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Home Burglar Alarm Auto Shut Off Tone Generator

2016-02-19 14:56  
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This is a typical home burglar alarm system of which once the alarm is triggered ON, it will not be shut OFF until the duration of time set has elapsed. This project is useful when built as one can carry it along wherever one goes or placed it in a vehicle. In times of emergency, one can easily switched ON the switch and the loud speaker will emit a loud sound that will frighten the uninvited guest.When SI (sensor) is closed, power is applied to U2, a dual timer. After a time determined by C2, CI is energized after a predetermined time determined by the value of C5, pin 9 of U2 becomes low, switching off the transistor in the optoisolater, cutting anode current ofSCR1 and de-energizing Kl. The system is now reset. Notice that (i6x C2) is less than (R7xC$). The ON time is approximately given by:(R7xC5)-(R6xC2) = Ton.In this auto shut off tone generator project, once the switch to the 9V power supply is connected, the alarm will trigger at a frequency of approximately 1.27 kHz. It will remain ON for a duration of approximately 170 seconds or 2.8 minutes before it stopped.
 

Burglar Alarm With Timed Shutoff