Émile Baudot - Baudot System

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.