| 摘要 |
PURPOSE:To obtain a telephone set circuit by which the monitor sound volume of a telephone line can be automatically decreased when a speech opponent is connected to the telephone line. CONSTITUTION:The speech opponent is dialed and called by increasing the monitor sound volume of the telephone line with a speaker 47. When the speech opponent is connected to the telephone line, the polarity of potential of the telephone line is inverted. Such polarity inversion is detected by a polarity inversion detector 32, and it is transmitted to a control circuit 35. Furthermore, the voice of the speech opponent is detected by a voice detector 40, and it is transmitted to the control circuit 35. The control circuit 35, after counting constant time after the detection of polarity inversion from a first time of voice detection by using a timer 41, decreases the monitor sound volume. When such signal is detected by a signal detector 45, a sound volume adjusting circuit 44 decreases the monitor sound volume. |
