Chapter 1

INTRODUCTION

1.1 Introduction of Intercom:

Intercom is one of the most useful devices in urban area. Which is used for

between the house and the shop, between the tree house and the fort, between your kids’

rooms, etc.? It also Keep in touch with your family members from one room to another

and also from outside areas such as the garage.

An intercom is personal telecommunications device which facilitates the exchange

of messages between two or more locations where standard vocal communication would

be difficult or impossible due to distance or obstructions. Basic intercom systems have

been in existence since about a decade into the twentieth century if you only consider

designs reliant on that rather handy invention of Alexander Bell’s; the telephone.

Also the intercom is used for purpose of security at many location, like Door bell,

offices, etc. The Security intercom systems are used to provide voice communications

between two or more locations for security purposes. Security intercom systems are

frequently used between a locked building entrance door and a constantly attended

location in the building, such as a manned security control room.

A simple intercom system consists of one “Master Station” and one “Sub-Station”.

The Master Station is typically located at the point inside the building where

communications is to be received. The Sub-Station is typically located at the point where

the communication is to be originated. For example, in an office building, it may be

desirable to keep the front entrance door locked, and to provide a security intercom system

to allow communications between the outside of the entrance door and the receptionist’s

desk in the lobby. In this situation, the intercom Master Station would be installed at the

receptionist’s desk, and the Sub-Station would be installed on the wall outside of the

entrance door.

1.2 Background History:

Intercom history has come a long way since these were first introduced as commu-

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nication system at the beginning of the 20th century. Descendant of the antique ring system

used on trains, intercom have involved a great deal. In the beginning there was use of

telephone technologies until eventually intercoms transformed into multi-way, multi-post

communications systems and wireless appliances.

Interoffice communication technology existed decades before the intercom. After

Kellogg patented the first Intercommunicating Telephone System in 1894, the ability to

communicate with an employee or broadcast official reports to an entire building took a

big step forward. As the name suggests, early intercoms relied on telephone technology,

but manufacturers continue to improve systems by adopting new tech.

We all know the ritual of ringing at a building entry door and waiting for the buzz

that will grant us access to the premises, after having dutifully identified ourselves.

These entry intercom systems became a part of our everyday life, and helped to improve

home security to a large extent.

1.3 Project Goals:

Nowadays, intercom security solutions no longer require costly maintenance and

heavy hard wiring. Wireless intercoms are now available for easy installation and

integration, to become at once, a part of a home intercom and entertainment system,

a phone intercom, an entry intercom and even ensure that your baby is sleeping tight.

Microphones and speakers can be set almost everywhere, depending on your needs.

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Chapter 2

DEVELOPMENT DESCRIPTION

2.1 Project Design:

The implementation of the project design can be divided in two circuit parts. Both

are the Transceiver, like Transmitter and as well as Receiver.

And each circuit have been divided in two parts which can describe in Transmitter

and Receiver. The two separate devices Unit1 and Unit2 which is shown in fig below in

Block Diagram. In this fig. shows the two PCB Unit (Unit1 & Unit2). The power section

can be supply to both PCB Unit either separate or with together. When signal send to the

PCB Unit1 from MIC1 the PCB1 operate and transmit the signal for Loudspeaker (LSP2).

Now the same operation will be process of PCB Unit2 from MIC2 to loudspeaker (LSP1),

and ground will be used common for both.

2.2 Block Diagram:

Fig.2.1: Block diagram of Intercom using LM386.

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2.3 Circuit Design:

Fig.2.2- Circuit diagram of PCB Unit1 & PCB Unit2 of Intercom.

2.4 Major Equipment:

2.4.1 Multimeter:

This measurement meter is very important device for developing kit. It is measure the voltage, ampere and also continuity check of circuit design wire.

2.4.2 Soldering Iron: This soldering Iron is used for solder of circuit wire through the soldering lid.

2.4.3 NI Instrument Application Software:

This application software used for check the circuit of waveform for exact result.

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2.5 Component Description:

This component can divide into two parts-

Major Component-

Basic Component-

This both component have been divide for specific in work of operation. Like LM386, BC547 Transistor etc.

2.5.1 Major Component:

2.5.1.1 IC LM386:

The LM386 is a power amplifier designed for use in low voltage consumer

applications. The gain is internally set to 20 to keep external part count low, but the

addition of an external resistor and capacitor between pins 1 and 8 will increase the gain to

any value from 20 to 200.

Fig.2.3: LM386 IC Amplifier.

The LM386 is a versatile, small power amplifier designed for use in low voltage

consumer applications. The gain is internally set to 20 to keep external part count low,

but with the addition of an external resistor and capacitor between pins 1-8 the gain can

be set to any value from 20 to 200.

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The inputs are ground referenced and the output automatically biases to one-half

the supply voltage. The quiescent power drain is only 24 milliwatts when operating from

a 6 Volt supply, making the LM386 ideal for battery operation.

Fig.2.4 : (a) Pin diagram, (b) Circuit diagram of LM386 IC Amplifier.

To make the LM 386 a more versatile amplifier, 2 pins (pin 1 and 8) are provided

for gain control. With pins 1 and 8 open the internal 1.35k resistor sets the gain at 20 (26

dB). If a capacitor is placed between pin 1-8, bypassing the built-in 1.35k resistor, the

gain will go up to 200.

If a resistor is placed in series with the capacitor, the gain can be set to any value

from 20 to 200. Gain control can also be done by capacitive coupling a resistor or FET

transistor from pin 1 to the ground.

2.5.1.2 BC547 Transistor:

BC 547 is a general purpose NPN Transistor which us very popularamong hobbyist and engineers alike. The naming or more specifically “numbering” of most transistor can follow any of three system :

1. Pro-Electron (European)

2. Joint Electron Device Council (JEDC)

3. Japanese industrial Standard (JIS)

BC 547 is a name registered under the Pro-Electron numbering System.

A BC547 transistor is a negative-positive-negative (NPN) transistor that is used for

many purposes. Together with other electronic components, such as resistors, coils, and

capacitors, it can be used as the active component for switches and amplifiers. Like all

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other NPN transistors, this type has an emitter terminal, a base or control terminal, and a

collector terminal. In a typical configuration, the current flowing from the base to the

emitter controls the collector current. A short vertical line, which is the base, can indicate

the transistor schematic for an NPN transistor, and the emitter, which is a diagonal line

connecting to the base, is an arrowhead pointing away from the base.

Fig. 2.5: BC 547 Transistor.

There are various types of transistors, and the BC547 is a bipolar

junction transistor (BJT). There are also transistors that have one junction, such as the

junction field-effect transistor, or no junctions at all, such as the metal oxide field-

effect transistor (MOSFET). During the design and manufacture of transistors, the

characteristics can be predefined and achieved. The negative (N)-type material inside an

NPN transistor has an excess of electrons, while the positive (P)-type material has a lack of

electrons, both due to a contamination process called doping.

The BC547 transistor comes in one package. When several are placed in a single

package, it is usually referred to as a transistor array. Arrays are commonly used in digital

switching. Eight transistors may be placed in one package to make layout much easier.

2.5.2 Basic Component:

2.5.2.1 Condenser Microphone:

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Fig.2.6 : Condenser Microphone

Principle: Sound pressure changes the spacing between athin metallic membrane andthe stationary back plate. The plates are charged to a total charge.

Q = CV = εAV

d

Where is the capacitance.

V is the voltage of the biasing battery.

A is the Area of each plate.

d is separation of the plate.

A change in plate spacing will cause a change in charge Q and force a current

through resistance R. This current “images” the sound pressure, making this a “pressure”

microphone.

2.5.2.2 Speaker 8Ω/ 0.5W :

Fig.2.7 :Speaker 8 ohm / 0.5 W (Small/Mini Speaker)

Good performance, generally used for all types of audio projects. The speaker with resistance of 8 ohm and power rating equals to 0.5W.

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Usage/Applications

• General warning alarm for some projects

• Simple amplifier projects

• Will also fit in robots projects

2.5.2.3 Radial Capacitor :

1000uf (micro Farad) 25volt aluminum radial electrolytic capacitor with low leaka-

age current and dissipation factor. Temperature range: 185 to -40 degrees Fahrenheit (+85

to -40 degrees Celsius) and ±20% tolerance. Dimensions: 5/16" by 9/16" (8 mm x 14 mm).

An electrolytic capacitor is a capacitor that uses an electrolyte (an ionic conducting

liquid) as one of its plates to achieve a larger capacitance per unit volume than other types,

but with performance disadvantages. All capacitors conduct alternating current (AC) and

block direct current (DC) and can be used, amongst other applications, to couple circuit

blocks allowing AC signals to be transferred while blocking DC power, to store energy,

and to filter signals according to their frequency. Most electrolytic capacitors are

polarized; hence, they can only be operated with a lower voltage on the terminal marked

"-" without damaging the capacitor. This generally limits electrolytic capacitors to supply-

decoupling and bias-decoupling, since signal coupling usually involves both positive and

negative voltages across the capacitor. The large capacitance of electrolytic capacitors

makes them particularly suitable for passing or bypassing low-frequency signals and

storing large amounts of energy. They are widely used in power suppliesand for

decoupling unwanted AC components from DC power connections.

Fig.2.8 : Redial Electrolite Capacitor

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2.5.2.4 Ceramic capacitor :

A ceramic capacitor is a fixed value capacitor in which ceramic material acts as the

dielectric. It is constructed of two or more alternating layers of ceramic and a metal layer

acting as the electrodes. The composition of the ceramic material defines the electrical

behavior and therefore applications. Ceramic capacitors are divided into two application

classes:

Class 1 ceramic capacitors offer high stability and low losses for resonant circuit

applications.

Class 2 ceramic capacitors offer high volumetric efficiency for buffer, by-pass and

coupling applications.

Fig.2.9 : Ceramic capacitor

2.5.2.5 Resistor :

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Fig.2.10: Resister

A resistor is a passive two-terminal electrical component that implements electrical

resistance as a circuit element.

The current through a resistor is in direct proportion to the voltage across the

resistor's terminals. This relationship is represented by Ohm's law:

I = V \over R

Where I am the current through the conductor in units of amperes, V is the

potential difference measured across the conductor in units of volts, and R is the resistance

of the conductor in units of ohms.

The ratio of the voltage applied across a resistor's terminals to the intensity of current in

the circuit is called its resistance, and this can be assumed to be a constant (independent of

the voltage) for ordinary resistors working within their ratings.

2.5.2.6 Potentiometer :

Potentiometers (or pots, as we’ll call them) are incredibly versatile devices. They

can act as voltage dividers, or as variable resistors. There are tons of resources on the web

about pots, so what I’m going to cover here are the basic types, operation, and uses

specifically for guitar audio.

Pots come in all sorts of shapes and sizes. The most common type we use in pedals

and amps are usually of the 24mm or 16mm round metal can type. There are also multi-

gang pots (which stack multiple independent pots on one shaft), slider pots, trimmer pots,

etc.

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In the case of a standard pot, as shown above, we have a round case with three

connectors and a shaft that turns. Here’s what it looks like in a schematic:

Fig.2.11 :Potentiometer or Variable Resister(Pot Type).

The pot has three lugs and by convention they are numbered 1, 2, and 3. Pin 2 is

called the wiper. These numbers map to the schematic symbol like this:

Fig.2.12 : Potentiometer Pin Mapping.

Potentiometer: as a trimmer resistor. Here’s what the schematic looks like:

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Fig.2.13 Schematic of Potentiometer

Here we have a potentiometer where lug three is the input, and lugs 1 and 2 are

connected together to form the output. As you turn the shaft, the resistance decreases. You

are forming a simple resistor whose value is variable.

Fig.2 14 Schematic in Increasing mode

Well that certainly works the same way. But what happens if the potentiometer fails for some reason (age, poor quality, dirty, etc.). If the wiper (which is the rotating part of the component and probably most prone to failure) shorts out, it will let the full amount of signal through.

Fig.2.15 : Potentiometer or Variable Resister(Trimmer Type).

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By attaching lug 1 to lug 2, we are building in a “fail-safe.” This ensures that the

circuit is never completely open—there will always be some resistive path in case the

wiper goes south.

A Volume Control

Now let’s look at a more interesting example: a volume control. Assume we have a

simple stomp box that does distortion or overdrive or something else interesting. At the

end of the circuit we have an output. Wouldn’t it be nice to control the output level (or

volume) of the pedal.

Fig.2.16 Schematics of Variable Resistor

Here we have the signal going to lug 3, the output coming out of lug 2, and lug 1

connected to ground. To see how this works, assume you have the shaft turned all the way

clockwise, i.e. turned all the way “up”. In this configuration, there is little if any resistance

across lugs 2 and 3 so the maximum output signal goes to the output.

As you turn the shaft counter-clockwise, the resistance across 2/3 increases and the

resistance across 1/2 decreases. This causes more of the signal to be dumped to ground.

This dumping essentially sends the signal into oblivion, thereby lowering the overall

output level.

So if you think about it, you are never really turning the volume up! The volume or

level in the circuit is always running at full tilt. What you are doing the above “volume”

control is actually attenuating (making smaller) the full volume that was there to begin

with.

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Chapter 3

WORK PROCEDURE

3.1 PROCEDURE:

The Kit Design mainly divided into two parts, which arranging in separated two

both hardware and circuit check on the software application (like, NI Instrument). In this

two PCB(Unit1 and Unit2) which construct separately. After that arrangement of

component and sufficient material for constructing the PCB and circuit design, decided the

circuit design on PCB. The Circuit Design makes over the use of Express PCB Software

which is very easy for designing to circuit. The printed designed circuit paste on the PCB

for printing of circuit strip wire and it remove the all remaining metal of PCB except the

wire strip metal by chemical of Ferric Chloride. After that Soldering process will started

according to circuit diagram.

There are mentioned in broadly process follows as,

3.1.1 COMPONENT REQUIREMENTS :

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3.1.1.1 Major Components

Condenser Microphone Speaker 8 ohm / 0.5 W (Small/Mini Speaker) BC547 Transistor LM386 IC Amplifier

3.1.1.2 Basic Components

LED Red Resistor Capacitor Variable Resistor PCB Board Two Pole Switch

3.1.2 CONSTRUCTION EQUIPMENT: Soldering Iron Soldering Lead Multimeter PCB Design Software Etching Chemical(Ferric Chloride) Terminal Drilling

3.2 PCB DESIGN:

The PCB design on the Express PCB software is a very much easy to design the circuit for wiring strip. In which arrangement the component of size of padding and wiring whose will place for better design.

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Fig.3.1 Normal PCB Circuit Design

3.2.1 PCB Etching Process:

Fig.3.2 PCB Etching Process

3.2.2 Terminal Drilling:

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Fig.3.3 PCB Terminal Padding Drill

3.2.2 PCB Soldering Process:

Fig.3.4 PCB Circuit Soldering Process

Chapter 418

OPERATION

4.1 CIRCUIT OPERATION :

The circuit operation can divided in three groups, first Power section, second Filter

section, and third Amplifying section. These are all section describe in following.

4.1.1 Power section:

The power circuit consist the capacitor, resistor, and LED which operate through the

9V Battery. Which is shown in below fig.3.1?

In this fig. 1kΩ resistor R15 connected in series with the LED1 and parallel with

capacitor. Capacitor C4 (1000µf) and capacitor C5 (0.33µf) connected in parallel and both

capacitor use for more voltage charge for the next circuit. Because when LED glow then

voltages decreases across the LED1.

Fig. 4.1 : Power source circuit.

So capacitor 1000µf maintains the voltage for next circuit if voltage decreases

across the LED.In this process voltage supply continuous in manner as per requirement.

4.1.2 Low Pass filter section :

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In this section signal is filtered by combination of resistor R2 and capacitor C2.

This circuit is known as Low Pass Filter which is shown in below fig. 3:2 .

Fig.4.2 : Low pass filter circuit.

The circuit is a RC low pass filter, it is use for passes low frequency AC signal, but

reduces or stop high frequency signals. The reason that these circuit react to the frequency

of a signals is because the reactance Xc of a capacitor depends on the frequency (f).

Xc = 1

2 πfc

In simple terms, at high frequency Xc is very small and so the capacitor behaves

like a short circuit. On the other hand at low frequency Xc is very large, and so the

capacitor behaves like an open circuit. In this low pass filter fig.4 looks like short circuit,

and therefore shorts the output signals, not letting high frequencies. We can find this

frequency by simply solving this equation for the frequency.

f = 1

2 πRC

Given the value of R2= 390Ω and C1= 3.3nf as shown in fig. 2, the corner

frequency is therefore.

f = 1

2 πRC= 1

6.28 ×390 × 0.0000033 = 123.6635 Hz

4.1.3 First stage Amplifying Signal :

In this stage Transistor BC547 use for Amplifying the signal incoming from low

pass filter. Here low-Level signal isamplified by the amplifier built around transistor T1

which is shown in below fig. 3.4.

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Fig. 4.3: Amplifier circuit Collector-Emitter feedback bias.

In this circuit consist of one transistor, resistor, and capacitor. Here operation with

the collector-emitter feedback bias in which further improve the level of stability, the

emitter resistance is connected in the collector bias circuited to provide both collector and

emitter feedback. According to fig.2 circuit there mention RC=R12= 3.3k should have a

minimal value. For example, if the emitter ofT1 is connected to ground, the value of R12

could be as low 1 kilo-ohm.

The resistor R11=Rib=470K it is selected such that the voltage between the

collector and emitter of T1 is approximately half the power supply voltage and use of

capacitor C18 is optional which is shown in fig.2. Also R1 resistor shows in fig.2.1 the

used for order to make the input circuit less vulnerable (pregnable) to electromagnetic

noise. Because, preamplifier may exhibit instability at very high frequencies. According to

fig.2.capacitor C2 and C18 use for block the DC component but allow AC signal to pass

and by variable potentiometer VR1 adjust the signal.

In this circuit analysis applying KVL to the base circuit shown fig.3.5 we have,

Vcc - (Ic + Ib)Rc – IbRb –Vbe –IeRe =0

Vcc – Vbe = (1+β)IbRc + IbRb + (1+β)IbRe

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Ib = Vcc−Vbe

Rb+ (1+ β ) ( Rc+ℜ )¿

¿

Ib = Vcc−Vbe

Rb+ β(Rc+ℜ)

FromCollectorCircuit applying KVL to collector circuit we have,

Vcc –(Ic + Ib)Rc- Vce-IeRe =0

Therefore,

Vce = Vcc – Ie(Rc + Re)

Fig.4.4 First Stage Amplifying Circuit

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4.1.5 Second stage Amplifier :

The first stage circuitamplify the signal and pass through capacitor C17 to the

second stage LM386 IC Amplifier. This type of amplifier is an audio amplifier and which

amplifier built around 200gains which are enough to work with the condenser

microphones. The amplified signal fed to the speaker (LSP2) by audio amplifier.

Fig.4.5 Second Stage Amplifying Circuit

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Chapter 5

Result and Discussion

5.1 RESULT:

The implementation of Realization of INTERCOM USING LM386 is done

successfully. The communication is properly done without any interference between

different circuit section in the design. Design is done to meet all the specifications and

requirements.

Circuit is implemented by several methods like, designing pcb, soldering ect. and

implemented on board. It can be concluded that the design implemented in the present

work provide portability, flexibility and the data transmission is also done with low power

consumption.

Fig.5.1 Final Project kit24

5.2 APPLICATION :

In this process an electronic device has been very useful for the communication. As

we know that, Intercom is one of the most useful devices in urban area. Which is used for

between the house and the shop, between the tree house and the fort, between your kids’

rooms, etc. It also Keep in touch with your family members from one room to another and

also from outside areas such as the garage.

CONCLUSION

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The project titled ‘INTERCOM USING LM386’ was successfully completed. Our

project provides an efficient method for communication in between two devices . The

system is easy to implement and has wide applications in the areas where large amount of

usage can be.

BIBLOGRAPHY:

[1]http:/wild-bohemian.com/electronics26

[2]http:/discovermagazine.com/2009/mar/24-leds-light-times-square-but-can-they-light-

your-office

[3]http:/en.wikipedia.0rg/wiki/sensor

[4]http:/www.fi.edu./fellows/fellow2/apr99/soundvib.html

[5]http:/www.wikipedia.org/wiki/Audio_Amplifier

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