| 摘要 |
PROBLEM TO BE SOLVED: To obtain the circuit reduced in the number of parts and reduced in the fluctuation of sound pressure and sound quality by connecting a switching transistor to a buzzer in series and driving the transistor with the PWM signals from a microcomputer. SOLUTION: A switching circuit 20 consists of resistors 11 to 13 and a switching transistor 14. The resistor 11 is connected between the PWM output terminal of a microcomputer 10 and the base terminal of the transistor 14. The resistor 12 is the bias resistor connected between the base terminal of the transistor 14 and a ground. When a switch SW is turned on, the microcomputer 10 repeatedly outputs pulse signals, in which the duty is changed in accordance with the characteristic, with a prescribed interval period, from the PWM output terminal for few times. In the pulse signals, the duty is continuously varied from 50% to 0% during a prescribed time. |
