HC-SR04 Ultrasonic Distance Sensor

Here's a simple sketch that shows how to use the HC-SR04 ultrasonic distance sensor.  I bought this one from Addicore.  They are inexpensive and work well for what they are, especially for the cost.  They are easy to get going and fun to play with.  The code is here on Github.

Here it is, measuring the distance from my laptop to the wall...