Patent GB-1507246-A (GB)
Title: Device for graphic communication
IPC: G08C21/00
Filed: 1976-10-26
Abstract: 1507246 Writing telegraph systems C J JOANNOU 26 Oct 1976 44356/76 Heading G1N [Also in Division H4] A writing telegraph system utilizes a send/  receive unit 1 Fig. 1 comprising (a) a first pen 5 for writing on a sheet of paper 3 held by clamp 4, the co-ordinate positions of the pen being sensed by a transducer 28 and transmitted via a telephone line as corresponding frequencies in a multiplexing arrangement, (b) a second pen 8 which is controlled by frequency signals-received on the telephone line and writes on sheet 3 in accordance with the received signals, and (c) a telephone handset 78 which is acoustically coupled to a microphone and loud-speaker and acts as a link in the send/receive system, or may be switched to an auxiliary microphone 87 and loud-speaker 85. The system is prepared for the desired mode of use by operating the appropriate switch button 113-115, which causes the operation of selected electronic switches at both the sending and receiving units inter-connected by the telephone line. When used as a writing telegraph transmitter the pen 5 is connected to an RF oscillator 88 Fig. 5 and its position on the paper 3 is sensed by transducer 28, located under the paper, consisting of two pairs of capacitor electrodes, one located parallel to the transverse, X axis of the paper 3 and the other pair parallel to the longitudinal, Y axis of the paper. The RF voltages picked up by the first pair are fed to a differential amplifier 90 to energize a motor 41 which drives the transducer 28 in the X direction until the output from amplifier 90 is zero, the motor simultaneously driving the slidar of a potentiometer 45 to produce a DC voltage indicative of the X co-ordinate of the position of pen 5. Similarly a motor 23 drives the transducer 28 in the Y direction and obtains from potentiometer 44 a voltage corresponding to the Y co-ordinate of the pen position. The X, Y co-ordinate voltages are converted to corresponding frequencies at 93, 94 and fed through an electronic commutator 99 to amplifier 84, speaker 82 and microphone 80 of handset 78. The commutator 99 also receives a fixed frequency signal from oscillator 97 or 98, as selected by switch 95 in pen 5, and the three frequencies are multi-plexed at commutator 99 Fig. 6A (not shown) for transmission via handset 78. When used as a writing telegraph receiver the multi-plexed signal (Fig. 6A) is received by earphone 79 of handset 78 and fed through microphone 81 and amplifier 83. The first frequency band, derived from an oscillator 97, is fed through filter 100 to produce a pulse which energizes a solenoid 52 to lower pen 8 on to the paper 3. This frequency band is also fed through filter 102 to produce pulses P1-P5 Figs. 6B-F (not shown) from inonostables 103-106. Pulses P3, P5 are used to open oscillators 109, 110 to the other two frequency bands to which they lock, the frequencies being converted to DC voltages at 111, 112, which are compared in amplifiers 92, 91 with the voltages at the sliders of potentiometers 45,  44, any difference being used to energize motors 41, 23 to drive pen 8 to the co-ordinate position corresponding to the frequencies in the second and third frequency bands.  In a modification the D.C. voltage signals from potentiometers 44, 45 are multi-plexed and converted to corresponding digital counts which are sent to a receiver or recorded for subsequent retrieval.