1. HIDDEN ACTIVE CELL PHONE DETECTOR

2. Introduction
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 same in the examination halls.
In this project an RF detector using tuned LC circuits is formed for detecting signals in the GHz frequency band used in mobile phones as the transmission frequency of mobile phone ranges from 0.9 to 3 GHz.
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.

3. EMBEDDED SYSTEMS Definition for :- EMBEDDED SYSTEMS
A combination of hardware and software which together
form a component of a larger machine.
An example of an embedded system is a microprocessor that
controls an automobile engine.
An embedded system is designed to run on its own without
human intervention, and may be required to respond to
events in real time.

4. EMBEDDED SYSTEMS

5. Contents Introduction Block diagram Hardware requirements Power supply
Piezo-buffer
555 TIMER
Schematic diagram
Working of the project
Advantages
Applications
Conclusion

6. BLOCK DIAGRAM

7. Hardware requirements
OP-AMP (CA3130)
555 TIMER
BC548
LED
PIEZO-BUFFER
PUSH BUTTONS
12V BATTERY
RESISTOR
CAPACITOR

8. 555 TIMER
The 555 Timer IC is an integrated circuit (chip) implementing a variety of timer and multivibrator applications
The 555 has three operating modes:
Monostable mode: in this mode, the 555 functions as a "one-shot". Applications include timers, missing pulse detection, switches, touch switches, frequency divider, capacitance measurement, pulse-width modulation (PWM) etc.
Astable - free running mode: the 555 can operate as an oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position modulation, etc.
Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if the DIS pin is not connected and no capacitor is used. Uses include bounce free latched switches, etc.

9. Internal architecture of 555 timer
Pin
Name
Purpose 1
GND
Ground, low level (0 V) 2
TRIG
OUT rises, and interval starts, when this input falls below 1/3 VCC. 3
OUT
This output is driven to +VCC or GND. 4
RESET
A timing interval may be interrupted by driving this input to GND. 5
CTRL
"Control" access to the internal voltage divider (by default, 2/3 VCC). 6
THR
The interval ends when the voltage at THR is greater than at CTRL. 7
DIS
Open collector output; may discharge a capacitor between intervals. 8
V+, VCC
Positive supply voltage is usually between 3 and 15 V.

10. LM358 (DUAL OPERATIONAL AMPLIFIER)
The LM358 series consists of two independent, high gain; internally frequency compensated operational amplifiers which were designed specifically to operate from a single power supply over a wide range of voltages
Operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage.
Pin description
1 ) Output )Inverting input
3 ) Non-inverting input 4 )VCC-
5 )Non-inverting input 2
6 ) Inverting input 2
7 ) Output ) VCC+

11. LM339( COMPARATOR)
The LM339 consists of four independent precision voltage comparators
The LM339 series was designed to directly interface with TTL and CMOS.
When operated from both plus and minus power supplies, the LM339 series will directly interface with MOS logic where their low power drain is a distinct advantage over standard comparators.

12. FEATURES
Wide single supply voltage range 2.0VDC TO 36VDC or dural supplies ±1.0VDC to ±18VDC
● Very low supply current drain (0.8㎃) independent
of supply voltage (1.0㎽/comparator at 5.0VDC)
● Low input biasing current 25㎁
● Low input offset current ±5㎁ and offset voltage
● Input common-mode voltage range includes ground
● Differential input voltage range equal to the power
supply voltage
● Low output 250㎷ at 4㎃ saturation voltage
● Output voltage compatible with TTL, DTL, ECL, MOS and CMOS logic system
● Moisture Sensitivity Level 3

13. BC547 (NPN –Transistor)
The BC547 transistor is an NPN Epitaxial Silicon Transistor.
It is used in general-purpose switching and amplification BC847/BC547 series 45 V, 100 mA NPN general-purpose transistors.
The ratio of two currents (Ic/Ib) is called the DC Current Gain of the device and is given the symbol of hfe or nowadays Beta, (β).

14. The current gain from the emitter to the collector terminal, Ic/Ie, is called Alpha, (α), and is a function of the transistor itself

15. PIEZO-BUZZER

16. A buzzer or beeper is an audio signaling device, which may be mechanical or electromechanical piezoelectric.
A piezoelectric element may be driven by an oscillating electronic circuit or other audio signal source, driven with a piezoelectric audio amplifier .
BATTERY

17. BATTERY
An electrical battery is a combination of one or more electrochemical cells, used to convert stored chemical energy into electrical energy.
The battery has become a common power source for many household, robotics and industrial applications.
Larger batteries provide standby power for telephone exchanges or computer data centers