2-Way Wired Intercom

8/10/2019 2-Way Wired Intercom

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CHAPTER ONE

1.0 INTRODUCTION

Intercom is a private telecommunication system that

allows typically two or more locations to communicate with

each other like telephone does.

This project (two-way wired intercom) consists of two

intercom stations linked to each other using wire. It uses full

duple mode ! a process where"y one can transmit and

receive voice calls simultaneously which made the

transmission medium to "e four wires "etween the two

nodes and typical headsets on the nodes (separate speaker

and microphone# good isolation from sound coming from

speaker to the mic element).

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1.1 POINTS RELATED TO INTERCOM SYSTEM

1.1.1 POINT-TO-POINT (P-P)

$oint-to-$oint is a direct# one-way# simple

communication "etween two intercom stations or "etween

stations and interfaces. It is the "asis of communication in

matri intercom systems and is esta"lished "y activating a

station key. The receiving station does not have to take any

action to receive the incoming call. %owever# a talk key at

the receiving station must "e pressed to answer.

1.1.& PARTY LINE (PL)

$arty-line communication (sometimes called

'onference# line# net# or ring) is a group of two or more

stations communicating with each other in a two-way# full

duple mode. ach station must activate the listen key to

the desired party line to listen and the talk key to talk. $arty

line re uires two actions to esta"lish a communication path

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(e.g.# activating "oth a talk key on the sending station and a

listen key on the receiving station). *tations are dynamically

added and su"tracted from a party line as users activate thetalk and listen keys. + party line is intended for use in a

conference with a signi,cant amount of "ack and forth

communication "etween users.

1.1. INTERRUPTIBLE FOLD BACK (IFB )

Interrupti"le old "ack allows a user to hear one audio

source# which may then "e interrupted "y another audio

source. + typical application is in "roadcasting where talent

hears program audio in his ear piece and a producer can

interrupt that audio to o/er the talent information and

instructions.

1.1. ISOLATION (ISO)

The isolation (I* ) function allows a user to speak

privately to another user. I* is generally used to provide

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private communication "etween two mem"ers of a party

line. In "roadcasting# I* is often used "y a video operator to

speak privately to one cameraman who is one of manycameramen on the camera party line. This was called

'amera Isolate as it was ,rst used to remove an individual

camera from a conference to allow private communications.

Typically# this works in the following way2 The person who

needs to interrupt presses a "utton or a key# and there is

esta"lished a private two person conversation with the

desired person. 3pon releasing the key# the two participants

are returned to whatever conversation(s) they were a part of

previously.

1.1.4 FIXED GROUP

+ i ed 5roup is a group of intercom stations and

interfaces. + user who has a talk key programmed for a , ed

group is a"le to simultaneously talk to everyone who is part

of that , ed group. + , ed group di/ers from a party line in

that the group6s mem"ership is set "y the con,guration of

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the intercom system (not changed dynamically). + , ed

group is intended to "e used for one-to-many type

communication.

1.1.7 TALLY

Tally is a signal sent for the purpose of indicating status

for a particular purpose. The sound of your telephone ringing

can "e descri"ed as a tally. In an intercom panel with

multiple channels# it can "e a visual signal to indicate to

which station a calling voice "elongs. It can "e used to

indicate that a particular function is not availa"le due to a

con8ict - just like the "usy signal you get when calling the

radio station to try and "e the tenth caller and win a year

long supply of cat litter.

1.& APPLICATION

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Two-way wired intercom system can "e used as an

intercom and door phone. ne can use an intercom system

from house to house# or from house to gate9door to screenvisitors.

:any productions which needs co-operation of more

than a few people need special intercoms that cover many

users. Intercom systems used in T; and stage productions

are usually headset type intercoms connected to one line

using party line arrangement. The primary use of this type of

system is in live or media productions where (for e ample)

the video director speaks to the camera operators# or where

the stage manager speaks to the stage hands and lighting

operator# etc.

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CHAPTER TWO

&.0 LITERATURE REVIEW

In the 1ell "oth independently designed devices that could

transmit speech electrically (the telephone). >oth men

rushed their respective designs to the patent o?ce within

hours of each other. +le ander 5raham >ell patented his

telephone ,rst. lisha 5ray and +le ander 5raham >ell

entered into a famous legal "attle over the invention of the

telephone# which >ell won.

The telegraph and telephone are "oth wire-"ased

electrical systems through which this project ( Two-way

w !"# $%"!&o' ) comes into "eing.

;arious types of components are used in "uilding the

intercom. This chapter e plains "rie8y some of their "asicfeatures.

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&.1 RESISTORS

+ resistor is an electronic component that opposes the

8ow of electric current "y producing a voltage drop across its

terminals# in accordance with ohm6s law. There are & types of

resistors@

i ed resistor ;aria"le resistor

>oth of them have their value of resistance written on

them using colour coding representation.

&.1.1 FIXED RESISTORS

i ed resistors maintain constant values of resistance

with small percentage of variation. The values can "e

determined through colour coding. ;arious colours are

chosen to represent various values. The ,rst and second

colours show the ,rst and second digits respectively. The

third colour shows the powers of ten while the last colour is

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the tolerance "and which shows the tolerance range of the

resistor.

&.1.& RESISTOR COLOUR CODING

Ta " *

' A 3B 1 st CI5IT & nd CI5IT D .

E B *

T A B+D'

>lack --- --- 0 --->rown 1 1 10 1FBed & & 10 & &Frange 10 ---

Gellow 10 ---5reen 4 4 10 4 --->lue 7 7 10 7 ---;iolet = = 10 = ---5ray < < 10 < ---Hhite 10 ---5old --- - --- 4F*ilver --- --- --- 10FDo colour --- --- --- &0F

Tolerance

1 st digit & nd digit no. of Jeros

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ig &.0a S&+"'a% & Sy' o o, a R" %o!

ig &.0 (") & !&. % y' o o, a !" %o!

&.1. VARIABLE RESISTORS

They can "e altered to give di/erent values from

particular resistors as desired. The variations in resistance

can either change current value or voltage settings.

ig &.1 Sy' o o, Va! a " R" %o!

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&.& DIODES

+ diode is a semiconductor component that restricts the

direction of 8ow of charge carriers in one direction.

ssentially# it allows an electric current to 8ow in one

direction "ut "locks it in the opposite direction# until when it

reaches the reverse "reakdown voltage of the diode. Their

various reverse voltage ($I;) that can force conduction in the

opposite direction are always contained in a semiconductor

data "ook. ample# diode ID4 & has a $I; of 700;# +

ma imum forward current.

There are some diodes that emit light in colours of red#

yellow# and green when they are "iased in the forward

direction. They are called Aight mitting Ciode (A C).

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Fig. 2.2a Schematic symbolof a diode

Fig. 2.2b Circuit symbol of a diode


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&. CAPACITOR

+ capacitor is an electronic component that has two

conductors separated "y a dielectric and it is used to store

charges in an electric ,eld. There are two types of

capacitors.

The polariJed capacitor The non ! polariJed capacitor

&. .1 POLARI/ED CAPACITOR

The polariJed capacitor (like electrolytic capacitor) has

two terminals marked positive and negative respectively.

'apacitors allow the +' signal to pass through them easily.

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+ -

Fig. 2.2c Circuit symbol of Light Emitting Diode (LED)


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Hhen connected in series with the signal line# their

reactance to the +' signal disappears as the fre uency

increases.

&. .& NON 0 POLARI/ED CAPACITOR

The non ! polariJed capacitor (like ceramic capacitor)

have either side marked. Their values are always very low.

&. TRANSFORMER

The transformer is an electric component that has two

separate windings (the primary and secondary windings)

used in transferring +' voltage from the primary coil to the

secondary coil. The transformer can either "e a step up or a

step down. The one used in this design is a step down

transformer.

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Fig. 2.3a Circuit symbol of olarized ca acitor

Fig. 2.3b Non polarizedcapacitor

+ -


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The step ! up transformer changes the voltage to a high

value from a low source input while the step ! down

transformer changes the voltage to a low value from a highsource input. $ower remains the same in "oth types of

transformation at the primary and secondary coils. The step

! down transformer has "een used in this design to reduce

the &&0; +' to a 1&; +' output value.

&.4 SPEAKER

It is a mechanical transducer that converts an electrical

signal to sound. It has a magnetic core that forms the "ase

of the speaker and a mechanical part called the diaphragm.

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*econdary coil$rimary

Fig. 2.4 Circuit diagram of a transformer

+' Input ;oltage


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In any electrical system# changing signal esta"lishes a

changing magnetic ,eld. This principle is used in pushing

the core at a speaker to move the diaphragm in or outdepending on the applied signal direction.

&.7 TRANSISTORS

+ transistor is an active component# a device capa"le of

producing an output signal with more power in it than the

input signal. It is the essential ingredient of every electronic

circuit# from the simplest ampli,er or oscillator to the most

ela"orate digital computer.

+ transistor has three terminals and it is divided into

two namely (D$D and $D$)# with properties that meet the

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+

-

ig &.4 Sy' o o, a$ " "&%!o$ &


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following rules for D$D transistors (for $D$ simply reverse all

polarities).

This collector must "e more positive than the emitter. The "ase ! emitter and "ase ! collector "ehaves like

diodes.

Dormally the "ase ! collector diode is reverse ! "iased#

i.e.# this applied voltage is in the opposite direction to easy

current 8ow. +ny given transistor has ma imum values of I'#

I># and ;' that cannot "e e ceeded. There are also limits

such as power dissipation (Ic ;c )# temperature# ;> # etc

that one has to keep in mind. Hhen the a"ove rules are

o"eyed# I' is roughly proportional to I> and can "e written as

I' K hf I> K >Is

Hhere hf # the current gain (also called "eta) is typically

a"out 100.

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collector

emitter

"ase

emitter

"ase

collector


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&.= INTEGRATED CIRCUIT (IC)

The evolution of I' reduces the comple ity of electronic

circuit. *ome active and passive discreet components are

integrated into a module called chip. There are three types

of I' used in this work# namely2 the 444 timer I' which is

used to generate the tone# 01= which are used to generate

a triggering pulse to the transistor and TC+&00 which is the

audio ampli,er.

>elow is the diagram showing the pin con,guration of

the I'

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$D$ transistorD$D

Fig. 2.6 Transistor symbol


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Fig 2.7 P $ Co$12.!a% o$ o, 34*5 #"&a#"


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&.< RELAY

The relay is an electromechanical switch that makes

and "reaks contact when current passes through the coil.

Belays are rated in operating voltage and the contact

current. The contact is for *$C= (single pole# dou"le thro).

There are many varieties# including Llatching6 and stepping

relays. The latter provided the cornerstone for telephoneswitching stations. Belays are availa"le for C' and +'

e citation and coil voltage from 4 volts up to 110 volts are

common.

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Coil

'onta

ig. &.< S&+"'a% & # a2!a' o, a


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CHAPTER THREE

.0 RESEARCH6METHODOLOGY

.1.0 PRINCIPLE OF OPERATION

The principle of operation of this work (Two-Hay Hired

Intercom) will "e properly understood "y taking the analysis

of the stages that make up the entire system. The complete

circuit is run on 7 volts .4+% "attery. The "attery is where

all the su" circuits such as the audio ampli,er and the tone

generator took their source. Hhen the circuit is powered "y

turning on the switch# all the su" circuits will "e set to

receive power from the source as the phone handle is lifted

up e cept the tone generator circuit which is powered

immediately so that any tone received from UNIT 7 will "e

ampli,ed to tell the user of UNIT * that UNIT 7 wants to

esta"lish conversation. +ny of the users will tell the second

user that he wants to esta"lish conversation "y pressing the

ringer "utton. This sends a tone signal to the phone and

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conversation is successfully esta"lished when the two users

must have picked up the phone.

The handle of the phone is where the microphone (mouth

piece) and the ear piece are located. +ny sound or speech

made "y any of the users is picked up "y the microphone as

mechanical vi"ration and converted to electrical signal that

has a voltage which its amplitude varies linearly with time

(alternating)# and a fre uency which is a replica of the

fre uency of vi"ration. This electrical signal has low

amplitude and it is ampli,ed "y the pre ampli,er "uilt with

the transistor ('1


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CHAPTER FOUR

.0 DESIGN AND CONSTRUCTION

This chapter e plains the set of methods# principles and

standards used to accomplish this project (Two-way wired

intercom). It should "e noted that there are a"out nine

"locks that make up the entire system of this project. our of

these "locks make up an individual unit (i.e. four "locks for

unit 1 and another four for unit &)# while the remaining one is

"eing shared "y the two as shown "elow.

UNIT * UNIT 7

22OUTPUT

DE !CE

TONE

"ENE#$TO#

$UD!O!NPUT%OU#CE

$UD!O

$&P'!F!E#&ED!U&

TONE

"ENE#$TO#

$UD!O!NPUT%OU#CE

OUTPUT DE !CE

$UD!O

$&P'!F!E#


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ig .0 B o&8 D a2!a' O, Two-Way W !"# I$%"!&o'9

The e planation of standards used and calculations

made as regards to the e ecution of this project will "e

properly understood "y taking it "locks.

.1 TONE GENERATOR

This "lock generates the ringing tone of the intercom.

Binging tone is an audio tone that signals the user of one of

the two phones (e.g. unit 1) that the other user (unit &)

wants to esta"lish a conversation in the network. The

process of generating the ringing tone involves researching

on the datasheet of top semiconductor manufacturers# to get

a suita"le I' (integrated circuit) for it. The semiconductor

guide of Toshi"a shows that the popular timer I' D 444 is

suita"le since it can "e connected to function as an asta"le

multivi"rator and generate an audio tone. This I'# D 444 as

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used in this project is connected as an asta"le multivi"rator

to generate an audio fre uency tone of 40%E. The pin out

of the I' and the test circuit is as shown "elow.

ig .1 P $ O.% o, N"::: T '"! IC

.1.1 APPLICATION CIRCUIT

ig .& A;; &a% o$ C !&. % ,o! %+" ::: T '"!

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CC

Di(c)a*g

T)* ()ol,

Con *ol ol ag

"*o n,

T*igg *

O /

# (


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The 444 monolithic timing circuits is a highly sta"le

controller capa"le of producing accurate time delays# or

oscillation. In the time delay mode of operation# the time isprecisely controlled "y e ternal resistors (B + and B >) and

capacitor ('). or a sta"le operation as an oscillator# the free

running fre uency and the duty cycle are "oth accurately

controlled with two e ternal resistors and one capacitor. The

circuit may "e triggered and reset on falling waveforms# and

the output structure can source or sink up to &00m+.

*peci,cation from producer shows that the I' operates at a

voltage range of 4 to 14 volts.

'+A'3A+TI D

The fre uency of oscillation is calculated "y using the

formula "elow.

T1 K Time f D K 0.7 (B A MBB) '

T& K Time f K 0.7 (B B) '

Total Time(T) K T1 M T&

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K 0.7 (B A M &BB) '.

rom the a"ove e pression# one can easily compute the

fre uency since it is the inverse of time. %ence K 19T

(%ertJ).

K 0.7 (1000 M & (14000) 100 10 -

T K &.1 < 10 -

K N.1 < 10-

K 74. < 74%J

The fre uency of the oscillator is set to 74 hertJ "y

using 1000 ohm as the B A and 14000 ohms as B B and 100

nanofarad as '.

.& AUDIO INPUT SOURCE

This "lock contains the transducer which converts the sound

(speech) in form of mechanical vi"ration to electrical signal.

The electrical signal has a voltage which its amplitude varies

linearly with time. The transducer in this "lock is a capacitor

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(condenser) microphone. 'ondenser :icrophones are

electronic component which stores energy in the form of an

electrostatic ,eld. The term condenser is actually o"solete"ut has stuck as the name for this type of microphone# which

uses a capacitor to convert acoustical energy into electrical

energy. 'ondenser microphones re uire power from a

"attery or e ternal source. The resulting audio signal is a

stronger signal than that from a dynamic. 'ondensers also

tend to "e more sensitive and responsive than dynamics#

making them well-suited to capturing su"tle nuances in a

sound. They are not ideal for high-volume work# as their

sensitivity makes them prone to distort.

.&.1 HOW CONDENSER MICROPHONE WORKS

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ig . C!o -S"&% o$ o, a Ty; &a Co$#"$ "!

M &!o;+o$"

+ capacitor has two plates with a voltage "etween

them. In the condenser microphone# one of these plates is

made of very light material and acts as the diaphragm. The

diaphragm vi"rates when struck "y sound waves# changing

the distance "etween the two plates and therefore changing

the capacitance. *peci,cally# when the plates are closer

together# capacitance increases and a charge current occurs.

Hhen the plates are further apart# capacitance decreases

and a discharge current occurs. + voltage is re uired across

the capacitor for this to work. This voltage is supplied either

"y a "attery in the microphone or "y e ternal phantom

power.

.&.& MICROPHONE IMPEDANCE

Hhen dealing with microphones# one consideration

which is often misunderstood or overlooked is the

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microphoneOs impedance rating. $erhaps this is "ecause

impedance isnOt a PcriticalP factor@ that is@ microphones will

still continue to operate whether or not the "est impedancerating is used. %owever# in order to ensure the "est uality

and most relia"le audio# attention should "e paid to getting

this factor right.

.&. WHAT IS MICROPHONE IMPEDANCEuilding this project successfully has "een a great

challenge to me# though it has e posed me to proper under

standing of "asic principles electronics components. This

project %wo - way w !"# $%"!&o' is a communication

system which can "e used as an intercom and door phone.

ne can use an intercom system from house to house# or

from house to gate9door to screen visitors# and also in o?ces

(e.g. "etween the o?ce of the % C and the C +D). It o/ers

a great advantage running with a rechargea"le "attery

which reduces cost. +lso# the system is very easy to install.

Its disadvantages include "eing a stationary unit# which

means not to "e carried a"out like we do with our 5*:

phones. +lso# it is wired and therefore any mechanical

damage to the wire interrupts esta"lishment of conversation.

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4.10 REMARK

The model design in this project is compara"le with

those from the market and could "e in organisations.

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4.&0 REFERENCES

4.&.1 Telecommunication ngineering "y ;. .

Idigo# I.I Dsionu# '. . haneme (&00 )

4.&.& + Te t"ook of lectrical Technology >.A. Theraja and +. . Theraja. ThoroughlyBevised Twenty ! Third Bevised dition &00&

4.&. lectronic and lectrical ngineering#$rinciples and $ractice (*econd dition) >yAionel Harnes 1 -1

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2-Way Wired Intercom