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  • Anti-theft Security Alarm Circuit

  • Created: Jan 30, 2014

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Summary

We are always vulnerable to thieves but we don’t know when will they strike. When they do, it will be too late for us to notice that our property was already taken. This project helps alert the owner if a thief is picking a lock. It can be used on doors, luggage or anything else with a lock.


The concept is simple, if the lock is opened without our consent, an alarm will be turned on indicating an intruder. This circuit is based on a NAND gates configuration that will turn the switching side on or off.


In this project we used the HEF4011B, a quad 2-input NAND gate. The outputs are fully buffered for the highest noise immunity and pattern insensitivity to output impedance. The configuration of the IC HEF4011B produces a HIGH output if the input is HIGH. Based on the figure, when the wire loop is closed, the IC HEF4011B will have a LOW input, and when the wire loop is triggered, the IC HEF4011B will have a HIGH input which will make its output also HIGH. The HIGH output of the IC HEF4011B will then be inputted to the base of the BC547 transistor allowing the current to flow on the relay switching the indicator or the buzzer ON.

3 Comments


Colin55

Why use a 4k7 on an emitter follower ????????

Posted: Mar 08, 2014


Anura

Hi I would prefer to receive stun gun circuit e-mail anuraxp@yahoo.com

Posted: Mar 13, 2014


Kristina Izarra

This project serves as a low cost alternative to a stun gun circuit. Since in this application we need to amplify the output, it is necessary to use a higher input impedance like the 4k7 ohms at the emitter follower.

Posted: Sep 19, 2014


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