Ultrasonic Sensor HC-SR04 for IoT: Working, Applications, Circuit, and Integration Guide

Discover how the Ultrasonic Sensor HC-SR04 works and how to use it in IoT projects. This detailed guide covers its working principle, pin configuration, interfacing with Arduino, applications in smart systems, and complete circuit setup. Ideal for beginners and IoT developers looking to integrate distance sensing in real-time projects.

Jul 15, 2025

Sensors

647 words

Ultrasonic Sensor HC-SR04 for IoT: Working, Applications, Circuit, and Integration Guide

Device Overview

Introduction

Ultrasonic sensors have become a key component in modern electronics and Internet of Things (IoT) applications. Among them, the HC-SR04 Ultrasonic Sensor is one of the most popular and affordable distance-measuring devices. It uses high-frequency sound waves to detect the distance between objects and is widely used in robotics, automation, water level monitoring, parking sensors, and more.

This guide provides complete insights into the Ultrasonic Sensor HC-SR04, including its working principle, specifications, interfacing with Arduino, applications, advantages, and integration tips for IoT projects.

What is Ultrasonic Sensor HC-SR04?

The HC-SR04 is an ultrasonic distance measuring sensor that calculates the distance to an object by sending and receiving sound waves. It uses the time-of-flight method to determine how long it takes for the sound to reflect back from a surface.

Working Principle

HC-SR04 works based on ultrasonic echolocation — similar to how bats and dolphins navigate.

The Trigger pin sends an ultrasonic pulse (40kHz).
This pulse travels through the air and hits an object.
The reflected signal is captured by the Echo pin.
The sensor calculates distance using the formula:

Distance = (Time × Speed of Sound) / 2
Speed of sound = ~343 m/s in air

Technical Specifications

Parameter	Value
Model	HC-SR04
Operating Voltage	5V DC
Operating Current	15mA
Frequency	40 kHz
Measuring Range	2 cm to 400 cm (4 meters)
Accuracy	±3 mm
Measuring Angle	≤ 15°
Trigger Input Signal	10µs TTL pulse
Echo Output Signal	TTL pulse (width = distance)
Module Size	45mm × 20mm × 15mm

Pin Configuration

Pin	Name	Description
1	VCC	+5V Power Supply
2	Trig	Trigger Input (10µs pulse)
3	Echo	Echo Output (pulse width)
4	GND	Ground

Interfacing HC-SR04 with Arduino

Required Components:

1x Ultrasonic Sensor HC-SR04
1x Arduino Uno / Nano / Mega
Jumper wires
Breadboard (optional)

Circuit Diagram:

HC-SR04 Arduino
-------- -------
VCC → 5V 
GND → GND 
Trig → Digital Pin 9 
Echo → Digital Pin 10

Sample Arduino Code

voidsetup() {
    Serial.begin(9600);
    pinMode(trigPin, OUTPUT);
    pinMode(echoPin, INPUT);
}

voidloop() {
    longduration;
    intdistance;

    digitalWrite(trigPin, LOW);
    delayMicroseconds(2);
   
    digitalWrite(trigPin, HIGH);
    delayMicroseconds(10);
    digitalWrite(trigPin, LOW);

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

    Serial.print("Distance: ");
    Serial.print(distance);
    Serial.println(" cm");

    delay(500);
}

Output:

The distance (in cm) of the object from the sensor will be displayed in the Serial Monitor.

Applications of HC-SR04 Ultrasonic Sensor

Water level measurement
Smart dustbins
Parking assistance system
Obstacle detection in robotics
Industrial automation
IoT-based security systems
Blind assistive devices
Smart agriculture (e.g., irrigation level detection)
Home automation

Advantages of Using HC-SR04

Low cost and easily available
High accuracy (±3 mm)
Easy to interface with microcontrollers
Reliable and consistent output
Works in dark or non-visual environments

Limitations

Can be affected by temperature and humidity
Works best with flat, smooth surfaces
Limited angle (15° cone)
Not suitable for transparent or absorbent objects

Types of Ultrasonic Sensors

Although HC-SR04 is the most popular, here are other types used in IoT:

Sensor Name	Features
HC-SR04	Standard, low-cost, most used
JSN-SR04T	Waterproof, suitable for outdoor projects
MB1020 (MaxBotix)	High precision, industrial grade
HY-SRF05	Enhanced range and accuracy over HC-SR04

Integration Tips for IoT Projects

Always add a small capacitor across VCC and GND to eliminate noise.
Use software or hardware filters to reduce false signals.
For long-range accuracy, prefer waterproof sensors like JSN-SR04T.
Combine with NodeMCU/ESP32 for WiFi-enabled IoT setups.
Ensure echo pin timing is handled properly to avoid incorrect distance readings.

Conclusion

The Ultrasonic Sensor HC-SR04 is an ideal choice for distance measurement in various DIY and professional IoT applications. With simple interfacing, accurate output, and affordable pricing, it remains a top pick among makers and engineers. Whether you’re building a smart water level detector or an obstacle-avoiding robot, the HC-SR04 is a reliable and efficient sensor to integrate.

Where to Buy

Platform	Price	Action
Amazon	₹279	Buy Now

Prices may vary. Click on "Buy Now" to check current availability and pricing.

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Frequently Asked Questions

Common questions about Ultrasonic Sensor HC-SR04 for IoT: Working, Applications, Circuit, and Integration Guide. Find answers to the most frequently asked questions.

The HC-SR04 is an ultrasonic distance measurement sensor that uses sound waves to detect objects. It sends out a 40kHz ultrasonic pulse and listens for the echo to calculate the distance to an object. In IoT projects, it's commonly used for obstacle detection, water level monitoring, and smart automation due to its accuracy and ease of interfacing with microcontrollers like Arduino, ESP8266, and ESP32.

The HC-SR04 can measure distances from 2 cm to 400 cm (4 meters) with an accuracy of approximately ±3 mm. It performs best on flat, solid surfaces and in indoor environments with minimal echo interference. For outdoor or waterproof applications, consider alternatives like JSN-SR04T.

Yes, the HC-SR04 sensor can be used with NodeMCU (ESP8266) or ESP32 microcontrollers. However, since these boards operate on 3.3V logic, you should use a logic level converter or a resistor voltage divider to protect the Echo pin. This integration allows real-time distance data to be transmitted over Wi-Fi for smart IoT applications.

No, the HC-SR04 is not waterproof and should only be used in dry indoor environments. If you need an ultrasonic sensor for outdoor or moisture-prone areas, the JSN-SR04T is a better choice as it comes with a waterproof probe and more robust casing suitable for harsh conditions.

One of the main challenges with the HC-SR04 is its sensitivity to environmental conditions such as temperature, humidity, and surface texture, which may slightly alter the accuracy. It also performs best when the target object is flat and directly in front of the sensor, as angled or irregular surfaces may deflect the ultrasonic waves and cause unstable readings, especially in open environments.

The HC-SR04 operates on a 5V power supply and uses TTL logic for its signal pins, making it fully compatible with 5V microcontrollers like Arduino Uno and Mega. However, when connecting it to 3.3V boards like NodeMCU or ESP32, a logic level shifter or resistor divider should be used on the echo pin to prevent potential damage, ensuring safe and stable performance in such configurations.

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Bavaliya Nayan

1 week ago

Super 😍 bro it's working 💪

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