| 摘要 |
PURPOSE:To secure alarming of nonturn-off of the loudspeaker talking switch to the user by lighting up the pilot lamp and also giving the singing intermittently after detecting discontinuation of the reception signal for over a fixed time. CONSTITUTION:When the loudspeaker talking is over and the remote subscriber hangs up the receiver, no receiving signal exists at line terminal 5. And in lapse of a fixed time, non-receiving signal detection circuit 13 operates to flash pilot lamp 16. Thus the output of pilot lamp control circuit 14 actuates aural switch control circuit 15 to give the forced reduction control to the insertion loss of transmitting and receiving aural switch circuits 3 and 6 in accordance with the flashing period of the pilot lamp. As a result, the acoustic combination is formed to microphone 1 to produce the ringing intermittently from speaker 8 and via the space, thus alarming the nonturn-off of the loudspeaker talking switch to the user. |
