If you have one ultrasonic sensor and a microcontroller, you can detect plenty of useful things, like the water level in a rain barrel or the distance traveled by a tablet along a rail.

Posted in Arduino Hacks Tagged adafruit wave shield, arduino, ultrasonic, ultrasonic distance sensor, wav shield ← Fabricate Your Own 7-Segment Displays Easy Capacitive Touch Sensors In Eagle → ...

I have seen too many posts highlighting the erroneous distance reports of the HC-SR04 ultrasonic sensor module. In principle, it can “conditionally” detect the distance of objects between 2 and 400 ...