Intruder Alarm

ELECTRONICS 2

INTRUDER ALARM

PREPARED BY:

MUHAMMAD ZAID MASOOD
SCHOOL OF ENGINEERING
FACULTY OF ENGINEERING
JANUARY 2016

ALARM INTRUDER

INTRODUCTION.

• This is the circuit of a simple burglar alarm  that

produces a loud beep when somebody crosses a
protected area or door. The circuit is highly sensitive
and can detect the shadow of the moving person from
a distance of up to 1 meter.
• Here IC2 uA 741 is wired as a sensitive comparator.
• IC555 is wired as a monostable multivibrator.
• When there is an intruder near the LDR the shadow
causes its resistance to increase. Based on this effect
the circuit gets activated.

TOPIC

ALARM INTRUDER

Components.
 555

timer IC.
 u741 IC
 LDR(Light Dependent Resistor).
 Resistor.
 Capacitor.
 Led(Diode).
 Transistor (NPN and PNP).
 Protoboard or Breadboard.
 Buzzer.
 Battery 9v.

ALARM INTRUDER

The

term operational amplier TOPIC
or
"op-amp" refers to a class of
high-gain DC coupled ampliers
with two inputs and a single
output.
 The op-amp is a linear amplier
with Vout / Vinp. The DC openloop voltage gain of a typical opamp is 103 to 106.
 The gain is so large that most
often feedback is used to obtain
a specific transfer function and
control the stability.
The input voltage range for a 741
IC is ±13V.

IC USED:
• 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
• 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 delays and
pulses.
• It has 8 pins.
Supply voltage is 4.5 to 15 V

OP AMP (741)

ALARM INTRUDER

Classes of Amplifier.

•
•

NE 555:

•

Saving electrical power is now
becoming a concern. Equipment
utilizing Class D systems save
significant operating power.

•

Class D systems attain 75% efficiency
without significant effort.

555 timers is a class D amplifier. In its
most simplistic form it can be built
with a single 555 and the 200mA
current capability is enough to drive a
small speaker, making it a good
replacement for a low power amplifier.

TOPIC

•
•

uA741:

•

It is a part of A class because of its
multipurpose applications, low power
consumption and the complete
amplification of an input signal.

A μA741 integrated circuit, one of the
most successful operational amplifiers.
It belongs to class A of the amplifier
due to its high gain. It can be used as
a comparator, integrator and
differentiator as well.

ALARM INTRUDER

Circuit Diagram.

TOPIC

ALARM INTRUDER

Working of the Circuit.
1.

The shadow of an intruder passing through a distance of up to one meter nearby the circuit
is enough to trigger the alarm.

2.

Here IC2 uA 741 is wired as a sensitive comparator ,whose set point is set by R6 &R7. The
voltage divide by LDR and R9 is given at non inverting pin of IC2. At standby mode these two
voltages are set equal by adjusting R9.

3.

Now the output (pin6) of comparator will be high. Transistor Q1 will be off. The voltage at
trigger pin of IC1 will be positive and there will be no alarm.

4.

When there is an intruder near the LDR the shadow causes its resistance to increase.

5.

Now the voltages at the inputs of comparator will be different and the out put of IC2 will be
low.

6.

This makes Q1 on. This makes a negative going pulse to trigger the IC1 which is wired as a
monostable multivibrator.

7.

The out put of IC1 will be amplified by Q2 (SL 100) to produce alarm.

ALARM INTRUDER

Applications
• To protect the entry of unauthorized person in restricted
•
•
•
•
•

area.
It is easy to understand that a security alarm system
provides peace of mind when you’re away from your place
of business, and is there to meet insurance requirements
while minimizing burglary loss.
It can be used as fence alarm to protect your garden from
animals.
It can be used at night by shopkeepers to protect the
valuables in their showrooms.
You can also use it at your doors to indicate that some
stranger is present on door.
This circuit can also be used for home securities too.

TOPIC

ALARM INTRUDER

Advantages.

TOPIC

• Cheaper and easier to build either on breadboard or Pcb board.
• This circuit is easy to implement and all the components used
•
•
•

in this circuit are available in the market.
Requires a very small power 9v to make the circuit run.
Can detect the shadow up to range of one meter.
The timing of the alarm can be adjusted on the basis of the
power of resistors by using IC 555.

ALARM INTRUDER

Disadvantages.

• False alarms that bring unnecessary police responses which
eventually can result in fines.
• Alarms being heard too often, along with car alarms, and
eventually being ignored by residents in densely urbanized
settings.
• If the alarm is set and the burglar happens to trip it, he will
immediately flee from the area and move on to a different home
or place.
• Most professional burglars are very familiar with home intruder
alarms and know exactly how to deal with them.
• Requires a very clean and stable power supply.
• Nowadays laser technologies that has a better of safety over LDR.

ALARM INTRUDER

TOPIC

CONCLUSION.
This electronic device is designed to alert the user to an
intrusion. It detects the interruption whenever an object or
person comes near the LDR. This interruption results in a
signal generation i.e, LED glows and buzzer sound. These
devices are installed at various locations in houses or
offices, especially near doors, windows. The circuit has to
found to have greater application in security reliable and
less expensive and is guaranteed to perform the best of the
duration of their life time.

ALARM INTRUDER

References.
1)Class D Power Amplifier. (2015). Retrieved from

TOPIC

Circuits Today. website:
http://www.circuitstoday.com/class-d-power-amplifiers.
2)Super Sensitive Intruder Alarm. (2015, October 11).
Retrieved from Electronics Hub. website:
http://www.electronicshub.org/super-sensitiveintruder-alarm/
3) Sethiya, A. (n.d.). Intruder Alarm. Retrieved from
Engineers Garage.
website:http://www.engineersgarage.com/electroniccircuits/intruderalarm#slider

ALARM INTRUDER

TOPIC

Thank You