mini project documentation
Post on 02-Nov-2014
78 Views
Preview:
TRANSCRIPT
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.
1
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
2
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
3
2.1.3 Pinouts
Fig.2.1.3 Pinouts of IC CA3140
4
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
5
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
6
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.
7
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
8
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
9
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.
10
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
11
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.
12
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.
13
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
14
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
15
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
16
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
17
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.
18
19
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.
20
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
21
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.
22
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
23
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.
24
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.
25
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.
26
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.
27
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.
28
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.
29
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.
30
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.
31
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
32
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
33
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
34
top related