Teleprinter

A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point and point-to-multipoint configurations.

[1] Electrical telegraphy had been developed decades earlier in the late 1830s and 1840s,[2] then using simpler Morse key equipment and telegraph operators.

Teleprinters are still widely used in the aviation industry (see AFTN and airline teletype system),[4] and variants called Telecommunications Devices for the Deaf (TDDs) are used by the hearing impaired for typed communications over ordinary telephone lines.

Teleprinters were invented in order to send and receive messages without the need for operators trained in the use of Morse code.

Cooke & Wheatstone received a British patent covering telegraphy in 1837 and a second one in 1840 which described a type-printing telegraph with steel type fixed at the tips of petals of a rotating brass daisy-wheel, struck by an "electric hammer" to print Roman letters through carbon paper onto a moving paper tape.

It used pulses of electricity created by rotating a dial over contact points to release and stop a type-wheel turned by weight-driven clockwork; a second clockwork mechanism rotated a drum covered with a sheet of paper and moved it slowly upwards so that the type-wheel printed its signals in a spiral.

Joy Morton needed to determine whether this was worthwhile and so consulted mechanical engineer Charles L. Krum, who was vice president of the Western Cold Storage Company.

It was Howard who developed and patented the start-stop synchronizing method for code telegraph systems, which made possible the practical teleprinter.

The new company combined the best features of both their machines into a new typewheel printer for which Kleinschmidt, Howard Krum, and Sterling Morton jointly obtained a patent.

The Model 3 tape printer, Creed’s first combined start-stop machine, was introduced in 1927 for the Post Office telegram service.

[22] By 1938, the teleprinter network, handling weather traffic, extended over 20,000 miles, covering all 48 states except Maine, New Hampshire, and South Dakota.

There were at least five major types of teleprinter networks: Before the computer revolution (and information processing performance improvements thanks to Moore's law) made it possible to securely encrypt voice and video calls, teleprinters were long used in combination with electromechanical or electronic cryptographic devices to provide secure communication channels.

If the sender has nothing more to send, the line simply remains in the marking state (as if a continuing series of stop bits) until a later space denotes the start of the next character.

"Speed", intended to be roughly comparable to words per minute, is the standard term introduced by Western Union for a mechanical teleprinter data transmission rate using the 5-bit ITA2 code that was popular in the 1940s and for several decades thereafter.

However, the limitations of HF transmission such as excessive error rates due to multipath distortion and the nature of ionospheric propagation kept many users at 60 and 66 speed.

Many teleprinters had built-in paper tape readers and punches, allowing messages to be saved in machine-readable form and edited off-line.

Ships, command posts (mobile, stationary, and even airborne) and logistics units took advantage of the ability of operators to send reliable and accurate information with a minimum of training.

Amateur radio operators continue to use this mode of communication today, though most use computer-interface sound generators, rather than legacy hardware teleprinter equipment.

However, instead of a more-or-less arbitrary mapping between 5-bit codes and letters in the Latin alphabet, all characters (letters, digits, and punctuation) printed by the ETK are built from 14 basic elements on a print head, very similar to the 14 elements on a modern fourteen-segment display, each one selected independently by one of the 14 bits during transmission.

1908) started to manufacture teleprinters in order to provide Italian post offices with modern equipment to send and receive telegrams.

Despite its long-lasting trademark status, the word Teletype went into common generic usage in the news and telecommunications industries.

[40] Teletype machines tended to be large, heavy, and extremely robust, capable of running non-stop for months at a time if properly lubricated.

The main difference from a standard teleprinter is that Telex includes a switched routing network, originally based on pulse-telephone dialing, which in the United States was provided by Western Union.

AT&T developed a competing network called "TWX" which initially also used rotary dialing and Baudot code, carried to the customer premises as pulses of DC on a metallic copper pair.

[44] Through the use of "shift in" and "shift out" codes, this six-bit code could represent a full set of upper and lower case characters, digits, symbols commonly used in newspapers, and typesetting instructions such as "flush left" or "center", and even "auxiliary font", to switch to italics or bold type, and back to roman ("upper rail").

In later years the incoming 6-bit current loop signal carrying the TTS code was connected to a minicomputer or mainframe for storage, editing, and eventual feed to a phototypesetting machine.

In early operating systems such as Digital's RT-11, serial communication lines were often connected to teleprinters and were given device names starting with tt.

Although printing news, messages, and other text at a distance is still universal, the dedicated teleprinter tied to a pair of leased copper wires was made functionally obsolete by the fax, personal computer, inkjet printer, email, and the Internet.

Soon, advanced multimode electronic interfaces such as the AEA PK-232 were developed, which could send and receive not only packet, but various other modulation types including Baudot.

This made it possible for a home or laptop computer to replace teleprinters, saving money, complexity, space and the massive amount of paper which mechanical machines used.