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A door alarm circuit principle

2016-02-20 22:51  
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The article describes a door alarm circuit principle. The circuit is very simple, very helpful. If you understand this principle is not very thorough, it is recommended to understand this circuit an important component: 1N4148 . In the circuit, IC1a is a fast oscillator, IC1b slow oscillator, combined emissions through IC1c high pulse pulse pulse warning sound when door (or window, etc.) is opened. This circuit is not too much to sound like fascinating siren or alarm device, but the impression: "You have to be noticed." R1 and D1 can be omitted, and the value of R2, perhaps, the door alarm sound reduction more like an alarm device. VR1 adjust sound frequency. IC1d is a timer, so that the door alarm is issued 20-30 after further pip door closed again, before falling silent, as if to say: "I'm smarter than a simple switching device." Piezoelectric disk S1 may be replaced by a leadership if necessary, LED connected in series 1 k resistor.

 


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