Telex machine T100

The telex machine is a device for text transmission over an electric line, the predecessor of the e-mail or SMS. It is a purely mechanical system, the only electric components are the driving motor, an electromagnet and a relay circuit providing the line connection. The user dialed the number of the other station which was equipped with the same machine. After the connection was established, the user could write on the keyboard and the other machine printed the same text on paper. To shorten the connection, which was paid depending on time, it was possible to firstly record the text on a punched tape and then send the text from the tape. The telex machines were also used as terminals for connecting to mainframe computers. The input data were sent to the computer using the keyboard and the computed results were sent back to the telex machine to be printed.

The system was developed in Germany in the thirties. The machine uses the principle of a series 5-bit digital transmission. The mechanical system decodes the serial transmission to parallel, the output is sent to an internal parallel 5-bit bus (five movable bars). The position of the bars determines the character that is then printed. Because the five bits enable only 32 possible combinations, which is not sufficient for the entire alphabet and numbers, the machine is equipped with two character sets, which are selected by two control characters. It was necessary to select the control character at the beginning of the transmission, otherwise the machine could print gibberish. The punched tape contains five positions on each row, which correspond to the five bits of the stored character.

The device was very delicate and required a precise maintenance. It was so noisy that it was placed in special rooms with sound insulation. Since the seventies, it was replaced by digital electronics in developed countries, but in Czechoslovakia, the hopelessly outdated mechanical telex machines were produced until the end of the eighties. They continued to be used until the early 21st century e. g. on the railway. The Czech telex network was finally shut down in 2008.