Flip-disc display

A computerized driver system reads data, typically characters, and flips the appropriate discs to produce the desired display.

Other driving schemes use diodes to isolate non-driven solenoids, which allows only the discs whose state needs changing to be flipped.

The first big opportunity for this system came in 1961 when the Montreal Stock Exchange decided to modernize its method of displaying trading information.

The $700,000 system (equivalent to $7,140,000 in 2023) was beset by delays and technical problems, but once it became fully operational it was considered very reliable.

As prices fell, they were soon found in wider roles, notably that of highway signs and information systems for public transport.

In 1974 Ferranti started a project to build smaller versions for the front of buses and trains, and by 1977 revenue from these had already surpassed that from other lines of business.

Their place has been filled by LED-based products, which use a small amount of power constantly rather than each time the message changes, but are easily visible in both light and darkness, and, having no moving parts, require little maintenance.

For example, the Czech company BUSE from Blansko supplies self-patented DOT-LED displays (only DOT and only LED as well) in Central and Eastern Europe.

Flip-disc display elements (close up). The disc rotates on the shaft that is carried in the two triangular posts. The magnet that powers the rotation can be seen embedded in the disc. Under the disc is the driving solenoid ; when powered, a field is induced into the two posts, flipping the discs. Rotation stops when the disc hits the post.
DOT-LED display of a bus Irisbus Citybus 18M (made 2004), photographed while a change is scrolling across the board
Faulty dots are a typical malfunction of flip-disc displays.
DOT-LED display at night