_PIN, HIGH);
  return dur * 0.034 / 2;  // distance in cm
}

void moveForward() {
  analogWrite(IN1, DRIVE_SPEED); digitalWrite(IN2, LOW);
  analogWrite(IN3, DRIVE_SPEED); digitalWrite(IN4, LOW);
}
void turnRight() {   // left wheel forward, right wheel backward: spins on the spot
  analogWrite(IN1, TURN_SPEED); digitalWrite(IN2, LOW);
  digitalWrite(IN3, LOW);       analogWrite(IN4, TURN_SPEED);
}
void turnLeft() {    // mirror image of turnRight()
  digitalWrite(IN1, LOW);       analogWrite(IN2, TURN_SPEED);
  analogWrite(IN3, TURN_SPEED); digitalWrite(IN4, LOW);
}
void stopMotors() {
  digitalWrite(IN1, LOW); digitalWrite(IN2, LOW);
  digitalWrite(IN3, LOW); digitalWrite(IN4, LOW);
}

void setup() {
  Serial.begin(9600);
  pinMode(TRIG_PIN, OUTPUT);   // we send the pulse
  pinMode(ECHO_PIN, INPUT);    // we listen for the echo
  pinMode(IN1, OUTPUT); pinMode(IN2, OUTPUT);
  pinMode(IN3, OUTPUT); pinMode(IN4, OUTPUT);
  stopMotors();
}

void loop() {
  long dist = getDistance();
  if (dist < STOP_DIST) {       // obstacle detected
    stopMotors();  delay(200);  // brake
    turnRight();   delay(500);  // try turnLeft() here
  } else {
    moveForward();              // clear path: go forward
  }
  delay(60);
}

Code it with blocks first

In the coding room it is built from blocks: repeat, if something is closer than 25 cm, distance ahead (cm), drive forward, turn left, back up, stop. The same decision, before the C++.

Try this in the lab

1. Change STOP_DIST to 15, then 40. Which one hits the wall?
2. Swap turnRight() for turnLeft() and watch it turn the other way.
3. Put moveForward() inside the if-block and watch it crash. Why?
4. Make it back up before it turns, using the blocks in the coding room.

Open the Obstacle Avoider lab

Obstacle Avoider: common questions

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Read more: an obstacle avoider simulation guide · obstacle avoiding robot simulation