I made a small outdoor vault (still in progress). The concrete pad surface is 14 inches across, and is 28 inches below grade. The pad is mostly 2 inches thick but the center part has a 6 inch cylinder going about a foot down. All told it used about 80 pounds of cement. Underneath the corners of the pad are 3.5 inch boreholes going 2 feet further down filled with sand, to help drainage. The sidewalls of the enclosure are made from 8x16x2 inch blocks and are just outside the pad, so they sit on surrounding sand and not directly on the pad. This was actually intended for a different device, but while I’m still getting that ready, I put a R-Shake AM.R79D5.00.EHZ into it to see what I could see. It uses a Pi Zero because I was originally thinking of putting it in a small diameter borehole and wanted the smallest possible package. Then I found out at my location even a 40 foot borehole wasn’t much lower-noise than the surface, and had the disadvantage of being underwater.
The vault is right next to a road, only about 5 feet away from the road edge. Not an ideal location, but the easiest place to build this, and during the night there isn’t much traffic. I knew I would see cars and trucks, but I was surprised to find that it easily picks up both pedestrians (each footfall makes a clear spike) as well as bicycles, due I guess to the texture of the road surface. Even though it’s not terribly deep, I notice the reported CPU temperature only varies +/- 1 degree C from day to night. I have a second RShake outdoors above ground in a small enclosure and it varies over 10 deg. C.