A teleprinter 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. They were used in telegraphy, which developed in the late 1830s and 1840s as the first use of electrical engineering; the machines were adapted to provide a user interface to early mainframe computers and minicomputers, sending typed data to the computer and printing the response. Some models could be used to create punched tape for data storage and to read back such tape for local printing or transmission. Teleprinters could use a variety of different communication media; these included a simple pair of wires. A teleprinter attached to a modem could communicate through standard switched public telephone lines; this latter configuration was used to connect teleprinters to remote computers in time-sharing environments. Teleprinters have been replaced by electronic computer terminals which have a computer monitor instead of a printer.
Teleprinters are still used in the aviation industry, variations called Telecommunications Devices for the Deaf are used by the hearing impaired for typed communications over ordinary telephone lines. The teleprinter evolved through a series of inventions by a number of engineers, including Samuel Morse, Alexander Bain, Royal Earl House, David Edward Hughes, Emile Baudot, Donald Murray, Charles L. Krum, Edward Kleinschmidt and Frederick G. Creed. Teleprinters were invented in order to send and receive messages without the need for operators trained in the use of Morse code. A system of two teleprinters, with one operator trained to use a keyboard, replaced two trained Morse code operators; the teleprinter system improved message speed and delivery time, making it possible for messages to be flashed across a country with little manual intervention. There were a number of parallel developments on both sides of the Atlantic Ocean. In 1835 Samuel Morse devised a recording telegraph, Morse code was born.
Morse's instrument used a current to displace an electromagnet, which moved a marker, therefore recording the breaks in the current. 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. In 1841 Alexander Bain devised an electromagnetic printing telegraph machine, 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. The critical issue was to have the sending and receiving elements working synchronously. Bain attempted to achieve this using centrifugal governors to regulate the speed of the clockwork, it was patented, along with other devices, on April 21, 1841. By 1846, the Morse telegraph service was operational between Washington, D. C. and New York.
Royal Earl House patented his printing telegraph that same year. He linked two 28-key piano-style keyboards by wire; each piano key represented a letter of the alphabet and when pressed caused the corresponding letter to print at the receiving end. A "shift" key gave each main key two optional values. A 56-character typewheel at the sending end was synchronised to coincide with a similar wheel at the receiving end. If the key corresponding to a particular character was pressed at the home station, it actuated the typewheel at the distant station just as the same character moved into the printing position, in a way similar to the daisy wheel printer, it was thus an example of a synchronous data transmission system. House's equipment could transmit around 40 readable words per minute, but was difficult to manufacture in bulk; the printer could print out up to 2,000 words per hour. This invention was first put in operation and exhibited at the Mechanics Institute in New York in 1844. Landline teleprinter operations began in 1849, when a circuit was put in service between Philadelphia and New York City.
In 1855, David Edward Hughes introduced an improved machine built on the work of Royal Earl House. In less than two years, a number of small telegraph companies, including Western Union in early stages of development, united to form one large corporation – Western Union Telegraph Co. – to carry on the business of telegraphy on the Hughes system. In France, Émile Baudot designed in 1874 a system using a five-unit code, which began to be used extensively in that country from 1877; the British Post Office adopted the Baudot system for use on a simplex circuit between London and Paris in 1897, subsequently made considerable use of duplex Baudot systems on their Inland Telegraph Services. During 1901, Baudot's code was modified by Donald Murray, prompted by his development of a typewriter-like keyboard; the Murray system employed an intermediate step, a keyboard perforator, which allowed an operator to punch a paper tape, a tape transmitter for sending the message from the punched tape. At the receiving end of the line, a printing mechanism would
Morse code is a character encoding scheme used in telecommunication that encodes text characters as standardized sequences of two different signal durations called dots and dashes or dits and dahs. Morse code is named for Samuel F. B. Morse, an inventor of the telegraph; the International Morse Code encodes the 26 English letters A through Z, some non-English letters, the Arabic numerals and a small set of punctuation and procedural signals. There is no distinction between lower case letters; each Morse code symbol is formed by a sequence of dashes. The dot duration is the basic unit of time measurement in Morse code transmission; the duration of a dash is three times the duration of a dot. Each dot or dash within a character is followed by period of signal absence, called a space, equal to the dot duration; the letters of a word are separated by a space of duration equal to three dots, the words are separated by a space equal to seven dots. To increase the efficiency of encoding, Morse code was designed so that the length of each symbol is inverse to the frequency of occurrence in text of the English language character that it represents.
Thus the most common letter in English, the letter "E", has the shortest code: a single dot. Because the Morse code elements are specified by proportion rather than specific time durations, the code is transmitted at the highest rate that the receiver is capable of decoding; the Morse code transmission rate is specified in groups per minute referred to as words per minute. Morse code is transmitted by on-off keying of an information carrying medium such as electric current, radio waves, visible light or sound waves; the current or wave is present during time period of the dot or dash and absent during the time between dots and dashes. Morse code can be memorized, Morse code signalling in a form perceptible to the human senses, such as sound waves or visible light, can be directly interpreted by persons trained in the skill; because many non-English natural languages use other than the 26 Roman letters, Morse alphabets have been developed for those languages. In an emergency, Morse code can be generated by improvised methods such as turning a light on and off, tapping on an object or sounding a horn or whistle, making it one of the simplest and most versatile methods of telecommunication.
The most common distress signal is SOS – three dots, three dashes, three dots – internationally recognized by treaty. Early in the nineteenth century, European experimenters made progress with electrical signaling systems, using a variety of techniques including static electricity and electricity from Voltaic piles producing electrochemical and electromagnetic changes; these numerous ingenious experimental designs were precursors to practical telegraphic applications. Following the discovery of electromagnetism by Hans Christian Ørsted in 1820 and the invention of the electromagnet by William Sturgeon in 1824, there were developments in electromagnetic telegraphy in Europe and America. Pulses of electric current were sent along wires to control an electromagnet in the receiving instrument. Many of the earliest telegraph systems used a single-needle system which gave a simple and robust instrument. However, it was slow, as the receiving operator had to alternate between looking at the needle and writing down the message.
In Morse code, a deflection of the needle to the left corresponded to a dot and a deflection to the right to a dash. By making the two clicks sound different with one ivory and one metal stop, the single needle device became an audible instrument, which led in turn to the Double Plate Sounder System; the American artist Samuel F. B. Morse, the American physicist Joseph Henry, Alfred Vail developed an electrical telegraph system, it needed a method to transmit natural language using only electrical pulses and the silence between them. Around 1837, therefore, developed an early forerunner to the modern International Morse code. William Cooke and Charles Wheatstone in England developed an electrical telegraph that used electromagnets in its receivers, they obtained an English patent in June 1837 and demonstrated it on the London and Birmingham Railway, making it the first commercial telegraph. Carl Friedrich Gauss and Wilhelm Eduard Weber as well as Carl August von Steinheil used codes with varying word lengths for their telegraphs.
In 1841, Cooke and Wheatstone built a telegraph that printed the letters from a wheel of typefaces struck by a hammer. The Morse system for telegraphy, first used in about 1844, was designed to make indentations on a paper tape when electric currents were received. Morse's original telegraph receiver used a mechanical clockwork to move a paper tape; when an electrical current was received, an electromagnet engaged an armature that pushed a stylus onto the moving paper tape, making an indentation on the tape. When the current was interrupted, a spring retracted the stylus and that portion of the moving tape remained unmarked. Morse code was developed so that operators could translate the indentations marked on the paper tape into text messages. In his earliest code, Morse had planned to transmit only numerals and to use a codebook to look up each word according to the number, sent. However, the code was soon expanded by Alfred Vail in 1840 to include letters and special characters so it could be used more generally.
Vail estimated the frequency of use of letters in the English language by counting the movable type he found in the type-cases of a local newspaper in Morristown. The shorter marks were called "dots" and the longer ones "dashes", the letters most used were assigned the shorter sequences of dots and dashes; this code was used since 1844 and became known as Morse lan