| 摘要 |
PURPOSE:To cause an incoming tone to be larger than a surrounding noise in an external part, slightly executing ringing when the noise is small and to output the incoming tone without fail by causing the volume level of the incoming tone to be variable in proportion to the surrounding noise outside of a telephone device when an incoming signal arrives at the telephone device. CONSTITUTION:When there is incoming to a telephone line and a calling signal is sent, the signal is rectified by a diode bridge 3 and operating power is supplied to an incoming tone signal generating circuit 5 and a power source circuit 4. The incoming signal is outputted from this circuit 5 and the power, which is caused to be a constant voltage, is supplied from the circuit 4 to a noise level detecting circuit 2. Then, the control signal of a level, which corresponds to the surrounding noise level to be picked up by a microphone 1, is outputted by the operation of the circuit 2. The incoming signal to be outputted from the circuit 5 is level-adjusted by a volume switch 7, which is set in advance, and inputted to a gain variable amplifier 6. By a signal which is outputted from the circuit 2 and corresponds to the external noise, the gain of the amplifier 6 is controlled and the optimum incoming volume to correspond to the external noise is executed by an incoming volume device 8. |
