HC-SR04 Ultrasonic Distance Sensor Module, 2-400cm

The HC-SR04 is one of the most widely used distance sensors in hobby electronics, measuring range by timing how long it takes an ultrasonic pulse to bounce off an object and return. The module sends eight 40KHz square wave pulses on its trigger pin and then automatically listens for the returning echo, raising its echo pin high for a duration exactly equal to the sound's round-trip travel time, which a microcontroller then converts into a distance figure using the known speed of sound.

Detection range spans a genuinely useful 2cm at the near end up to 400cm (4 meters) at the far end, covering everything from close-range obstacle detection on a small robot to room-scale distance measurement. Precision is rated up to 0.3cm, fine enough for most hobby robotics, automated measurement, and simple proximity-sensing projects without needing a more expensive laser or lidar-based alternative.

Running on a straightforward 5V supply with static current draw under 2mA, it interfaces easily with essentially any microcontroller platform, outputting a standard high-level 5V digital signal on the echo pin that's simple to read with a timer or pulse-width measurement function. Because the sensing approach relies purely on sound wave timing rather than any complex analog circuitry, the module is inexpensive, reliable, and extremely well documented, with existing libraries available for virtually every common microcontroller platform.

Builders working on obstacle-avoidance robots, parking-assist projects, liquid level sensing, or any application needing straightforward non-contact distance measurement will find the HC-SR04 a proven, low-cost, and genuinely capable starting point, backed by one of the largest bodies of existing tutorials and example code for any sensor in the hobby space.