This document describes the design of a cellphone detector circuit. The circuit uses a step-down transformer, bridge rectifier, and filter to supply power to the rest of the circuit. An antenna and receiver section use a capacitor to detect signals from nearby cellphones. An IC regulates the output and indicators like an LED and buzzer are triggered when a phone is detected. The circuit can sense activated phones within 1.5 meters and has applications to restrict phone use in secure areas. Future work may extend the range using a preamplifier.

1. MINI PROJECT ON
CELLPHONE DETECTOR

2. INTRODUCTION
 This is a handy, pocket-size mobile transmission
detector or sniffer
 It works from a distance of one and-a-half
meters.
 The circuit can detect the incoming and
outgoing calls, and SMS even if the mobile
phone is kept in the silent mode.

3. BLOCK DIAGRAM

4. POWER SUPPLY

5. TRANSFORMER

A transformer is a device that transfers
electrical energy from one circuit to another
through inductively coupled conductors — the
transformer's coils or "windings".

The transformer used here is a 230/(12V-
0-12V) step down transformer.

6. BRIDGE RECTIFIER

7. FILTER CIRCUIT
 Filter may involve capacitors, inductors, and/or resistors in
some combination
 To eliminate ripple components

8. REGULATOR SECTION

A
voltage
regulator
is
an
electrical
regulator designed to automatically maintain a
constant voltage level.

IC 7809 is used here.

9. CIRCUIT DIAGRAM

10. ANTENNA
 A small loop RF antenna is used for reception of signal.
RECEIVER
 The signal captured by the antenna is taken to receiver.
This part consists of disc capacitor along with its leads
acting as tank circuit.

11. USE OF CAPACITOR
 To detect the signal, the sensor part should be like an aerial.
 So the capacitor is arranged as a mini loop aerial (similar to the
dipole antenna used in TV).
 In short with this arrangement, the capacitor works like an air
core coil with ability to oscillate and discharge current.

12. COMPONENT DISCRIPTION
ABOUT IC CA3130

13.  This IC is a 15 MHz BiMOS Operational amplifier with
MOSFET inputs and Bipolar output.

Gate-protected P-Channel MOSFET (PMOS) transistors are
used
in
the
input
circuit
to
impedance, very-low-input current,
provide
very-high-input
and exceptional speed
performance.
 We can also use this CA3130 as voltage to current converter.

14. ABOUT NE555 TIMER IC

15.  The NE555 IC is a highly stable controller capable of
producing accurate timing pulses.

For astable multi vibrator operation as an oscillator, the free
running frequency and the duty cycle are both accurately
controlled with two external resistors and one capacitor.

The NE555 Timer ic is also used for Precision Timing, Pulse
Generation, Time Delay Generation and Sequential Timing.

16. ABOUT TRANSISTOR BC548
 Transistor BC548 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.

17. ABOUT LED
 LEDs are used as indicator lamps in many kinds of electronics
and increasingly for lighting. LEDs work by the effect of
electroluminescence.

18. ABOUT PIZEO BUZZER
 A buzzer is a signaling device, usually electronic, typically used
in automobiles, household appliances such as microwave ovens,
or game shows.

19. APPLICATIONS
 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.

It is useful where the use of mobile phone is prohibited Like
petrol pumps and gas stations, historical places, religious places
and court of laws.

20. CONCLUSION
This pocket-size mobile transmission detector or sniffer
can sense the presence of an activated mobile 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.

21. FUTURE WORK
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.