This is a 555 chip to do with a multi-harmonic oscillation of the alarm

报警器\History\PCB1.~(1).PcbDoc.Zip
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......\PCB1 PCB ECO 2009-12-24 20-26-56.LOG
......\PCB1 PCB ECO 2009-12-24 20-42-05.LOG
......\PCB1 PCB ECO 2009-12-24 21-29-01.LOG
......\PCB1.PcbDoc
......\PCB1.PcbDocPreview
......\PCB1.pcbdoc_viewstate
......\PCB_Project1.PrjPCB
......\PCB_Project1.PrjPCBStructure
......\Sheet1.SchDoc
......\Sheet1.SchDocPreview
......\History
报警器

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