Signalling device for key telephone systems

Details Signalling device for key telephone systems Signalling device for key telephone systems

1975-07-17

1976-07-27

Claffy, Kathleen H.

179 84VF, H04M 150

Patent

active

039718999

ABSTRACT:
A device used in conjunction with key telephone systems, for example, intercom systems. The device consists of a circuit for decoding the tone output from touch-tone telephones, indicating which digit has been operated and selectively signalling the called party. Special features include a minimum latcing time for received signals and a time-out circuit. A noise, or "talk-down" protection circuit is included; if a signal of any type is present in the slot between the low group and the high group touch tone signals, the input to the decoders is shunted out and the time-out circuit is disabled. Also included is a second phase lock loop connected to the lowest frequency decoder in order to decrease the recognition time. A relay decoding matrix is also provided, arranged to accommodate either single or two-digit codes. The device may be used in key telephone systems which include rotary dial equipment as well as touch tone equipment.

REFERENCES:
patent: 3582562 (1971-06-01), Sellari
patent: 3622710 (1971-11-01), Tothill
patent: 3701854 (1972-10-01), Anderson et al.
patent: 3780230 (1973-12-01), Bowen et al.
patent: 3795775 (1974-03-01), Cowpland
patent: 3806664 (1974-04-01), Bowen et al.
patent: 3845249 (1974-10-01), Sellari et al.

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