Simulating an Hourglass on a Flip Dot Display

I got my hands on a sizable 16x21 flip dot display. You have probably seen one before, maybe displaying the destination of your bus. Its mechanism is relatively simple. Each pixel/dot is represented by a disk that is yellow on one side, black on the other side and includes a permanent magnet. Beneath each disc is a electro magnet with a ferrite core. The ferrite cores are magnetized and keep the the discs with its yellow or black side up even when the power is off. A current though the electro magnet can be used to reverse the direction of the stored field which flips the dot.

For the display, arrange the dots are arranged in an array and the magnets are managed by a micro contoller.

Here you can see the display in slow motion:

Currently, I also have an accellerometer connected to the micro controller. This lets us measure the direction of gravity. The micro controller runs a continuous loop that checks for every “grain of sand” if there is a free position below and moves it if possible. Add an artificial bottleneck in the middle and we get a flip dot hourglass.