Electromagnetic flip-disc technology - How it works
The flip disk assembly includes a permanent magnet. The selected flip disc changes position according to the controlled change in the magnetic field of a closely coupled electromagnetic coil. The control signal simply reverses the direction of the current pulse through the coil that reverses the magnetic field of the coil. The permanent magnet located in the disc assemble is either attracted or repelled by the field produces in the coil. The flip disc remains in the position to which it was last turned until the coil field is reversed by another current pulse.
For larger disks (up to 2.2" diameter) a permanent magnet is attached to one end of the disc and there is a single driving coil and pole assembly.
Other principle used for example in small and large seven segment displays uses especially constructed mechanics which gives two positions of equilibrium. A flag is a moving part which is either visible to observer or hidden. It contains a magnet which is either retracted or repelled by electromagnet. The flag is kept in position by combination of mechanical and magnetic forces, however it can be moved manually out of its equilibrium position.