1. Under the guidance of Submitted by Project Title
FOUR TELEPHONES IN PARALLEL BUT STILL ACCESSED BY ONLY ONE USER AT A TIME TO MAINTAIN SECRECY
Under the guidance of
Submitted by

2. ABSTRACT
This Project can be used in houses and offices where more than one telephone is connected in parallel through a single telephone line
When any one of the phone is lifted, all the other lines are disconnected from the telephone line whether in incoming mode or outgoing mode.
All these are achieved by microcontroller duly interfaced with opto isolator that keeps a track of the hand set lifting with a digital indication by a seven segment LCD display and relays being driven from a relay driver IC.

3. PROJECT BLOCK DIAGRAM

4. POWER SUPPLY BLOCK SEVEN SEGMENT DISPLAY OPTOCOUPLER PUSHBUTTON RELAYS
HARDWARE REQUIREMENTS
POWER SUPPLY BLOCK
MICROCONTROLLER(AT89c51/52)
SEVEN SEGMENT DISPLAY
OPTOCOUPLER
PUSHBUTTON
RELAYS
RELAY DRIVER ULN2003
1N4007

5. POWER SUPPLY Bridge rectifier 5v Regulator 230 V AC 50 Hz 5V DC
Filter(470µf)
12V step down
transformer

6. It is a smaller computer Has on-chip RAM, ROM, I/O ports...
MICROCONTROLLER
It is a smaller computer
Has on-chip RAM, ROM, I/O ports...
RAM
ROM
I/O Port
Timer
Serial COM Port
Microcontroller
CPU
A single chip

7. INTERNAL STRUCTURE OF A MICRO CONTROLLER-AT89S52/51
CPU
On-chip RAM
On-chip ROM for program code
4 I/O Ports
Timer 0
Serial Port
OSC
Interrupt Control
External interrupts
Timer 1
Timer/Counter
Bus Control
TxD RxD
P0 P1 P2 P3
Address/Data
Counter Inputs

8. Features of AT89S51/52 Compatible with MCS®-51 Products
8K Bytes of In-System Programmable (ISP) Flash Memory
Endurance: 10,000 Write/Erase Cycles
4.0V to 5.5V Operating Range
Fully Static Operation: 0 Hz to 33 MHz
256 x 8-bit Internal RAM
32 Programmable I/O Lines
Three 16-bit Timer/Counters
Eight Interrupt Sources
Full Duplex UART Serial Channel
Interrupt Recovery from Power-down Mode
Watchdog Timer
Dual Data Pointer

9. Pin Description

10. Opto-isolator Opto coupler is a 6 pin IC.
It is a combination of 1 LED and a transistor.
when light falls on the Base-Emitter junction then it switches pin5 goes to zero.
When logic zero is given as input then the light doesn’t fall on transistor so it doesn’t conduct which gives logic zero as output.
When logic 1 is given as input then light falls on transistor so that it conducts, that makes transistor switched ON and it forms short circuit this makes the output is logic zero as collector of transistor is connected to ground.

11. RELAY IT IS A ELECTRO MAGNETIC SWITCH
USED TO CONTROL THE ELECTRICAL DEVICES
COPPER CORE MAGNETIC FLUX PLAYS MAIN ROLE HERE

12. The relay's switch connections are usually labeled COM, NC and NO:
COM = Common, always connect to this; it is the moving part of the itch.
NC = Normally Closed, COM is connected to this when the relay coil is off.
NO = Normally Open, COM is connected to this when the relay coil is on

13. RELAY DRIVER (ULN 2003)
ULN2003 is a high voltage and high current Darlington transistor array
It consists of seven NPN Darlington pairs that feature high-voltage outputs with common-cathode Clamp diode for switching inductive loads.
The ULN2003 has a 2.7kW series base resistor for each Darlington pair for operation directly with TTL or 5V CMOS devices.
Current, Output Max:500mA
Voltage, Input Max:5V
Voltage, Output Max:50V

14. Fig: ULN 2003

15. SEVEN SEGMENT DISPLAY
The segments themselves are identified with lower-case letters "a" through "g," with segment "a" at the top and then counting clockwise.

16. The LED’S in a seven-segment display are not isolated from each other
The LED’S in a seven-segment display are not isolated from each other. Rather, either all of the cathodes, or all of the anodes, are connected together into a common lead, while the other end of each LED is individually available.
This means fewer electrical connections to the package, and also allows us to easily enable or disable a particular digit by controlling the common lead.
There is no automatic advantage of the common-cathode seven-segment unit over the common-anode version, or vice-versa. Each type lends itself to certain applications, configurations, and logic families.

17. The project uses 4 telephones connected in series with relay contacts and Opto isolators individually while a telephone line is fed to the common points of the contactor forming parallel connection
While any instrument is lifted it makes the corresponding Opto isolator to be active & there by a logic low is loaded onto the input pins at port 3.
The program is so returned that while executed it displays the corresponding number on the 7 segment display being fed to MC Simultaneously relay driver IC ULN2003 receives logic high command to enable all the relays excepting the one which is lifted such that the balance 3 telephones are disconnected from the common telephone line.
Thus complete secrecy is achieved even though all the telephone instruments were connected in parallel. Similarly for outgoing calls any handset is lifted the same condition happens as stated above and disconnects all other instruments.
Working of Project

18. Software Requirements
Keil an ARM Company makes C compilers, macro assemblers, real-time kernels, debuggers, simulators, integrated environments, evaluation boards, and emulators for ARM7/ARM9/Cortex-M3, XC16x/C16x/ST10, 251, and 8051 MCU families.
Compilers are programs used to convert a High Level Language to object code. Desktop compilers produce an output object code for the underlying microprocessor, but not for other microprocessors.

19. i.e the programs written in one of the HLL like ‘C’ will compile the code to run on the system for a particular processor like x86 (underlying microprocessor in the computer).
For example compilers for Dos platform is different from the Compilers for Unix platform  So if one wants to define a compiler then compiler is a program that translates source code into object code.

20. BIBILOGRAPHY
“The Microcontroller and Embedded systems” by Muhammad Ali Mazidi and Janice Gillispie Mazidi , Pearson Education.
ATMEL 89S52 Data Sheets.

21. THANKYOU