A passive flipdot display to indicate the water level in a storage tank. A magnet in a pill bottle, floating inside the tank, flips the pixels as it moves up and down with the water level. The original version of this project (https://hackaday.io/project/172388) used painted steel washers in a spot-welded frame. This worked well enough for a few years, but a clumsy incident damaged it, necessitating at least a rebuild, which turned into a redesign, which is presented here for your enjoyment. More details and video at https://hackaday.io/project/193519/

Prusa

MINI+

No

No

0.2mm

The flaps are printed in two colours: start off with black, and then, after two or three layers, stop the print, swap with something bright (I had green, so that is what I used) and continue.

The flippy flappies contain less than 1g of material, so there is not much for gravity to work with in the overbalancing mechanism. Ensure therefore that the flaps and the frames are quite clear of any filament strings or even the merest wisp of a fibre. 'Painting' the components with the flame of one of those blowtorchy type of lighters worked well for me. Just be careful not to heat the components to the point where they may deform.
Clean out the holes for the axles (35mm stainless steel sewing pins) in the flap and the frame by running a thin drill bit through it by hand. I used a 1mm bit, which worked well enough.

Print and assemble as many pixels as needed - they are each 20mm in functional height, and they interlock securely to simplify assembly and handling. The entire stack of pixels then slips into a glass tube (which started life as a T12 fluorescent lamp), with spacers at top and bottom if and as needed. I then also stuffed some dessicant bags into the spacers at each end before sealing the tube as well as I could, and then mounting it on the water tank.
Simply scale the spacer height vertically as needed, or, if you really feel like it, edit the Freecad file, which is supplied for those who care.

Inside the water tank are two stainless steel rods, constraining a floating pill bottle to a well-defined vertical trajectory. It also prevents the bottle from rotating, thereby ensuring the magnet inside it remains oriented correctly. The magnet can actuate the pixels over a distance of almost 100mm, which is more than ample in this case.