If you need a seven-segment display for a project, you could just grab some LED units off the shelf. Or you could build something big and electromechanical out of Lego. That’s precisely what [upir] ...
The project illustrates a Charlieplexing of a group of 7-segment LED displays which is similar to the Charlieplexing of discrete LEDs but with some changes since all the LED segments have a common pin ...