2. Concept of Laser Based Intruder Alarm
During the olden days a watchman would be
hired to take care of property and offer
needed security in the home. Some homes
also had fierce dogs that would be let out
only at night. The two were supposed to
provide security to our belongings even in
the absence of the owner. However, hiring a
watchman was not an effective method since
most of them would be killed in the line of
duty. Sometimes dogs would attack even
visitors while some watchmen looted
property.
3. During the olden days where there were no security
systems houses were being raided by the thieves
4. A alarm is a type of security
equipment that can be used to
safeguard homes and property. If
we love our home then buying
burglar alarm should be our first
priority when moving to a new
home. Burglar crimes are
continually rising with each
passing day. Many have lost their
homes and families through
violent burglaries in many
countries today. Some have lost
what they considered precious and
valuable to them. Things such as
jewelry, vehicles, and clothes are
huge investments to many. This
led to the development of the
alarm equipment.
5. About the circuit
The circuit is divided into two parts i.e. the
transmitter and the receiver.
The transmitter circuit is nothing but a laser
diode driven by a battery connected to the diode
In order to ensure that the current remains
constant in the diode a 5V or 7.5V is applied to
the diode.
The laser diode here can be the one typically
used in laser pointers emitting in red. This
would be more economical than buying one.
6. An infrared diode can also be used for invisible
laser beam.
The pointer has in-built suitable series
resistance and an ON/OFF switch and a battery.
The drive current in this would be 3500/47mA.
The receiver part consists of a current to
voltage converter section which converts the
photocurrent produced by the photodiode as a
result of laser light falling.
When the laser light falls on the photodiode, the
opamp output is same as Dc voltage
8. Laser diode pointer: The laser diode is a laser
where the active medium is a semiconductor
similar to that found in a light-emitting diode. The
most common type of laser diode is formed from
a p-n junction and powered by injected electric
current. In this we are using 593 nm – Yellow-
Orange laser pointers.
Photo transistor: A photodiode is a type
of photo detector capable of
converting light into either current or voltage,
depending upon the mode of operation. The
common, traditional solar cell used to generate
electric solar power is a large area photodiode.
9. Op-Amp LM 356: The LM356 is a power
amplifier designed for use in low voltage
consumer applications. The gain is internally
set to 20 to keep external part count low, but the
addition of an external resistor and a capacitor
between 1 and 8 will increase the gain to any
value up tp 200. The inputs are grounded
referenced while the output is automatically
biased to one half the supply voltage. The
quiescent power drain is only 24mW when
operating from a 6V supply, making the LM356
ideal for battery operation.
10. 555 Timer: The 555 timer IC is an integrated
circuit (chip) used in a variety of timer, pulse
generation and oscillator applications. It
includes over 20 transistors, 2 diodes and
15 resistors on a silicon chip installed in an 8-
pin mini dual-in-line package. In the
monostable mode, the 555 timer acts as a “one-
shot” pulse generator. The pulse begins when
the 555 timer receives a signal at the trigger
input that falls below a third of the voltage
supply. The width of the output pulse is
determined by the time constant of an RC
network, which consists of a capacitor (C) and
a resistor (R).
11.
12. Piezo buzzer: The piezo buzzer produces sound
based on reverse of the piezoelectric effect. The
generation of pressure variation or strain by the
application of electric potential across a
piezoelectric material is the underlying
principle. These buzzers can be used alert a user
of an event corresponding to a switching action,
counter signal or sensor input. They are also
used in alarm circuits.
Capacitor: A capacitor is a passive electronic
component consisting of a pair
of conductors separated by
a dielectric (insulator). When there is a potential
difference (voltage) across the conductors, a
static electric field develops across the
dielectric causing positive charge to collect on
13. one plate and negative charge on the other plate
Resistor: A linear resistor is a two-terminal,
linear, passive electronic component that
implements electrical resistance as a circuit
element.
Diode: A p–n junction is formed by joining P-
type and N-type semiconductors together in
very close contact.
Switch: It’s an electrical component that break
an electrical circuit.
14. Battery: It is used to convert chemical energy
to electrical energy.
Relay: It is as an electrically operated switch.
It uses an electromagnetic to operate a
switching mechanism mechanically
It is used to control a circuit by a low power
signal
Relays are used extensively in telephone
exchange and early computers to perform
logical operations.
16. The transmitter circuit is nothing but a laser
diode (LD1) driven by a 9V PP3 battery. The
output of IC1 is regulated 5V as long as its
input remains equal to or more than 7.5V, thus
ensuring a constant drive current for the laser
diode. The battery (Batt1) is connected to the
circuit through switch S1. The laser diode
(LD1) can be replaced with a laser pointer
(torch) emitting red laser beam. The laser
pointer itself can be used as a transmitter. The
pointer has in-built series resistance, on/off
switch and battery. The receiver circuit is
basically a current-to-voltage converter built
around IC LM356 (IC3). The output of IC3 is
fed to the monostable built around 555 timer
(IC4). The high output of the monostable drives
17. the piezobuzzer to sound an audio alarm. The
receiver section operates off 5V DC generated from
another 9V battery and voltage regulator IC 7805
(IC2). The battery (Batt.2) is connected to the
circuit through switch S2. When the laser light
transmitted through LD1 falls on phototransistor
T1, the output of the op-amp (IC3) at its pin 6
remains high. In this condition, the output of IC4
remains low and the buzzer does not sound. When
the laser beam falling on phototransistor T1 is
interrupted by someone, the output of op-amp
IC3 goes low and IC3 produces a pulse. This
pulse triggers monostable IC4 and its output
goes high to sound the alarm for a time period
of about
18. R8xc8. Assemble the transmitter and receiver
circuits on separate generalpurpose PCBs and
enclose in suitable cabinets. Mount the
transmitter and receiver units on opposite
pillars of the entrance, aligning the two such
that the laser beam from the transmitter directly
falls on the phototransistor. Block the laser
beam with your hand and measure the op-amp
output. It should not be low. At pin 3 of IC4, we
should get a positive-going pulse of one-second
duration beginning with high-to-low edge of the
trigger pulse appearing at pin 2 of IC4 or
collector of transistor T2.
19. Testing
Switch on the transistor circuit. Align the
transmitter and receiver circuit so that the
laser beam falls on the photodiode. We
can use a small transmitter receiver
distance, even a few feet, for the purpose.
If necessary, change the value of one or
more resistors(R5,R6,R7) to get a signal
peak magnitude of 2 to 3 V at opamp
output.
Block the laser radiation with our hand
and again measure the opampoutput. It
should be near zero.
20. Block the laser radiation with our hand and
again measure the opamp output. It should be
near zero volt.
If we have the services of an oscilloscope,
observe the pulse waveforms appearning at pin-
8 of IC-1 and pin-6 of IC-3. At pin-8 of IC-4,
we would see a HIGH-to-LOW transition every
time we block the laser beam.
We can observe change in the pitch of the audio
beep by changing the frequency of the signal on
the transmitter card.
21.
22. Advantages
Simplicity of installation.
The effective ability to be used indoors
and outdoors.
It could be used as an effective alarm for
the house/company boundaries.
It uses the normal power outlets and
telephone jacks in case it used indoors.
23. Disadvantages
The disadvantage of laser
beam system is that it may
get activated by a cat walking
on the wall or a large bird
sitting on the wall.
They are more expensive
compared to simple security
alarm systems.
Applications: Can be used as
home security system
Can be used in Museums,
Banks, Offices for safe guard
many valuable things
24. Conclusion
The Laser Based Intruder Alarm was built to
our satisfaction. This project is about how to
prevent theft in homes, offices, banks,
museums etc, This project can be implemented
by both wired and wireless technologies.
Another application of this instrument is as an
"ANTI-THEFT SYSTEM", that means to
protect vehicles from kidnapping. In short I am
sure that this device is highly useful to mankind
especially present scenario.
