Émile Baudot

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Émile Baudot : biography

September 11, 1845 – March 28, 1903

Jean-Maurice-Émile Baudot (September 11, 1845 – March 28, 1903), French telegraph engineer and inventor of the first means of digital communication Baudot code, was one of the pioneers of telecommunications. He invented a multiplexed printing telegraph system that used his code and allowed multiple transmissions over a single line.

Early life

Baudot was born in Magneux, Haute-Marne, France, the son of farmer Pierre Emile Baudot, who later became the mayor of Magneux. His only formal education was at his local primary school, after which he carried out agricultural work on his father’s farm before joining the French Post & Telegraph Administration as an apprentice operator in 1869.

The telegraph service trained him in the Morse telegraph and also sent him on a four-month course of instruction on the Hughes printing telegraph system, which was later to inspire his own system.

After serving briefly during the Franco-Prussian War, he returned to civilian duties in Paris in 1872.

Telegraphy

The Telegraph Service encouraged Baudot to develop during his own time a multiple Hughes system for time-multiplexing several telegraph messages. He realised that with most printing telegraphs of the period the line is idle for most of the time, apart from the brief intervals when a character is transmitted. Baudot devised one of the first applications of time-division multiplexing in telegraphy. Using synchronized clockwork-powered switches at the transmitting and receiving ends, he was able to transmit five messages simultaneously; the system was officially adopted by the French Post & Telegraph Administration five years later.

Baudot invented his telegraph code in 1870 and patented it in 1874. It was a 5-bit code, with equal on and off intervals, which allowed telegraph transmission of the Roman alphabet, punctuation and control signals. By 1874 or 1875 (various sources give both dates) he had also perfected the electromechanical hardware to transmit his code. His inventions were based on the printing mechanism from Hughes’ instrument, a distributor invented by Bernard Meyer in 1871, and the five-unit code devised by Carl Friedrich Gauss and Wilhelm Weber. Baudot combined these, together with original ideas of his own, to produce a complete multiplex system.

Notes

Baudot system

On June 17, 1874, Baudot patented his first printing telegraph (Patent no. 103,898 "Système de télégraphie rapide"), in which the signals were translated automatically into typographic characters. Baudot’s hardware had three main parts: the keyboard, the distributor, and a paper tape.

The main element of Baudot’s system was the distributor in which a rotating contact made brief contact with a series of sectors. Five contacts were used to send a group of signals making up a single character for transmission. The distributor was driven by falling weights or an electric motor. Correcting signals were transmitted to keep both ends in synchronisation.

Each operator – there were as many as four – was allocated a single sector. The keyboard had just five piano type keys, operated with two fingers of the left hand and three fingers of the right hand. The five unit code was designed to be easy to remember. Once the keys had been pressed they were locked down until the contacts again passed over the sector connected to that particular keyboard, when the keyboard was unlocked ready for the next character to be entered, with an audible click (known as the "cadence signal") to warn the operator. Operators had to maintain a steady rhythm, and the usual speed of operation was 30 words per minute.

The receiver was also connected to the distributor. The signals from the telegraph line were temporarily stored on a set of five electromagnets, before being decoded to print the corresponding character on paper tape.

Accurate operation of this system depended on the distributor at the transmitting end keeping in synchronization with the one at the receiving end and operators only sending characters when the contacts passed over their allocated sector. This could be achieved at a speed of 30 wpm by strictly observing the "cadence" of rhythm of the system when the distributor gave the operator the use of the line.