| 摘要 |
PURPOSE:To switch transmission and reception automatically and to simplify the call operation, by controlling the switching between transmission and reception in accordance with a voice input or the output of an oscillating circuit, which is set preliminarily, and the presence or the absence of a receiving signal. CONSTITUTION:The carrier signal sent from an interphone IP I2 to an IP I1 is propagated through a power line mm. and passes through a plug 1, coupling capacitors 2 and 3, a BPF6, and a relay contact 19, and a voice signal is taken out by a demodulating circuit 7, and the signal is detected by a detecting circuit 8, and a negative voltage is applied to a logic gate 15. Then, a transistor TR16 is turned off, and a relay 17 is made inactive, and the voice signal is amplified by an amplifier 10 and is outputted from a speaker 18. In case of no transmission from the IP I2, a positive voltage is applied to the gate 15 from the circuit 8; and when a person speaks to the speaker 18, it is detected by a voice signal detecting circuit 12 to open the gate 15, and the TR16 is turned on to operate the relay 17, and contacts 19 and 20 are switched to set the transmission state. If a noise is inputted to the speaker, a switch 21 is turned off to operate an oscillator 13, and the transmission state is set. |
