Height of a loose solid material

[Hatallica]

Below is my initial thought when reading the project details.

DIY Ultrasonic sensor with Zigbee Interface

I wanted to sense if my vehicle was in the garage without using a "presence sensor". I decided the best way (for me) was to sense the distance from the rafters down to either the floor or to the roof of my vehicle. So I built an ultrasonic distance sensor with a zigbee interface. The most difficult step was mounting it in an enclosure. I used a box I had lying around. It was a little larger than needed but in my garage room was no issue and the larger box made assembly easier. The most dif…