Patent GB-1499314-A (GB)
Title: Wired broadcasting systems
IPC: G07F7/00
Filed: 1975-03-14
Abstract: 1499314 Wired broadcasting systems COMMUNICATIONS PATENTS Ltd 14 March 1975 [16 March 1974] 11792/74 Heading H4R In a subscribers unit for a wired broadcasting system in which some programmes may be denied to some subscribers, a coded signal is generated in the subscribers unit and compared with a coded signal received with the programme signal selected in the subscribers unit and the selected programme is allowed or denied as a result of the comparison. As described some programmes are freely available for selection by selector 1, Fig. 1, in the subscribers unit whilst others are barred by gate 2. For reception of a barred programme selector 1 is positioned as shown and a card 7 inserted in a reading mechanism. The position of card aperture 8, as determined by light source 5 and photosensitive transistors 4 enables one of gates 3 to pass the selected programme to the input of gate 2 and to a code detector 9. A code transmitted with the programme signal comprises a start pulse 0À06 secs. long of a 13 MHz oscillation followed by a code sequence of 0À02 sec. pulses of 13 MHz oscillation 8 bits long. The code detector 9 includes a circuit 12 which is charged by the long start pulse and holds for the duration of the code sequence, and a circuit 13 which follows the code sequence and a comparator 14 provides an output whenever the output from circuit 13 exceeds half the output from circuit 12 and thereby reproduces the code sequence. The comparator output is applied to a start pulse detector 16, a clock signal generator 17 and an identifier 15. The start pulse and clock pulses cause operation of a shift register 18 to sequentially light LED's 20 at a rate corresponding to the code sequence pulse rate, and the holes 22 in the card 7 produce a local code sequence, dependent on the card, from the large area light detector 21. The local code is compared with the received code in the identifier 15 and if they are identical switch 19, which has been enabled by the start pulse from 16, enables gate 30 to allow the eighth pulse from the shift register 18 to pass the integrator circuits 32. If the locally generated code and the received code differ the switch 19 is reset and the "and" gate 31 is enabled. After a sufficient number of correct codes have been received Schmitt trigger 33 is set, which enables gate 2 to allow the selected programme to be received, and actuates a solenoid 34 which locks the card 7 in position against removal. Subsequent resetting of switch 19 enables gate 31, and operates Schmitt trigger 36, which operates a cutter solenoid 37 to cut off the portion of the card 7 carrying the code holes 22, so that it is of no further use. The card may also be cut by operation of manual switch 38 to allow change of card. In an alternative embodiment, Fig. 3 (not shown), the card 7 instead of being apertured to allow light transmission has conductive areas which, when the card is located in the slot of the card reader, screens terminals connected to a 13 MHz oscillator from terminals connected to detectors and FET gate circuits which, together with a shift register operate similarly to the optical card reader. The card reader is the subject of divisional Specification 1,499,315.