INTERCOM FOR MULTIPLE DWELLING HOUSES AND INTERCOM SYSTEM FOR MULTIPLE DWELLING HOUSES USING THE SAME

摘要

PROBLEM TO BE SOLVED: To prevent the generation of unpleasant sidetone or hauling by matching an impedance generated on a speech line by discriminating a calling source, switching and controlling the impedance of a power source circuit corresponding to the discriminated result. ;SOLUTION: An intercom 1 for multiple dwelling house is electrically connected to a door phone 3 in a standby state. When a calling is received from a lobby intercom 2, a calling signal is sent from an alarm monitor panel 4 via a multiple transmission line L, a signal processing part 10 receives this signal and discriminates it as being a calling from the lobby intercom 2, a relay RY1 is closed to a side (b), a relay RY2 is closed to a side (a), the intercom 1 is connected to the lobby intercom 2, a capacitor is connected to a power source circuit 13 by closing the relay of an impedance change control means 15, and the impedance generated in the power source circuit 13 is reduced. When calling is received from the door phone 3, however, this call is discriminated from the voltage level drop of a notice line LS' and the electrical connection with the door phone 3 is maintained.;COPYRIGHT: (C)2000,JPO