| 摘要 |
PURPOSE:To prevent malfunction of a ringing device of a telephone call tone transmission circuit by a dial pulse by turning on/off a switching circuit through the detection of the presence of an incoming signal. CONSTITUTION:When an incoming signal exists, a square wave is outputted from two terminals of a telephone tone transmission circuit 4, a voltage of a capacitor C2 is E1, a switching circuit 2 is set, the square wave is fed to a ring device 3 and a call tone is generated. When a dial pulse is inputted, a voltage across the capacitor C2 is E2, the switching circuit 2 is reset, and even if a square wave is outputted from the two terminals of the telephone tone transmission circuit 4, no square wave is fed to the ring device 2 and no telephone call tone is generated. |
