Luggage Security Alarm

Summary

While travelling in public transport such as buses or trains, people usually carry expensive belongings and are quite insecure about their safety. Even though after locking the luggage thoroughly, there is always a worry about it.
 
To solve this problem here is a simple luggage security alarm circuit based on NAND gate. When somebody tries to steal the luggage, the circuit will give a warning alarm. An audio visual indication can also be provided by connecting it to the relay.
 
This project circuit can also be used in home to prevent the attempt of burglary as when somebody tries to open the door, the loop breaks and the alarm starts sounding.

Description

 

The project is built around CD4011 with components like LDR, variable resistor, capacitor, transistor and relay.. It generates a warning beep when somebody attempts to open the locker. To understand the working you should know about the truth table of NAND gate which is as follows-

 

 

INPUT
INPUT
OUTPUT
A
B
Y
0
0
1
0
1
1
1
0
1
1
1
0

 

 

The truth table of NAND gate shows that the output will remain HIGH until any of the signals is LOW. If both the signals go HIGH then in that case the output will be LOW.

 
The output of circuit depends on Pin 5. When power supply is connected to the circuit the voltage at pin 5 is zero as loop is intact. Therefore voltage at pin 4 becomes high which is connected to pin 1 and 2 which are also high. As the truth table of NAND gate says that if both the inputs are high then the output is low , so we will receive LOW at pin 3 of gate 1 which is connected to pin 12 and 13 making them also LOW. Hence, pin 11 goes HIGH making pin 8 and 9 also HIGH and voltage at pin 10 as LOW. As a result transistor connected to it through resistor will not be energized and we will not receive the alarm.
 
Now imagine somebody tries to take the luggage therefore the loop connected to it breaks. When loop breaks pin 5 and 6 goes high and reverse action take place. As a result pin 10 will become high and the transistor will start conducting and we will an alarm will sound. This alarm will not go off until the loop is intact again.
 
In this circuit we can use battery of 6-15V depending on the rating of the relay. The buzzer can also be connected directly without using Relay. The relay is used in the circuit because if the alarm to be connected works on AC an extra isolation would be needed from sudden current spikes. A diode is used with the relay because any reverse-voltage spike can short-circuit at source and they can do any damage to the circuit.

 

Circuit Diagram

Components
Resistor Image
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 Resistor

Resistor is a passive component used to control current in a circuit. Its resistance is given by the ratio of voltage applied across its terminals to the current passing through it. Thus a particular value of resistor, for fixed voltage, limits the current through it. They are omnipresent in electronic circuits.

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Capacitor image
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 Capacitor

 

 

Capacitor is a passive component used to store charge. The charge (q) stored in a capacitor is the product of its capacitance (C) value and the voltage (V) applied to it. Capacitors offer infinite reactance to zero frequency so they are used for blocking DC components or bypassing the AC signals. The capacitor undergoes through a recursive cycl...

1N4001 Diode Image
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 Diode 1N4001

1N4001 is a member of 1N400x diodes. Diode is a rectifying device which conducts only from anode to cathode. Diode behaves open circuited for the current flow from cathode to anode. 1N4001 is a 1A diode with low forward voltage drop and high surge current capability. It comprises of diffused PN junction and has low reverse leakage current of 5µA. Its DC blocking voltage is 50V.

...
2N2222 Transistor Image
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 Transistor 2N2222
2N2222 is an NPN BJT transistor. It is used for general purpose low-power amplification and switching applications. These are designed for high speed switching applicati...
Relay Switch Image
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 Relay Switch

Relay is an electromagnetic device which is used to isolate two circuits electrically and connect them magnetically. They are very useful devices and allow one circuit to switch another one while they are completely separate....

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