The display is made up of 8 individual 'modules', each of which can display a single character. There are 40 flaps in each module, able to display characters A-Z, 0-9, '?', '!', and '+' as well as a blank.
Messages are sent via USB as plain text (serial). The driving microcontroller interprets those messages and moves the module motors accordingly. Magnets embedded in each flap spool are measured with hall effect sensors to keep track of the display's position.
The build is based on Scott Bezek's open-source design, and I've made a number of improvements to the enclosure, flap lettering, and electronics assembly. Those changes have been submitted as pull requests to the original project and are now included in the latest release (v0.7).