Chapter 1

Introduction

1.1 General introduction

This is a nice project to show the pressure of an input audio signal. Here it

gives the output in micro amps. It makes use of the National Semiconductor CA 3140. This

chip is a bidirectional chip. It can be modified for adjusting all audio levels in same level.

1.2Uses of Sound pressure meters

The sound pressure meters is amongst the simplest of meter designs and have been used

since the very beginnings of the broadcast, recording and live audio industries. These come in

the form of the Moving-coil Meter - the traditional 'needle' type of meter - or as a bar-graph

of LEDs. [LEDs are the most common, with moving-coil meters now more often seen on

'retro' gear.]

1.3 Types of Sound Pressure Meters

We have different types of audio level meters (VU meters) in general.

Those are

Analog Sound pressure meter

Magnetoelectric Sound pressure meter

Digital display Sound pressure meter

LED Sound pressure meter

1.4 Applications

Used in audio processing equipment industries like loud speaker.

Used to show the o/p audio level of tape recorders and players etc.

Can be used to adjust home cinema set-up loud speakers output to same level.

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Chapter 2

Basic Components Used In the Circuit

The circuit of sound pressure meter is constructed by using various

components. In this section the components which are used are discussed.

2.1 IC CA3140 Operational Amplifier.

2.2 Electret Condenser Microphone.

2.3 Diodes

2.4 Power Supply

2.5 Resistors.

2.6 Capacitors.

2.7 Switches.

2.8 Bridge Rectifier

2.9 100uA Full Scale Deflection Meter

2.1 CA3140 Operational Amplifier

2.1.1General Description

The CA3140A and CA3140 are integrated circuit operational amplifiers that combine

the advantages of high voltage PMOS transistors with high voltage bipolar transistors on a

single monolithic chip. The CA3140A and CA3140 BiMOS operational amplifiers feature

gate protected MOSFET (PMOS) transistors in the input circuit to provide very high input

impedance, very low input current, and high speed performance. The CA3140A and CA3140

operate at supply voltage from 4V to 36V (either single or dual supply). These operational

amplifiers are internally phase compensated to achieve stable operation in unity gain follower

operation, and additionally, have access terminal for a supplementary external capacitor if

additional frequency roll-off is desired. Terminals are also provided for use in applications

requiring input offset voltage nulling. The use of PMOS field effect transistors in the input

stage results in common mode input voltage capability down to 0.5V below the negative

supply terminal, an important attribute for single supply applications. The output stage uses

bipolar transistors and includes built-in protection against damage from load terminal short

circuiting to either supply rail or to ground. The CA3140 Series has the same 8-lead pinout

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used for the “741” and other industry standard op amps. The CA3140A and CA3140 are

intended for operation at supply voltages up to 36V (-18v to +18v)

2.1.2 Block Diagram

Fig.2.1.2 Block Diagram of IC CA3140

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2.1.3 Pinouts

Fig.2.1.3 Pinouts of IC CA3140

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2.1.4 Schematic Diagram

Fig.2.1.4 Schematic Diagram of IC CA3140

Circuit Description

As shown in the block diagram, the input terminals may be operated down to 0.5V

below the negative supply rail. Two class A amplifier stages provide the voltage gain, and a

unique class AB amplifier stage provides the current gain necessary to drive low-impedance

loads. A biasing circuit provides control of cascoded constant current flow circuits in the first

and second stages. The CA3140 includes an on chip phase compensating capacitor that is

sufficient for the unity gain voltage follower configuration.

Input Stage

The schematic diagram consists of a differential input stage using PMOS field-effect

transistors (Q9, Q10) working into a mirror pair of bipolar transistors (Q11, Q12) functioning

as load resistors together with resistors R2 through R5. The mirror pair transistors also

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function as a differential-to-single-ended converter to provide base current drive to the

second stage bipolar transistor (Q13). Offset nulling, when desired, can be effected with a

10kΩ potentiometer connected across Terminals 1 and 5 and with its slider arm connected to

Terminal 4. Cascode-connected bipolar transistors Q2, Q5 are the constant current source for

the input stage. The base biasing circuit for the constant current source is described

subsequently. The small diodes D3, D4, D5 provide gate oxide protection against high

voltage transients, e.g., static electricity.

Second Stage

Most of the voltage gain in the CA3140 is provided by the second amplifier stage,

consisting of bipolar transistor Q13 and its cascode connected load resistance provided by

bipolar transistors Q3, Q4. On-chip phase compensation, sufficient for a majority of the

applications is provided by C1. Additional Miller-Effect compensation (roll off) can be

accomplished, when desired, by simply connecting a small capacitor between Terminals 1

and 8. Terminal 8 is also used to strobe the output stage into quiescence. When terminal 8 is

tied to the negative supply rail (Terminal 4) by mechanical or electrical means, the output

Terminal 6 swings low, i.e., approximately to Terminal 4 potential.

Output Stage

The CA3140 Series circuits employ a broad band output stage that can sink loads to

the negative supply to complement the capability of the PMOS input stage when operating

near the negative rail. Quiescent current in the emitter-follower cascade circuit (Q17, Q18) is

established by transistors (Q14, Q15) whose base currents are “mirrored” to current flowing

through diode D2 in the bias circuit section. When the CA3140 is operating such that output

Terminal 6 is sourcing current, transistor Q18 functions as an emitter-follower to source

current from the V+ bus (Terminal 7), via D7, R9, and R11. Under these conditions, the

collector potential of Q13 is sufficiently high to permit the necessary flow of base current to

emitter follower Q17 which, in turn, drives Q18. When the CA3140 is operating such that

output Terminal 6 is sinking current to the V- bus, transistor Q16 is the current sinking

element. Transistor Q16 is mirror connected to D6, R7, with current fed by way of Q21, R12,

and Q20. Transistor Q20, in turn, is biased by current flow through R13, zener D8, and R14.

The dynamic current sink is controlled by voltage level sensing. For purposes of explanation,

it is assumed that output Terminal 6 is quiescently established at the potential midpoint

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between the V+ and V- supply rails. When output current sinking mode operation is required,

the collector potential of transistor Q13 is driven below its quiescent level, thereby causing

Q17, Q18 to decrease the output voltage at Terminal 6. Thus, the gate terminal of PMOS

transistor Q21 is displaced toward the V- bus, thereby reducing the channel resistance of

Q21. As a consequence, there is an incremental increase in current flow through Q20, R12,

Q21, D6, R7, and the base of Q16. As a result, Q16 sinks current from Terminal 6 in direct

response to the incremental change in output voltage caused by Q18. This

sink current flows regardless of load; any excess current is internally supplied by the emitter-

follower Q18. Short circuit protection of the output circuit is provided by Q19, which is

driven into conduction by the high voltage drop developed across R11 under output short

circuit conditions. Under these conditions, the collector of Q19 diverts current from Q4 so as

to reduce the base current drive from Q17, thereby limiting current flow in Q18 to the short

circuited load terminal.

Bias CircuitQuiescent current in all stages (except the dynamic current sink) of the CA3140 is

dependent upon bias current flow in R1. The function of the bias circuit is to establish and

maintain constant current flow through D1, Q6, Q8 and D2. D1 is a diode connected

transistor mirror connected in parallel with the base emitter junctions of Q1, Q2, and Q3. D1

may be considered as a current sampling diode that senses the emitter current of Q6 and

automatically adjusts the base current of Q6 (via Q1) to maintain a constant current through

Q6, Q8, D2. The base currents in Q2, Q3 are also determined by constant current flow D1.

Furthermore, current in diode connected transistor Q2 establishes the currents in transistors

Q14 and Q15.

Typical ApplicationsWide dynamic range of input and output characteristics with the most desirable high

input impedance characteristics is achieved in the CA3140 by the use of an unique design

based upon the PMOS Bipolar process. Input common mode voltage range and output swing

capabilities are complementary, allowing operation with the single supply down to 4V. The

wide dynamic range of these parameters also means that this device is suitable for many

single supply applications, such as, for example, where one input is driven below the

potential of Terminal 4 and the phase sense of the output signal must be maintained – a most

important consideration in comparator applications.

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2.1.5 Features• MOSFET Input Stage

- Very High Input Impedance (ZIN) -1.5TΩ (Typ)

- Very Low Input Current (Il) -10pA (Typ) at }15V�- Wide Common Mode Input Voltage Range (VlCR) - Can be Swung 0.5V Below Negative

Supply Voltage Rail

- Output Swing Complements Input Common Mode Range

• Directly Replaces Industry Type 741 in Most Applications

2.1.6 Applications

• Ground-Referenced Single Supply Amplifiers in Automobile and Portable Instrumentation

• Sample and Hold Amplifiers

• Long Duration Timers/Multivibrators (μseconds-Minutes-Hours)

• Photocurrent Instrumentation

• Peak Detectors

• Active Filters

• Comparators

• Interface in 5V TTL Systems and Other Low Supply Voltage Systems

• All Standard Operational Amplifier Applications

• Function Generators

• Tone Controls

• Power Supplies

• Portable Instruments

• Intrusion Alarm Systems

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2.2 Electret microphone

An Electrets microphone is a type of condenser microphone, which eliminates the

need for a +polarizing power supply by using a permanently-charged material.

Fig.2.2 Internal Diagram of Electret Microphone

Fig. Electret condenser microphone capsules and its equivalent circuit.

A typical electret microphone preamp circuit uses an FET in a common source configuration.

The two-terminal electret capsule contains an FET which must be externally powered by

supply voltage V+. The resistor sets the gain and output impedance. The audio signal appears

at the output, after a DC-blocking capacitor.

An electret is a stable dielectric material with a permanently-embedded static electric charge

(which, due to the high resistance and chemical stability of the material, will not decay for

hundreds of years). The name comes from electrostatic and magnet; drawing analogy to the

formation of a magnet by alignment of magnetic domains in a piece of iron. Electrets are

commonly made by first melting a suitable dielectric material such as a plastic or wax that

contains polar molecules, and then allowing it to re-solidify in a powerful electrostatic field.

The polar molecules of the dielectric align themselves to the direction of the electrostatic

field, producing a permanent electrostatic "bias". Modern electret microphones use PTFE

plastic, either in film or solute form, to form the electret.

Electret materials have been known since the 1920s, and were proposed as condenser

microphone elements several times, but were considered impractical until the foil electret

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type was invented at Bell Laboratories in 1962 by Gerhard Sessler and Jim West, using a thin

metallized Teflon foil. This became the most common type, used in many applications from

high-quality recording and lavaliere use to built-in microphones in small sound recording

devices and telephones.

Though electret mics were once considered low cost and low quality, the best ones can now

rival capacitor mics in every respect apart from low noise and can even have the long-term

stability and ultra-flat response needed for a measuring microphone. Few electret

microphones rival the best DC-polarized units in terms of noise level, but this is not due to

any inherent limitation of the electret. Rather, mass production techniques needed to produce

electrets cheaply do not lend themselves to the precision needed to produce the highest

quality microphones.

2.2.1 Types

There are three major types of electret microphone, differing in the way the electret material

is used:

Foil-type or diaphragm-type 

A film of electret material is used as the diaphragm itself. This is the most common

type, but also the lowest quality, since the electret material does not make a

particularly good diaphragm.

Back electret 

An electret film is applied to the back plate of the microphone capsule and the

diaphragm is made of an uncharged material which may be mechanically more

suitable for the transducer design being realized.

Front electret 

In this newer type, the back plate is eliminated from the design, and the condenser is

formed by the diaphragm and the inside surface of the capsule. The electret film is

adhered to the inside front cover and the metalized diaphragm is connected to the

input of the FET. It is equivalent to the back electret in that any conductive film may

be used for the diaphragm.

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Unlike other condenser microphones electret types require no polarizing voltage, but they

normally contain an integrated preamplifier which does require a small amount of power

(often incorrectly called polarizing power or bias). This preamp is frequently phantom

powered in sound reinforcement and studio applications. Other types simply include a 1.5V

battery in the microphone housing, which is often left permanently connected as the current

drain is usually very small.

2.3 DIODE 1N4148

2.3.1 About diodes

In electronics, a diode is a type of two-terminal electronic component with nonlinear

resistance and conductance (i.e., a nonlinear current–voltage 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.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.

Fig. 2.3 Diode and its symbol

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

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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 receivers—

these diodes are forms of rectifiers.

However, diodes can have more complicated behavior than this simple on–off 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 current–voltage 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 (varactor diodes), to

generate radio frequency oscillations (tunnel diodes, Gunn diodes, IMPATT diodes), and to

produce light (light emitting diodes). Tunnel diodes exhibit negative resistance, which makes

them useful in some types of circuits.

Diodes were the first semiconductor electronic devices. The discovery of crystals' rectifying

abilities was made by German physicist Ferdinand Braun in 1874. The first semiconductor

diodes, called cat's whisker diodes, developed around 1906, were made of mineral crystals

such as galena. Today most diodes are made of silicon, but other semiconductors such as

germanium are sometimes used.

2.3.2 Types of diodes

It is sometimes useful to summarize the different types of diodes that are available. Some of

the categories may overlap, but the various definitions may help to narrow the field down and

provide an overview of the different diode types that are available.

Avalanche diode: The avalanche diode by its very nature is operated in reverse bias. It uses

the avalanche effect for its operation. In general the avalanche diode is used for photo-

detection where the avalanche process enables high levels of sensitivity to be obtained, even

if there are higher levels of associated noise.

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Laser diode: This type of diode is not the same as the ordinary light emitting diode because

it produces coherent light. Laser diodes are widely used in many applications from DVD and

CD drives to laser light pointers for presentations. Although laser diodes are much cheaper

than other forms of laser generator, they are considerably more expensive than LEDs. They

also have a limited life. See related articles list in left hand margin.

Light emitting diodes: The light emitting diode or LED is one of the most popular types of

diode. When forward biased with current flowing through the junction, light is produced. The

diodes use component semiconductors, and can produce a variety of colours, although the

original colour was red. There are also very many new LED developments that are changing

the way displays can be used and manufactured. High output LEDs and OLEDs are two

examples. See related articles list in left hand margin.

Photodiode: The photo-diode is used for detecting light. It is found that when light strikes a

PN junction it can create electrons and holes. Typically photo-diodes are operated under

reverse bias conditions where even small amounts of current flow resulting from the light can

be easily detected. Photo-diodes can also be used to generate electricity. For some

applications, PIN diodes work very well as photodetectors. See related articles list in left

hand margin.

PIN diode: This type of diode is typified by its construction. It has the standard P type and

N-type areas, but between them there is an area of Intrinsic semiconductor which has no

doping. The area of the intrinsic semiconductor has the effect of increasing the area of the

depletion region which can be useful for switching applications as well as for use in

photodiodes, etc. See related articles list in left hand margin.

PN Junction: The standard PN junction may be thought of as the normal or standard type of

diode in use today. These diodes can come as small signal types for use in radio frequency, or

other low current applications which may be termed as signal diodes. Other types may be

intended for high current and high voltage applications and are normally termed rectifier

diodes. See related articles list in left hand margin.

Rectifier diode: This definition refers to diodes that are used in power supplies for rectifying

alternating power inputs. The diodes are generally PN junction diodes, although Schottky

diodes may be used if low voltage drops are needed. They are able to rectify current levels

that may range from an amp upwards.

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Schottky diodes: This type of diode has a lower forward voltage drop than ordinary silicon

PN junction diodes. At low currents the drop may be somewhere between 0.15 and 0.4 volts

as opposed to 0.6 volts for a silicon diode. To achieve this performance they are constructed

in a different way to normal diodes having a metal to semiconductor contact. They are widely

used as clamping diodes, in RF applications, and also for rectifier applications.

Fig.2.3.2 Different types of diodes

Zener diode: The Zener diode is a very useful type of diode as it provides a stable reference

voltage. As a result it is used in vast quantities. It is run under reverse bias conditions and it is

found that when a certain voltage is reached it breaks down. If the current is limited through a

resistor, it enables a stable voltage to be produced. This type of diode is therefore widely used

to provide a reference voltage in power supplies.

2.3.3 1N4148 Diode

Fig. 2.3.31N4148 diode

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The 1N4148 diode is a fast, standard small signal silicon diode with high conductance used in

signal processing. Its name follows the JEDEC nomenclature. The diode 1N4148 is generally

available in a DO-35 glass package and is very useful at high frequencies with a reverse

recovery time of no more than 4ns. This permits rectification and detection of radio

frequency signals very effectively, as long as their amplitude is above the forward conduction

threshold of silicon (around 0.7V) or the diode is biased.

Specification:

VRRM = 100V (Maximum Repetitive Reverse Voltage)

IO = 200mA (Average Rectified Forward Current)

IF = 300mA (DC Forward Current)

IFSM = 1.0 A (Pulse Width = 1 sec), 4.0 A (Pulse Width = 1 uSec) (Non-Repetitive

Peak Forward Surge Current)

PD = 500 mW (power Dissipation)

TRR < 4ns (reverse recovery time)

The 1N4148 is a standard silicon switching diode. Its name follows the JEDEC

nomenclature. The 1N4148 has a DO-35 glass package and is very useful at high frequencies

with a reverse recovery time of no more than 4ns. It was second sourced by many

manufacturers; Texas Instruments listed their version of the device in an October 1966 data

sheet. The diode 1N4148 is a fast, standard small signal silicon diode with high conductance

used in signal processing. Its name follows the JEDEC nomenclature.

2.4 Power Supply

An electrical battery is one or more electrochemical cells that convert stored

chemical energy into electrical energy. Since the invention of the first battery in 1800

by Alessandro Volta, batteries have become a common power source for many household and

industrial applications. According to a 2005 estimate, the worldwide battery industry

generates US$48 billion in sales each year, with 6% annual growth.

2.4.1 Types of Batteries

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There are two types of batteries: primary batteries (disposable batteries), which are

designed to be used once and discarded, and secondary batteries(rechargeable batteries),

which are designed to be recharged and used multiple times. Miniature cells are used to

power devices such as hearing aids and wristwatches; larger batteries provide standby power

for telephone exchanges or computer data centers.

Fig 2.4.1 various types of cells

2.4.2 Symbol of Batteries

The symbol for a battery in a circuit diagram is as shown in the figure below. It

originated as a schematic drawing of the earliest type of battery, a voltaic pile.

Fig 2.4.2 Symbol of power supply

Strictly, a battery is a collection of multiple electrochemical cells, but in popular

usage battery often refers to a single cell. The first electrochemical cell was developed by

the Italian physicist Alessandro Volta in 1792, and in 1800 he invented the first battery—for

him, a "pile" of cells.

2.5 Resistors

A resistor is a two-terminal electronic component which implements electrical

resistance as a circuit element. When a voltage V is applied across the terminals of resistor, a

current I will flow through the resistor in direct proportion to that voltage. The reciprocal of

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the constant of proportionality is known as the resistance R, since, with a given voltage V, a

larger value of R further "resists" the flow of current I as given by Ohm's law:

Fig.2.5.Types of Resistors

2.6 Capacitors

A capacitor is a passive electronic component consisting of a pair of conductors separated

by a dielectric (insulator). When there is a potential difference (voltage) across the

conductors, a static electric field develops in the dielectric that stores energy and produces a

mechanical force between the conductors. 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.

Fig 2..6 various forms of capacitor

2.6.1 Polyester Capacitor

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Fig.2.6.1 Poly Capacitor

2.6.2 Introduction

Low noise Polyester capacitors are very important for electronic equipment. They are

needed in AC applications when noise may be created in a capacitor which impacts the

environment. With certain frequencies Polyester capacitors may create a noise level of up to

80dB(A) - this “humming” or “whistling” can be observed e.g. in ballasts in the lighting

industry, in monitors and TV sets or in audio equipment. With a new construction principle

noise creation has been considerably reduced, at the same time several electrical properties

have been substantially improved.

2.6.3 Construction Principle

By means of a modified construction of the capacitor there is no longer an electrical

field in the gaps between the layers of the winding element and, as a consequence no force

can be active and create vibrations of the film. Thus a considerable reduction of noise

intensity is obtained.

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Fig.2.6.3 Graph of IC CA3140

2.6.4 Features

1. NOISE INTENSITY: LN capacitors are up to 20dB(A) less noisy than

conventional Polyester capacitors, i.e: With =10dB(A): 1 conventional capacitor

creates the same noise as 10 LN capacitors! With =20dB(A): 1 conventional capacitor

creates the same noise as 100 LN capacitors!

2. ELECTRICAL PROPERTIES: In comparison to conventional Polyester

capacitors LN capacitors feature a considerably lower variation of the noise level

values and considerably lower deviation of capacitance and dissipation factor with

temperature. according to the data sheet are available as of now in production

quantities. be 20 % to 30 % higher

2.6.5 Fields of Applications

Lighting industry

TV/Monitor sets

Audio/Video applications

Communication technology etc.

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2.7 Switch

In electronics, a switch is an electrical component that can break an electrical circuit,

interrupting the current or diverting it from one conductor to another. Each set of contacts can

be in one of two states: either 'closed' meaning the contacts are touching and electricity can

flow between them, or 'open', meaning the contacts are separated and nonconducting.

2.7.1 Various forms of switches

Fig 2.7.1 various forms of switches

Electrical switches. Top, left to right: circuit breaker, mercury, wafer switch, DIP switch,

surface mount switch, reed switch. Bottom, left to right: wall switch (U.S. style), miniature

toggle switch, in-line switch, push-button switch, rocker switch, micro switch.

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

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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 DC characterized 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.

2.8.1 Bridge Rectifier

A diode bridge is an arrangement of four (or more) diodes in a bridge circuit

configuration that provides the same polarity of output for either polarity of input. When used

in its most common application, for conversion of an alternating current (AC) input into

direct current a (DC) output, it is known as a bridge rectifier. A bridge rectifier provides full-

wave rectification from a two-wire AC input, resulting in lower cost and weight as compared

to a rectifier with a 3-wire input from a transformer with a center-tapped secondary winding.

Fig.2.8.1 Bridge Rectifier

2.8.2 Basic Operation

According to the conventional model of current flow originally established by Benjamin

Franklin and still followed by most engineers today, current is assumed to flow through

electrical conductors from the positive to the negative pole.[2] In actuality, free electrons in a

conductor nearly always flow from the negative to the positive pole. In the vast majority of

applications, however, the actual direction of current flow is irrelevant. Therefore, in the

discussion below the conventional model is retained.

In the diagrams below, when the input connected to the left corner of the diamond is positive,

and the input connected to the right corner is negative, current flows from the upper supply

terminal to the right along the red (positive) path to the output, and returns to the lower

supply terminal via the blue (negative) path.

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When the input connected to the left corner is negative, and the input connected to the right

corner is positive, current flows from the upper supply terminal to the right along the red

(positive) path to the output, and returns to the lower supply terminal via the blue (negative)

path.

In each case, the upper right output remains positive and lower right output negative. Since

this is true whether the input is AC or DC, this circuit not only produces a DC output from an

AC input, it can also provide what is sometimes called "reverse polarity protection". That is,

it permits normal functioning of DC-powered equipment when batteries have been installed

backwards, or when the leads (wires) from a DC power source have been reversed, and

protects the equipment from potential damage caused by reverse polarity.

AC, half-wave and full wave rectified signals.

Prior to the availability of integrated circuits, a bridge rectifier was constructed from "discrete

components", i.e., separate diodes. Since about 1950, a single four-terminal component

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containing the four diodes connected in a bridge configuration became a standard commercial

component and is now available with various voltage and current ratings

2.8.3 Different types of Bridge rectifiers

2.9 100uA Full Scale Deflection Meter

An ammeter is a measuring instrument used to measure the electric current in a

circuit. Electric currents are measured in amperes (A), hence the name. Instruments used to

measure smaller currents, in the mill ampere or microampere range, are designated as

milliammeters or microammeters. Early ammeters were laboratory instruments which relied

on the Earth's magnetic field for operation. By the late 19th century, improved instruments

were designed which could be mounted in any position and allowed accurate measurements

in electric power systems.

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2.9.1 Types of Ammeters

The D'Arsonval galvanometer is a moving coil ammeter. It uses magnetic deflection,

where current passing through a coil causes the coil to move in a magnetic field. The modern

form of this instrument was developed by Edward Weston, and uses two spiral springs to

provide the restoring force. By maintaining a uniform air gap between the iron core of the

instrument and the poles of its permanent magnet, the instrument has good linearity and

accuracy. Basic meter movements can have full-scale deflection for currents from about 25

microamperes to 10 milliamperes and have linear scales.

Moving iron ammeters use a piece of iron which moves when acted upon by the

electromagnetic force of a fixed coil of wire. This type of meter responds to both direct and

alternating currents (as opposed to the moving coil ammeter, which works on direct current

only). The iron element consists of a moving vane attached to a pointer, and a fixed vane,

surrounded by a coil. As alternating or direct current flows through the coil and induces a

magnetic field in both vanes, the vanes repel each other and the moving vane deflects against

the restoring force provided by fine helical springs. The non-linear scale of these meters

makes them unpopular.

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An electrodynamic movement uses an electromagnet instead of the permanent magnet of the

d'Arsonval movement. This instrument can respond to both alternating and direct current.

In a hot-wire ammeter, a current passes through a wire which expands as it heats. Although

these instruments have slow response time and low accuracy, they were sometimes used in

measuring radio-frequency current.

Digital ammeter designs use an analog to digital converter (ADC) to measure the voltage

across the shunt resistor; the digital display is calibrated to read the current through the shunt.

There is also a whole range of devices referred to as integrating ammeters. In these ammeters,

the amount of current is summed over time, giving as a result the product of current and time,

which is proportional to the energy transferred with that current. These can be used for

energy meters (watt-hour meters) or for estimating the charge of battery or capacitor.

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2.10 Printed circuit board:

A printed circuit board, or PCB, is used to mechanically support and electrically

connect electronic components using conductive pathways, tracks, or traces, etched from

copper sheets laminated 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 (PCBA).

PCBs are inexpensive, and can be highly reliable. They require much more layout

effort and higher initial cost than either wire-wrapped or point-to-point constructed circuits,

but are much cheaper and faster for high-volume production. Much of the electronics

industry's PCB design, assembly, and quality control needs are set by standards that are

published by the IPC organization.

Fig 2.10 Picture of printed circuit board

Conducting layers are typically made of thin copper foil. Insulating layers dielectric

is typically laminated together with epoxy resin prepreg. The board is typically coated with a

solder mask that is green in colour. Other colours that are normally available are blue and red.

There are quite a few different dielectrics that can be chosen to provide different

insulating values depending on the requirements of the circuit. Some of these dielectrics are

polytetrafluoroethylene (Teflon), FR-4, FR-1, CEM-1 or CEM-3.

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Well known prepreg materials used in the PCB industry are FR-2 (Phenolic cotton

paper), FR-3 (Cotton paper and epoxy), FR-4 (Woven glass and epoxy), FR-5 (Woven glass

and epoxy), FR-6 (Matte glass and polyester), G-10 (Woven glass and epoxy), CEM-1

(Cotton paper and epoxy), CEM-2 (Cotton paper and epoxy), CEM-3 (Woven glass and

epoxy), CEM-4 (Woven glass and epoxy), CEM-5 (Woven glass and polyester). Thermal

expansion is an important consideration especially with BGA and naked die technologies,

and glass fiber offers the best dimensional stability.

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Chapter 3

Working of Sound Pressure Meter

The advantage of Sound Pressure meter is we can set the all sound levels to a constant

level of sound by cascading the CA 3140 IC’s and it is very simple too. Reference voltage

will decide the reference dB level (which is zero signal dB level).

3.1 Block diagram of Sound Pressure Meter

As it can be shown in the block diagram, the gadget can be divided as below

3.1.1 Audio amplifier section

We have an audio amplifier section which will amplify the speech signal output from

the condenser microphone (it will be in the order of mA). Here we have used CA3140

operational amplifier as an amplifier section with gain defined by the feedback resistor.

3.1.2 Bridge Rectifier

The output from the IC CA3140 is given to the bridge rectifier. Here the bridge rectifier

will convert the a.c. signal into d.c. signal.

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3.2 100uA d.c. Ammeter

This 100uA d.c. ammeter is used as an output for Sound Pressure Meter. This ammeter

is used to give the current ratings in micro amps.

3.3 Circuit description

The circuit is quite simple. It is more or less the same as that given in the

datasheets of the chip. This circuit is to setup home-cinema set adjusting all the loudspeaker

outputs to the same level when heard from the listening position. In practice this device is a

simple (though linear and precise) 100µAac millivolt meter.

Fig. 3.3 Sound Pressure Meter

The precision of the measure is entirely depending on the frequency response of the

microphone used but, fortunately, for the main purpose of this circuit an absolutely flat

response is not required. Therefore, a cheap miniature electret microphone can be used.

The circuit is based on non- inverting amplifier based on op-amp CA3140 (IC1).The sound

picked by the condenser mic will be amplified by the IC1 and rectified by the bridge D1 to

drive the meter M1.The deflection on the meter will be proportional to the pressure of the

sound falling on the mic. The switch S1 can be used as an ON/OFF switch.

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Chapter 4

Results and Discussions

4.1 Results & Discussions

Hence the circuit of Sound Pressure Meter is constructed on the PCB and the output is

verified. This circuit on the PCB is shown in the figure below.

Fig 4.1 Sound Pressure Meter circuit on PCB

The d.c.meter in the circuit is varied for the desired audio levels. We used the DPST switch to switch

between dot and bar modes. Here we shown both circuits i.e audio amplifier and level meter and

connected them with a connector. Any noises around the circuit are also received by the microphone

and can affect the output so for perfect output we have to place the circuit at noise less environment.

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S.no Audio System Sound in DecibelsCurrent in

milliamps (mA)Current in

microamps (uA)

1. Laptop More than 3 decibels More than 1mA More than 100uA

2. Tape Recorder More than 3 decibels More than 1mA More than 100uA

3. F.M. More than 3 decibels More than 1mA More than 100uA

4. Samsung Mobile 3decibels 1mA 100uA

5. Nokia Mobile 2.5decibels 0.09mA 90uA

6. L.G. Mobile 2 decibels 0.08mA 80uA

7. Apple Ipod 1.5 decibels 0.07mA 70uA

8. Sony Ipod 1 decibels 0.06mA 60uA

9. Clap Sound 1 decibels 0.06mA 60uA

10. Air 0 decibels 0.04mA 40uA

Chapter 5

Conclusion & Future scope

5.1 Conclusion

Hence the project Sound Pressure Meter worked successfully and this

project can be used in audio processing equipment industries like loud speaker and to show

the same and equal o/p audio level of home cinema setup, tape recorders and players etc. The

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sound or speech is received by microphone it converts that into electrical signal and Sound

Pressure Meter will show the current ratings output using 100uA d.c. meter.

5.2 Future scope

Here in this circuit we showed the output dB level from -20dB to +3dB. And there is scope to

extend to any dB level by cascading the LM3916 IC’s.

References

1) Electronic circuit analysis-K. Lalkishore, BS Publications, 2004.

2) Electronic devices and circuits-J. Mill man and C.C. Hawkins, Tata McGraw Hill, 1988.

3) Micro Electronics-Milliman, McGraw Hill, 1988.

4) Linear integrated circuits- D. Roy Chowdary, New Age International (p) Ltd,2nd edition

5) Op-amps & Linear ICs-Ramakanth A.Gayakwad, PHI, 1987

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6) http://www.electronicsforu.com/electronicsforu/lab/ad.asp?url=/EFYLinux/circuit/

June2007/CI-2_june07.pdf&title=Light%20Fence

7) www.wikipedia.com

8) www.alldatasheets.com

9) www.newagepublishers.com

10) www.national.com

11) www.nxp.com/documents/data_sheet/BC556_557.pdf

12) www.allaboutcircuits.com

13) www.sunrom.com/files/3190-datasheet.pdf

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