On-hook/off-hook detector circuit

Details On-hook/off-hook detector circuit On-hook/off-hook detector circuit

1979-10-25

1981-08-04

Robinson, Thomas

H04M 322, H04B 300

Patent

active

042824087

ABSTRACT:
An on-hook/off-hook detection circuit comprises a light-emitting device 54 connected across the tip T and ring R leads of a subscriber's telephone set 50 and between current source 56 and ground 57. A photo-transistor 60 is optically coupled to the light-emitting device 54 for signaling a line scanner 53. When the subscriber's telephone set 50 goes off-hook, a short circuit comprising tip T, telephone set 50 and ring lead R causes light-emitting device 54 to become non-conducting while the light-emitting device 54 is conducting when subscriber's telephone set 50 is on-hook.

REFERENCES:
patent: 3410961 (1968-11-01), Slana
patent: 3819866 (1974-06-01), Hawley
Glowienka et al., "Telephone On/Off Hook Detector", IBM Tech. Dis. Bull., vol. 16, No. 5, Oct. 1973, pp. 1558-1559.

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