Inside [Klaus]’ device is an Arduino Uno, an HC-SR04 ultrasonic ... to the sensor from 10 cm to 1 m in 5cm increments. This isn’t the limit of the sensor, though, and the device can be easily ...

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 ... of these little Arduino-compatible modules ...