| 摘要 |
PURPOSE:To identify various receiving signals precisely without malfunction with a simple constitution by using an off-hook detecting circuit and a call signal detecting circuit in common and multiplying the frequency of a call signal. CONSTITUTION:When a calling AC signal arrives at a subscriber's line 100 under the on-hook state of a telephone set, current flows into LEDs D1 and D2 alternately and the collectors of TRs Q1, Q2 are alternately turned on and off. Therefore, the call AC signal is multiplied by twice and inputted to an inverter 28. The output of the inverter 28 is inputted to a tone detector 32 and detected as a call signal by a CPU38. When the telephone set is turned to the off-hook state, DC current flows in one direction. Consequently, any one of diodes D1, D2 is steadily turned on, the collector of the TRQ1 or Q2 is turned to the low level and an off-hook detecting signal with the H level is outputted by the output of the inverter 28. Subsequently, a dial pulse is outputted from the output of the TRQ1 by dialing. |
