The flip-disc display (or flip-dot display) is an electromechanical dot matrix display technology used for large outdoor signs, normally those that will be exposed to direct sunlight. Flip-disc technology has been used for

destination sign A destination sign (North American English) or destination indicator/destination blind (British English) is a sign mounted on the front, side or rear of a public transport vehicle, such as a bus, tram/streetcar or light rail vehicle, that di ...

s in buses across

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

and

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

, as well as for variable-message signs on highways. It has also been used extensively on public information displays.Norman Ball, John Vardalas
"Ferranti-Packard"
McGill Queen's Press, 1994, A few game shows have also used flip-disc displays, including Canadian shows like ''

Just Like Mom ''Just Like Mom'' is a Canadian television game show which ran from 1980 to 1985 on CTV. A total of 595 episodes were taped at CFTO-TV Studios in the Toronto suburb of Scarborough, Ontario. It was hosted by Stephen Young during the show's f ...

'', ''

The Joke's on Us ''The Joke's On Us!'' is a Canadian game show that aired from September 1983 to 1984. It was hosted by Monty Hall, joined by Sylvie Garant as assistant very early on in the run, with Sandy Hoyt as the show's announcer. Taped at Showline Milton S ...

'' and '' Uh Oh!'', but most notably the American game show ''

Family Feud ''Family Feud'' is an American television game show created by Mark Goodson. It features two families who compete to name the most popular answers to survey questions in order to win cash and prizes. The show has had three separate runs, th ...

'' from 1976 to 1995 and its British version ''

Family Fortunes ''Family Fortunes'' is a British television game show based on the American game show ''Family Feud''. The programme ran on ITV from 6 January 1980 to 30 December 2002. A celebrity version, '' All Star Family Fortunes'', followed from 2006 to ...

'' from 1980 to 2002. The Polish version of Family Feud, Familiada, still uses this board, which was bought from the Swedish version of the show. In 2012,

Brooklyn Brooklyn () is a borough of New York City, coextensive with Kings County, in the U.S. state of New York. Kings County is the most populous county in the State of New York, and the second-most densely populated county in the United States, be ...

-based artist studio, BREAKFAST, began engineering a modernized Flip-Disc technology which was eventually able to flip the discs at over 60 times per second.

Design

The flip-disc display consists of a grid of small metal discs that are black on one side and a bright color on the other (typically white or

day-glo The Day-Glo Color Corp. (also styled as DayGlo) is a privately held American paint and pigments manufacturer based in Cleveland, Ohio. It was founded in 1946 by brothers Joseph and Robert Switzer and is currently owned by RPM International. It ...

yellow), set into a black background. With power applied, the disc flips to show the other side. Once flipped, the discs will remain in position without power. The disc is attached to an axle which also carries a small permanent magnet. Positioned close to the magnet is a

solenoid upright=1.20, An illustration of a solenoid upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whose ...

. By pulsing the solenoid coil with the appropriate

electrical polarity An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...

, the

permanent magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel ...

on the axle will align itself with the

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

, also turning the disc. Another style uses a magnet embedded in the disc itself, with separate solenoids arranged at the ends or side to flip it. A computerized driver system reads data, typically characters, and flips the appropriate discs to produce the desired display. Some displays use the other end of the solenoid to actuate a

reed switch Reed or Reeds may refer to: Science, technology, biology, and medicine * Reed bird (disambiguation) * Reed pen, writing implement in use since ancient times * Reed (plant), one of several tall, grass-like wetland plants of the order Poales * ...

, which controls an LED array behind the disc, resulting in a display that is visible at night but requires no extra drive electronics. Various driving schemes are in use. Their basic purpose is to reduce the amount of wiring and electronics needed to drive the solenoids. All common methods connect the solenoids in some sort of matrix. One driving method is similar to that of

core memory Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...

: the solenoids are connected in a simple matrix. Those solenoids at the crossing point of two powered wires are driven with enough

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...

to flip their discs; those powered on only the vertical or horizontal line see only 1/2 of the required force (as

flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ...

is proportional to current, which in turn is proportional to the

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...

). Those on unpowered lines also do not flip. Typically, the driving scheme works its way from top to bottom, powering each horizontal line "on" and then powering the needed vertical lines to set up that row. The whole process takes a few seconds, during which time the sound of the discs being flipped over is quite distinctive. Other driving schemes use

diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diod ...

s to isolate non-driven solenoids, which allows only the discs whose state needs changing to be flipped. This uses less power and may be more robust.

History

The flip-disc display was developed by

Kenyon Taylor Maurice Kenyon Taylor (26 June 1908 – 29 June 1986) was an English electrical engineer and inventor, responsible for many diverse technological developments and inventions, producing over 70 patents during his career. He spent most of his career ...

at Ferranti-Packard at the request of

Trans-Canada Air Lines Trans-Canada Air Lines (also known as TCA in English, and Trans-Canada in French) was a Canadian airline that operated as the country's flag carrier, with corporate headquarters in Montreal, Quebec. Its first president was Gordon Roy McGreg ...

(today's

Air Canada Air Canada is the flag carrier and the largest airline of Canada by the size and passengers carried. Air Canada maintains its headquarters in the borough of Saint-Laurent, Montreal, Quebec. The airline, founded in 1937, provides scheduled an ...

). By the time the system had been patented in 1961, TCA had already lost interest and Ferranti's management didn't consider the project very interesting. The first big opportunity for this system came in 1961 when the Montreal Stock Exchange decided to modernize its method of displaying trading information. Ferranti-Packard and Westinghouse both bid on the project, Westinghouse using an electro-luminescent technology. Ferranti won the contract after demonstrating the system with a mock-up they built in a disused warehouse across the street from the exchange's new offices, using hand-painted dots moved by hand to show how the system would work. The dots were slowly replaced with operating modules as they became available. The $700,000 system () was beset by delays and technical problems, but once it became fully operational it was considered very reliable. The systems were relatively expensive because of their manual construction, typically completed by women who "sewed" the displays in a fashion very similar to the construction of

magnetic-core memory Magnetic-core memory was the predominant form of random-access computer memory for 20 years between about 1955 and 1975. Such memory is often just called core memory, or, informally, core. Core memory uses toroids (rings) of a hard magnet ...

. Worse, Ferranti signed maintenance contracts that were, by 1971, losing $12,000 a month. A re-organization of the engineering and maintenance department addressed the problems, and prices started to fall. By 1977 the system had won sales with half the world's major stock exchanges. As prices fell, they were soon found in wider roles, notably that of highway signs and information systems for public transport. In Europe and in the United States, vane displays based on the same technology became popular for displaying prices at gasoline stations. 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. The displays often required minor maintenance to free up "stuck" discs.

Alternative technologies

Flip-disc systems are still widespread but are not often found in new installations. 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 light and darkness and, having no moving parts, require little maintenance. Some producers offer combined displays that use flip-dot and LED technologies together (every dot-disc has its own LED) and thereby they combine their advantages. For example, the Czech company BUSE from Blansko supplies self-patented DOT-LED displays (only DOT and only LED as well) in Central and East Europe.BUSE s. r. o. - Technology
/ref> This combined technology was used for outside displays of most of new buses and trams.

Application

File:Tatra KT8D5.N2P, čelní orientace, 9 Spojovací.jpg, Destination and line number signs on public transport vehicles (tram in Prague, Czech Republic) File:Esko S7 Praha hlavní nádraží – Řevnice.jpg, Destination and line number signs on public transport vehicles (a suburban train in Prague, Czech Republic) File:Elbfähre Bad Schandau, Tafel.jpg, Departure boards at public transport stations and terminals (Elbe ferry Bad Schandau, Germany) File:Děčín, autobusové nádraží, displej odjezdů.jpg, Departure boards at public transport stations and terminals (bus station in Děčín, Czech Republic) File:Podbabská, zastávka Podbaba, displeje.jpg, Line signs at public transport stops (Prague, Czech Republic) File:Proměnná tabule Radlická.jpg, Road transport information (Prague, Czech Republic) File:2002 D4500 2905.jpg, Destination sign on a MCI D4500 operating for the

Metropolitan Transportation Authority The Metropolitan Transportation Authority (MTA) is a public benefit corporation responsible for public transportation in the New York City metropolitan area of the U.S. state of New York. The MTA is the largest public transit authority in th ...

(New York City, United States) File:Familiada Tablica.png, Board used in Polish game show Familiada File:BREAKFAST Flip-Disc Panel.jpg, alt=Flip-Disc Panel, BREAKFAST Studio's Flip-Disc Panel invented in 2016. File:Flip-Disc Interactive Kinetic Artwork - Vanishing Forest.jpg, alt=Flip-Disc Art, An interactive Flip-Disc Artwork created by BREAKFAST Studio in 2022.

References

External links