| 摘要 |
PURPOSE:To use a public telephone line, to which a periodically polarity-inverted signal comes, to make the originating call from a general subscriber's telephone set possible, by connecting a specific additional circuit to the preceding position of the general subscriber's telephone set through the contact of a response monitor relay of magnetic latch type. CONSTITUTION:A public telephone set TEL1 and a general subscriber's telephone set TEL2 are connected to connection terminals L1 and L2 of the public telephone circuit by switching switches SW1 and SW2. When the telephone set TEL2 is hooked off and a response signal of a called subscriber comes, a response monitor relay M is operated to switch a contact (m), and a current is flowed to a light emitting diode LD. As the result, transistors TRs PT and Tr1 are made conductive to make continuation of the cell possible. When the handset is hooked on, the light emitting diode LD stops emitting light by cut-off of the current, and TRs PT and Tr1 are turned off, and therefore, loop formation due to a diode bridge is stopped, and a thyristor SCR1 is made conductive, and the relay M is released. A current in the release direction is prevented from being flowed to the relay M during call by a constant voltage diode ZD4, a capacitor C6, and the thyristor SCR1. |
