HC-SR04 Ultrasonic Sensor

The HC-SR04 Ultrasonic Sensor Module is one of the most popular and widely used distance measurement sensors in the maker, robotics, and embedded electronics communities. It provides non-contact distance measurement using the principle of ultrasonic sound wave reflection , similar to how bats and submarines navigate using sonar. The module consists of two main components: an ultrasonic transmitter that emits 40kHz sound pulses , and a receiver that detects the echoes reflected from nearby objects. By measuring the time elapsed between transmission and reception and applying the speed of sound (~343 m/s) , the module calculates the precise distance to the target. The formula used is simple: Distance (cm) = (Echo Time in µs) / 58 . The HC-SR04 features a straightforward 4-pin interface ( VCC, GND, TRIG, ECHO ) that connects effortlessly to any microcontroller. To trigger a measurement, the user sends a 10µs HIGH pulse on the TRIG pin , after which the module emits 8 ultrasonic bursts at 40kHz and outputs a HIGH pulse on the ECHO pin with a duration proportional to the distance. This pulse can be measured using the pulseIn() function in Arduino , the gpio library on Raspberry Pi , or any timer-input capability on other MCUs. With a measurement range of 2cm to 400cm and an accuracy of ±3mm , the HC-SR04 is suitable for a wide variety of applications — from simple obstacle avoidance in robots to water level monitoring in IoT systems. The module is lightweight, low-power , and affordable , making it an essential component for hobbyists, students, and engineers alike. The HC-SR04 is fully supported by popular Arduino libraries such as NewPing and Ultrasonic.h , which simplify integration and allow for non-blocking measurements in complex projects. It is also compatible with ESP32, ESP8266, STM32, PIC, AVR, Raspberry Pi , and any platform with timer or pulse-measuring capability. How It Works Trigger: Send a 10µs HIGH pulse to the TRIG pin Transmit: Module emits 8 ultrasonic pulses at 40kHz Receive: Module waits for the echo to return Echo Output: ECHO pin goes HIGH for a duration proportional to the round-trip time Calculate Distance: Distance (cm) = (Echo Time µs) × 0.0343 / 2 Specifications Sensor Model: HC-SR04 Operating Voltage: 5V DC Operating Current: ~15 mA Quiescent Current: <2 mA Working Frequency: 40 kHz Measuring Range: 2 cm – 400 cm (0.78" – 13 ft) Resolution: 0.3 cm Accuracy: ±3 mm Measuring Angle: ~15° (effective beam angle) Trigger Input Pulse Width: 10 µs (minimum) Echo Output Signal: Pulse-width proportional to distance Number of Pins: 4 (VCC, GND, TRIG, ECHO) Module Dimensions: 45 × 20 × 15 mm Weight: ~9 g Operating Temperature: -15°C to +70°C Compliance: RoHS Compliant Pinout Pin 1 (VCC): +5V Power Supply Pin 2 (TRIG): Trigger Input (10µs pulse to start measurement) Pin 3 (ECHO): Echo Output (pulse width = distance) Pin 4 (GND): Ground Applications Mobile Robotics — obstacle detection and avoidance for autonomous robots Parking Assist Sensors — proximity warning systems for vehicles Object Detection & Tracking — automated counting and presence detection Range-Finding Devices — DIY tape-measure replacements Autonomous Mobile Robots (AMR) — SLAM, navigation, and mapping Smart Home Automation — proximity-triggered lights and devices Liquid Level Monitoring — water tanks, reservoirs, and aquariums Drone Altitude Control — short-range terrain following Educational & STEM Projects — teaching ultrasonic principles and timing Door & Gate Sensors — automated opening based on proximity Security & Alarm Systems — perimeter intrusion detection People Counting Systems — entrance traffic monitoring Industrial Automation — object presence on conveyor belts Interactive Art Installations — proximity-triggered displays and exhibits Smart Trash Cans — automatic lid opening when approached Touchless Devices — gesture-triggered hand sanitizer dispensers Replacement Sensor — for damaged HC-SR04 modules in existing projects