| 摘要 |
PURPOSE:To decrease the call tone volume when the surrounding is quiet and to increase the call tone when the surrounding noise is large by using a detected output of a surrounding sound volume detector to control the sound volume adjusting circuit so as to adjust automatically the call tone volume of a caller. CONSTITUTION:The call signal outputted from a call signal generator 1 is amplified by an amplifier 2 and fed to a speaker 3, from which a call tone is outputted. When the surrounding sound is small, a smoothed output level by a resistor 6 and a capacitor 7 is small and a control transistor (TR)15 is nonconductive. Thus, a power supply voltage VCC is impressed to the base of a switching TR9 via a collector resistor 16 to turn on the TR9, then the sound volume of the speaker 3 is decreased by a sound volume attenuation resistor 11. When the surrounding sound is larger, the smoothed output level is increased, the TR15 is conductive, its base-emitter circuit of the TR9 is short-circuited by the TR15 and nonconductive, and the resistor 11 is disconnected from the circuit. Thus, the call tone volume from the speaker 3 is increased. |
