SWITCHING DEVICE FOR OFF-TALK COMMUNICATION SERVICE DEMONSTRATION

PURPOSE:To easily carry out a demonstration of the off-talk communication service by validating an LPF at the inactivation of a photocoupler. CONSTITUTION:When a telephone of a subscriber's private home is used for calling, the voltage is divided by resistances R1-R4 down to such a level where a transistor Tr1 is unable to work. Then the divided voltage is inputted to a base terminal of the Tr1. Thus the Tr1 is turned off and then a Tr2 is also turned off. As a result, no current flows to a relay 121 from a DC power terminal 131 and the switches a and a are closed and opened respectively within the relay 121. Thus a terminal side terminal 111 is connected to a line terminal 113 only and the calling is possible. When the switch a is closed, the call signal reaches the telephone after bypassing an LPF 151. Thus it is possible to simply perform a demonstration of the off-talk communication service without lowering the impedance of a telephone circuit.