Well Pump Controller
So, here is the problem. My high-quality, German-made water level sensor in my water tank works some of the time. It's failure mode is to say the tank is empty so we regularly end up with a small flood near the water tank.
I was going to buy another sensor but guy who sells non-German ones in Estelí moved or vanished. So, Plan B. The in-tank sensor is a piece of copper-clad (both sides), fiberglass PC board. It's about 1 x 4 inches. I soldered wires to the two sides and covered the connection with RTV. It's mounted in the tank.
This monster then senses the change in resistance when the water reaches the sensor and turns off the pump. The pump is controlled by a solid state relay so I only need 5 or so volts at 10ma.