| 摘要 |
PROBLEM TO BE SOLVED: To relax driver's tension due to the incoming call tone of a portable telephone set during his automobile driving. SOLUTION: The incoming call tone of the portable telephone set is increased/reduced in units seconds by a time series increasing/reducing device 3. An interval designation menu 4 and a sound volume designation menu 5 are used to designate the interval of sound volume change and increase/reduction of the the sound volume. The number of seconds of duration of the incoming call tone is counted by a ring second number detector 6, and the frequency of change is counted by according to the output of a counter 7. The sound volume in changed by a sound volume level adjuster 8 to sound a loudspeaker 9. The incoming call tone during driving is set so that the sound volume increases with time. In the case of automatic incoming call to a personal computer or the like, it is so set that the sound volume becomes smaller. In the case of emergency communication, the sound volume is increased to the maximum level and is continued to be sound.
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