| 摘要 |
PURPOSE:To vary the sound volume of a piezoelectric buzzer with a single power source by driving the piezoelectric buzzer with the output obtained by gating a pulse signal selected among plural pulse signals which have frequencies higher than a frequency nearly equal to the resonance frequency of the piezoelectric buzzer and differ in duty by using a pulse signal of frequency nearly equal to the resonance frequency. CONSTITUTION:Pulse generating circuits 23-25 generate the pulse signals PA, PB, and PC which have frequencies higher than the resonance frequency of the piezoelectric buzzer 31 and differ in duty according to a basic clock and a pulse selecting circuit 26 selects the pulse signals PA, PB, and PC according to a control signal from a microcomputer 27. Then the selected pulse signal P is gated by an AND circuit 28 with the pulse signal P outputted by a pulse generating circuit. Consequently, the amplitude of a component having a frequency close to the resonance frequency can be varied with the duty of the pulse signal, to the sound volume of the piezoelectric buzzer can be varied with the single power source. |
