| 摘要 |
PURPOSE:To surely inform the operator with incoming call by inputting audible signal for a incoming call display to a reception circuit of the operator, when a call is incoming to an switchboard. CONSTITUTION:When a call is incoming to an switchboard and an incoming signal is inputted to a terminal CL, a transistor TRQ1 turns to be conductive and a lamp LP is illuminated and upon connecting a terminal T1 or T2 as required, activates a buzzer. A monostable multivibrator OSM is started and a pulse signal is outputted for a predetermined suceeding time. This output signal energizes a TRQ2 via a gate G kept in conductive state with the incoming signal and makes an analog switch SW conductive for the periord. As a result, an audible signal is inputted to a reception circuit RL via an amplifier AMP and a transformer Tr and transmitted to a receiver R. |
