CALL SIGNAL CONTROL CIRCUIT IN KEY TELEPHONE SET

摘要

PURPOSE:To prevent a call signal from being giving to an ear and to keep pleasant call state by providing a photocoupler in a DC loop at the transmission of the call signal and stopping forcedly the transmission of the call signal ahead the stopping operation of a loop monitor relay by a loop detecting output of the coupler. CONSTITUTION:An interface board IFB is inserted between a main device KSU of a key telephone set and a standard telephone set TEL5. The board IFB is provided with a loop monitor relay LE, a calling signal generating circuit RGO, a busy tone signal circuit BTG, a relay FE controlled by a control circuit CPU of the device KSU an I and a BU. Further, a photocoupler PC is provided in a DC loop at the transmission of a call signal of the circuit RGO. The transmission of the call signal of the circuit RGO is stopped forcibly ahead the stop of the relay LE by the loop detecting output of the coupler PC so as to prevent a call signal from giving to the telephone set TEL5 in a large sound.