Home Security System Using Cell Phone

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Home Security System Using Cell Phone
The project is about a home security system in which a cell phone is used as a device that will alert the owner
of the house when an intruder enters the house.The owner just have to turn on the system before leaving his
house.When an intruder enters the house in the absence of the owner the owner receives a call from a
registered number which is the phone number of the hacked mobile phone at his/her house.Cell phones have
switches which when pressed short the terminals (gold plated) hence a number is seen on the screen
so what i have done is put my cell phone number on speed dial on the phone i hacked and when this number is
pressed for a while i get a call.
so basically what we r doing is a circuit that will short the phone terminals. when a intruder enters the house.
IC LM358 is a dual op amp.
The output of an op amp is difference of the input times the gain of the op amp. ie. it compares the 2 inputs.
NOTE: refer datasheet for more details about the IC.
pin 2 of IC 358 is threshold a potentiometer is connected to it so it forms a voltage divider and a particular
voltage is set up at pin 2 which the op amp compares with voltage at pin 3.
to pin 3 an LDR is connected it behaves in following way.
1) when light shines on LDR its resistance decreases hence a more positive voltage is set up at pin 3 which
forces the output to be high.hence there is a potential difference at the terminals of the number on the cell
phone.
2)when the light is cut off by the door which is opened by the intruder the LDR resistance increases hence a
more negative voltage is set up at pin 3 which forces output to be low (0v).
in the equivalent op amp circuit shown Avid is approximately 0v when output is low and resistance Ro is very
small hence the output is shorted to the ground thus shorting the 2 terminals of the cell phone.

Materials (electronic components) required
1) A Cellphone having press buttons (i used an old one which i had).
2) A 10K ohm resistor.
3) A 10K ohm potentiometer.
4) An LDR (Light Dependent Resistor) 10K ohm or A 2 legged IR sensor (IR sensors are better bcoz
they are not affected by surrounding light).
5) An LM358 (Dual op-Amp) IC.
6) An Optical LASER (I used a red LASER). In case you are using IR sensors use an IR LASER.
7) wires.
The cell phone i used is an old nokia phone.
Remove the battery then remove the front cover then the keypad an then the transparent cover over the keys.
You will see a thin white film on the key terminals dont worry just remove this film using forceps but
remember only cut the film on a single key from 0 to 9. I just pulled it out in excitement and now i have
problems starting the device i have to manually start it by shorting the terminals using any metallic object.
Insert the battery back into the cell phone and turn it on.
I wanted to use key 3 for the speed dial so i was checking the terminals on key 3.
Put a multimeter on dc voltage measurement then touch the probes to the 2 terminals on the key then reverse
the probes on the key terminals either way the multimeter will show a reading but it will show +ve DC voltage
when the probes are on correct -ve ,+ve terminals.
In my case the inner one was positive and the outer one negative.
Solder a red wire to the +ve terminal and a black wire to the -ve terminal.
According to the circuit diagram solder the circuit.a small dotted board is enough as there are hardly any
components.
NOTE: the circuit remains same if a 2 legged IR sensor is used.
Solder the red wire from the cell phone key to the output of the op-amp IC ie. at pin 1 and the black wire to the
ground.
Solder the LDR to a small piece of board and solder wires to it (LDR does not have polarity so it can be
connected any way to the main board).

Place the sensor and LASER on opposite sides of a door.
focus the LASER on the Sensor such that LASER falls on the sensor when door is closed and it is cut off from
the sensor when door is open.
Insert any active sim card into the cell phone and register its number on your cell phone as 'security' or
anything you like.insert the battery and turn the cell phone on.
turn on the power supply to the circuit.

Extending the circuit
Any intruder will never come through a given door so every door in the house needs this circuit.
the main boards will increase the times you have doors and the output of each and every op amp should
be AND'ed (connected to inputs of AND gate (Digital IC 7408) and the final output should be connected
to the mobile +ve terminal so only 1 cell phone is required.
http://www.instructables.com/id/Home-Security-System-Using-Cell-Phone/?ALLSTEPS
LM358 - Single Supply Dual Operational Amplifiers
Utilizing the circuit designs perfected for Quad
Operational Amplifiers, these dual operational amplifiers
feature low power drain, a common mode input voltage
range extending to ground/VEE, and single supply or split
supply operation. The LM358 series is equivalent to
one−half of an LM324.
These amplifiers have several distinct advantages over
standard operational amplifier types in single supply
applications. They can operate at supply voltages as low
as 3.0 V or as high as 32 V, with quiescent currents about
one−fifth of those associated with the MC1741 (on a per
amplifier basis). The common mode input range includes
the negative supply, thereby eliminating the necessity for
external biasing components in many applications. The
output voltage range also includes the negative power
supply voltage.

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