1

CHAPTER 1

INTRODUCTION

This is a nice project to display the level of an input audio signal. It makes use of the

National Semiconductor LM3916 bargraph/LED driver chip. This chip is a complete LED

VU meter driver chip. It is similar to the LM3914 linear bargraph driver and the LM3915

logarithmic bargraph driver. Its LEDs correspond to the standard VU scale from -20dB to

+3dB, excluding -2dB. This project provides for only a mono display. It can be modified for

a stereo display as well.

1.1 Uses of Audio level meters

The audio level/volume unit (VU) 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.]

1.2 Types of Volume Unit (VU) meters

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

Those are

Analog VU meter

Magnetoelectric VU meter

Digital display VU meter

LED VU meter

1.3 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 by police to control the audio output power from loud speakers.

2

CHAPTER 2

BASIC COMPONENTS USED IN THE CIRCUIT

The circuit of audio level meter is constructed by using various

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

2.1 IC LM3916 Dot/Bar Display Driver.

2.2 IC CA3140 operational amplifier.

2.3 Electret condenser microphone.

2.4 Transistor BC558.

2.5 Diode 1N4148

2.6 Variable resistor.

2.7 LED-light emitting diodes (any color).

2.8 Battery 9V.

2.9 Resistors.

2.10 Capacitors.

2.11 Switches.

2.1 LM3916 Dot/Bar Display Driver

2.1.1 General Description

The LM3916 is a monolithic integrated circuit that senses analog voltage levels and

drives ten LEDs, LCDs or vacuum fluorescent displays, providing an electronic version of

the popular VU meter. One pin changes the display from a bar graph to a moving dot display.

LED current drive is regulated and programmable, eliminating the need for current limiting

resistors. The whole display system can operate from a single supply as low as 3V or as high

as 25V. The IC contains an adjustable voltage reference and an accurate ten-step voltage

divider. The high- impedance input buffer accepts signals down to ground and up to within

1.5V of the positive supply. Further, it needs no protection against inputs of ±35V. The input

buffer drives 10 individual comparators referenced to the precision divider. Accuracy is

typically better than 0.2 dB. Audio applications include average or peak level indicators, and

power meters. The LM3916 is extremely easy to apply. A 1.2V full-scale meter requires only one

resistor in addition to the ten LEDs. One more resistor programs the full-scale anywhere from 1.2V to

12V independent of supply voltage. LED brightness is easily controlled with a single pot. The

3

LM3916 is very versatile. The outputs can drive LCDs, vacuum fluorescents and incandescent bulbs

as well as LEDs of any color. Multiple devices can be cascaded for a dot or bar mode display for

increased range and/or resolution. Useful in other applications are the linear LM3914 and the

logarithmic LM3915.

2.1.2 Features

Fast responding electronic VU meter

Drivers LEDs, LCDs, or vacuum fluorescents

Bar or dot display mode externally selectable by user

Expandable to displays of 70 dB

Internal voltage reference from 1.2V to 12V

Operates with single supply of 3V to 25V

Inputs operate down to ground

Output current programmable from 1 mA to 30 mA

Input withstands ±35V without damage or false outputs

Outputs are current regulated, open collectors

Directly drives TTL or CMOS

The internal 10-step divider is floating and can be referenced to a wide range of

voltages.

The LM3916 is rated for operation from 0°C to +70°C.

LM3916N-1 is available in an 18-lead molded DIP package.

2.1.3 INTERNAL VOLTAGE REFERENCE OF LM3916

The reference is designed to be adjustable and develops a nominal 1.25V between the

REF OUT (pin 7) and REF ADJ (pin 8) terminals. The reference voltage is impressed across

program resistor R1 and, since the voltage is constant, a constant current I1 then flows

through the output set resistor R2 giving an output voltage of

Since the 120 μA current (max) from the adjust terminal represents an error term, the

reference was designed tominimize changes of this current with V+ and load changes. For

4

correct operation, reference load current should be between 80 μA and 5 mA. Load

capacitance should be less than 0.05 μF.

Fig.2.1 internal circuit of LM3916

5

2.1.4 Functional Description

The simplified LM3916 block diagram is included to give the general idea of the

circuit’s operation. A high input impedance buffer operates with signals from ground to 12V,

and is protected against reverse and overvoltage signals. The signal is then applied to a series

of 10 comparators; each of which is biased to a different comparison level by the resistor

string. The resistor string is connected to the internal 1.25V reference voltage. As the input

voltage varies from 0 to 1.25, the comparator outputs are driven low one by one, switching on

the LED indicators. The resistor divider can be connected between any 2 voltages, providing

that they are at least 1.5V below V+ and no lower than V−.

2.2 CA3140 Operational Amplifier

2.2.1 General Description

An operational amplifier is a DC-coupled high-gain electronic voltage amplifier with a

differential input and, usually, a single-ended output. An op-amp produces an output voltage

that is typically hundreds of thousands times larger than the voltage difference between its

input terminals. The popularity of monolithic op-amps was further improved upon the release

of the LM101 in 1967, which solved a variety of issues, and the subsequent release of the

μA741 in 1968.

2.2.2 CA3140

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

6

against damage from load terminal short circuiting to either supply rail or to ground.

2.2.3 Features of CA3140

• 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

2.3 Electret microphone

2.3.1 Description

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 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

7

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

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 lavalier 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.

2.3.2 Types

There are three major types of electret microphone

1)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.2)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.

8

3)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.

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.

2.4 Transistor

A transistor is a semiconductor device used to 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 the controlling (input) power, a transistor

can amplify a signal.

Fig. 2.3 different types of transistors

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 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

9

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

is determined by other circuit elements.

2.4.1 General description

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 labeled gate, 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.

2.4.2 Transistor as a switch

Transistors are commonly used as electronic switches, both for high-power

applications such as switched-mode power supplies and for low-power applications such as

logic gates.

Fig.2.4 BJT used as an electronic switch, in grounded-emitter configuration.

In a grounded-emitter transistor circuit, such as the light-switch circuit shown, as the

base voltage rises, the base and collector current rise exponentially. The collector voltage

drops because of the collector load resistance (in this example, the resistance of the light

bulb). If the collector voltage was zero, the collector current would be limited only by the

light bulb resistance and the supply voltage. The transistor is then said to be saturated - it will

10

have a very small voltage from collector to emitter. Providing sufficient base drive current is

a key problem in the use of bipolar transistors as switches. The transistor provides current

gain, allowing a relatively large current in the collector to be switched by a much smaller

current into the base terminal. The ratio of these currents varies depending on the type of

transistor, and even for a particular type, varies depending on the collector current. In the

example light-switch circuit shown, the resistor is chosen to provide enough base current to

ensure the transistor will be saturated.

In any switching circuit, values of input voltage would be chosen such that the output

is either completely off,or completely on. The transistor is acting as a switch, and this type of

operation is common in digital circuits where only "on" and "off" values are relevant.

2.4.3 Transistor as an amplifier

Fig.2.5 Amplifier circuit with common-emitter configuration

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

Various configurations of single transistor amplifier are possible, with some providing

current gain, some voltage gain, and some both.

From mobile phones to televisions, vast numbers of products include amplifiers for

sound reproduction, radio transmission, and signal processing. The first discrete transistor

audio amplifiers barely supplied a few hundred milliwatts, but power and audio fidelity

gradually increased as better transistors became available and amplifier architecture evolved.

11

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

inexpensive.

2.4.4 BC558

BC558 Transistor Parameters and Characteristics:

Name: BC558

Material of transistor: Si

Polarity: pnp

Maximum collector power dissipation (Pc): 500mW

Maximum collector-base voltage (Ucb): 30V

Maximum collector-emitter voltage (Uce): 25V

Maximum emitter-base voltage (Ueb): 5V

Maximum collector current (Ic max): 100mA

Maximum junction temperature (Tj): 150°C

Transition frequency (ft): 75MHz

Collector capacitance (Cc), Pf: -

Forward current transfer ratio (hFE), min/max: 75/475

Manufacturer of BC558 transistor: PHILIPS

Package of BC558 transistor: TO92

Application of BC558 transistor: Low Power, General Purpose

BC558 is a general purpose PNP transistor. It is used in switching and amplifier

applications. The DC current gain varies in range 110 to 800. It is also used as a complement

for transistors BC546 to BC550.

Pin Diagram:

12

Fig. 2.6 pinout of BC558

The transistor terminals require a fixed DC voltage to operate in the desired region of

its characteristic curves. This is known as the biasing. For amplification applications, the

transistor is biased such that it is partly on for all input conditions. The input signal at base is

amplified and taken at the emitter. BC558 is used in common emitter configuration for

amplifiers. The voltage divider is the commonly used biasing mode. For switching

applications, transistor is biased so that it remains fully on if there is a signal at its base. In

the absence of base signal, it gets completely off.

2.5 DIODE 1N4148

2.5.1 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.

13

Fig.2.7 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 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.

14

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.

2.5.2 Types of diodes

It is sometimes useful to summarise 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.

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.

15

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.

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.

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.

16

Fig.2.8 Different types of diodes

2.5.3 1N4148 Diode

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

signal processing.

Fig.2.9 1N4148 diode

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)

17

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.

2.6 Variable Resistor

Variable resistors consist of a resistance track with connections at both ends and

a wiper which moves along the track as you turn the spindle. The track may be made from

carbon, cermets (ceramic and metal mixture) or a coil of wire (for low resistances). The track

is usually rotary but straight track versions, usually called sliders, are also available.

Fig 2.10 Real time view of variable resistors

Fig 2.11 Internal view of variable resistors

18

Variable resistors are often called potentiometers in books and catalogues. They are

specified by their maximum resistance, linear or logarithmic track, and their physical size.

The standard spindle diameter is 6mm.

2.6.1 Connection of Potentiometer

Variable resistors used as potentiometers have all three terminals connected. This

arrangement is normally used to vary voltage, for example to set the switching point of a

circuit with a sensor, or control the volume (loudness) in an amplifier circuit. If the terminals

at the ends of the track are connected across the power supply then the wiper terminal will

provide a voltage which can be varied from zero up to the maximum of the supply.

2.7 Light Emitting Diode

A light-emitting diode (LED) is a semiconductor light source. LEDs are used as

indicator lamps in many devices, and are increasingly used for lighting. Introduced as a

practical electronic component in 1962, early LEDs emitted low-intensity red light, but

modern versions are available across the visible, ultraviolet and infrared wavelengths, with

very high brightness.

Fig 2.12 Real time view of led

19

2.7.1 Internal view of LED

The internal view of led is as shown in the figure below

Fig 2.13 Internal view of LED

2.7.2 Advantages

Efficiency: LEDs emit more light per watt than incandescent light bulbs.[82]

Their

efficiency is not affected by shape and size, unlike fluorescent light bulbs or tubes.

Color: LEDs can emit light of an intended color without using any color filters as

traditional lighting methods need. This is more efficient and can lower initial costs.

Size: LEDs can be very small (smaller than 2mm2[83]

) and are easily populated onto

printed circuit boards.

2.8 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.

2.8.1 Types of Batteries

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.

20

Fig 2.14 various types of cells

2.8.2 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 2.15 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.

2.9 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

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:

21

2.10 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 2.16 various forms of capacitor

2.10.1 TANTALUM CAPACITOR

Tantalum (atomic number 73) is a dense and ductile metal that is silver-gray in color.

It is considered both a refractory metal, due to its high melting point of 5,425 degrees

Fahrenheit (2,996 degrees Celsius), and a valve metal, due to its tendency to oxidize, which

forms an insulating film. For these reasons, tantalum is commonly used in capacitors, or

devices that store electrical charges. Cell phones, computers, mp3 players and many other

electronic devices use tantalum capacitors, which have several advantages over other types of

capacitors.

Fig.2.17 tantalum capacitor

There are numerous advantages to using tantalum capacitors over other types of capacitors.

22

1. Tantalum capacitors have a higher volumetric efficiency (CV/cc) when compared to

other types of capacitors.

2. Tantalum capacitors have superior frequency characteristics than many other types of

capacitors

3. These are highly reliable - electrical performance qualities do not degrade over time.

4. Has very low ESR (equivalent series resistance) of ceramic caps.

5. Finally, tantalum capacitors have an excellent wide operating range, from -55 degrees

Centigrade to +125 degrees Centigrade.

2.11 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.

2.11.1 Various forms of switches

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

Fig 2.17 various forms of switches

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.

23

CHAPTER 3

WORKING OF AUDIO LEVEL METER

The advantage of LED based audio level meter is we can extend the circuit to any

level of dB by cascading the LM 3916 IC’s and it is very simple too. Reference voltage will

decide the reference dB level (which is zero signal dB level). This reference voltage can be

set by varying the potentiometer connected to IC as we have internal reference voltage

generator in LM3916 IC.

We have two modes of display, dot and bar modes. We can alter between these modes by

using the DPST switch connected to IC.

3.1 What is BAR mode?

In this, all the LED’s representing dB levels which are below the present audio dB level are

turned ON.

3.2 What is DOT mode?

In this, only the LED representing the present audio level will be turned ON.

3.3 Block diagram of Audio level meter

Bellow figure shows the block diagram of audio level meter.

Fig.3.1 block diagram of audio level meter

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

3.3.1 Audio amplifier section

3.3.2 Audio level meter

3.3.2.1 Peak level detector

3.3.2.2 Dot/bar display LM 3916

24

3.3.2.3 LED section

3.3.1 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.

3.3.2 audio level meter section

The audio level meter consists of three sections they are discussed in the following section

3.3.2.1 Peak level detector

It makes audio level meter as peak reading one, so the circuit does not respond to the

lower levels or negative levels (which stabilizes the output which in turn makes the output to

be stable for a period that is required by human eye).

3.3.2.2 Dot/bar display LM3916

It is the heart of the total circuit. It receives signal from peak level detector and

processes it by using internal op-amp circuitry. It has the capability of interface with LED or

LCD as an output device. Here LED’s represent the audio dB levels from -20dB to +3dB.

3.3.2.3 LED section

The last part i.e. output part of the gadget is designed with LED’s. Total 10 LED’s are

used in the circuit to display the dB level from -20 to +3dB. LM3916 IC has the internal

current control. So there is no need of resistors in series with the LED’s. But in the circuit we

used the resistors for safety purpose.

3.4 Circuit description

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

of the chip. The LM3916 is fully configurable through the use of external components. In the

circuit shown, the potentiometer connected to pins 6, 7 and 8 set the reference for +3dB

signal. It should be adjusted so that when a 0dB audio signal is fed into the input, the 0dB

LED should just light. In addition to the LM3916, a peak detector circuit is built around the

BC558 transistor. Its purpose is to make the level meter a peak-reading one. This is

accomplished by rectifying the signal using a 1N4148 signal diode and then filtering using a

capacitor. This is essentially a clamper circuit. The 1M resistor acts as a bleeder resistor.

25

Hence, the value of this and the clamp capacitor determines the hold time of the meter. It is

meant to provide a fast attack and slow decay time. Experimenters may want to use a 1M pot

instead, to allow the decay time to be fixed.

Fig.3.2 circuit diagram of Audio Level Meter

A simple diode clamp is not used, since the diode's 0.6V forward drop will cause errors.

The Vbe drop of the transistor, however, compensates for this drop. Please note that the input

may be DC coupled, but it's wise to use a coupling capacitor to remove any possible offsets

present (due to improperly balanced opamps in previous stages.)

The LM3916 VU-meter chip can drive the LEDs in either dot mode or bar mode, which is

selected by connecting pin 9 to Vcc (Bar mode) or leaving it open (Dot mode). In bar mode,

the LED power consumption is quite high, and this might cause large currents to flow

through the GND pin of the chip. To avoid any problems that may occur, use a large supply

decoupling capacitor at the power entry of the board, and a 0.1μF decoupling capacitor close

to the chip. Keep all ground leads short and terminate them at a single point.

The LM3916 may be substituted by the LM3915, but the range of the display will be

rather limited, and will not correspond to the standard VU meter markings. An LM3914 may

be used only if a logarithmic amplifier is placed before driving the circuit. As with any

device, it is a good idea to read the LM3916 datasheets before constructing this circuit.

26

CHAPTER 4

RESULTS AND DISCUSSIONS

4.1 Results & Discussions

Hence the circuit of audio level 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 audio level meter circuit on PCB

The potentiometer in the circuit is varied for the desired reference level. 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.

27

CHAPTER 5

CONCLUSION & FUTURE SCOPE

5.1 Conclusion

Hence we have successfully fulfilled the project Audio level meter and

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

show the o/p audio level of tape recorders and players etc. This project has the power supply

of two 9V batteries. If any sound or speech is received by microphone it converts that into

electrical signal and audio level meter will show the dB level output using output LED’s.

5.2 Future scope

Here in this circuit we showed the output dB level from -20dB to +3dB. But this

circuit can be extended to any dB level by cascading the LM3916 IC’s.