Project Hub /Test & Measurement Instrumentation/Sensors & Signal Measurement Tools/How does an HC-SR04 Ultrasonic Range Sensor Works and How to Interface with ESP32

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How does an HC-SR04 Ultrasonic Range Sensor Works and How to Interface with ESP32

Learn how the HC-SR04 ultrasonic distance sensor works and follow a guide to interface it with an ESP32 microcontroller using an OLED display for real-time readings.

Originally published on CircuitDigest

View original tutorial

Parts You'll Need

This project is sourced from another site, not written by us — this list is our best match of their components against what we stock, not a verified bill of materials. Always check the original blog (linked above) for the actual parts list before buying.

ESP32 WiFi+Bluetooth CP2102 Development Board Rs. 520.00
Ultrasonic Sensor Module HC-SR04 Rs. 89.00
0.96 Inch I2C/IIC 4pin OLED Display Module White Rs. 349.00
10pcs - 220 ohm 1/4 W Resistor Set Rs. 39.00
Jumper Wire 10 Pin Male To Male 20cm Rs. 45.00
MB102 Adjustable Breadboard Power Supply Module (3.3V & 5V) for Arduino & Raspberry Pi Rs. 139.00
400 Points Mini Solderless Prototype PCB Breadboard High Quality Rs. 89.00
Jumper Wire 10 Pin Male To Female 20cm Rs. 45.00

Selected: Rs. 0.00

This list includes a generic resistor set as a placeholder — it is not matched to the exact value or part number this circuit needs. The correct one is specified on the original source page linked above; check it before buying.

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How It Works

This project creates a digital distance-measuring instrument using an ESP32 microcontroller, an HC-SR04 ultrasonic sensor, and a 128x64 I2C OLED display, all wired together on a breadboard. The HC-SR04 sensor operates by emitting a high-frequency sound wave pulse through its transmitter. When this sound wave strikes a nearby physical obstacle, it bounces back as an echo and is captured by the sensor's receiver. The ESP32 coordinates this process by sending a trigger signal, and then carefully measures the exact duration of the resulting echo pulse. Using the known speed of sound in air, the microcontroller calculates the precise distance to the object. Because the HC-SR04 requires a 5V power supply while the ESP32 operates on 3.3V logic, a voltage divider made of resistors is placed on the sensor's echo output line. This protects the ESP32's sensitive GPIO pins from receiving an over-voltage signal. Finally, the calculated distance data is transmitted over the I2C communication protocol to the 128x64 OLED display, where it is rendered in real time using the Adafruit graphics libraries.

Why Build This

Create a foundational distance-measuring tool for prototyping obstacle-avoidance robots and automated guided vehicles (AGVs).

Build practical proximity detection systems for automated tasks like water level monitoring or smart bin fill-level tracking.

Gain hands-on experience interfacing mixed-voltage electronics by safely connecting a 5V sensor to a 3.3V microcontroller.

Real-World Application

Obstacle avoidance robots, automated guided vehicles (AGVs), proximity detection, water surface level monitoring, and dumpster fill-level monitoring systems.

Skills You'll Learn

Ultrasonic distance calculation

I2C bus communication

Level shifting with voltage dividers

Interfacing OLED displays

GPIO pulse timing

Safety Precautions

Ensure the 5V power supply to the HC-SR04 does not directly connect to the ESP32 GPIO pins; use a voltage divider on the Echo pin to protect the 3.3V logic level inputs of the ESP32.

Technology Tags

ESP32

HC-SR04 ULTRASONIC SENSOR

OLED DISPLAY

I2C

NEWPING LIBRARY

ADAFRUIT SSD1306

DISTANCE MEASUREMENT

SENSORS

Frequently Asked Questions

Why do I need resistors on the Echo pin if the ESP32 powers the circuit?

The HC-SR04 sensor runs on a 5V power supply and outputs a 5V logic signal on its Echo pin, but the ESP32 GPIO pins operate at 3.3V and can be damaged by 5V. A voltage divider steps the 5V signal down to a safe level for the ESP32.

How does the OLED display connect to the ESP32 without using up too many pins?

The 128x64 OLED display uses the I2C communication protocol, which only requires two data lines (SDA and SCL) to connect to the ESP32, leaving plenty of other pins free.

Can I power the HC-SR04 directly from the ESP32's 3.3V pin?

The HC-SR04 is designed to operate on 5V. While it might occasionally respond on 3.3V, its range and reliability will be severely reduced, so it should be powered from a proper 5V source while protecting the input pins.

Gallery

This page is part of Kitkraft's Project Hub — a curated collection of electronics & robotics projects gathered from the maker community to help students and hobbyists discover and learn to build. Kitkraft does not claim authorship of the original project, and makes no representation as to the accuracy, completeness or safety of third-party source material. The summary and "How It Works" explanation above are AI-generated, rewritten with reference to the original tutorial — not a reproduction of it. Full credit and a direct link to the original source are provided above. If you're the original creator and have a concern about how your work is represented here, please contact us and we'll address it promptly.

Kitkraft Project Hub — curated from the maker community, credited at the source.

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