| 摘要 |
A microwave oven includes a piezo-electric speaker for audible announcement purposes and a microcomputer for controlling operations of the microwave oven. The mocrocomputer always develops a frequency signal for activating the piezo-electric speaker. A gate signal is developed from the microcomputer so that the gate signal and the frequency signal are commonly applied to the base electrode of a switching transistor. When the gate signal bears the logic "L", the switching transistor repeats the ON/OFF operation in response to the frequency signal applied thereto. The piezo-electric speaker is connected to the switching transistor, whereby the piezo-electric speaker generates the sound whenever the gate signal bears the logic "L".
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