A project report_at_cell_phone_detector - copy

B.TECH MINI PROJECT REPORT 2016 CELL PHONE DETECTOR CUM
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Department of EEE.GEC THRISSUR Page 1
ACKNOWLEDGEMENT
Our sincerest appreciation must be extended by our faculties. We also want to thank
faculties of the College. They have been very kind and helpful to us. We want to thank all
teaching and non‐teaching staff to support us. Especially we are thankful to Mr.jayanand B
(HOD) for providing this golden opportunity to work on this project, inspiration during the
course of this project and to complete the project within stipulated time duration and four
walls of College Lab. We would like to express our sincere gratitude to our Guide Mr.
Chandrabose K N for his support during the course of the project right from selection of the
project, their constant encouragement, expert academic and practical guidance.

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ABSTRACT
This handy, pocket-size cell phone detector cum appliances controller can sense the
presence of an activated mobile cell phone from a distance of one and-a-half meters and also
control to connect this device. So 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 unauthorized video transmission. The circuit can detect the incoming
and outgoing calls, SMS and video transmission even if the mobile phone is kept in the silent
mode. The moment the Bug detects RF transmission signal from an activated mobile phone,
it starts the LED blinks. The alarm continues until the signal transmission ceases. Assemble
the circuit on a general purpose PCB as compact as possible and enclose in a small box like
junk mobile case. As mentioned earlier, capacitor C3 should have a lead length of 18 mm
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 C3 for the
desired frequency. You may use a short telescopic type antenna.
Use the miniature 12V battery of a remote control to make the gadget pocket-size.
The unit will give the warning indication if someone uses Mobile phone within a radius of
1.5 meters.

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TABLE OF CONTENTS
1. Introduction (4)
2. Cellular Phone Technology (6)
2.1. Cellular Phone Features. (6)
2.2. Cellular Phone Communication Standards (7)
2.3. Overview of Cell Phone Detector (8)
2.4. Mobile Bug (10)
3. Circuit Diagram (10)
3.1. Description of Circuit Diagram (12)
3.2. Block Diagram. (12)
3.3 Block Diagram Explanation (13)
4. Transmission Lines. (14)
5. PCB Layout (15)
6. List of Components (15)
6.1. Components Description (15)
6.2. Timer circuit (16)
6.3. Pin Diagram of ICs. (17)
7. IC CA3130, Working, Applications, and Features. (17)
8. IC NE555, Working, Applications, and Features. (20)
9. Circuit Testing on Breadboard. (25)
10. Working of Cell Phone Detector. (25)
10.1. Purpose of the circuit. (25)
10.2. Concept (25)
11. How the capacitor senses the RF? (27)
12. Applications (27)
13. Advantages (29)
14. Limitations (29)
15. Future Scope (29)
16. Conclusion (30)
17. References (30)

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1.INTRODUCTION:
In this chapter we will discuss the overview of Cell Phone Detector and see its demo
circuits. We will also discuss about circuit diagram and description of the circuit diagram.
But before we discuss the above we have to know about the previous detection techniques
which has been introduced already in the market.
The first signal detection technique, an existing design utilizing discrete component is
difficult to implement. They are very affordable to construct, but require precision tuning.
This design is analyzed and found to be inaccurate.
The second signal detection technique, a design using a down converter, voltage
controlled oscillator (VCO), and a bandpass filter was investigated for cellular phone
detection. The performance of this technique through hardware and computer modeling is
discussed and the results are presented. The new system is accurate and a practical solution
for detecting cellular phone in a secure facility.
A mobile phone (also known as a cellular phone, cell phone, and a hand phone) is a
device that can make and receive telephone calls over a radio link while moving around a
wide geographic area. It does so by connecting to a cellular network provided by a mobile
phone operator, allowing access to the public telephone network. By contrast, a cordless
telephone is used only within the short range of a single, private base station.
In addition to telephony, modern mobile phones also support a wide variety of
other services such as text messaging, MMS, email, Internet access, short-range wireless
communications (infrared, Bluetooth), business applications, gaming and photography.
Mobile phones that offer these and more general computing capabilities are referred to
as smart phones.
A cellular network or mobile network is a radio network distributed over land areas
called cells, each served by at least one fixed-location transceiver known as a cell site or base
station. In a cellular network, each cell uses a different set of frequencies from neighboring
cells, to avoid interference and provide guaranteed bandwidth within each cell.

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When joined together these cells provide radio coverage over a wide geographic area.
This enables a large number of portable transceivers (e.g., mobile phones, pagers, etc.) to
communicate with each other and with fixed transceivers and telephones anywhere in the
network, via base stations, even if some of the transceivers are moving through more than
one cell during transmission.
In a cellular radio system, a land area to be supplied with radio service is divided into
regular shaped cells, which can be hexagonal, square, circular or some other regular shapes,
although hexagonal cells are conventional. Each of these cells is assigned multiple
frequencies (f1 – f6) which have corresponding radio base stations. The group of frequencies
can be reused in other cells, provided that the same frequencies are not reused in adjacent
neighboring cells as that would cause co-channel interference.
The increased capacity in a cellular network, compared with a network with a single
transmitter, comes from the fact that the same radio frequency can be reused in a different
area for a completely different transmission. If there is a single plain transmitter, only one
transmission can be used on any given frequency. Unfortunately, there is inevitably some
level of interference from the signal from the other cells which use the same frequency. This
means that, in a standard FDMA system, there must be at least a one cell gap between cells
which reuse the same frequency.
In the simple case of the taxi company, each radio had a manually operated channel
selector knob to tune to different frequencies. As the drivers moved around, they would
change from channel to channel. The drivers knew which frequency covered approximately
what area. When they did not receive a signal from the transmitter, they would try other
channels until they found one that worked. The taxi drivers would only speak one at a time,
when invited by the base station operator (this is, in a sense, time division multiple
access (TDMA).
Practically every cellular system has some kind of broadcast mechanism. This can be
used directly for distributing information to multiple mobiles, commonly, for example
in mobile telephony systems, the most important use of broadcast information is to set up
channels for one to one communication between the mobile transceiver and the base station.

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This is called paging. The three different paging procedures generally adopted are sequential,
parallel and selective paging.
The details of the process of paging vary somewhat from network to network, but
normally we know a limited number of cells where the phone is located (this group of cells is
called a Location Area in the GSM or UMTS system, or Routing Area if a data packet session
is involved; in LTE, cells are grouped into Tracking Areas). Paging takes place by sending
the broadcast message to all of those cells. Paging messages can be used for information
transfer. This happens in pagers, in CDMA systems for sending SMS messages, and in
the UMTS system where it allows for low downlink latency in packet-based connections.
In a cellular system, as the distributed mobile transceivers move from cell to cell
during an ongoing continuous communication, switching from one cell frequency to a
different cell frequency is done electronically without interruption and without a base station
operator or manual switching. This is called the handover or handoff. Typically, a new
channel is automatically selected for the mobile unit on the new base station which will serve
it. The mobile unit then automatically switches from the current channel to the new channel
and communication continues.
2. CELLULAR PHONE TECHNOLOGY:
Cellular Phone Technology is rapidly changing. Features like Bluetooth, USB, high
resolution cameras, microphones, Internet, 802.11 wireless, and memory cards added every
year.
Also, the communication technology a cellular phone uses such as CDMA, GSM, 3G and 4G
are rapidly changing.
2.1. CELLULAR PHONE FEATURES:
Bluetooth is a secure wireless protocol that operates at 2.4GHz. The protocol uses a
master slave structure and is very similar to having a wireless USB port on your cellular
phone. Device like a printer, keyboard, mouse, audio device, and storage device can be
connected wirelessly. This feature is only use for hands-free devices but can also be used for
file transfer of picture, music, and other data.

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Universal Serial Bus (USB) is a way for cellular phone to connect to a computer for
data transfer. This feature is very similar to Bluetooth for cellular phone with the exception of
using a cable. On today’s cellular phones this feature is mainly used for charging the battery
or programming by the manufacturer. It can also be used to transfer picture, music, and other
data.
Cameras on cellular phones are a very popular feature that was added in the last 10
years. In recent years, high resolution cameras have become a standard feature. Most cellular
phones will come with at least a 2 mega pixel camera and the more expensive phones can be
as much as 8 mega pixels.
Microphones have been featured on cellular phone since they first came out. In the
last 10 years the microphones have become dual purpose; now there are programs on the
phone that record voice to file such a simple voice recorder or as part of a video.
Some cellular phones come with 802.11 wireless built in and allows the phone to
connect to any nearby wireless network. This provides an alternate connection method to the
Internet and saves money if you are on a limited data plan. Also, connecting with 802.11 is
most likely going to provide better throughput than using the cellular phone network.
All these features make cellular phone today very versatile. They can connect with
almost any storage medium or computer. In the years to come, cellular phones will continue
to gain more and more features.
2.2. CELLULAR PHONE COMMUNICATION STANDARDS:
Currently the three main technologies used by cellular phone providers are 2G, 3G,
and 4G. Each generation of technology uses a different transmission protocol. The
transmission protocols dictate how a cellular phone communicates with the tower. Some
examples are: frequency division multiple access (FDMA), time division multiple access
(TDMA), code division multiple access (CDMA), Global System for Mobile Communication
(GSM), CDMA2000, wide-band code division multiple access (WCDMA), and time division
synchronous code division multiple access (TD-SCDMA). All of these protocols typically
operates in the 824-894 MHz band in the United States. Some protocols such as GSM
(depending on the provider) will use the 1800-2000 MHz band.

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2.3. OVERVIEW OF CELL PHONE DETECTOR:
Demo Circuit:
IC1 is designed as a
differential amplifier Non
inverting input is connected to the
potential divider R1, R2. Capacitor
C2 keeps the non inverting input
signal stable for easy swing to + or
– R3 is the feedback resistor
Figure: 1.1
IC1 functions as a current to voltage converter, since it converts the tiny current
released by the 0.22 capacitor as output voltage.
At power on output go high and LED lights for a short period. This is because + input
gets more voltage than the – input. After a few seconds, output goes low because the output
current passes to the – input through R2. Meanwhile, capacitor C1 also charges. So that both
the inputs gets almost equal voltage and the output remains low. 0.22 capacitor (no other
capacitor can be substituted) remains fully charged in the standby state.
When the high frequency radiation from the mobile phone is sensed by the circuit,
0.22 cap discharges its stored current to the + input of IC1 and its output goes high
momentarily. (in the standby state, output of the differential amplifier is low since both inputs
get equal voltage of 0.5 volts or more). Any increase in voltage at + input will change the
output state to high.
R1 1M
R2 100K
C1 0.22
C2 47 UF
R3 1M
LED
IC 3130

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The circuit can detect both the incoming and outgoing calls, SMS and video
transmission even if the mobile phone is kept in the silent mode. The moment the bug detects
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. The transmission frequency of mobile phones ranges from 0.9 to
3 GHz with a wavelength of 3.3 to 10 cm. So a circuit detecting gigahertz signals required for
a mobile bug.
Here the circuit uses a 0.22µF disk capacitor (C3) to capture the RF signals from the
mobile phone. The lead length of the capacitor is fixed as 18 mm with a spacing of 8 mm
between the leads to get the desired frequency. The disk capacitor along with the leads acts as
a small gigahertz loop antenna to collect the RF signals from the mobile phone.
Op-amp IC CA3130 (IC1) is used in the circuit as a current-to-voltage converter with
capacitor C3 connected between its inverting and non-inverting inputs. It is a CMOS version
using gate-protected p-channel MOSFET transistors in the input to provide very high input
impedance, very low input current and very high speed of performance. The output CMOS
transistor is capable of swinging the output voltage to within 10 mV of either supply voltage
terminal.
Capacitor C3 in conjunction with the lead inductance acts as a transmission line that
intercepts the signals from the mobile phone. This capacitor creates a field, stores energy and
transfers the stored energy in the form of minute current to the inputs of IC1.This will upset
the balanced input of IC1 and convert the current into the corresponding output voltage.
Capacitor C4 along with high-value resistor R1 keeps the non-inverting input stable
for easy swing of the output to high state. Resistor R2 provides the discharge path for
capacitor C4.Feedback resistor R3 makes the inverting input high when the output becomes
high. Capacitor C5 (47pF) is connected across ‘strobe’ (pin 8) and ‘null’ inputs (pin 1) of IC1
for phase compensation and gain control to optimise the frequency response.
When the mobile phone signal is detected by C3, the output of IC1 becomes high and
low alternately according to the frequency of the signal as indicated by LED1. This triggers

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mono stable timer IC2 through capacitor C7. Capacitor C6 maintains the base bias of
transistor T1 for fast switching action. The low-value timing components R6 and C9 produce
very short time delay to avoid audio nuisance.
Assemble the circuit on PCB and enclose in a small box like junk mobile case. As
mentioned earlier, capacitor C3 should have a lead length of 18 mm with lead spacing of 8
mm. Carefully solder the capacitor in standing position with equal spacing of the leads. The
response can be optimised by trimming the lead length of C3 for the desired frequency. You
may use a short telescopic type antenna.
2.4. Mobile Bug:
Normally IC1 is off. So IC2 will be also off. When the power is switched on, as
stated above, IC1 will give a high output and T1 conducts to trigger LED and Timer .This can
be a good indication for the working of the circuit.
3. CIRCUIT DIAGRAM:
Figure 1.2: Circuit Diagram of Cell Phone Detector
3.1. CIRCUIT DIAGRAM DESCRIPTION:
An ordinary RF detector using tuned LC circuits is not suitable for detecting signals in
the GHz frequency band used in mobile phones. The transmission frequency of mobile
phones ranges from 0.9 to 3 GHz with a wavelength of 3.3 to 10 cm. So a circuit detecting

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gigahertz signals is required for a cell phone detector. Here the circuit uses a 0.22pF disk
capacitor (C3) to capture the RF signals from the mobile phone. The lead length of the
capacitor is fixed as 18 mm with a spacing of 8 mm between the leads to get the desired
frequency. The disk capacitor along with the leads acts as a small gigahertz loop antenna to
collect the RF signals from the mobile phone.
Op-amp IC CA3130 (IC1) is used in the circuit as a current-to-voltage converter with
capacitor C3 connected between its inverting and non-inverting inputs. It is a CMOS version
using gate-protected p-channel MOSFET transistors in the input to provide very high input
impedance, very low input current and very high speed of performance. The output CMOS
transistor is capable of swinging the output voltage to within 10 mV of either supply voltage
terminal.
Capacitor C3 in conjunction with the lead inductance acts as a transmission line that
intercepts the signals from the mobile phone. This capacitor creates a field, stores energy and
transfers the stored energy in the form of minute current to the inputs of IC1. This will upset
the balanced input of IC1 and convert the current into the corresponding output voltage.
Capacitor C4 along with high-value resistor R1 keeps the non-inverting input stable
for easy swing of the output to high state. Resistor R2 provides the discharge path for
capacitor C4. Feedback resistor R3 makes the inverting input high when the output becomes
high. Capacitor C5 (47pF) is connected across ‘strobe’ (pin 0 and ‘null’ inputs (pin 1) of IC1
for phase compensation and gain control to optimise the frequency response.
When the mobile phone signal is detected by C3, the output of IC1 becomes high and
low alternately according to the frequency of the signal as indicated by LED1. This triggers
monostable timer IC2 through capacitor C7. Capacitor C6 maintains the base bias of
transistor T1 for fast switching action. The low-value timing components R6 and C9 produce
very short time delay to avoid audio nuisance.

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3.2.Block Diagram
Above diagram shows how a cellular phone detector works by using Down Converter,
Bandpass Filter, and Voltage Controlled Oscillator (VCO). Now we will see how our cell
phone detector works without using above devices.
3.3. BLOCK DIAGRAM EXPLANATION :

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There are five major blocks in the case of cell phone detector. They are
(i) Antenna
(ii) LC tuner circuit
(iii) Current to voltage converter
(iv) 555 monoshot circuit
(v) Output stage
The first stage is the Antenna stage. The transmission frequency of mobile phone ranges
from 0.9 to 3 GHz with a wavelength of 3.3 to 10 cm. These frequencies send by an active
mobile phone need to be received. This function is carried out by the receiving antenna. An
ordinary RF detector using tuned circuit is not suitable for detecting signals in the GHz
frequency band used in mobile phones. So a circuit detecting GHz signal is required for a
mobile detector.
Here the circuit uses 0.22µF disk capacitor to capture RF signals from the mobile
phones. The lead length of the capacitor is fixed as 18mm with a spacing of 08mm between
the leads to get the desired frequency. The disk capacitor along with the leads acts as a small
gigahertz loop antenna to collect the RF signals from the mobile phones. This capacitor along
with the lead inductance act as a transmission lines to intercept the signals from the mobile.
The capacitor creates a field, stores energy and transfers the stored energy in the form of
minute current to the input of a current to voltage converter circuit. This forms the second
stage which is LC Tuner stage.
The current coming to the input of the converter IC, upset its balanced input and then
convert the current into corresponding output voltage. When the mobile phone signals are
detected by the input capacitor, the output of the converter IC, becomes high and low as
indicated by the LED. This triggers the monostable circuit also. The low value timing
components R and C produce very short time delay to avoid audio nuisance. A buzzer is
triggered by using the output of the monoshot timer. The buzzer along with the LEDF forms
the output stage that provide us the indication as sound and light respectively.

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4. TRANSMISSION LINE:
A transmission line conveys electromagnetic waves. A pair of parallel wires and
coaxial cables is the commonly employed transmission lines. It is used to connect transmitter
and antenna, receiver and antenna etc. At low frequency the energy loss in the connecting
wires is negligible. But for higher frequency the loss can be reduced by using two parallel
wires, one for forward connection and the other for return current. A transmission line is
characterized by its lumped parameter as described below.
Series Resistance:
Due to finite conductivity of the conductors, there is a uniform distributed resistance.
There is also power loss due to radiation from the lines. Thus the finite conductivity and
radiation loss can be modeled as a series resistance per loop of length.
Series Inductance:
A current carrying conductor has an associated magnetic field. Both, the grow and
decay of the current is opposed, and hence it possesses inductance. This inductance is
distributed throughout the line. It acts in series.
Series Capacitance:
The two conducting wires is separated by a distance, situated in a dielectric medium
gives rise to a capacitance that acts parallel with the wires.
Shunt Leakage Conductance:
Since the wires are separated by a dielectric medium that cannot be perfect in its
insulation, current leaks through it when the lines carry a current. This leakage of current
through the dielectric between the wires is represented by a shunt conductance per unit
length.

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5. PCB Layout of the Cell Phone Detector Circuit:
Figure: 2.3 PCB Layouts
6. LIST OF COMPONENTS:
6.1. Components Description
RESISTORS
1. R1 ________2.2M
2. R2 ________100K
3. R3 ________2.2M
4. R4 ________1K
5. R5________12K
6. R6________15K
CAPACITORS
7. C1 ________22P
8. C2 ________22P
9. C3 ________0.22 µF
10. C4 ________100 µF
11. C5_________47P
12. C6 _________0.1 µF
13. C7_________ 0.1 µF
14. C8_________ 0.01 µF
15. C9__________4.7 µF
16. IC CA3130
17. IC NE555

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18. T1 BC548
19. LED
20. ANTENNA
21. TIMER CIRCUT
22. 5 INCH LONG ANTENNA
23. ON/OFF SWITCH
24. POWER SUPPLY
6.2. TIMER CIRCUT
Monostable 555 time out calculator
This calculator is designed to give te timeout value for a Monostable 555 timer circuit.
When power is applied to a mono stable circuit the output is low until the delay time as
elapsed, the output then goes high and remains high
The formula used is:
Time out delay (sec) = 1.1*R1*c1

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6.3. Pin diagram of ICs:
IC CA3130:
Figure 3.9: IC CA3130
7. Working, Applications, and Features of IC CA3130:
General Description:
CA3130 are op amps that combine the advantage of both CMOS and bipolar
transistors.

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Gate-protected P-Channel MOSFET (PMOS) transistors are used in the input circuit to
provide very-high-input impedance, very-low-input current, and exceptional speed
performance. The use of PMOS transistors in the input stage results in common-mode input-
voltage capability down to 0.5V below the negative-supply terminal, an important attribute in
single-supply applications.
A CMOS transistor-pair, capable of swinging the output voltage to within 10mV of
either supply-voltage terminal (at very high values of load impedance), is employed as the
output circuit.
CA3130A and CA3130 are op amps that combine the advantage of both CMOS and
bipolar transistors. Gate protected P-Channel MOSFET (PMOS) transistors are used in the
input circuit to provide very-high-input impedance, very-low-input current, and exceptional
speed performance. The use of PMOS transistors in the input stage results in common-mode
input-voltage capability down to 0.5V below the negative-supply terminal, an important
attribute in single-supply applications.
either supply-voltage terminal (at
very high values of load impedance), is employed as the output circuit. The CA3130 Series
circuits operate at supply voltages ranging from 5V to 16V, ( }2.5V to }8V). They can be
phase compensated with a single external capacitor, and have terminals for adjustment of
offset voltage for applications requiring offset-null capability. Terminal provisions are also
made to permit striding of the output stage. The CA3130A offers superior input
characteristics over those of the CA3130
The CA3130 op amp has the following pin outs:
1. Offset null
2. Inv. input
3. Non-inv. input
4. V- and case
5. Offset null
6. Output
7. V+
8. Strobe

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(i) Role of IC CA3130:
This IC is a 15 MHz BIMOS Operational amplifier with MOSFET inputs and bipolar
output. The inputs contain MOSFET transistors to provide very high input impedance and
very low input current as low as 10pA. It has high speed of performance and suitable for low
input current applications.
CA3130A and CA3130 are op amps that combine the advantage of both CMOS and
bipolar transistors. Gate-protected P-Channel MOSFET (PMOS) transistors are used in the
input circuit to provide very-high-input impedance, very-low-input current, and exceptional
speed performance. The use of PMOS transistors in the input stage results in common-mode
input-voltage capability down to0.5V below the negative-supply terminal, an important
attribute in single-supply applications.
either supply-voltage terminal (at very high values of load impedance), is employed as the
output circuit.
The CA3130 Series circuits operate at supply voltages ranging from 5V to 16V, (2.5V
to 8V). They can be phase compensated with a single external capacitor, and have terminals
for adjustment of offset voltage for applications requiring offset-null capability. Terminal
provisions are also made to permit striding of the output stage. The CA3130A offers
superior input characteristics over those of the CA3130.
(ii) Features:
(i) MOSFET Input Stage Provides:
Very High ZI = 1.5 T
Very Low current . . . . . . =5pA at 15V Operation
(ii) Ideal for Single-Supply Applications
(iii) Common-Mode Input-Voltage Range Includes Negative Supply Rail; Input Terminals
can be Swung 0.5VBelow Negative Supply Rail
(iv) CMOS Output Stage Permits Signal Swing to Either (or both) Supply Rails.

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(iii) Applications:
(i) Ground-Referenced Single Supply Amplifiers
(ii) Fast Sample-Hold Amplifiers
(iii) Long-Duration Timers/ Mono stables
(iv) High-Input-Impedance Comparators (Ideal Interface with Digital CMOS)
(v) High-Input-Impedance Wideband Amplifiers
(vi)Voltage Followers (e.g. Follower for Single-Supply D/A Converter )
(vii) Voltage Regulators (Permits Control of Output Voltage Down to 0V)
(viii) Peak Detectors
(ix) Single-Supply Full-Wave Precision Rectifiers
(x) Photo-Diode Sensor Amplifiers.
8. IC NE555:
Figure 3.10: IC NE555

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Working, Applications and Features of IC NE555:
The NE555 IC is a highly stable controller capable of producing accurate timing
pulses. With a monostable operation, the time delay is controlled by one external resistor and
one capacitor. With an astable operation, the frequency and duty cycle are accurately
controlled by two external resistors and one capacitor.
(i) Details of Pin:
Ground, is the input pin of the source of the negative DC voltage trigger, negative input
from the lower comparators (comparator B) that maintain oscillation capacitor voltage in the
lowest 1 / 3 Vcc and set RS flip-flop output, the output pin of the IC 555.
Reset, the pin that serves to reset the latch inside the IC to be influential to reset the IC
work. This pin is connected to a PNP-type transistor gate, so the transistor will be active if
given a logic low. Normally this pin is connected directly to Vcc to prevent reset control
voltage, this pin serves to regulate the stability of the reference voltage negative input
(comparator A). This pin can be left hanging, but to ensure the stability of the reference
comparator A, usually associated with a capacitor of about 10nF to berorde pin ground
threshold, this pin is connected to the positive input (comparator A) which will reset the RS
flip-flop when the voltage on the capacitor from exceeding 2 / 3 V discharge, this pin is
connected to an open collector transistor Q1 is connected to ground emitter. Switching
transistor serves to clamp the corresponding node to ground on the timing of certain vcc, pin
it to receive a DC voltage supply. Usually it will work optimally if given a 5-15V. the current
supply can be seen in the datasheet, which is about 10-15mA.
One of the most versatile linear ICs is the 555 timer which was first introduced in early
1970 by Signetic Corporation giving the name as SE/NE 555 timer. This IC is a monolithic
timing circuit that can produce accurate and highly stable time delays or oscillation. Like
other commonly used op-amps, this IC is also very much reliable, easy to use and cheaper in
cost. It has a variety of applications including monostable and astable multivibrators, dc-dc
converters, digital logic probes, waveform generators, analog frequency meters and
tachometers, temperature measurement and control devices, voltage regulators etc. The timer

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basically operates in one of the two modes either as a monostable (one-shot) multivibrator or
as an astable (free-running) multivibrator. The SE 555 is designed for the operating
temperature range from – 55°C to 125° while the NE 555 operates over a temperature range
of 0° to 70°C.
(ii) The important features of the 555 timer are :
(i) It operates from a wide range of power supplies ranging from + 5 Volts to + 18 Volts
supply voltage.
(ii) Sinking or sourcing 200 mA of load current.
(iii) The external components should be selected properly so that the timing intervals can be
made into several minutes Proper selection of only a few external components allows timing
intervals of several minutes along with the frequencies exceeding several hundred kilo hertz.
(iv) It has a high current output; the output can drive TTL.
(v) It has a temperature stability of 50 parts per million (ppm) per degree Celsius change in
temperature, or equivalently 0.005 %/ °C.
(vi) The duty cycle of the timer is adjustable with the maximum power dissipation per
package is 600 mW and its trigger and reset inputs are logic compatible.
Pin Configuration:
Pin 1: Grounded Terminal: All the voltages are measured with respect to this terminal.
Pin 2: Trigger Terminal: This pin is an inverting input to a comparator that is responsible
for transition of flip-flop from set to reset. The output of the timer depends on the amplitude
of the external trigger pulse applied to this pin.
Pin 3: Output Terminal: Output of the timer is available at this pin. There are two ways in
which a load can be connected to the output terminal either between pin 3 and ground pin
(pin 1) or between pin 3 and supply pin (pin 8). The load connected between pin 3 and
ground supply pin is called the normally on load and that connected between pin 3 and
ground pin is called the normally off load.
Pin 4: Reset Terminal: To disable or reset the timer a negative pulse is applied to this pin
due to which it is referred to as reset terminal. When this pin is not to be used for reset
purpose, it should be connected to + VCC to avoid any possibility of false triggering.

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Pin 5: Control Voltage Terminal: The function of this terminal is to control the threshold
and trigger levels. Thus either the external voltage or a pot connected to this pin determines
the pulse width of the output waveform. The external voltage applied to this pin can also be
used to modulate the output waveform. When this pin is not used, it should be connected to
ground through a 0.01 micro Farad to avoid any noise problem.
Pin 6: Threshold Terminal: This is the non-inverting input terminal of comparator 1, which
compares the voltage applied to the terminal with a reference voltage of 2/3 VCC. The
amplitude of voltage applied to this terminal is responsible for the set state of flip-flop.
Pin 7: Discharge Terminal: This pin is connected internally to the collector of transistor and
mostly a capacitor is connected between this terminal and ground. It is called discharge
terminal because when transistor saturates, capacitor discharges through the transistor. When
the transistor is in cut-off region, the capacitor charges at a rate determined by the external
resistor and capacitor.
Pin 8: Supply Terminal: A supply voltage of + 5 V to + 18 V is applied to this terminal
with respect to ground (pin 1).
Figure illustrate some basic ideas that will prove useful in coming blog posts of the
555 timer. Assuming output Q high, the transistor is saturated and the capacitor voltage is
clamped at ground i.e. the capacitor C is shorted and cannot charge.
The non-inverting input voltage of the comparator is referred to as the threshold
voltage while the inverting input voltage is referred to as the control voltage. With R-S flip
flop set, the saturated transistor holds the threshold voltage at zero. The control voltage,
however, is fixed at 2/3 VCC (i.e. at 10 V) because of the voltage divider.
Suppose that a high voltage is applied to the R input. This resets the flip-flop R-
Output Q goes low and the transistor is cut-off. Capacitor C is now free to charge. As this
capacitor C charges, the threshold voltage rises. Eventually, the threshold voltage becomes
slightly greater than (+ 10 V). The output of the comparator then goes high, forcing the R S
flip-flop to set. The high Q output saturates the transistor, and this quickly discharges the
capacitor. The two waveforms are depicted in figure. An exponential rise is across the

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capacitor C, and a positive going pulse appears at the output Q. Thus capacitor voltage VC is
exponential while the output is rectangular.
(iii) Working Principle:
Comparator 1 has a threshold input (pin 6) and a control input (pin 5). In most
applications, the control input is not used, so that the control voltage equals +2/3 VCC. Output
of this comparator is applied to set (S) input of the flip-flop. Whenever the threshold voltage
exceeds the control voltage, comparator 1 will set the flip-flop and its output is high. A high
output from the flip-flop saturates the discharge transistor and discharge the capacitor
connected externally to pin 7. The complementary signal out of the flip-flop goes to pin 3, the
output. The output available at pin 3 is low. These conditions will prevail until comparator 2
triggers the flip-flop. Even if the voltage at the threshold input falls below 2/3 VCC, that is
comparator 1 cannot cause the flip-flop to change again. It means that the comparator 1 can
only force the flip-flop’s output high.
To change the output of flip-flop to low, the voltage at the trigger input must fall
below + 1/3 Vcc. When this occurs, comparator 2 triggers the flip-flop, forcing its output
low. The low output from the flip-flop turns the discharge transistor off and forces the power
amplifier to output a high. These conditions will continue independent of the voltage on the
trigger input. Comparator 2 can only cause the flip-flop to output low.
From the above discussion it is concluded that for the having low output from the
timer 555, the voltage on the threshold input must exceed the control voltage or + 2/3 VCC.
They also turn the discharge transistor on. To force the output from the timer high, the
voltage on the trigger input must drop below +1/3 VCC. This also turns the discharge
transistor off.
A voltage may be applied to the control input to change the levels at which the
switching occurs. When not in use, a 0.01 nano Farad capacitor should be connected between
pin 5 and ground to prevent noise coupled onto this pin from causing false triggering
Connecting the reset (pin 4) to a logic low will place a high on the output of flip-flop.
The discharge transistor will go on and the power amplifier will output a low. This condition
will continue until reset is taken high. This allows synchronization or resetting of the circuit’s
operation. When not in use, reset should be tied to +VCC.

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(iv) Features:
(i) High Current Drive Capability (200mA)
(ii) Adjustable Duty Cycle
(iii) Temperature Stability of 0.005%C
(iv) Timing From Sec to Hours
(v) Turn off Time Less Than 2mSec
(v) Applications:
(i) Precision Timing
(ii) Pulse Generation
(iii) Time Delay Generation
(iv) Sequential Timing
9. Circuit Testing
Before the assembling of circuit on PCB we tested it on the bread-board using the
components, connecting wires, and a 9V battery.
10. Working of Cell Phone Detector:
10.1. Purpose of the circuit:
This circuit is intended to detect unauthorized use of mobile phones in examination
halls, confidential rooms etc. It also helps to detect unauthorized video and audio recordings.
It detects the signal from mobile phones even if it is kept in the silent mode. It also detects
SMS
10.2. Concept:
Mobile phone uses RF with a wavelength of 30cm at 872 to 2170 MHz. That is the
signal is high frequency with huge energy. When the mobile phone is active, it transmits the
signal in the form of sine wave which passes through the space. The encoded audio/video
signal contains electromagnetic radiation which is picked up by the receiver in the base
station. Mobile phone system is referred to as “Cellular Telephone system” because the
coverage area is divided into “cells” each of which has a base station. The transmitter power
of the modern 2G antenna in the base station is 20-100 watts.

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When a GSM (Global System of Mobile communication) digital phone is
transmitting, the signal is time shared with 7 other users. That is at any one second, each of
the 8 users on the same frequency is allotted 1/8 of the time and the signal is reconstituted by
the receiver to form the speech. Peak power output of a mobile phone corresponds to 2 watts
with an average of 250 milli watts of continuous power. Each handset with in a ‘cell’ is
allotted a particular frequency for its use. The mobile phone transmits short signals at regular
intervals to register its availability to the nearest base station. The network data base stores
the information transmitted by the mobile phone. If the mobile phone moves from one cell to
another, it will keep the connection with the base station having strongest transmission.
Mobile phone always tries to make connection with the available base station. That is why,
the back light of the phone turns on intermittently while traveling. This will cause severe
battery drain. So in long journeys, battery will flat with in a few hours.
AM Radio uses frequencies between 180 kHz and 1.6 MHz. FM radio uses 88 to 180
MHz. TV uses 470 to 854 MHz. Waves at higher frequencies but within the RF region is
called Micro waves. Mobile phone uses high frequency RF wave in the micro wave region
carrying huge amount of electromagnetic energy. That is why burning sensation develops in
the ear if the mobile is used for a long period. Just like a micro wave oven, mobile phone is
‘cooking’ the tissues in the ear. RF radiation from the phone causes oscillation of polar
molecules like water in the tissues. This generates heat through friction just like the principle
of microwave oven. The strongest radiation from the mobile phone is about 2 watts which
can make connection with a base station located 2 to 3 km away.
How the circuit works?
Ordinary LC (Coil-Capacitor) circuits are used to detect low frequency radiation in
the AM and FM bands. The tuned tank circuit having a coil and a variable capacitor retrieve
the signal from the carrier wave. But such LC circuits cannot detect high frequency waves
near the microwave region. Hence in the circuit, a capacitor is used to detect RF from mobile
phone considering that, a capacitor can store energy even from an outside source and oscillate
like LC circuit.

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11. How the capacitor senses RF?
One lead of the capacitor gets DC from the positive rail and the other lead goes to the
negative input of IC1. So the capacitor gets energy for storage. This energy is applied to the
inputs of IC1 so that the inputs of IC are almost balanced with 1.4 volts. In this state output is
zero. But at any time IC can give a high output if a small current is induced to its inputs.
There a natural electromagnetic field around the capacitor caused by the 50Hz from electrical
wiring. When the mobile phone radiates high energy pulsations, capacitor oscillates and
release energy in the inputs of IC. This oscillation is indicated by the flashing of the LED and
beeping of Buzzer. In short, capacitor carries energy and is in an electromagnetic field. So a
slight change in field caused by the RF from phone will disturb the field and forces the
capacitor to release energy.
12. Applications:
(i) Colleges and Universities:
During tests and exams the use of mobile phones is prohibited, for the students could
use it to send answers among each other.
By using a GSM-detector this kind of fraud is prohibited. The presence of a GSM-
detector can work in a preventing way, because when a GSM-detector is present, the use of
mobile phones does not stay unnoticed.
(ii) Cinemas:
In a cinema the use of a mobile phone is undesired. Being called by someone during a
movie is of course very bothering for other people.
With a GSM-detector the use of mobile phones is detected, so the visitor can be
informed that this is not allowed.
(iii) Theatres:
Just like with a cinema, in theatres the use of mobile phones is not allowed. The gsm-
detector can be used to prevent use.
(iv) Restaurants / Hotels:
In hotels and restaurants it is often undesired that a mobile phone is used at the table
or in other areas. A GSM-detector can be installed in these areas to notify guests.

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(v) Petrol stations:
When tanking at a petrol station, the use of mobile phones is prohibited, because the
mobile signals can interfere with the tanking equipment and because a small spark within the
mobile phone could set fire to possible gasoline vapour. With the GSM-detector this
prohibition is pointed out to the tanking customer.
(vi) Airplanes:
In airplanes the use of mobile phones is prohibited, for it could interfere with the
equipment in the airplane. All the while phones are still used illegally, especially in
restrooms. By installing a GSM-detector there, this can be prevented.
(vii) Conference rooms:
It is often distracting to be called during a meeting. Also, confidential conversation
could be overheard by using cell phones, especially by those with a spy function (when
someone calls that phone it automatically is picked up without ringing, so that the person on
the other end of the line can hear conversations in the room where the spy phone is placed).
By using a GSM-detector you can be assured that this is not the case.
(viii) Hospitals:
The signals emitted by mobile phones can interfere with some electronic equipment
inside the hospital. This could have fatal consequences.
The GSM-detector can be placed in any area where the use of mobile phones could
interfere with sensitive devices. The audio alarm will sound when a phone is used and this
way, the person should immediately switch off his/her phone
(ix) Prisons:
In prisons the use of mobile phones is not allowed. It could occur anyway. By using
the gsm-detector the staff can be notified when a mobile phone is used inside the facility.
(x) Power plants:

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Power plants contain -just like hospitals- a lot of electronic devices that are sensitive
for interference by mobile phones. Therefore, it is prohibited to use mobile phones there. Use
a GSM-detector to inspect this.
13. Advantages:
Our mission is to be the leading provider of cellular phone detection capabilities to
both business and government institutions around the world. We are striving to bring a
national debate to the growing proliferation of cell phone use in our society today. Using our
state of the art products we are hoping to provide individuals and businesses the tools to
detect and prevent the use of cell phone in sensitive areas.
This product was created in reaction to the growing use of cell phones around the
world, and how that use was beginning to interfere with our daily lives. When businesses
tried to find solutions to problems involving cell phones, they found a huge shortcoming in
products and services.
Hence, our solution was created to supply this need. To date we have sold thousands
of products to a very wide audience of businesses and government institutions. Many of
these include prisons, casinos, embassies, classrooms and testing facilities, oil rigs,
conferences, golf clubhouses, computer-rooms, data centers, hospitals, and restaurants, to
name just a small few of the vast capabilities of our product.
.
14. Limitation:
Range of the circuit:
The prototype version has only limited range of 2 meters. But if a preamplifier stage
using JFET or MOSFET transistor is used as an interface between the capacitor and IC, range
can be increased.
15. Future scope:
Trying to increase the detecting range of mobile bug to few more meters for observing wide
ranges of area. In the future time this detector will be improved in all ways.
In future we could be able to detect any range of frequency over a meters of range and
this will be very useful to detect the cell phones where the cell phones are prohibited.

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16. Conclusion:
This pocket-size mobile transmission detector or sniffer can sense the presence of an
activated mobile cell phone from a distance of one and-a-half meters. So 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 unauthorized video transmission.
In this project we made an attempt to design a mobile detector which can detect both
the incoming and outgoing calls as well as video transmission even if the mobile is kept at the
silent mode. Our circuit has detected the presence of an active mobile phone even at a
distance of about one and half a meter. It gave the indication of an active mobile phone by
glowing the LED, according to the receiving frequency and by buzzing the sound of the
buzzer. The alarm continues until the signal is ceases.
17. References:
(i) www.google.com
(ii) www.wikipedia.org
(iii) www.pdfmachine.com
(iv)www.ecproject.com
(v) www.datasheets4u.com

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