LAPTOP PROTECTOR
7/29/2010 09:32:00 PM SKY GROUPS © NO COMMENTS
Protect your valuable laptop against theft using this miniature
alarm generator. Fixed inside the laptop case, it will sound a
loud alarm when someone tries to take the laptop.
This highly sensitive circuit uses a homemade tilt switch to
activate the alarm through tilting of the laptop case.
The circuit uses readily available components and can be
assembled on a small piece of Vero board or a generalpurpose PCB. It is powered by a 12V miniature battery used
in remote control devices.
The components require to prepare this .

tilt swtich

Diode

piezzo buzzer

ON -OFF switch

Battery

IC's IC TL071

ICCD 4538

Resistor & capacitor

Transistor.
IC TLO71 (IC1) is used as a voltage comparator with a
potential divider comprising R2 and R3 providing half supply
voltage at the non-inverting input (pin 3) of IC1. The inverting
input receives a higher volt- age through a water-activated tilt
switch only when the probes in the tilt switch make contact
with water.
When the tilt switch is kept in the horizontal position,
the inverting input of IC1 gets a higher voltage than its
non -inverting input and the output remains low.
IC CD4538 (IC2) is used as a monostable with timing
elements R5 and C1.
With the shown values, the output of IC2 remains low
for a period of three minutes. CD4538 is a precision
monostable multivibrator free from false triggering and is
more reliable than the popular timer IC 555. Its
output becomes high when power is switched on and it
becomes low when the trigger input (pin 5) gets a low-tohigh
transition pulse.
The unit is fixed inside the laptop case in horizontal position.
In this position, water inside the tilt switch effectively
shorts the contacts, so the output of IC1 remains low.
The alarm generator remains silent in the standby mode as
trigger pin 5 of IC2 is low.
When someone tries to take the laptop case,
the unit takes the vertical position and the tilt switch breaks the
electrical contact between the probes. Immediately the output
of IC1 becomes high and monostable IC2 is triggered.
The low output from IC2 triggers the pnp transistor (T1) and the
buzzer starts beeping. Assemble the circuit as compactly
as possible so as to make the unit matchbox size.
Make the tilt switch using a small (2.5cm long and 1cm wide)
plastic bottle with two stainless pins as contacts.
Fill two-third of the bottle with water such that the contacts never
make electrical path when the tilt switch is in vertical position.
Make the bottle leakproof with adhesive or wax.
Fix the tilt switch inside the enclosure of the circuit in
horizontal position.
Fit the unit inside the laptop case in horizontal
position using adhesive. Use a miniature buzzer and a
micro switch (S1) to make the gadget compact. Keep the
laptop case in horizontal position and
switch on the unit. Your laptop is now protected.
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INTRODUCTION
COMPONENTS USED
CIRCUIT EXPLANATION
ADVANTAGES
PRECAUTIONS
CONCLUSION
INTRODUCTION
NOW-A-DAYS DESKTOP HAS BEEN REPLACED BY LAPTOP WHICH IS A DEFORMED
FORM.
SO IT HAS BECOME EASIER FOR THEFT TO STEEL OUR VALUABLE LAPTOP.
TO OVERCOME THIS KIND OF STEELING A LAPTOP PROTECTOR IS
REALISED,WHICH WILL PROTECT BY ITS MINIATURE ALARM.
i) REGISTERS:
RESISTORS ARE THE ELECTRONIC COMPONENTS WHICH OPPOSES CURRENT.
RESISTORS OBEY OHMâ„¢S LAW.
DIFFERENT KIND OF RESULT COMES WITH RESPECT TO APPLICATION OF
VARIOUS VOLTAGES.
ii) CAPACITORS:
A CAPACITOR IS AN ELECTRICAL OR ELECTRONICS DEVICE THAT CAN STORE
ENERGY THE ELECTRIC FIELD BETWEEN A PAIR OF CONDUCTORS.
THE PROCESS OF STORING ENERGY IS CALLED ËœCHARGINGâ„¢.
A 47microF 25V CAPACITOR IS USED.
iii) INTEGRATED CIRCUITS:
IT CONSISTS OF
MINIATURIZED
ELECTRONIC
COMPONENTS BUILT INTO
AN ELECTRICAL NETWORK.
HERE TWO ANALOG
DESIGNED IC ARE USED.
- IC TLO71(IC1):IC1 IS USED AS
VOLTAGE COMAPARATOR.
- IC CD4538(IC2):IC2 IS USED AS A
MONOSTABLE WITH TIMING
ELEMENTS R5 AND C1.
iv) DIODE:
IN DIODES CURRENT IS DIRECTLY RELATED TO VOLTAGE.
DIODES ARE NON-LINEAR,TWO TERMINAL,
PASSIVE ELECTRICAL DEVICES.
A 1 JUNCTION DIODE (1N4148) IS USED IN THIS CIRCUIT.
v) BATTERY:
A 9V BATTERY IS USED
vi) TRANSISTOR:
TRANSISTOR AMPLIFY CURRENT AND VOLTAGE.
IT MAY BE USED AS SWITCH.
A pnp TRANSISTOR BC558(T1) IS USED IN THIS CIRCUIT.
vii) SWITCHES:
a) TILT SWITCH:
A TILT SWITCH IS
MADE UP OF PLASTIC BOTTLE
WITH TWO STAINLESS PINS AS
CONTACT OR PROBES.
IN TILT SWITCH 2/3RD OF THE
BOTTLE IS FILLED WITH WATER
SUCH THAT THE WATER CANNOT
MAKE CONTACT WITH THE PINS.
b) ON/OFF SWITCH:
A ON/OFF SWITCH OF 3A IS
USED.
THE USER CAN USE THE SWITCH
AS PER HIS REQUIREMENTS.
viii) PIEZO BUZZER:
A PIEZO-BUZZER IS USED AS AN ALARM.
USERS CAN USE ANY BUZZER AS PER THEIR CONVINIENCE.
ix) PRINTED CIRCUIT BOARD:
ALL THE ABOVE EQUIPMENTS ARE MOUNTED ON THE GENERAL
PURPOSE PCB.
THE UNIT IS INSIDE THE LAPTOP CASE IN HORIZONTAL
POSITION. IN THIS POSITION, WATER INSIDE THE TILT
SWITCH EFFECTIVELY SHORTS THE CONTACTS, SO THE
OUTPUT OF IC1 REMAINS LOW . THE ALARM GENERATOR
REMAINS SILENT IN THE STAND BY MODE AS TIGGER PIN 5 OF IC2 IS
LOW.
WHEN SOMEONE TRIES TO TAKE THE LAPTOP CASE, THE UNIT TAKES THE
VERTICAL POSITION & THE TILT SWITCH BREAKS THE ELECTRICAL CONTACT
BETWEEN THE PROBES. IMMEDIATELY THE OUTPUT OF IC1 BECOMES HIGH
& MONOSTABLE IC2 IS TRIGGERED. THE LOW OUTPUT OF IC2 TRIGGERS THE
pnp TRANSISTOR(T1) & THE BUZZER STARTS BEEPING.
1. CHEAPNESS: It is affordable for general use.
2. CLEANLINESS: It is clean as it doesnâ„¢t produce fume or poisonous gas.
3. AVAILABILITY: All equipments used in this circuit are easily available in the market.
4. EASY CONSTRUCTION: It is easy to construct for a person who has general idea about
circuitry elements.
5. THERE SHOULD BE NO LEAKAGE IN TILT SWITCH.
6. BEFORE LEAVING THE LAPTOP THE USER SHOULD CONSIOUSLY ON THE
SWITCH.