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The HC-SR04 is a classic ultrasonic distance sensor for Arduino and other microcontrollers. It measures from 2 cm to 400 cm with up to 3 mm accuracy and works in sunlight or darkness, unlike optical rangefinders. It suits hobbyists, students, and makers building robots, parking sensors, or fish-finder prototypes. Compared with newer sensors like the JSN-SR04T, it is not waterproof and has a wider beam angle, but it is simple, well-documented, and widely supported.
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Lowest price we've seen: $5.25 on Nov 12 at Amazon. Tracked across 1 store since Nov 12.
Reviewers find the HC-SR04 reliable and easy to use for Arduino projects, praising its accuracy and range. Common complaints include limited accuracy at the extremes and the need for careful mounting.
The HC-SR04 is an ultrasonic distance sensor for Arduino projects. It uses sonar to find the distance to an object, much as a bat does. It detects objects without touching them, from 2 cm to 400 cm (1 inch to 13 feet), with accuracy up to 3 mm.
The module has an integrated ultrasonic transmitter and receiver. Sunlight and black material do not affect it, unlike optical rangefinders. Acoustically soft materials such as cloth can be difficult to detect.
To take a reading, supply the module with 5 V and apply a 10 us high-level TTL signal to the Trigger pin. The module sends out an ultrasonic signal and listens for the return. If a signal comes back, the Echo pin goes high for the time between transmit and receive. Distance to the object = duration of the Echo high level × sound velocity (340 m/s) ÷ 2.