Hidden Active Cell Phone Detector
Project synopsis:
The main scope of
project is to sense the presence of an activated mobile phone from a distance
of one-and-a-half meters to prevent the use of mobile phone in the examination
halls.
Certain places
where uses of mobile phones are not allowed like exam hall, temple, offices and
theaters. In those places to detect and restrict the use of mobile phones this
proposed system is very helpful. This system can detect any active cell phone
i.e. when someone is trying to make a call or receive a call or sending a
message or receiving a message. In any of the above mentioned conditions a
buzzer will sound, in the presence of an active cell phone in the radius of one
and half meters.
In
this project an RF detector is used along with a tuned LC circuit which isformed
for detecting signals of GHz frequency range a band traditionally used in
mobile phones as the transmission frequency from 0.9 to 3 GHz.
A
capacitor is used to form a part of the LC circuit as C while the lead of the
same forms the L to receive RF signals from the mobile phone. The project uses 8 numbers 1.5v batteries in two containers for 12V dc
availability to the remote control and includes a small buzzer to make the
gadget pocket-size. When the mobile phone is activated the RF transmission
signal is detected by the detector and starts sounding a beep alarm and the LED
blinks. An active cell phone detector is also used to detect the use of mobile
phone for spying and unauthorized video transmission.
Block
diagram:
Hardware used:
·
Op amp
·
555 timers
·
Transistor
·
LED
·
|
Resistors
·
Capacitors
·
Piezo buzzer
·
Switch
·
Battery
·
And finally an antenna
Block diagram explanation:
The above block
diagram representation of the hidden active cell phone detector consists of an
operational amplifier, a multi-vibrator and a buzzer.
·
Operational
amplifier:
Antenna signal
is given as input to an operational amplifier, which is an 8 pin IC. The
operational amplifier (op-amp) is also referred to as a voltage amplifier which
is used for amplifying a voltage.It is an integrated circuit with differential
inputs i.e. it has two inputs of opposite polarities. The output signal of the
op-amp is very high while compared to the input signal and the op-amp is also
designed for performing arithmetic operations in an analog circuit
·
Monostable
multivibrator:
The output from
the op-amp is fed to a monostable multi vibrator. The monostable multi vibrator
is a one shot multivibrator which is used to generatea single pulse.In this one
state of output is stable and other state ofoutput is in unstable mode. It is
triggered when a logic low signal is given to the input and a high logic signal
appears at the output. When not
triggered, the output is normally low and when triggered, it will go high for a
short length of time depending on the values of the resistor and capacitor
components.
·
Piezo
buzzer:
When the output from the multivibrator reaches
the buzzer, the buzzer rings to indicate the active action of the mobile phone.A
piezoelectric element may be driven by an oscillating
electronic circuit or other audio signal sourcedriven with a piezoelectric audio amplifier. Sounds commonly used to indicate that a button
has been pressed are a click, a ring or a beep.
It most commonly
consists of a number of switches or sensors connected to a control unit that
determines if and which button was pushed or a preset time has lapsed, and
usually illuminates a light on the appropriate button or control panel, and sounds
a warning in the form of a continuous or intermittent buzzing or beeping sound.
The effect of piezo buzzer is related to a change of polarization density with
the material, a buzzer is placed for signaling the device at the output.
CIRCUIT EXPLANATION:
The circuit can sensethe incoming and outgoing calls,
SMS and video communication even if the mobile phone is kept in the silent
mode. The instant the system detects the RF transmission signal from an
activated mobile phone, it starts sounding a beep alarm and the LED blinks. The
alarm continues until the signal transmission ceases. An ordinary RF detector
using tuned LC circuits is not suitable for detecting signals in the GHz
frequency band used in mobile phones. Here the circuit use a disk capacitor is
used to capture the RF signals from the mobile phone. The lead length of the
capacitor is fixed with some spacing between the leads to get the desired
frequency signal. The disk capacitor along with the leads acts as a small loop
antenna to collect the RF signals from the mobile phone. Op-amp IC is used in
the circuit as a current-to-voltage converter with capacitor connected between
its inverting and non-inverting inputs. The output CMOS transistor is capable
of swinging the output voltage to within supply voltage terminal. Capacitor
should have a lead length with lead spacing of 8 mm. carefully solder the
capacitor in standing position with equal spacing of the leads. The response
can be optimized by trimming the lead length of for the desired frequency. You
may use a short telescopic type antenna. The unit will give the warning
indication if someone uses mobile phone within a radius of 1.5 meters.
Project Functioning:
The concept of this project to sense whether mobile
phone is active or not and detect the use of mobile phones in restricted
places.If any cell phone is operated by a person and the moment the person
comes closer to the mobile the buzzer will ring based on the principle of
detecting the megahertz oscillation that takes place inside the mobile phones when
the phone is in active mode.It detects any active moment of the cell phone and
the buzzer will ring whenever the number
is dialed on the cell phone, or while sending or receiving any text messages
etc.
CONCLUSION:
This project has
been designed successfully so that the pocket-size mobile transmission detector
can sense in the presence of an activated mobile phone from a distance of one
and- a-half meters. It can be used to prevent use of mobile phones in
examination halls, confidential rooms, etc. It is also useful for detecting the
use of mobile phone for spying and un-authorized video transmission.
FUTURE SCOPE:
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