| 摘要 |
PURPOSE:To accurately transmit incoming calls to a telephone set, by detecting a call signal from an exchange with a receiver in an on-hook state, oscillating a tone signal with an output signal as the tone signal increases according to the lapse of time and driving a speaker. CONSTITUTION:A call signal (a) is rectified of full wave at a diode bridge circuit 1, and inputted to a photocoupler 9 to change the voltage level. A signal b' through an inverter 10 is applied to a clock terminal C of a counter 11 changing the number of call signals. When a hook switch 18 is hooked on and no output of a counter 15 is given, the reset of the counter 11 is released, and when the signal b' is inputted, contacts 221...22n of relays 131...13n are sequentially closed through a decoder 12 with counter outputs (Q1...Qn). The current flowing to a speaker 3 is stepwise increased in response to the number of the signals (a). This operation is continued until the switch 18 is hooked off through the picking up of a handset, and the counter 11 is reset. |
