Patent GB-946670-A (GB)
Title: Electrical identification circuits
IPC: H04Q3/62
Filed: 1960-06-10
Abstract: 946,670. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. June 10, 1960 [June 15, 1959], No. 20498/60. Heading H4K. In a parallel coding identification circuit of the type described in Specification 769,915 in which a particular combination of detectors is operated in response to an electrical condition applied to one of a plurality of conductors, including arrangements to render the operation of more than one combination, or of a combination not corresponding to a conductor, unstable, each detector includes at least one transistor operated in an " on-off " manner under control of the applied electrical condition and providing an amplified output in function thereof, and the detectors of each group are interconnected by mutual lock-out circuits, such as rectifiers, each arranged between the output of one detector and the inputs of the others of the group so as to create, on the actuation of one or more detectors of a group, a multi-stable electronic arrangement having as many stable conditions as there are detectors in the group. As shown, groups of five (Aar-Aer), six (Bar-Bfr) and four (Car-Cdr) detectors are provided each input conductor being connected via rectifiers G1, G2, G3 to one detector in each group, each detector including two transistors (T1, T2) and a relay (Aar). Choosing an idle outlet of a wanted group.-A common control circuit (not shown) effects the connection of negative battery through a 47 K ohm resistor to the identification circuit in respect of each idle outlet of the group, but with the transistors of the detectors not yet energized this has no effect thereon. However, provision is made of a cyclic preferance circuit which favours certain detector combinations, which is effective at this stage. This circuit includes a 10 mF condenser having one plated grounded and the other wired to the wiper pin of a 12-point uniselector PM which switch takes one step after each identification operation, and has its bank contacts respectively wired to the collectors of the T2 transistors of all the detectors of group Aar-Aer, to three of those of Bar-Bfr and to all of those of Car-Cdr. The connection of negative battery, with pin connected to Aar as shown, causes a transient current to flow via the four rectifiers such as G4 to the input terminals of Abr-Aer and thence via the decoupling rectifiers such as G1-G3 over all the battery connections not associated with Aar, so that those conductors which would initiate the operation of Aar are favoured. On the operation of relays S and OK (not shown) battery and ground are connected up to two potential dividers at the bottom left of the Figure, the upper of which connects - 4 volts to the emitters of transistors T2, - 20 volts to the relays such as Aar, and ground to the bases of transistors T1 and T2 via 33 K ohm and 47 K ohm resistors respectively, while the lower connects -14 volts to the collectors of transistors T1. In those detectors not driven by a negative battery connection the transistors T1 and T2 are blocked. In the others such as Aar current flows from ground via G6 and G1 to the negative connection, the resulting voltage drop at its base causing T1 to conduct. The emitter current flow of T1 reduces the base potential of T2 which also conducts, whereupon relay Aar operates and current flows via rectifiers G4 to the negative battery connections of other free outlets. With one relay of each group operated (and held over contacts such as aa1, aa2 ... OK3) the collector-emitter paths of the relevant transistors T2 are short-circuited. The circuit described may also be employed to identify a calling line, the operated group relays controlling the setting of a line switch, such as a crossbar switch, to extend the calling line to a link. Specification 767,367 also is referred to.