Ultrasonic Distance Sensor Module - HC-SR04

The HC-SR04 is the sensor most hobbyists reach for first when a project needs to know how far away something is. One transducer sends a short burst of ultrasonic sound and the other listens for its echo, and the time between the two translates directly into a distance reading through simple timing logic that nearly every microcontroller platform already has a ready-made library for. It covers a practical range of a couple of centimetres out to around four metres, which is plenty for obstacle-avoiding robots, automatic parking-assist demos, liquid-level gauges, and security projects that need to notice when someone walks within range. Because it has shipped in such huge volumes for over a decade, wiring diagrams, example code, and troubleshooting advice are easy to find for whichever board a builder is pairing it with, making it a forgiving starting point for a first distance-sensing project.