Electronic selector for telecommunications switching

Abstract

An improved telephone system selector unit employing an electronic control arrangement is capable of directly replacing or being added on to existing electro-mechanical switching arrangements of the Strowger or other types which position themselves directly in response to subscriber dial pulses. The electronic circuitry establishes rapid outlet scanning via a matrix of twelve-pole relays, each of which permits selection of three four-wire lines or four three-wire lines, depending upon a pre-selected operating mode. A digit treatment circuit evaluates the counter digits, selects the appropriate outlet group, and precludes scanning of restricted lines or numbers not present in the numbering plan. During scanning each three or four-wire circuit of each relay is scanned in turn until an available circuit is found. The digit treatment arrangement permits additional outlet groups to be added without regard to the numbering sequence. All of the pulses of a digit are counted before any switching takes place in the selector.