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CHAPTER-1

Electrical Equipments Control through Sound

The electrical equipment control through sound circuit is a circuit

which operates by sound from a remote point. When the circuit receives a

sound from anywhere, the first output of the circuit is turned on. If another

one sound receives, the second output is switched off. For example, fan,

fluorescent light, TV and other appliances can be switched on (or) off by

sound. This circuit can be used by changing individual situations.

In this project, we can ON or OFF the electrical equipments through

sound, for example, when for the first time we clap with our hands, the light

circuit enabled through relay connected to the light and the light is ON. For

the next time when we clap the hands, the circuit switches OFF the relay

and the bulb is OFF.

1.1 BLOCK DIAGRAM AND OPERATION

In this project, the clap signal is received by sensor ( microphone )

which convert it into electric signal and this signal is further given to the

multi vibrator which turns ON and OFF the relay and load (bulb), when

the relay is ON, bulb will be ON and when relay is at OFF state, bulb will also

be switched OFF.

Block diagram is contains on major parts such as power supply, microphone,transistors, relay, connected load (bulb) as shown below.

1

INTRODUCTION

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SIGNAL

INPUT (AC ) 220 VOLTS

BLOCK DIAGRAM

1.2 Materials used in Project

The following materials are used in this project;

i. Printed circuit board.

ii. Power Supply ( Transformer, Diode, Rectifier, Filter, capacitors).

iii. Resistors and variable resistors.

iv. Transistors ( as multi vibrator ).

v. Micro Phone.

vi. Relay and LED.

1.3 PRINTED CIRCIUIT BOARD

A printed circuit board, or PCB, is used

to mechanically support and

electrically connect electronic

components using conductive

pathways, tracks or signal traces

etched from copper sheets laminated

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MICRO-PHONE

POWERSUPPLY(AC TO

BULBOR

LOAD

MULTI-VIBRAT

OR

RELAY

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onto a non-conductive substrate. It is also referred to as printed wiring

board (PWB) or etched wiring board.

A PCB populated with electronic

components is a printed circuit assembly(PCA), also known as a printed circuit board

assembly or PCB Assembly (PCBA). Printed

circuit boards are used in virtually all but

the simplest commercially produced

electronic devices.

Alternatives to PCBs include wire wrap and point-to-point construction. PCBs

are often less expensive and more reliable than these alternatives, though

they require more layout effort and higher initial cost. PCBs are much

cheaper and faster for high-volume production since production and

soldering of PCBs can be done by automated equipment. Much of the

electronics industry's PCB design, assembly, and quality control needs are

set by standards that are published by the IPC organization.

After the printed circuit board (PCB) is completed, electronic

components must be attached to form a functionalprinted circuit assembly,

or PCA. In through-hole construction, component leads are inserted in holes.

In surface-mountconstruction, the components are placed on pads or lands

on the outer surfaces of the PCB. In both kinds of construction, component

leads are electrically and mechanically fixed to the board with a molten

metal solder.

After the board has been populated it may be tested in a variety of

ways:

While the power is off, visual inspection, automated optical

inspection, component placement, soldering, and inspection are

commonly used to maintain quality control in this stage of PCB

manufacturing.

While the power is off, analog signature analysis, power-off testing.

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While the power is on, in-circuit test, where physical measurements

(i.e. voltage, frequency) can be done.

While the power is on, functional test, just checking if the PCB does

what it had been designed to do.

When boards fail the test, technicians may de solder and replace

failed components, a task known as rework.

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CHAPTER-2

5

POWER SUPPLY

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2.1 INTRODUCTION

In this project the main part is power supply, which converts A.C

power supply 220 volt to 12 volt D.C supply. The term of power supply is

most commonly applied to electric power converters that convert one form

of electrical energy to another, though it may also refer to devices that

convert another form of energy to electrical energy.

Every power supply must obtain the energy it supplies to its load, as well as

any energy it consumes while performing that task, from an energy source.

Depending on its design, a power supply may obtain energy from:

A power supply may be implemented as a discrete, stand-alone device or as

an integral device that is hardwired to its load. Examples of the latter case

include the low voltage DC power supplies that are part of desktop

computers and consumer electronics devices.

A power supply is a hardware component that supplies power to an

electrical device. It receives power from an electrical outlet and converts the

current from AC (alternating current) to DC (direct current), which is whatthe computer requires. It also regulates the voltage to an adequate amount,

which allows the circuit to run smoothly without overheating. The power

supply an integral part of any circuit and must function correctly for the rest

of the components to work.

You can locate the power supply on a system unit by simply finding the

input where the power cord is plugged in.

While most appliances have internal power supplies, many electronic

devices use external ones. For example, some monitors and external hard

drives have power supplies that reside outside the main unit. These power

supplies are connected directly to the cable that plugs into the wall. They

often include another cable that connects the device to the power supply.

Some power supplies, often called "AC adaptors," are connected directly to

the plug (which can make them difficult to plug in where space is limited).

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Both of these designs allow the main device to be smaller or sleeker by

moving the power supply outside the unit.

Since the power supply is the first place an electronic device receives

electricity, it is also the most vulnerable to power surges and spikes.Therefore, power supplies are designed to handle fluctuations in electrical

current and still provide a regulated or consistent power output. Some

include fuses that will blow if the surge is too great, protecting the rest of

the equipment. After all, it is much cheaper to replace a power supply than

an entire computer.

In this project a built in power supply provided. The Power supply contains

on many parts such as under;

i. Transformer.

ii. Rectifier ( semi conductor diodes ).

iii. Filter.

iv. Capacitors.

2.2 Transformer

Transformer is a device that transfers electrical energy from one

circuit to another through inductively coupled conductors. A varying current

in the first or primary winding creates a varying magnetic flux in the

transformer's core and thus a varying magnetic field through the secondary

winding. This varying magnetic field induces a varying electromotive force

(EMF), or "voltage", in the secondary winding. This effect is called inductive

coupling.

If a load is connected to the secondary, current will flow in the

secondary winding, and electrical energy will be transferred from the

primary circuit through the transformer to the load. In an ideal transformer,

the induced voltage in the secondary winding (Vs) is in proportion to the

primary voltage (Vp) and is given by the ratio of the number of turns in the

secondary (Ns) to the number of turns in the primary (Np) as follows:

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By appropriate selection of the ratio of turns, a transformer thus

enables an alternating current (AC) voltage to be "stepped up" by making Ns

greater than Np, or "stepped down" by making Ns less than Np.

In the vast majority of transformers, the windings are coils wound around a

ferromagnetic core, air-core transformers being a notable exception.

Basic Principle of TransformerIn ideal transformer, the secondary current arises from the action of the

secondary EMF on the (not

shown) load impedance.

The transformer is based on two

principles:

first, that an electric current can

produce a magnetic field (Electro

Magnetism) and second, that a

changing magnetic field within a

coil of wire induces a voltage across the ends of the coil ( Electromagnetic

Induction). Changing the current in the primary coil changes the magnetic

flux that is developed. The changing magnetic flux induces a voltage in the

secondary coil.

An ideal transformer is shown in the adjacent figure. Current passing

through the primary coil creates a magnetic field. The primary and

secondary coils are wrapped around a core of very high magnetic

permeability, such as iron, so that most of the magnetic flux passes through

both the primary and secondary coils. If a load is connected to the

secondary winding, the load current and voltage will be in the directions

indicated, given the primary current and voltage in the directions indicated.

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The voltage induced across the secondary coil may be calculated

from Faraday's law of induction, which states that:

Where Vs is the instantaneous voltage, Ns is the number of turns in the

secondary coil and is the magnetic flux through one turn of the coil. If the

turns of the coil are oriented perpendicularly to the magnetic field lines, the

flux is the product of the magnetic flux density B and the area A through

which it cuts. The area is constant, being equal to the cross-sectional area

of the transformer core, whereas the magnetic field varies with time

according to the excitation of the primary. Since the same magnetic fluxpasses through both the primary and secondary coils in an ideal

transformer, the instantaneous voltage across the primary winding equals.

Taking the ratio of the two equations for Vs and Vp gives the basic

equation for stepping up or stepping down the voltage.

Np/Ns is known as the turns ratio, and is the primary functional characteristic

of any transformer. In the case of step-up transformers, this may sometimes

be stated as the reciprocal, Ns/Np. Turns ratio is commonly expressed as an

irreducible fraction or ratio.

Detailed Operation of Transformer

Models of an ideal transformer typically assume a core of negligible

reluctance with two windings of zero resistance. When a voltage is applied

to the primary winding, a small current flows, driving flux around the

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magnetic circuit of the core. The current required to create the flux is

termed the magnetizing current. Since the ideal core has been assumed to

have near-zero reluctance, the magnetizing current is negligible, although

still required, to create the magnetic field.

The changing magnetic field induces an electromotive force (EMF)

across each winding. Since the ideal windings have no impedance, they

have no associated voltage drop, and so the voltages VP and VS measured at

the terminals of the transformer, are equal to the corresponding EMFs. The

primary EMF, acting as it does in opposition to the primary voltage, is

sometimes termed the "back EMF". This is in accordance with Lenz's law,

which states that induction of EMF always opposes development of any such

change in magnetic field.

2.3 Rectifier

A rectifier is an electrical device that converts alternating current (AC),

which periodically reverses direction,

to direct current (DC), which flows in

only one direction. The process is

known as rectification. Physically,

rectifiers take a number of forms,

including vacuum tube diodes,

mercury-arc valves, solid-state diodes, silicon-controlled rectifiers and other

silicon-based semiconductor switches. Historically, even synchronous

electromechanical switches and motors have been used. Early radio

receivers, called crystal radios, used a "cat's whisker" of fine wire pressing

on a crystal ofgalena (lead sulfide) to serve as a point-contact rectifier or

"crystal detector".

Rectifiers have many uses, but are often found serving as

components of DC power supplies and high-voltage direct current power

transmission systems. Rectification may serve in roles other than to

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generate direct current for use as a source of power. As noted, detectors of

radio signals serve as rectifiers. In gas heating systems flame rectification is

used to detect presence of flame.

The simple process of rectification produces a type of DCcharacterized by pulsating voltages and currents (although still

unidirectional). Depending upon the type of end-use, this type of DC current

may then be further modified into the type of relatively constant voltage DC

characteristically produced by such sources as batteries and solar cells.

A device which performs the opposite function (converting DC to AC) is

known as an inverter.

Rectifier Devices

Before the development of silicon semiconductor rectifiers, vacuum

tube diodes and copper oxide or selenium rectifier stacks were used. High

power rectifiers, such as are used in high-voltage direct current power

transmission, now uniformly employ silicon semiconductor devices of

various types. These areThyristors or other controlled switching solid-state

switches which effectively function as diodes to pass current in only one

direction.

Half-Wave Rectification

In half wave rectification, either the positive or negative half of the AC

wave is passed, while the other half is blocked. Because only one half of the

input waveform reaches the output, it is very inefficient if used for power

transfer. Half-wave rectification can be achieved with a single diode in a

one-phase supply, or with three diodes in a three-phase supply. Half wave

rectifiers yield a unidirectional but pulsating direct current.

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The output DC voltage of a half wave rectifier can be calculated with the

following two ideal equations

Full-Wave Rectification

A full-wave rectifier converts the whole of the input waveform to one

of constant polarity (positive or negative) at its output. Full-wave

rectification converts both polarities of the input waveform to DC (direct

current), and is more efficient. However, in a circuit with a non-center

tappedtransformer, four diodes are required instead of the one needed for

half-wave rectification (see semiconductors and diode). Four diodesarranged this way are called a diode bridge or bridge rectifier.

Bridge rectifier: A full-wave rectifier using 4 diodes.

For single-phase AC, if the transformer is center-tapped, then two diodes

back-to-back (i.e. anodes-to-anode or cathode-to-cathode) can form a full-

wave rectifier. Twice as many windings are required on the transformer

secondary to obtain the same output voltage compared to the bridge

rectifier above.

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Full-wave rectifier using a center tap transformer

and 2 diodes.

Diode

In electronics, a diode is a type of two-

terminal electronic component with

nonlinear resistance and conductance (i.e.,

a nonlinear currentvoltage characteristic),

distinguishing it from components such as

two-terminal linear resistors which obey

Ohm's law. A semiconductor diode, the most

common type today, is a crystalline piece of

semiconductor material connected to two

electrical terminals.[1] A vacuum tube diode (now rarely used except

in some high-power technologies) is a vacuum tube with two

electrodes: a plate and a cathode.

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The most common function of a diode is to

allow an electric current to pass in one

direction (called the diode's forward

direction), while blocking current in the

opposite direction (the reverse direction).

Thus, the diode can be thought of as an

electronic version of a check valve. This

unidirectional behavior is called

rectification, and is used to convert

alternating current to direct current, and to

extract modulation from radio signals in radio receiversthese diodes

are forms ofrectifiers.

However, diodes can have more complicated behavior than this

simple onoff action. Semiconductor diodes do not begin conducting

electricity until a certain threshold voltage is present in the forward

direction (a state in which the diode is said to be forward-biased). The

voltage drop across a forward-biased diode varies only a little with

the current, and is a function of temperature; this effect can be used

as a temperature sensor or voltage reference.

Semiconductor diodes nonlinear currentvoltage characteristic

can be tailored by varying the semiconductor materials and

introducing impurities into (doping) the materials. These are exploited

in special purpose diodes that perform many different functions. For

example, diodes are used to regulate voltage (Zener diodes), to

protect circuits from high voltage surges (avalanche diodes), to

electronically tune radio and TV receivers (variactor diodes) etc.

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Semiconductor Diodes

A PN Junction Diode is made of a

crystal ofsemiconductor. Impurities are

added to it to create a region on one

side that contains negative charge

carriers (electrons), called n-type

semiconductor, and a region on the other side that contains positive charge

carriers (holes), called p-type semiconductor. The diode's terminals are

attached to each of these regions. The boundary between these two

regions, called a PN Junction, is where the action of the diode takes place.

The crystal allows electrons to flow from the N-type side (called the

cathode) to the P-type side (called the anode), but not in the opposite

direction.

CurrentVoltage Characteristics

A semiconductor diodes behavior in a circuit is given by its current

voltage characteristic, or IV graph (see graph below). The shape of the

curve is determined by the transport of charge carriers through the so-

called depletion layer or depletion region that exists at the PN Junction

between differing semiconductors. When a pn junction is first created,

conduction-band (mobile) electrons from the N-doped region diffuse into the

P-doped region where there is a large population of holes (vacant places for

electrons) with which the electrons "recombine". When a mobile electron

recombines with a hole, both hole and electron vanish, leaving behind an

immobile positively charged donor (dopant) on the N side and negatively

charged acceptor (dopant) on the P side. The region around the PN Junction

becomes depleted ofcharge carriers and thus behaves as an insulator.

However, the width of the depletion region (called the depletion

width) cannot grow without limit. For each electronhole pair that

recombines, a positively charged dopant ion is left behind in the N-doped

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region, and a negatively charged dopant ion is left behind in the P-doped

region. As recombination proceeds more ions are created, an increasing

electric field develops through the depletion zone that acts to slow and then

finally stop recombination. At this point, there is a "built-in" potential across

the depletion zone.

If an external voltage is placed across the diode with the same

polarity as the built-in potential, the depletion zone continues to act as an

insulator, preventing any significant electric current flow (unless

electron/hole pairs are actively being created in the junction by, for

instance, light. see photodiode). This is the reverse bias phenomenon.

However, if the polarity of the external voltage opposes the built-in

potential, recombination can once again proceed, resulting in substantialelectric current through the PN Junction (i.e. substantial numbers of

electrons and holes recombine at the junction). For silicon diodes, the built-

in potential is approximately 0.7 V (0.3 V for Germanium and 0.2 V for

Schottky). Thus, if an external current is passed through the diode, about

0.7 V will be developed across the diode such that the P-doped region is

positive with respect to the N-doped region and the diode is said to be

"turned on" as it has a forward bias.

A diodes IV characteristic can be approximated by four regions of

operation.

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Figure shows the IV characteristics of a pn junction diode (not to scale

the current in the reverse region is magnified compared to the forward

region, resulting in the apparent slope discontinuity at the origin; the actual

IV curve is smooth across the origin).

At very large reverse bias, beyond the peak inverse voltage or PIV, a

process called reverse breakdown occurs that causes a large increase in

current (i.e., a large number of electrons and holes are created at, and

move away from the pn junction) that usually damages the device

permanently. The avalanche diode is deliberately designed for use in the

avalanche region. In the Zener diode, the concept of PIV is not applicable. A

Zener diode contains a heavily doped pn junction allowing electrons to

tunnel from the valence band of the p-type material to the conduction bandof the n-type material, such that the reverse voltage is "clamped" to a

known value (called theZener voltage), and avalanche does not occur. Both

devices, however, do have a limit to the maximum current and power in the

clamped reverse-voltage region. Also, following the end of forward

conduction in any diode, there is reverse current for a short time. The

device does not attain its full blocking capability until the reverse current

ceases.

The second region, at reverse biases more positive than the PIV, has

only a very small reverse saturation current. In the reverse bias region for a

normal PN rectifier diode, the current through the device is very low (in the

A range). However, this is temperature dependent, and at sufficiently high

temperatures, a substantial amount of reverse current can be observed.

The third region is forward but small bias, where only a small forward

current is conducted.

As the potential difference is increased above an arbitrarily defined

"cut-in voltage" or "on-voltage" or "diode forward voltage drop (Vd)", the

diode current becomes appreciable (the level of current considered

"appreciable" and the value of cut-in voltage depends on the application),

and the diode presents a very low resistance. The currentvoltage curve is

exponential. In a normal silicon diode at rated currents, the arbitrary cut-in

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voltage is defined as 0.6 to 0.7 volts. The value is different for other diode

types Schottky diodes can be rated as low as 0.2 V, Germanium diodes

0.25 to 0.3 V, and red or blue light-emitting diodes (LEDs) can have values

of 1.4 V and 4.0 V respectively.

At higher currents the forward voltage drop of the diode increases. A

drop of 1 V to 1.5 V is typical at full rated current for power diodes.

2.4 Filter Circuit (Rectifier Output Smoothing)

While half-wave and full-wave rectification suffice to deliver a form ofDC output, neither produces constant-voltage DC. In order to produce

steady DC from a rectified AC supply, a smoothing circuit or filter is

required. A filter is a device or process that removes from a signal some

unwanted component or feature. In its simplest form this can be just a

reservoir capacitor or smoothing capacitor, placed at the DC output of the

rectifier. There will still remain an amount of AC ripple voltage where the

voltage is not completely smoothed.

Sizing of the capacitor represents a tradeoff. For a given load, a larger

capacitor will reduce ripple but will cost more and will create higher peak

currents in the transformer secondary and in the supply feeding it. The peak

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current is set in principle by the rate of rise of the supply voltage on the

rising edge of the incoming sine-wave, but in practice it is reduced by the

resistance of the transformer windings. In extreme cases where many

rectifiers are loaded onto a power distribution circuit, peak currents may

cause difficulty in maintaining a correctly shaped sinusoidal voltage curve

on the ac supply.

For a given tolerable ripple the required capacitor size is proportional

to the load current and inversely proportional to the supply frequency and

the number of output peaks of the rectifier per input cycle. The load current

and the supply frequency are generally outside the control of the designer

of the rectifier system but the number of peaks per input cycle can be

affected by the choice of rectifier design.

A half-wave rectifier will only give one peak per cycle and for this and

other reasons is only used in very small power supplies. A full wave rectifier

achieves two peaks per cycle and this is the best that can be done with

single-phase input. For three-phase inputs a three-phase bridge will give six

peaks per cycle and even higher numbers of peaks can be achieved by

using transformer networks placed before the rectifier to convert to a higher

phase order.

To further reduce this ripple, a capacitor-input filter can be used. This

complements the reservoir capacitor with a choke (inductor) and a second

filter capacitor, so that a steadier DC output can be obtained across the

terminals of the filter capacitor. The choke presents a high impedance to

the ripple current.[2] Inductors include iron or other magnetic materials, and

add unavoidable weight and size. Their use in power supplies for electronic

equipment has therefore dwindled in favor of semiconductor circuits such as

voltage regulators.

A more usual alternative to a filter, and essential if the DC load is

very demanding of a smooth supply voltage, is to follow the reservoir

capacitor with a voltage regulator. The reservoir capacitor needs to be large

enough to prevent the troughs of the ripple getting below the voltage the

DC is being regulated to. The regulator serves both to remove the last of the

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ripple and to deal with variations in supply and load characteristics. It would

be possible to use a smaller reservoir capacitor (these can be large on high-

current power supplies) and then apply some filtering as well as the

regulator, but this is not a common strategy. The extreme of this approach

is to dispense with the reservoir capacitor altogether and put the rectified

waveform straight into a choke-input filter. The advantage of this circuit is

that the current waveform is smoother and consequently the rectifier no

longer has to deal with the current as a large current pulse, but instead the

current delivery is spread over the entire cycle. The downside, apart from

extra size and weight, is that the voltage output is much lower

approximately the average of an AC half-cycle rather than the peak.

Filtering is a class of signal processing, the defining feature of filters being

the complete or partial suppression of some aspect of the signal. Most often,

this means removing some frequencies and not others in order to suppress

interfering signals and reduce background noise. However, filters do not

exclusively act in the frequency domain; especially in the field of image

processing many other targets for filtering exist.

The drawback of filtering is the loss of information associated with it.

Signal combination in Fourier space is an alternative approach for removal

of certain frequencies from the recorded signal.

There are many different bases of classifying filters and these overlap

in many different ways; there is no simple hierarchical classification.

2.5 Capacitor s

A capacitor (formerly known as condenser) is a passive

two-terminalelectrical component used to store energy in

an electric field. The forms of practical capacitors vary

widely, but all contain at least two electrical conductors

separated by a dielectric (insulator); for example, one

common construction consists of metal foils separated by

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a thin layer of insulating film. Capacitors are widely used as parts of

electrical circuits in many common electrical devices.

When there is a potential difference (voltage) across the conductors, a static

electric field develops across thedielectric, causing positive charge to

collect on one plate and negative charge

on the other plate. Energy is stored in the

electrostatic field. An ideal capacitor is

characterized by a single constant value, capacitance, measured in farads.

This is the ratio of the electric charge on each conductor to the potential

difference between them.

The capacitance is greatest when there is a narrow separation

between large areas of conductor; hence capacitor conductors are often

called "plates," referring to an early means of construction. In practice, the

dielectric between the plates passes a small amount of leakage current and

also has an electric field strength limit, resulting in a breakdown voltage,

while the conductors and leads introduce an undesired inductance and

resistance.

Capacitors are widely used in electronic circuits for blocking direct

current while allowing alternating current to pass, in filter networks, for

smoothing the output ofpower supplies, in the resonant circuits that tune

radios to particular frequencies, in electric power transmission systems for

stabilizing voltage and power flow, and for many other purposes.

Theory Of Operation

A capacitor consists of two conductors

separated by a non-conductive region. The non-

conductive region is called the dielectric. In simpler

terms, the dielectric is just an electrical insulator.

Examples of dielectric media are glass, air, paper,

vacuum, and even a semiconductor depletion

region chemically identical to the conductors. A

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capacitor is assumed to be self-contained and isolated, with no net electric

charge and no influence from any external electric field. The conductors

thus hold equal and opposite charges on their facing surfaces, and the

dielectric develops an electric field. In SI units, a capacitance of one farad

means that one coulomb of charge on each conductor causes a voltage of

one volt across the device.

The capacitor is a reasonably general model for electric fields within

electric circuits. An ideal capacitor is wholly characterized by a constant

capacitance C, defined as the ratio of charge Q on each conductor to the

voltage Vbetween them

Sometimes charge build-up affects the capacitor mechanically, causing its

capacitance to vary. In this case, capacitance is defined in terms of

incremental changes:

CHAPTER -3

3.1 Resistor

A resistor is a passive two-terminal

electrical component that implements electrical

resistance as a circuit element. The currentthrough a resistor is in direct proportion to the

voltage across the resistor's terminals. Thus, the

ratio of the voltage applied across a resistor's

terminals to the intensity of current through the circuit is called resistance.

This relation is represented by Ohm's law:

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Where I is 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 ofohms. More specifically, Ohm's

law states that the R in this relation is constant, independent of the current.

Resistors are common elements of electrical networks and electronic

circuits and are ubiquitous in electronic equipment. Practical resistors can

be made of various compounds and films, as well as resistance wire (wire

made of a high-resistivity alloy, such as nickel-chrome). Resistors are also

implemented within integrated circuits, particularly analog devices, and can

also be integrated into hybrid and printed circuits.

The electrical functionality of a resistor is specified by its resistance:

common commercial resistors are manufactured over a range of more than

nine orders of magnitude. When specifying that resistance in an electronic

design, the required precision of the resistance may require attention to the

manufacturing tolerance of the chosen resistor, according to its specific

application. The temperature coefficient of the resistance may also be of

concern in some precision applications. Practical resistors are also specified

as having a maximum power rating which must exceed the anticipated

power dissipation of that resistor in a particular circuit: this is mainly of

concern in power electronics applications. Resistors with higher power

ratings are physically larger and may require heat sinks. In a high-voltage

circuit, attention must sometimes be paid to the rated maximum working

voltage of the resistor.

Practical resistors have a

series inductance and a small

parallel capacitance; these

specifications can be important in

high-frequency applications. In a

low-noise amplifier or pre-amp, the

noise characteristics of a resistor

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may be an issue. The unwanted inductance, excess noise, and temperature

coefficient are mainly dependent on the technology used in manufacturing

the resistor. They are not normally specified individually for a particular

family of resistors manufactured using a particular technology. A family of

discrete resistors is also characterized according to its form factor, that is,

the size of the device and the position of its leads (or terminals) which is

relevant in the practical manufacturing of circuits using them.

3.2 Carbon Composition Resistors

Carbon composition resistors consistof a solid cylindrical resistive element with

embedded wire leads or metal end caps to

which the lead wires are attached. The body

of the resistor is protected with paint or

plastic. Early 20th-century carbon

composition resistors had un-insulated bodies; the lead wires were wrapped

around the ends of the resistance element rod and soldered. The completed

resistor was painted for color coding of its value.

The resistive element is made from a mixture of finely ground

(powdered) carbon and an insulating material (usually ceramic). A resin

holds the mixture together. The resistance is determined by the ratio of the

fill material (the powdered ceramic) to the carbon. Higher concentrations of

carbon, a good conductor, result in lower resistance. Carbon composition

resistors were commonly used in the 1960s and earlier, but are not so

popular for general use now as other types have better specifications, suchas tolerance, voltage dependence, and stress (carbon composition resistors

will change value when stressed with over-voltages). Moreover, if

internal moisture content (from exposure for some length of time to a humid

environment) is significant, soldering heat will create a non-reversible

change in resistance value. Carbon composition resistors have poor stability

with time and were consequently factory sorted to, at best, only 5%

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tolerance. These resistors, however, if never subjected to over voltage nor

overheating was remarkably reliable considering the component's size.

They are still available, but comparatively quite costly. Values ranged from

fractions of an ohm to 22 mega ohms. Because of the high price, theseresistors are no longer used in most applications. However, carbon resistors

are used in power supplies and welding controls.

3.3 Variable Resistor ( Potentiometer)

A potentiometer informally, a pot, inelectronics technology is a component, a three-

terminalresistor with a sliding contact that forms an

adjustable voltage divider. If only two terminals are

used, one end and the wiper, it acts as a variable

resistoror rheostat.

In circuit theory and measurement a

potentiometer is essentially a voltage divider used

for measuring electric potential (voltage); the component is an

implementation of the same principle, whence its name.

Symbol: Potentiometer

Potentiometers are commonly used to control electrical devices such

as volume controls on audio equipment. Potentiometers operated by a

mechanism can be used as position transducers, for example, in ajoystick.

Potentiometers are rarely used to directly control significant power (more

than a watt), since the power dissipated in the potentiometer would be

comparable to the power in the controlled load (see infinite switch). Instead

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they are used to adjust the level of analog signals (e.g. volume controls on

audio equipment), and as control inputs for electronic circuits. For example,

a light dimmer uses a potentiometer to control the switching of aTRIAC and

so indirectly to control the brightness of lamps.

3.4Potentiometer Construction

Potentiometers comprise a resistive element, a sliding contact (wiper)

that moves along the element, making good electrical contact with one part

of it, electrical terminals at each end of the element, a mechanism that

moves the wiper from one end to the other, and a housing containing the

element and wiper.

The resistive element of inexpensive potentiometers is often made of

graphite. Other materials used include resistance wire, carbon particles in

plastic, and a ceramic/metal mixture called cermet. Conductive track

potentiometers use conductive polymer resistor pastes that contain hard-

wearing resins and polymers, solvents, and lubricant, in addition to the

carbon that provides the conductive properties. The tracks are made byscreen-printing the paste onto a paper-based phenolic substrate and then

curing it in an oven. The curing process removes all solvents and allows the

conductive polymer to polymerize and cross-link. This produces a durable

track with electrical resistance which is stable throughout its working life.

Low-resistance wire-wound potentiometers may be made with resistive wire

close-wound round a former with a slider jumping from turn to turn.

Some potentiometers are designed to be operated by the user of

equipment, and are fitted with a slider or rotating shaft which extends

outside the housing of the equipment using it and is fitted with a knob; a

familiar example is the volume control knob of analog audio equipment.

Others are enclosed within the equipment and are intended to be adjusted

to calibrate equipment during manufacture or repair, and not otherwise

touched. They are usually physically much smaller than user-accessible

potentiometers, and may need to be operated by a screwdriver rather than

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having a knob. They are usually called "preset potentiometers". Some

presets are accessible by a small screwdriver poked through a hole in the

case to allow servicing without dismantling.

User-accessible rotary potentiometers can be fitted with a switchwhich operates usually at the anti-clockwise extreme of rotation. Before

digital electronics became the norm such a component was used to allow

radio and television receivers and other equipment to be switched on at

minimum volume with an audible click, then the volume increased, by

turning a knob.

Many inexpensive potentiometers are constructed with a resistive

element formed into an arc of a circle usually a little less than a full turn,

and a wiper rotating around the arc and contacting it. The resistive element,

with a terminal at each end, is flat or angled. The wiper is connected to a

third terminal, usually between the other two. On panel potentiometers, the

wiper is usually the center terminal of three. For single-turn potentiometers,

this wiper typically travels just under one revolution around the contact. The

only point of ingress for contamination is the narrow space between the

shaft and the housing it rotates in.

Another type is the linear slider potentiometer, which has a wiper

which slides along a linear element instead of rotating. Contamination can

potentially enter anywhere along the slot the slider moves in, making

effective sealing more difficult and compromising long-term reliability. An

advantage of the slider potentiometer is that the slider position gives a

visual indication of its setting. While the setting of a rotary potentiometer

can be seen by the position of a marking on the knob, an array of sliders

can give a visual impression of, for example, the effect of a multi-channel

equalizer.

Multi-turn potentiometers are also operated by rotating a shaft, but

by several turns rather than less than a full turn. Some multi turn

potentiometers have a linear resistive element with a slider which moves

along it moved by a worm gear; others have a helical resistive element and

a wiper that turns through 10, 20, or more complete revolutions, moving

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along the helix as it rotates. Multi turn potentiometers, both user-accessible

and preset, allow finer adjustments; rotation through the same angle

changes the setting by typically a tenth as much as for a simple rotary

potentiometer.

CHAPTER-4

4.1 TRANSISTORS

A transistor is a semiconductor device usedto amplify and switch electronic signals and

power. It is composed of a semiconductor

material with at least three terminals for

connection to an external circuit. A voltage or

current applied to one pair of the transistor's

terminals changes the current flowing through

another pair of terminals. Because the controlled

(output) power can be much more than thecontrolling (input) power, a transistor can amplify

a signal. Today, some transistors are packaged individually, but many more

are found embedded in integrated circuits.

The transistor is the fundamental building block of modern electronic

devices, and is ubiquitous in modern electronic systems. Following its

release in the early 1950s the transistor revolutionized the field of

electronics, and paved the way for smaller and cheaper radios, calculators,

and computers, among other things.

4.2Simplified Operation of transistor

The essential usefulness of a transistor comes from its ability to use a

small signal applied between one pair of its terminals to control a much

larger signal at another pair of terminals. This property is called gain. A

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transistor can control its output in proportion to the input signal; that is, it

can act as an amplifier. Alternatively, the transistor can be used to turn

current on or off in a circuit as an electrically controlled switch, where the

amount of current is determined by other circuit elements.

There are two types of transistors, which

have slight differences in how they are used in a

circuit. A bipolar transistor has terminals labeled

base, collector, and emitter. A small current at the

base terminal (that is, flowing from the base to the

emitter) can control or switch a much larger current

between the collector and emitter terminals. For a

field-effect transistor, the terminals are labeledgate, source, and drain, and a voltage at the gate

can control a current between source and drain.

The image to the right represents a typical bipolar transistor in a

circuit. Charge will flow between emitter and collector terminals depending

on the current in the base. Since internally the base and emitter

connections behave like a semiconductor diode, a voltage drop develops

between base and emitter while the base current exists. The amount of this

voltage depends on the material the transistor is made from, and is referred

to as VBE.

4.3 Transistor As An Amplifier

The common-emitter amplifier is designed so that a small change in

voltage (Vin) changes the small current through the base of the transistor;

the transistor's current amplification combined with the properties of the

circuit mean that small swings in Vin produce large changes in Vout

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Various configurations of single transistor

amplifier are possible, with some providing

current gain, some voltage gain, and some both.

From mobile phones to televisions, vastnumbers of products include amplifiers for

sound reproduction, radio transmission, and

signal processing. The first discrete transistor

audio amplifiers barely supplied a few hundred

milli watts, but power and audio fidelity gradually increased as better

transistors became available and amplifier architecture evolved.

Modern transistor audio amplifiers of up to a few hundred watts are

common and relatively inexpensive.

4.4 Transistor as Multi vibrator

A multi vibrator is an electronic circuit used to implement a variety of

simple two-state systems such as oscillators, timers and flip-flops. It is

characterized by two amplifying devices (transistors, electron tubes or other

devices) cross-coupled by resistors or capacitors. The name "multi vibrator"

was initially applied to the free-running oscillator version of the circuit

because its output waveform was rich in harmonics. There are three types

of multi vibrator circuits depending on the circuit operation:

A stable, in which the circuit is not stable in either state it

continually switches from one state to the other. It does not require

an input such as a clock pulse.

Mono stable, in which one of the states is stable, but the other state

is unstable (transient). A trigger causes the circuit to enter the

unstable state. After entering the unstable state, the circuit will return

to the stable state after a set time. Such a circuit is useful for creating

a timing period of fixed duration in response to some external event.

This circuit is also known as a one shot.

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Bi stable, in which the circuit is stable in either state. The circuit can

be flipped from one state to the other by an external event or trigger.

Multi vibrators find applications in a variety of systems where square

waves or timed intervals are required. For example, before theadvent of low-cost integrated circuits, chains of Multi vibrators found

use as frequency dividers. A free-running multi vibrator with a

frequency of one-half to one-tenth of the reference frequency would

accurately lock to the reference frequency. This technique was used

in early electronic organs, to keep notes of different octaves

accurately in tune. Other applications included early television

systems, where the various line and frame frequencies were kept

synchronized by pulses included in the video signal.

4.5A stable Multi vibrator

A stable multi vibrator is a regenerative circuit consisting of two

amplifying stages connected in a positive feedback loop by two capacitive-

resistive coupling networks. The amplifying elements may be junction or

field-effect transistors, vacuum tubes, operational amplifiers, or other types

of amplifier. The example diagram shows bipolar junction transistors.

The circuit is usually drawn in a symmetric form as a cross-coupled

pair. Two output terminals can be defined at the active devices, which will

have complementary states; one will have high voltage while the other has

low voltage, (except during the brief transitions from one state to the other).

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Operation of a stable multivibrator

The circuit has two stable states that

change alternatively with maximum

transition rate because of the

"accelerating" positive feedback. It is

implemented by the coupling capacitors

that instantly transfer voltage changes

because the voltage across a capacitor

cannot suddenly change. In each state,

one transistor is switched on and the other is switched off.

Accordingly, one fully charged capacitor discharges (reverse charges)

slowly thus converting the time into an exponentially changing

voltage. At the same time, the other empty capacitor quickly charges

thus restoring its charge (the first capacitor acts as a time-setting

capacitor and the second prepares to play this role in the next state).

The circuit operation is based on the fact that the forward-biased

base-emitter junction of the switched-on bipolar transistor can

provide a path for the capacitor restoration.

State 1: (Q1 is switched on, Q2 is switched off):

In the beginning, the capacitor C1 is fully charged (in the previous

State 2) to the power supply voltage Vwith the polarity shown in Figure 1.

Q1 is on and connects the left-hand positive plate of C1 to ground. As its

right-hand negative plate is connected to Q2 base, a maximum negative

voltage (-V) is applied to Q2 base that keeps Q2 firmly off. C1 begins

discharging (reverse charging) via the high-resistive base resistor R2, so

that the voltage of its right-hand plate (and at the base of Q2) is rising from

below ground (-V) toward +V. As Q2 base-emitter junction is backward-

biased, it does not impact on the exponential process (R2-C1 integrating

network is unloaded). Simultaneously, C2 that is fully discharged and even

slightly charged to 0.6 V (in the previous State 2) quickly charges via the

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low-resistive collector resistor R4 and Q1 forward-biased base-emitter

junction (because R4 is less than R2, C2 charges faster than C1). Thus C2

restores its charge and prepares for the next State 2 when it will act as a

time-setting capacitor. Q1 is firmly saturated in the beginning by the

"forcing" C2 charging current added to R3 current; in the end, only R3

provides the needed input base current. The resistance R3 is chosen small

enough to keep Q1 (not deeply) saturated after C2 is fully charged.

When the voltage of C1 right-hand plate (Q2 base voltage) becomes

positive and reaches 0.6 V, Q2 base-emitter junction begins diverting a part

of R2 charging current. Q2 begins conducting and this starts the avalanche-

like positive feedback process as follows. Q2 collector voltage begins falling;

this change transfers through the fully charged C2 to Q1 base and Q1begins cutting off. Its collector voltage begins rising; this change transfers

back through the almost empty C1 to Q2 base and makes Q2 conduct more

thus sustaining the initial input impact on Q2 base. Thus the initial input

change circulates along the feedback loop and grows in an avalanche-like

manner until finally Q1 switches off and Q2 switches on. The forward-biased

Q2 base-emitter junction fixes the voltage of C1 right-hand plate at 0.6 V

and does not allow it to continue rising toward +V.

State 2 :( Q1 is switched off, Q2 is switched on):

Now, the capacitor C2 is fully charged (in the previous State 1) to the

power supply voltage Vwith the polarity shown in Figure 1. Q2 is on and

connects the right-hand positive plate of C2 to ground. As its left-hand

negative plate is connected to Q1 base, a maximum negative voltage (-V) is

applied to Q1 base that keeps Q1 firmly off. C2 begins discharging (reverse

charging) via the high-resistive base resistor R3, so that the voltage of its

left-hand plate (and at the base of Q1) is rising from below ground (-V)

toward +V. Simultaneously, C1 that is fully discharged and even slightly

charged to 0.6 V (in the previous State 1) quickly charges via the low-

resistive collector resistor R1 and Q2 forward-biased base-emitter junction

(because R1 is less than R3, C1 charges faster than C2). Thus C1 restores its

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charge and prepares for the next State 1 when it will act again as a time-

setting capacitor.

Mono stable Multi vibrator Circuit

In the mono stable multi vibrator, the one

resistive-capacitive network (C2-R3 in figure 1) is

replaced by a resistive network (just a resistor).

The circuit can be thought as a 1/2 a stable multi

vibrator. Q2 collector voltage is the output of the

circuit (in contrast to the a stable circuit, it has aperfect square waveform since the output is not

loaded by the capacitor).

When triggered by an input pulse, a mono stable multi vibrator will

switch to its unstable position for a period of time, and then return to its

stable state. The time period mono stable multi vibrator remains in unstable

state is given by t= ln (2)R2C1. If repeated application of the input pulse

maintains the circuit in the unstable state, it is called a retrigger able mono

stable. If further trigger pulses do not affect the period, the circuit is a non-

re trigger able multi vibrator.

For the circuit in Figure 2, in the stable state Q1 is turned off and Q2

is turned on. It is triggered by zero or negative input signal applied to Q2

base (with the same success it can be triggered by applying a positive input

signal through a resistor to Q1 base). As a result, the circuit goes in State 1

described above. After elapsing the time, it returns to its stable initial state.

Bi stable Multi vibrator Circuit

In the bi stable multi vibrator, both the resistive-capacitive network is

replaced by resistive networks (just resistors or direct coupling).

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This latch circuit is similar to an a stable

multi vibrator, except that there is no charge or

discharge time, due to the absence of

capacitors. Hence, when the circuit is switched

on, if Q1 is on, its collector is at 0 V. As a result,

Q2 gets switched off. This results in more than

half +V volts being applied to R4 causing

current into the base of Q1, thus keeping it on.

Thus, the circuit remains stable in a single state c