| 摘要 |
Local lines (La,Lb) with resistors (R1) connected on the opposite ends thereof are grounded through diacs (V1,V2), while the local line (La) is connected through a transformer (T2) to the local line (Lb). One end of a relay (RL2) is connected through a transformer (T1) and zener diodes (ZD1,ZD2) in parallel to the local line (La), and, at the same time, the same end of the relay (RL2) is also connected through a resistor (R2), a diode (D1), a light emitting diode (LED1) and a current limiting booster (PD) to the local line (Lb). The other end of the relay (RL2) is connected through zener diodes (ZD3,ZD4) to the light emitting diode (LED1) and to the booster (PD). The circuit satisfies a European protocol, while efficiently detecting dials.
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