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HC-SR04 Ultrasonic Distance Sensor - Complete Guide & Arduino Code

Published on August 2025 by RobuKits 8 min read
HC-SR04 Ultrasonic Distance Sensor
The HC-SR04 Ultrasonic Distance Sensor is perfect for robotics, obstacle detection, and distance measurement projects.

The HC-SR04 Ultrasonic Distance Sensor is one of the most popular and affordable sensors for measuring distance and detecting objects. Using sound waves to determine distance, this sensor is widely used in robotics, automation, and IoT projects for obstacle avoidance, liquid level measurement, and proximity detection.

In this comprehensive guide, we'll explore how the HC-SR04 works, its technical specifications, and provide ready-to-use Arduino code examples for your projects.

Did You Know?

Ultrasonic sensors work on the same principle as bats and dolphins use for echolocation. They emit high-frequency sound waves (inaudible to humans) and measure the time it takes for the echoes to return, calculating distance based on the speed of sound.

How HC-SR04 Ultrasonic Sensor Works

The HC-SR04 uses ultrasonic waves to measure distance. Here's the working principle:

  1. You send a 10µs trigger pulse to the Trigger pin
  2. The sensor emits 8 cycles of ultrasonic bursts at 40kHz
  3. The sound waves travel through air and bounce off objects
  4. The Echo pin goes high and remains high until the echo is received
  5. You calculate distance based on the time the Echo pin was high

The formula for distance calculation: Distance = (Time × Speed of Sound) / 2

HC-SR04 Technical Specifications

Parameter Specification
Operating Voltage 5V DC
Working Current 15mA
Measuring Angle 15°
Measuring Range 2cm - 400cm (0.8in - 13ft)
Resolution 0.3cm
Frequency 40kHz
Dimensions 45mm × 20mm × 15mm

HC-SR04 Pinout

  • VCC: 5V Power Supply
  • Trig: Trigger Input (send 10µs pulse to start measurement)
  • Echo: Echo Output (pulse width proportional to distance)
  • GND: Ground

Arduino Code Example - Basic Distance Measurement

Here's a simple Arduino code to get started with the HC-SR04:

// Define pins for HC-SR04
const int trigPin = 9;
const int echoPin = 10;

// Variables for measurement
long duration;
int distance;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  Serial.begin(9600); // Start serial communication
}

void loop() {
  // Clear the trigPin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  // Send 10µs pulse to trigPin
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read the echoPin, returns the sound wave travel time in microseconds
  duration = pulseIn(echoPin, HIGH);

  // Calculate the distance
  distance = duration * 0.034 / 2; // Speed of sound = 0.034 cm/µs

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

  delay(1000); // Wait 1 second between measurements
}

Advanced Arduino Code - Object Detection with LED Feedback

This example adds an LED that turns on when an object is detected within a certain range:

const int trigPin = 9;
const int echoPin = 10;
const int ledPin = 13; // Built-in LED

long duration;
int distance;
int detectionRange = 50; // Distance in cm to trigger detection

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);
  distance = duration * 0.034 / 2;

  // Control LED based on distance
  if (distance <= detectionRange && distance >= 2) {
    digitalWrite(ledPin, HIGH); // Object detected - turn on LED
    Serial.print("Object detected at: ");
    Serial.print(distance);
    Serial.println(" cm");
  } else {
    digitalWrite(ledPin, LOW); // No object - turn off LED
    Serial.println("No object detected");
  }

  delay(500); // Shorter delay for more responsive detection
}

Popular HC-SR04 Project Ideas

This versatile sensor can be used in countless applications:

  • Obstacle avoidance robots
  • Parking assistance systems
  • Liquid level monitoring
  • Proximity-activated lighting
  • Gesture recognition systems
  • Smart trash cans (open when hand approaches)
  • Distance measurement tools

Pro Tip

For more accurate measurements, take multiple readings and average them. Also, note that temperature affects the speed of sound - for precision applications, you might want to add temperature compensation to your code.

Where to Buy HC-SR04 Ultrasonic Sensor

Ready to add distance sensing capabilities to your projects? Get the HC-SR04 Ultrasonic Distance Sensor from RobuKits here:

Buy HC-SR04 Sensor from RobuKits