What do you do when you have a reserve tank full of water, but no way to measure it? Build your own non-contact water level indicator like Johan did. Looking for a way to monitor water levels without relying on expensive electronics or Internet connectivity, they went back to basics and built a fairly simple setup using a vertical array of magnetic flip-dot pixels.
Wanting to create a system that automatically turns on the borehole pump when water levels are low, Johan came up with the idea to use a magnet floating in a food-safe polyethylene bottle placed inside of the tank. The reed switches on the outside of the tank sense the magnet, ensuring water and electricity don’t mix. The two nonmagnetic stainless steel rods within the tank then form a track constraining the movement of the floating bottle to a vertical trajectory near the side of the tank.
The bottom of the tank houses an open reed switch, which shuts when dropping water levels cause the magnet to approach it. When this occurs, it energizes a relay that self-latches using one of its sets of contacts. The second set is connected to the contractor controlling the borehole pump, which is also turned on.
With the magnet already in the water, all that was needed was something to sense its position. Johan employed a 32mm steel washer and spot-welded it to an axle using a 3D-printed jig to get it properly centered. The axles of the washers were then placed into the steel uprights’ slots. A U-shaped crosspiece is spot-welded over these slots to capture the axles, and also to act as an end-stop for the washer when it’s turned over by the magnet. After placing spacers between the mounted washers, they're put in a glass tube to keep out wind, rain, and bugs. As the water level rises or falls, the magnet moves to cause the washers to flip, which displays the water level.