| 摘要 |
PURPOSE:To attain calling with a speaker, by operating a switching circuit and returning a voice signal from a remote caller by switching to the speaker, when the circuit is switched from the speaker to a receiver and no-sound state of the transmitter output is detected for a prescribed time or over. CONSTITUTION:When an order-line telephone is not used, an order-line 2 is connected to a speaker circuit 4 and the calling from the remote caller is outputted from the speaker. The called party operates a selection switch 6 with a loudspeaking signal from the speaker, the switching circuit 3 is activated and the voice signal of the caller 1 is switched to the receiver 5, and correspondence is done by using the receiver 5 and the transmitter 7. After the end of call, the called party connects the selection switch 6 to the speaker circuit 4 by operating the switching circuit 3 for further calls. When the circuit 3 is switched to the receiver side, an output signal 8 of the transmitter 7 is monitored at a no-sound detection circuit 9, and when the output signal 8 does not exist for a prescribed time or over, a return signal 10 is outputted from the circuit 9 to attain automatic switching to the speaker side. |
