We all know that plants crave electrolytes, but how do you know how bad their craving is? Now you can, with your very own Electrolyte Crave-o-meter!
It's a dead simple Arduino controlled sensor that changes the LED from red (dry) to green (moist) to blue (saturated), depending on the range of values you input in the Arduino sketch. You can probably get more colors out of it, it looks like I tried at one point but I suck at seeing shades of red and green, so I probably wouldn't have seen the difference anyway.
I made this a couple of years ago, so I'm sorry if some of the parts are outdated, I'm including the original .SLDPRT and a .STEP version if you want to make changes to fit other components. I designed the switch port for mine specifically for a switch that I scavenged and liked, so one of the .STL files has that removed in case you wanted to maybe drill out one yourself. I also designed it for thread inserts, but if you don't want to bother with those there's a version that just has little pilot holes instead.
I think this would be a great PETG candidate, my first print was PLA and warped significantly after years out in the sun. My reprint is ABS, but I had a hell of a time keeping the box from eventually warping with the long print time. No supports needed for the box. The Nano fits nice and snugly, but there's a little cover to secure it in place if you need. Arduidno sketch is included!