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Door ajar alarm

2016-02-20 03:01  
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Door ajar alarm can senses to the door ajar. If the door ajar longer than 20 seconds, the alarm will beep alarm. The alarm circuit is driven by magnetic reed switch and magnet on the door control. Door closed when the switch is turned off, the alarm is disarmed. Open the door is opened by the switch, CL begins to charge through the RL. After about 20 seconds, the voltage at pin 9 is high enough, from the C, D, R 2, R 3, and C2 form a quantum oscillator.


For lower backup battery consumption, changing RL66 M {} and Cl1 MF (film). Pulse piezoelectric transducer 3-kHz oscillator.


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