| 摘要 |
PROBLEM TO BE SOLVED: To provide a method and a device to reduce the number of pins used for volume control signal and to control an audio output volume. SOLUTION: The invention relates to a method and a device 50 to generate and control a volume of a speaker 14 in an instrument. The instrument 50 contains an IC chip 60 connected to an amplifier sub-system 80. The IC chip 60 contains a rectangular wave audio signal generating device 22, a counter 62, a resistor 64, a comparator 66, and an AND gate 68 which are used for generating a rectangular wave signal 69 with a modulated audio frequency. The signal 69 has pulses each of which has a width which is determined by a volume control value. The signal 69 is sent from the IC chip 60 to the amplifier sub-system 80 by single connection. The amplifier sub-system 80 integrates, filters, and amplifies the signal 69, and the speaker 14 is activated to generate an intended sound. By adjusting the volume control value, not only the pulse width but also the volume of a sound to be generated can be controlled. COPYRIGHT: (C)2005,JPO&NCIPI
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