[Clint] was working with the Arduino library, based on the Parallax PING, which uses a single pin for trigger and echo. The HC-SR04 uses separate pins.

This activates the Arduino, which prompts the HC-SR04 to take several readings. The code averages these readings, does a little math, and displays the percentage of water remaining in the barrel.

The HC-SR04 ultrasonic range sensor is a pretty cool pre-wired module that you actually enjoy using when you start playing with electronics, microcontrollers, and robotics. As you might have noticed, ...