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

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.

PROJECT BLOCK DIAGRAM

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

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

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

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

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

Pin Description

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.

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

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

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

Fig: ULN 2003

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.

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.

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

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.

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.

BIBILOGRAPHY “The 8051 Microcontroller and Embedded systems” by Muhammad Ali Mazidi and Janice Gillispie Mazidi , Pearson Education. ATMEL 89S52 Data Sheets. www.atmel.com www.beyondlogic.org www.wikipedia.org www.howstuffworks.com www.alldatasheets.com

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