Tutorial 3 - Ultrasonic Distance Sensor

Use the HC-SR04 ultrasonic sensor to detect the distance of an object moving closer or farther away. This tutorial introduces sensor-based input and real-world object interaction.

Circuit Diagram

💡Tip: Objects need to reflect sound waves clearly — Keep objects flat and centered for the most accurate distance readings.

What You'll Need

Arduino Uno x 1
HC-SR04 Ultrasonic Sensor x 1
Jumper wires x 4
USB Cable x 1
Arduino IDE installed

Instructions

Connect VCC on the sensor to 5V on the Arduino.
Connect GND on the sensor to GND on the Arduino.
Connect Trig and Echo to any digital pins — this example uses pins 9 and 10.
Upload the code below using the Arduino IDE.
Open the Serial Monitor (top-right corner of IDE) and set it to 9600 baud.
Move your hand toward and away from the sensor to see distance readings update live!

The Code


// Define the pins connected to the ultrasonic sensor
const int trigPin = 9;  // Pin used to send a signal
const int echoPin = 10; // Pin used to receive the signal

void setup() {
  Serial.begin(9600); // Start the Serial Monitor for viewing results

  pinMode(trigPin, OUTPUT); // Set the trig pin as an output
  pinMode(echoPin, INPUT);  // Set the echo pin as an input
}

void loop() {
  // Clear the trig pin to start fresh
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  // Send a 10 microsecond pulse to trigger the sensor
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read how long the echo pin stays HIGH (in microseconds)
  long duration = pulseIn(echoPin, HIGH);

  // Convert time into distance in centimeters
  float distance = duration * 0.034 / 2;

  // Print the distance to the Serial Monitor
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Wait half a second before the next reading
  delay(500);
}

Schematic Diagram