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A teleprinter (teletypewriter, teletype or TTY) is a now largely obsolete electro-mechanical typewriter which can be used to communicate typed messages from point to point through a simple electrical communications channel, often just a pair of wires.
The most modern form of these devices are fully electronic and use a screen instead of a printer. These teletypewriters are still in use by the deaf for typed communications over the telephone, usually called a TDD or TTY. For more information, please see Telecommunications devices for the deaf.
The teleprinter evolved through a series of inventions by a number of engineers, including Royal E. House , David Edwin Hughes , Charles Krum and Emile Baudot. A predecessor to the teleprinter, the stock ticker machine, was used as early as the 1870s as a method of displaying text transmitted over wires. A specially-designed telegraph typewriter was used to send stock exchange information over telegraph wires to the ticker machines.
Most teleprinters used the 5-bit Baudot code (also known as ITA2). This limited the character set to 32 codes. One had to use a "FIGS" shift key to type numbers and special characters. Special versions had FIGS codes for specific applications like weather reports. Print quality was poor by modern standards. The Baudot code was used asychronously with start and stop bits: the asynchronous code design was intimately linked with the start-stop electro-mechanical design of teleprinters. (Early systems had used synchronous codes, but were hard to synchronise mechanically). Other codes, such as Fieldata and Flexowriter, were introduced but never became as popular as Baudot.
The teletype circuit was often linked to a paper tape punch and reader, allowing messages received to be resent on another circuit. Complex military and commercial communications networks were built using this technology. Message centers had rows of teleprinters and large racks for paper tapes awaiting transmission. Skilled operators could read the priority from the hole pattern and might even feed a "FLASH PRIORITY" tape into a reader while it was still coming out of the punch. Routine traffic often had to wait hours for relay. Many teleprinters had built-in paper tape readers and punches, allowing messages to be created and, to a limited extent, edited off-line.
More than two teleprinters could be connect to the same wire circuit by means of a current loopA communication interface akin to RS-232 that uses current instead of voltage for signaling. 20mA current loop uses the absence of 20mA current for high, and the presence of current in the loop for low. Used for long-distance and optically isolated links. (a possible source of the phrase "being in the loop"). Communication by radio, RTTY, was also common. Amateur radioAmateur radio commonly called ham radio , is a hobby enjoyed by many people throughout the world; as of 2004 about 3 million worldwide, 70,000 in Germany, 5,000 in Norway, 57,000 in Canada, and 700,000 in the USA. A holder of an Amateur Radio license has operators still use this communications mode.
Teletype was a trademark of the Teletype Corporation of Skokie, IllinoisIllinois is a state in the United States named after the Illiniwek Indian tribe, which used to live there. The capital of Illinois is Springfield and the U. postal abbreviation for the state is IL . Illinois is pronounced ill-len-NOY, or jokingly, ill-len, USA. Founded in 1906Events January 8 Landslide in Haverstraw, New York kills 20 January 31 Earthquake in Ecuador (8. 6 in Richter scale) February 11 Pope Pius X publishes the encyclical Vehementer nos''. February 15 Representatives of the Labour Representation Committee in t, it became part of ATT in 19301930 is the common year starting on Wednesday. see link for calendar) Events January-February January 6 The first diesel-engine automobile trip is completed ( Indianapolis, Indiana, to New York City). January 27 Miguel Primo de Rivera resigns January 30 G. Operations ceased around 1990. Teletype machines were given a model number, often followed by letters indicating the configuration:
Major models and their dates: