| 摘要 |
<p>PURPOSE:To turn down the volume of main speakers automatically when a telephone is in use by providing an attenuator to the amplifier of main speakers. CONSTITUTION:When a switch SW2 for personal radio use is turned on, conductors l4 and l7 of a key matrix conduct. Consequently, a microcomputer 40 generates a signal S1 containing 101 as the high-order three bits b4-b2 to put a switch circuit 42 in operation, and the sound output of a personal radio equipment 16 is applied to headrest speakers 34 and 36 whereas a microphone is made effective; and a signal S2 is also generated to turn on the transistor Q of the attenuator ATT. Consequently, sound outputs of main speakers 28 and 30 are lowered in level when these are being outputted. When the use of the radio equipment ends, the output levels are raised automatically.</p> |
