With a standard old HC-SR04 ultrasonic sensor, an audio module and a servo to drive a custom gauge needle he’s made a device which can warn people around you if they’re too close for comfort.

Spherical Quadruped Arduino Robot. 9 Comments . by: Orlando Hoilett. May 21, 2020. Title: ... [Greg06] even included an ultrasonic distance sensor for the obstacle avoidance mechanism.

A low-cost (~$100), do-it-yourself (DIY) ultrasonic water level sensor/datalogger has been designed, constructed, and tested for use in education, citizen/community science, and research settings. The ...