| 摘要 |
PURPOSE:To form a telephone automatic changeover equipment having an automatic changeover function and a privacy call function in common with a simple circuit constitution by providing a rectifier circuit inserted to a subscriber line, a switching element connected to the output terminal and a threshold level setting means interposed between the output terminal of the rectifier circuit and the switching element in a common telephone set. CONSTITUTION:Telephone sets T1, T2 are connected to a subscriber line via a bridge type rectifier circuit 1, the output side of the circuit 1 is connected to a thyristor element 3 via a display device 2 and a series circuit comprising a constant voltage diode 4 of 20-24V and a resistor 5 is interposed between a gate G and the noninverting output terminal of the circuit 1. In receiving an incoming call signal, a voltage over a threshold voltage of the diode 4 is outputted from the circuit 1, a switching element connected to each telephone set is turned on, the element of the telephone set hooked off at first keeps the ON state and the element of the other telephone set is turned off. Since the line voltage of the subscriber line is lowered than the threshold level, even if other telephone sets are hooked off, the element is not turned on. Thus, the privacy call is attained. When a party desiring the changeover hooks on after both the telephone sets hook off, the element of the party desiring the changeover is turned off and the element of the party subjected to be switching is turned on to attain the changeover.
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