| 摘要 |
PURPOSE:To easily control the sound volume of a speaker from the external by varying the duty cycle of a driving pulse impressed to the speaker. CONSTITUTION:A CPU 4 incorporated in a key input device has a function to output a repetitions cycle or pulse signals of different pulse widths in compliance with a control signal inputted from the external. The CPU 4 incorporated in the key input device is used as a source of the driving signal. The speaker 1 is driven by the pulse signal outputted form the CPU 4 via a driving circuit 5. According, by inputting to the CPU 4 a suitable controlling signal from outside a key switch and the key input device, the sound volume of the speaker 1 can be controlled to fit the purpose of operation.
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