| 摘要 |
PURPOSE:To ensure an assued output of both the hook detection output and the call signal detection output with no malfunction by the dial pulse signal of 10PPS or 20PPS and through a simple constitution in which a detection element is shared. CONSTITUTION:The duplex current flowing to the DC loop of telephone TEL is detected by the duplex current detecting circuit DET, and the output of the circuit DET is integrated by the integral network INT. The output of the network INT is applied to the 1st timer circuit TIM1, and a repetitive charging/discharging is given to the capacitor C2 by the output of the network INT. Then the call signal TELCAL is delivered when the level of the capacitor reaches the prescribed value. At the same time, the output of the transistor TRQ1 which is controlled by the ON/ OFF of the photocoupler PC1 of the circuit DET is applied to the 2nd timer circuit TIM2, and the hook-off HOKOF is delivered when the output of the circuit DET continues more than a prescribed time. At the same time, the capacitor C2 of the circuit TIM1 is discharged forcibly via the diode D3 to ensure an assured output of both TELCAL and HOKOF. |
