| 摘要 |
PURPOSE: To unnecessitate the installation of a calling sound generation circuit to each interphone terminal by generating an incoming call detection signal when a sent voltage and set voltage are coincide. CONSTITUTION: At the time of calling another station by pressing a matrix key from one of plural interphone terminals I1 to In , a calling detection circuit 9 provided for one of the plural interphone terminals I1 to In is started by voltage from a voltage sending circuit, which is sent from plural calling control lines L1 and L2 , to drive the calling sound generation circuit 10 provided for one of the plural interphone terminals I1 to In . Then a voltage comparing circuit 4 in the called interphone terminal compares voltage called respectively from the plural calling control lines L1 and L2 to which a calling signal is impressed from the calling sound generation circuit 10 in order, generates the incoming call detection signal when they are respectively coincide, and drives a calling sound speaker SP with the incoming call detection signal. |
