GB1040580A - Data processing apparatus - Google Patents

Abstract

1,040,580. Automatic character reading. ENGLISH ELECTRIC-LEO-MARCONI COMPUTERS Ltd. Feb. 3, 1965 [Feb. 6, 1964], No. 5171/64. Heading G4R. A typewriter adapted to type legible characters readable also by machine has sensing means for automatically sensing the characters and produce representative signals. The paper carriage used in the typing operation is also used to move the characters past the sensing head. Alternatively, the sensing head may move, or flexible light guides may be used, the sensing end moving over the characters and the photo-cell end being fixed. In the form described the head comprises two halves 20, 21, Fig. 3 (not shown), each consisting of a transparent body. Light is shone on to the surface of the paper on lines A and B and is reflected on to photo-cells 22, 23. The character is formed of seven vertical bars two of which are wide and five narrow according to a code. Each half of the head is the width of one of the narrow bars or the spaces between. The outputs from the two photo-cells are subtracted so that when the head senses blank paper there is zero output. When one is on a bar and the other on a space a maximum output is obtained. When both are on a wide bar the output is again zero. The waveform obtained from the subtractor is used to set and reset a trigger as it crosses upper and lower threshold levels close to the zero. The output then consists of seven pulses of which two are long corresponding to the wide bars, and the rest are narrow. This signal is used to frequency-modulate a carrierwave which is transmitted to a distant receiver where it is demodulated. At the receiver the signal is applied to a circuit which gives a signal on one lead for a short pulse and a signal on a second lead for a long pulse and these are entered at " 1's " and " 0's " into a shift register under the control of the seven leading edge pulses suitably delayed. The seven parallel outputs are applied to a decoding matrix to identify the character, as a marking on one of a group of leads. These are passed through a control unit to another typewirter, a punch or a magnetic tape recorder. At the end of a line a special symbol causes the control unit to send a signal back via the H.F. link to the control unit at the transmitter to initiate sensing the next line.