World University Of Bangladesh
A Project on
Design And Construction of Anti-Bag Snatching Alarm
Submitted by
Al-Imran Masum
Reg. No: WUB 09/11/47(A)/1491
&
Saddam Hossain
Reg. No: WUB 09/11/47(A)/1485
Department of Electrical & Electronic Engineering
World University of Bangladesh
Supervised by
Tabassum E Nur
Lecturer
Department of Electrical & Electronic Engineering
World University of Bangladesh
Background
Nowadays people always remains terrified of snatchers. Day by
day it is increasing in a society. Specially, the women are not safe
with their purse outside. For this reason, to remove snatching the
American inventors Richard W. Dixon invented purse theft alarm
on 1971. it was the first use of theft alarm. It was based on the
theory that a sudden pull or jerking force exerted by the purse
handle will cause the alarm to be actuated. A few years ago, in
2010 Tsang-Chu SHH was invented Burglar proof purse. A burglar
proof purse installs a control switch and an alarm for issuing a
warning sound at hidden positions of the purse, and a closed and
opened loop is distributed all over each surface of the purse and
connected to the control switch and the alarm.
Executive Summary
Here is a very simple as well as very useful project anti bag snatching
alarm, used in bag or suitcase in order to prevent from snatching. The
heart of this entire circuit anti bag snatching alarm is operational
amplifier IC CA3140 (IC1), configured as a comparator. The two inputs
(inverting and non – inverting) is given to pin no 3 and 2 of operational
amplifier respectively and output is obtained from pin no 6. Here IC2
(timer IC NE555) is used as monostable multivibrator. The timing
component of anti bag snatching alarm is R5, VR1, and capacitor C2 with
the given value in this circuit diagram lets the time of timer is about 1
minute. For audio section, IC3 is used as alarm tone generator with an
inbuilt oscillator. Finally the output is obtained from pin no 3 of IC3 and
amplified by transistor T1 in order to get desire level and lastly fed to
loudspeaker for output.
Objectives
 To design and construct Anti-Bag snatching alarm for
getting rid of snatching and captured the snatchers.
 To provide a thief alarm device that practically
eliminates accidental triggering thereof.
Methodology
 Collection of books, magazines data from different websites.
 Collection of equipment from local market.
Block Diagram of Anti-Bag snatching alarm
With 9V power supply
Loudspeaker
Mono jack &
mono Socket
Transistor
(BD139)
Operation
Amplifier
(CA3140)
Complex
ROM with an
inbuilt
oscillator
(UM3561)
Timer IC
(NE555)
Circuit Diagram of Anti-bag snatching alarm
Internal circuit of Anti-bag snatching alarm
Working principle of Anti-bag snatching alarm
Here is a simple alarm circuit to thwart snatching of your valuables
while travelling. The circuit kept in the bag or suitcase sounds a loud
alarm, simulating a police horn, if someone attempts to snatch the bag
or suit-case. This will draw the attention of other passengers and the
burglar can be caught red handed. In the standby mode, the circuit is
locked by a plug and socket arrangement (a mono plug with shorted
leads plugged into the mono-jack socket of the unit). When the burglar
tries to snatch the bag, the plug detaches from the unit’s socket to
activate the alarm.
 The circuit is designed around op-amp IC CA3140 (IC1), which is
configured as a comparator.
 The non-inverting input (pin 3) of IC1 is kept at half the supply
voltage (around 4.5V) by the potential divider comprising resistors R2
and R3 of 100 kilo-ohms each.
 The inverting input (pin 2) of IC1 is kept low through the shorted
plug at the socket. As a result, the voltage at the non-inverting input is
higher than at the inverting input and the output of IC1 is high.
Working principle of Anti-bag snatching alarm
 The output from pin 6 of IC1 is fed to trigger pin 2 of IC NE555 (IC2)
via coupling capacitor C1 (0.0047 μF). IC2 is configured as a monostable.
 Its trigger pin 2 is held high by resistor R4 (10 kilo-ohms). Normally,
the output of IC2 remains low and the alarm is off.
 Resistor R6, along with capacitor C3 connected to reset pin 4 of IC2,
prevents any false triggering. Resistor R5 (10 mega-ohms), preset VR (10
mega- ohms) and capacitor C2 (4.7 μF, 16V) are timing components.
 With these values, the output at pin 3 of IC2 is about one minute, which
can be increased by increasing either the value of capacitor C2 or preset
VR.
 When there is an attempt at snatching, the plug connected to the circuit
detaches. At that moment, the voltage at the inverting input of IC1
exceeds the voltage at the non-inverting input and sub-sequently its output
goes low.
 This sends a low pulse to trigger pin 2 of IC2 to make its output pin 3
high. Consequently, the alarm circuit built around IC UM3561 (IC3) gets
the supply voltage at its pin 5. IC UM3561 is a complex ROM with an
inbuilt oscillator. Resistor R8 forms the oscillator component.
Working principle of Anti-bag snatching alarm
 Its output is fed to the base of single-stage transistor amplifier
BD139 (T1) through resistor R9 (1 kilo-ohm). The alarm tone
generated from IC3 is amplified by transistor T1.
 A loudspeaker is connected to the collector of T1 to produce the
alarm. The alarm can be put off if the plug is inserted into the socket
again. Transistor T1 requires a heat-sink.
 Resistor R7 (330 ohms) limits the current to IC3 and zener diode
ZD1 limits the supply voltage to IC3 to a safe level of 3.3 volts.
Resistor R9 limits the cur- rent to the base of T1.
 The circuit can be easily constructed on a vero board or generalpurpose PCB. Using a small case for housing the circuit and 9V
battery. The speaker should be small so as to make the gadget handy.
Connecting a thin plastic wire to the plug and securing it in hand or
tie up somewhere else so that when the bag is pulled, the plug
detaches from the socket easily.
Circuit Instrument Description
Operational Amplifier:
The IC requires very low input current as low as 10pA to change
the output status, high or low. The IC has very fast response and
high speed of performance. The output stage of the IC uses bipolar
transistors and includes built in protection against damage from
load terminal short circuiting to either supply rails or to ground.
Circuit Instrument Description
Timer IC (NE555):
555 is a very commonly used IC for generating accurate timing
pulses. It is an 8pin timer IC and has mainly two modes of operation:
monostable and astable. In monostable mode time delay of the pulses
can be precisely controlled by an external resistor and a capacitor
whereas in astable mode the frequency & duty cycle are controlled
by two external resistors and a capacitor. 555 is very commonly used
for generating time delay and pulses.
Circuit Instrument Description
Complex ROM with an inbuilt oscillator (UM3561):
UM 3561 is an excellent Siren generator IC widely used in Toy applications
and Surveillance systems to generate different tones. It a ROM (Read Only
Memory) IC which can be operated in 2 pen cells and it functions normally
down to 2.4 volts. Using only a few components, it is very easy to construct a
siren generator. The IC is designed to generate sirens like Police siren,
Ambulance siren, Fire brigade siren and Machine gun sound. The IC has an
inbuilt oscillator and tone selection pins. Only one external resistor and a
soeaker driver transistor are sufficient to make a simple siren generator
circuit.
Circuit Instrument Description
Transistor(BD139):
BD139, BD140 are epitaxial planar transistors which are mounted
in the SOT-32 plastic package. They are designed for audio
amplifiers and drivers utilizing complementary or quasicomplementary circuits.
Circuit Instrument Description
Variable resistor:
A potentiometer informally a pot, is a three-terminal resistor with a
sliding or rotating contact that forms an adjustable voltage divider. If
only two terminals are used, one end and the wiper, it acts as a variable
resistor or rheostat.
Circuit Instrument Description
Zener Diode:
A Zener diode is a diode which allows current to flow in the forward
direction in the same manner as an ideal diode, but also permits it to flow
in the reverse direction when the voltage is above a certain value known
as the breakdown voltage. We use 3.3v Zener diode in this circuit.
Circuit Instrument Description
Speaker:
A loudspeaker (or loud-speaker or speaker) is an electroacoustic
transducer, a device which converts an electrical audio signal into a
corresponding sound.
List of components with price
Name of component
Quantity
Price TK.
Resistors(100K,10K, 10M,220K,1K,330)Ω
9
18
Capacitors(0.0047, 0.01,4.7)µF
4
20
Variable Resistor(1MΩ)
1
10
Op-amp IC(CA3140)
1
30
Timer IC(NE555)
1
15
Complex ROM with an inbuilt oscillator
(UM3561)
1
30
Loud speaker(8Ω 0.5W)
1
45
Transistor(BD139)
1
15
Zener Diode (3.3v)
1
5
Battery (4.5V)
2
90
Mono jack with mono socket and switch and
connecting wire
1
40
Total price =
318 TK.
Advantages:
Simple circuit design.
Low cost.
Bias voltage is low.
Its easy to carry anywhere.
Effectively applied in daily activities.
Disadvantages:
 Its create noise because of police siren in the public
place.
Applications
 used in motor cycle to prevented theft.
 used in door of your Private room.
 used in laptop, if anyone open it, the alarm activated.
 used in suitcase, bag, purse etc. to prevented theft.
Discussion of Anti-bag snatching alarm
The design and construction of Anti-Bag snatching alarm was
outlined in a block diagram and then circuits were designed and
tested. Finally the circuits were arranged and connected properly
and
tested.
In
this
project
we
use
three
IC(CA3140,NE555,UM3561). The circuit of the Ant-Bag
Snatching Alarm is designed around the operational amplifier
CA3140 (IC1)which is configured as a comparator. Normally, the
non-inverting input is higher than inverting input and the output is
high from the pin 6 and the output pin is fed to the trigger pin 2 of
IC NE555. The cause of high output of IC1 the trigger pin 2 is high
and as a result the IC 2 output pin 3 is low and the alarm is off. A
resistor along with a capacitor is connected to reset pin 4 of IC2 in
order to prevent false triggering. When there is a bag-snatching
attempt, the plug connected to the circuit detaches. At that moment,
the voltage at the inverting input of IC1 exceeds the voltage at the
non-inverting input and subsequently its output goes low.
Discussion of Anti-bag snatching alarm
This sends a low pulse to trigger pin 2 of IC2 to make its
output pin 3 high. Consequently, the alarm circuit built
around IC UM3561 (IC3) gets the supply voltage at its pin 5.
Its output is fed to the base of single-stage transistor
amplifier BD139 (T1) that amplifies the generated alarm
signal. A loudspeaker is connected to the collector of T1 to
produce the alarm. The alarm can be put off if the plug is
inserted into the socket again. It is a simple circuit and low
costly. Its easy to carry anywhere with bag, suitcase and
purse.
Conclusion
It can be used in a bag which prevents snatching and saves our
life. When the bag is snatched then plug is detached and the
alarm is activated immediately. Everyone can use this device by
exchanging a small amount of price of just 320tk.
Recommendation
This anti-bag snatching alarm system is developed by
using more high variable resistor, and loudspeaker for
proper sound. It makes rechargeable by using circuit.