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8 USERS MICROCONTROLLER BASED TELEPHONE EXCHANGE

BY-AMOL BABUJITENDRA KUMAR PALNEHA SINGHSHUBHAM SONI

PROJECT GUIDE-Mr. B.R.DUTTA

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A telephone exchange is a telecommunication system used in the public switched network or in large enterprises.

An exchange consists of electronic components and in older systems also human operators that interconnect (switch) telephone subscriber lines or virtual circuits of digital systems to establish telephone calls between subscribers.

TELEPHONE EXCHANGE

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INTRODUCTION OBJECTIVE PRINCIPLE HARDWARE/SOFTWARE BLOCK DIAGRAM CIRCUIT DIAGRAM PIC 16F877A DTMF RELAY DRIVER RELAYS CONCLUSION REFERENCES

CONTENTS

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The project is basically a telephone sharer based on microcontroller.

An intercom (intercommunication device), talkback or door phone which is a stand-alone voice communication system for use within a building or small collection of buildings, functioning independently of the public telephone network.

The design and construction of microcontroller based telephone exchange is done using PIC16F877A and DTMF MT8870D

INTRODUCTION

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DTMF stands for dual tone multiple frequency and MT-8870D is a DTMF Receiver that integrates both band split filter and decoder functions into a single 18-pin DIP package.

The results of this telephone exchange system are perfect for homes and small businesses.

It requires the phone operation control system, the analog interface circuit and the switching circuit.

This exchange design will contain eight channels. It is the best low cost, good quality telephone exchange for today’s telecommunication needs.

Cont…

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The goal of this project is to handle eight independent telephones (using a single telephone line pair) located at eight different locations, say, up to a distance of 100m from each other, for receiving and making outgoing calls, while maintaining conversation secrecy.

This circuit is useful when a single telephone line is to be shared by more members residing in different rooms/apartments.

OBJECTIVE

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The microcontroller PIC16F877A and the DTMF CM8870D are collectively working as a telephone exchange to which eight subscribers are connected together

The DTMF CM8870D is decoding the different tones entered by the subscribers into the binary numbers which are accepted by the microcontroller which is acting as a call routing apparatus

Initially the microcontroller detects which one of the eight handsets is off-hooked and thereby provides the dial tone. Thereafter the subscriber dials the desired number and ringing is provided to the called party by the tone generator

PRINCIPLE

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For making use of this facility, the calling subscriber is required to initially dial the normal phone number of the called subscriber.

When the call is established, no ring-back tone is heard by the calling party. The calling subscriber has then to press the asterik (*) button on the telephone to activate the tone mode and dial extension number, say, ‘1’, within 10 seconds.

In case the calling subscriber fails to dial the required extension number within 10 seconds, the line will be disconnected automatically. Also, if the dialed extension phone is not lifted within 10 seconds, the ring-back tone will cease.

Contd…

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FLOWCHART

Start

Telephone Exchange

Optocoupler

Pic Microcontroller Circuit is receiving signal

DTMF Decoder

Relays 1-8

End 

 

 

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PIC 16F877A MICROCONTROLLER DTMF CM8870 ULN 2003 DRIVER IC RELAYS MPLAB IDE HI-TECH COMPILER PROTEUS (SIMULATOR) BURNER

HARDWARE/SOFTWARE USED

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BLOCK DIAGRAM

DTMFDECODE

RPIC MICRO

CONTROLLER

DRIVER

ARRAY OF 8 RELAYS

INPUT SECTION

CONTROL SECTION OUTPUT SECTION

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CIRCUIT DIAGRAM

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PIC16F877A

Flash memory Re-programmable program storage.

RAM Memory storage for variables.

EEPROMLong term stable memory : Electrically Erasable Programmable Read Only Memory.

I/O portsHigh current Input/Output ports (with pin direction change).

Timers/Counters Typically 3.

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USARTBuilt in RS232 protocol (only needs level translator chip).

CCP Capture/Compare/PWM module.

SSP I2C and SPI Interfaces.

ComparatorAn analogue comparator and internal voltage reference.

ADC Analogue to digital converter.

Special features WDT,SLEEP

ICSPSimple programming using In Circuit Serial Programming.

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MAGNETIC SENSOR

The magnetic sensors are generally used to find out the on hook and off hook condition of the phone

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The DTMF is a popular signaling method between telephones and switching centers

DTMF is also used for signaling between the Telephone network and computer networks

The DTMF signals are Transmitted over a telephone line

Uses speech frequency signals

DTMF signals are the superposition of 2 sine waves with different frequencies

DTMF (Dual tone multi frequency)

The DTMF Keypad

1209 Hz 1336 Hz 1477 Hz

697 Hz 1 2 3

770 Hz 4 5 6

852 Hz 7 8 9

941 Hz * 0 #

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DTMF Generation

697 Hz770 Hz852 Hz941 Hz

1209 Hz1336 Hz1477 Hz

RowSelector

ColumnSelector

Desired Digit + Dual

toneon

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RELAY DRIVER (ULN2003)

ULN2003  is a high voltage and high current Darlington array IC.

It is used to maintain the voltage level between the pic microcontroller and the relay section.

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It contains seven open collector darlington pairs with common emitters.

A darlington pair is an

arrangement of two bipolar transistors,as shown.

RELAY DRIVER FUNCTION

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A relay is a switch which is actuated by an electrical signal. Contemporary electronic relays fall into two main categories: electromagnetic, and solid state.

We are using here single pole double throw relay (SPDT).

Relay requires a D.C. low voltages upto 24V or could be 240V a.c.

12 march 2013

RELAYS

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FUNCTION OF RELAY

Relay when connected

Relay when open

POLE POLE

NCNC

NONO

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HARDWARE

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Till now 60% of the project has been completed and presently the work on the software part is in progress.

CONCLUSION

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PIC Microcontroller [Muhammad Ali Mazidi, Rolin D. McKinlay, Danny Causey]

www.labcenter.com

www.google.com

www.microchip.com

www.youtube.com

REFERENCES

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