| 摘要 |
PURPOSE:To realize a ringer signal detecting circuit which is not influenced by the dial of a telephone set and is stable by detecting the direction of the electric current to flow at a telephone line in the network control circuit to connect the telephone line and an external signal input output part and disconnect the telephone set. CONSTITUTION:When a ringer signal is impressed between telephone line connecting terminals L1 and L2, through the telephone set connected to telephone set connecting terminals T1 and T2, a ringer signal electric current flows, when the electric current flows from the terminal L1 to an L2 direction, the electric current flows at a light emitting part 2-1 of a photocoupler, when the electric current flows from a terminal L2 to an L1 direction, the electric current flows at a light emitting part 3-1 of the photocoupler, and as the result, at light receiving parts 2-2 and 3-2 of the photocoupler, signals (to show electric current) 201 and 202 are obtained. The signals 201 and 202 are waveform-shaped by buffer circuits 7 and 11 and signals 205 and 206 are obtained. When 'and' circuit 12, a signal 207 is obtained. The signal 207 is noise-removed by a resistor 13 and a capacitor 14, waveform-shaped further by a buffer circuit 15 and an output signal 209 of a ringer signal detecting circuit is obtained.
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