| 摘要 |
<p>PURPOSE: To automatically control the sound volume of the alarm tone of the character processor according to an ambient noise level by detecting the ambient noise by a noise detecting means and controlling the sound volume of the alarm tone by an alarm tone volume control means according to the detected value. CONSTITUTION: The level of the ambient noise detected by a microphone 9 is amplified by an amplifier 10 to a proper value and converted by a rectifying circuit 11 into a DC potential. The DC voltage which is proportional to the level of the ambient noise is held by a holding circuit 4 which is controlled with the output of an alarm signal generation part 2. With the output of the alarm signal generation part 2, an oscillator 6 is driven and its output is amplified by a variable gain amplifier 7; and a bell circuit 8 is placed in operation with the output of the amplifier 7 to sound the alarm tone. The alarm tone volume of this bell circuit 8 is proportional to the output of the variable gain amplifier 7, which varies in amplification gain in proportion to the output voltage of a control voltage generating circuit 5, so calling tone volume is proportional to the output voltage of the holding circuit 4, namely the level of the ambient noise.</p> |
