| 摘要 |
PURPOSE:To detect and discriminate a dial pulse faithfully without being influenced by the condition of a transmission line, by detecting a magnetic flux of a repeating coil, and making it a level variable input of a deciding level value setting means for detecting and discriminating the dial pulse. CONSTITUTION:When a subscriber's telephone set 1 is hooked off, a direct current is supplied to the telephone set 1 through a subscriber's line 2 from an office electric power source 3. Subsequently, when a dial is operated, a dial pulse is sent out, a Hall element circuit 9 detects intermittence of a current of a hybrid coil 7, and it is inputted to a comparator 14 being a dial pulse deciding means, through an operational amplifying circuit 10. To the comparator 14, an operational amplifier 17 being deciding level value setting means is connected, and a deciding level which is varied in accordance with increase or decrease of a value of a current flowing in the subscriber's line 2 is provided to the comparator 14. In this way, a dial pulse is discriminated faithfully irrespective of whether the subscriber's line is long or short. |
