PURPOSE: To realize omission of various lines while a caller and a called party are in busy in either case where the caller and the called party are on the same line or on a different circuit by enabling detection with the same trunk.
CONSTITUTION: A current, when a caller 1 is forming a loop, is converted into a voltage respectively by resistors 3, 4, 5, and 6, consequently and reduced to 7 and 8. The current then is displaced by digital data at an A/D convertor 9 and stored in a microcomputer 10. Afterward, an oscillating circuit 11 outputs a selective signal and a call signal to the called party, however, voltage values 7 and 8 are not fluctuated by AC cut coils 12 and 13 and an AC bypass capacitor 14, and a new loop is superposed because of HOOK OFF by the called party 2, thus the voltage values 7 and 8 are fluctuated. These values are read by the microcomputer at any time and detected. In the same way, the change in a HOOK condition of the telephone is all detected by the present system, thereby this circuit can cope with any situation irrespective of the same line talk or some other line talk.
KUNIDA TSUTOMU
MATSUI TAROU
SHIRAISHI KATSUMI
