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 external destination signs on buses and trains across

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

and

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

, as well as for

variable-message sign A variable- (also changeable-, electronic-, or dynamic-) message sign or message board, often abbreviated VMS, VMB, CMS, or DMS, and in the UK known as a matrix sign, is an electronic traffic sign often used on roadways to give travelers info ...

s 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'', '' The Joke's on Us'' and '' Uh Oh!'', but most notably the American game show ''

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

'' from 1976 to 1995, and its British version '' Family Fortunes'' 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.

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 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 whos ...

. By pulsing the solenoid coil with the appropriate

electrical polarity The following Outline (list), outline is provided as an overview of and topical guide to electrical polarity (also called electric polarity). Positive and negative polarity * In electrical engineering, electrical polarity defines the direction ...

, 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, c ...

on the axle will align itself with the

magnetic field A magnetic field (sometimes called B-field) is a physical 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 ...

, 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 The reed switch is an Electromechanics, electromechanical switch operated by an applied magnetic field. It was invented in 1922 by professor Valentin Kovalenkov at the Peter the Great St. Petersburg Polytechnic University#Soviet era, Petrogra ...

, which controls an

LED A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresp ...

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: the solenoids are connected in a simple matrix. Those solenoids at the crossing point of two powered wires are driven with enough current to flip their discs; those powered on only the vertical or horizontal line see only half 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 in physics. For transport phe ...

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

voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

). 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 (electronics), terminal electronic component that conducts electric current primarily in One-way traffic, one direction (asymmetric electrical conductance, conductance). It has low (ideally zero) Electrical resistance ...

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 at Ferranti-Packard at the request of Trans-Canada Air Lines (today's

Air Canada Air Canada is the flag carrier and the largest airline of Canada, by size and passengers carried. Air Canada is headquartered in the borough of Saint-Laurent in the city of Montreal. The airline, founded in 1937, provides scheduled and cha ...

). 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 The Montreal Exchange (MX; ), formerly the Montreal Stock Exchange (MSE), is a derivatives exchange, located in Montreal, Quebec, Canada that trades futures contracts and options on equities, indices, currencies, ETFs, energy and interest rates. ...

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 In computing, magnetic-core memory is a form of random-access memory. It predominated for roughly 20 years between 1955 and 1975, and is often just called core memory, or, informally, core. Core memory uses toroids (rings) of a hard magneti ...

. 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

-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. 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 Blansko (; ) is a town in the South Moravian Region of the Czech Republic. It has about 20,000 inhabitants. It lies on the Svitava River on the border of the Moravian Karst. It is mainly an industrial town. Administrative division Blansko consi ...

supplies self-patented DOT-LED displays (only DOT and only LED as well) in Central and Eastern Europe.Flip DOT-LED BS 210 signs, BUSE s.r.o.
/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 New York state public benefit corporations, public benefit corporation in New York (state), New York State responsible for public transportation in the New York metropolitan area, New York Ci ...

(New York City, United States)

References

External links