NOISE METER
ABSTRACT
Impact of noise pollution is very high in industrialized areas and metropolitan
cities compared to other parts. Elevated noise in factories, workplaces can cause
hearing impairments, hypertension, annoyance, sleep disturbance, decreased
attention in children etc. The most important effect of chronic exposure to high
sound level is hearing loss. The reason for this is the damage in the stereo cilia
present in the cochlea of internal ear. The middle ear of human beings along with
the ear pinna amplifies the sound by a factor of 20 so that very high pressure reach
the internal ear which can create trauma in the cochlear structures leading to
irreversible hearing loss. The maximum sound level is considered as 140 dB and
permanent damage of hearing tissue occurs when the sound level is above 180 dB.
Since noise pollution creates this much harm to living creatures, it is the time to
implement a device which can indicate how much sound is get produced and
thereby we can reduce it.
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INTRODUCTION
Unwanted sound is considered as the noise pollution which can cause both
behavioral and health problems in human beings. Noise pollution can cause
Physiological changes in the body like hypertension, high stress level, sleep
disturbances etc. Normal pleasing sound level is around 30 dB but the normal
environmental noise is around 40-60 dB which can be considered as normal. But if
the noise level increases above 80dB, it can affect our psychomotor performance
and creates high stress level, loss of attention, Physiological changes etc. Over
exposure to high intensity affects the hearing ability of many animals. Very high
sound causes the reduction in the number of animals in the habitats leading to
habitat loss and may lead to extinction of species. Noise interferes with the use of
their own sound for communication related to reproduction and migration.
Noise level above 70 dB can increase the risk of cardiovascular problems due
to hypertension, increased Cortsol production etc. Elevated noise can cause arterial
constriction leading to elevated blood pressure and reduced blood flow. Annoyance
due to very high sound increases the Adrenaline level which is the most important
reason of arterial constriction and elevated blood pressure. Other effects include
fatigue, headache, gastric problem etc.
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UNIT OF SOUND
Decibel (dB) is the unit used to measure the intensity of sound. Decibel is
considered as a value between two powers rather than a specific unit. It is the
logarithmic unit used to describe a ratio. The ratio may be power, sound pressure,
voltage or intensity or several other things. ‘0 dB’ occurs when the measured
intensity is equal to the reference level ie, it is the sound level corresponding to
0.02 mpa. In this case, sound level is,
20 log (P measured / Preference) = 20 log 1 = 0 dB
0 dB does not mean no sound ; it means a sound level where the sound
pressure is equal to that of the reference level. It is also possible to have negative
sound levels. For example, -20 dB means a sound with pressure 10 times smaller
than the reference pressure. That is 2 kPa Sound pressure level is given in units of
dB(A) or dBA. Sound pressure level on the dBA scalar is easy to measure and is
therefore widely used. For sound pressure level, the reference level, (reference
level for air) is usually chosen as 20 micropascals (20 kPa), or 0.02 mPa.
Some of the common sound levels in terms of decibel are,
1.
Weakest sound
0 dB
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2.
Silent environment with natural sound
30 dB
3.
Normal human conversation
60-70 dB
4.
City with heavy traffic
80-90 dB
5.
Drilling or grinding machinery
90-110 dB
6.
Jet aircraft & explosion
140-150 dB
Psychologists say that sense of hearing is roughly logarithmic. That is, we
have to increase the sound intensity by the same factor to have the same increase in
loudness.
The ‘Phon’ is a unit that is related to dB by the psychophysically measured
frequency response of the ear. “Sone” is defined to be equal to 40 Phon. The Sone
is derived from Psychophysical measurements which involved volunteers adjusting
sounds until they judge them to be twice as loud.
Here we introduce a simple circuit that senses and displays the noise intensity level
in your room.
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MATERIALS REQUIRED
Components Description
1. Resistors
A resistor is a component of an electrical circuit that resists the flow of
electrical current .A resistor has two terminals across which electricity must
pass, and is designed to drop the voltage of the current as it flows from one
terminal to the next. A resistor is primarily used to create and maintain a
known safe current within an electrical component.
Resistor
Resistance is measured in ohms, after Ohm’s law. This rule states that
electrical resistance is equal to the drop in voltage across the terminals of the
resistor divided by the current being applied to the resistor .A high ohm rating
indicates a high resistance to current. This rating can be written in a number
of different ways depending on the ohm rating.
The amount of resistance offered by a resistor is determined by its physical
construction. A resistor is coated with paint or enamel, or covered in molded
plastic to protect it. Because resistors are often too small to be written on, a
standardized colour coding systems used to identify them. The first three
colors represent ohm value, and fourth indicate tolerance or how close by
percentage the resistor is to its ohm value. This is important for two reasons;
the nature of resistor construction is imprecise, and if used above its
maximum.
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Maximum power handling capacity of Resistors is
¼ Watt Max. 50mA
½ Watt Max. 70mA
1 Watt Max. 100mA
2 Watt Max. 140mA
20 Watt
Max.440Ma
2. Capacitors
The capacitor’s function is to store electricity or electrical energy. The
capacitor also functions as a filter passing alternating current (AC) and
blocking direct current (DC).The symbol is used to indicate a capacitor in a
circuit diagram. The capacitor is constructed with two electrode plates facing
each other but separated by an insulator. When DC voltage is applied to the
capacitor an electric charge is stored on each electrode. While the capacitor is
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charging up, current flows. The current will stop flowing when the capacitor
has fully charged.
Disc Capacitor
Electrolytic Capacitor
Different kinds of capacitors use different materials for the dielectric.
Different kinds of capacitors are as follows
 Electrolytic capacitors(electro chemical type capacitors)
 Tantalum capacitors
 Ceramic capacitors
In Disc capacitors, only a number is printed on its body so it is very difficult to
determine its value in PF, KPF, uF, n etc. In some capacitor, its value is printed
in uF eg.0.1 in some others EIA code is used e.g. 104.
One or two numbers on the capacitor represents value in PF e.g. 8 = 8PF
If the third number is zero, then the value is in P e.g. 100 = 100PF
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If the capacitor has three numbers and the third number is not a zero, it
represents the number of zeros after the first and second digits e.g. 104 = 10 –
0000 PF
If the value is obtained in PF, it is easy to convert it into KPF or uF
PF / 1000 = KPF or n
PF / 10, 00000 = uF
For example, if the capacitor is 104, then it is 10-0000 PF or 100 KPF or n
or 0.1 uF
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Multilayer ceramic capacitors
Polystyrene film capacitors
Electric double layer capacitors(super capacitors)
Polyester film capacitors
Poly propylene capacitors
Mica capacitors
Metalized polyester film capacitors
Variable capacitors
3. Integrated Circuits
Op Amp
The OpAmp was originally designed to carry out mathematical operations in
analogue computers, such as bombsights, but was soon recognized as having
many other applications. The OpAmp usually comes in the form of an 8 pin
integrated circuit, the most common one being the type 741. It has two
inputs and one output. The input marked with a - sign produces an amplified
inverted output. The input marked with a + sign produces an amplified but
non inverted output. The OpAmp requires positive and negative power
supplies, together with a common ground. Some circuits can be designed to
work from a single supply. If the two inputs are joined together, then the
output voltage should be midway between the two supply rails, i.e. zero
volts.
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If it is not, then there are two connections for adding a potentiometer, to
remove this OFFSET. The OpAmp has a very high gain, typically (100 dB)
100,000 times. Looking at the left hand diagram, an input with a swing of a
fraction of millivolts produces an output that changes between + 12 volts
and - 12 volts. In most cases this gain is excessive, and is reduced by
negative feed back. Looking at the right hand diagram we can see that the
OpAmp amplifies right down to dc. Gain falls quite rapidly as the frequency
increases. In fact the bandwidth (the point at which the output has fallen by 3
dB) is only 1 kHz. This is also improved upon by the use of negative
feedback. The input impedance is high, 1M. The output impedance is low,
150 ohms.
Display Driver
LM 3914 / 3915 / 3916 versions ICs are used in display circuits to drive
either individual LED or Matrix LED. These are mainly used in circuits
where precision output display is needed. Its each output becomes low one
by one with the increment of 125 milli volts in the input. These ICs are used
in Audio displays, Temperature meters, Decibel meters etc.
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The major difference between LM 3914, LM3915 and LM 3916 are
LM 3914 Internal resistors have equal value. Produce linear response. Used
as volt meter
LM 3915 Scale Logarithmically and span 0dB to 30 dB in ten 3 dB steps.
Used in signal strength measurements.
LM 3916 Internal resistors related to semi-log fashion to simulate VU meter.
Pin connections are same in all ICs.
These ICs have 10 outputs each capable of sinking current to light LEDs
brightly. Up to 4 LEDs can be connected to each output serially if the supply
voltage is more than 9 volts. LED does not require a series resistor since the
IC can regulate output current according to the value of the Programme
resistor in the pins 6 and 7.
4. LEDs
The LED has a semiconductor chip placed in its centre. The semiconductor
consists of two regions namely a P region that has positive charge carriers and
an N region with negative charge carriers. There are three layers in the chip.
An active photon generating material is sandwiched between the P and N type
materials so that photons will be generated when the electrons and holes
combines. That is when a potential difference is applied between the P and N
materials through the LED terminals, holes from the P layer and electrons
from the N layer move towards the active material where they combine to
produce the light though the phenomenon of Electroluminescence
As the name implies light emitting diodes exploit the property of the pn
junction to emit photons when it is biased. LEDs are specially made to emit
light and there was a revolution in the LED industry during the past few
years. LEDs form an inevitable part in the modern electronics as simple
indicators to optical communication devices. The history of LED date backs
to 1907 when Captain Henry Joseph observed the property of electro10
luminescence in Silicon Carbide. The first LED was born in 1962. It was
developed by Holonyak worked at General Electric (GE). It was a GaAsP
device. The first commercial version of LED came on 1960s. LED industry
made a boom during 1970s with the introduction of Gallium Aluminium
Arsenide (GaAlAs). These LEDs are high bright types and are ten times
brighter than the diffused varieties. Blue and White LEDs born in 1990 and
used Indium Gallium Nitride (InGaN) as the semiconductor. White LED
contains a blue chip with white inorganic Phosphor. When blue light strikes
the phosphor, it emits white light.
Secrets behind LEDs
Brightness is an important aspect of LED. Human eye has maximum
sensitivity to light near 550 nm region of yellow – green part of the
spectrum. That is why a Green LED looks brighter than a Red LED even
though both uses same current. Three parameters of LED are responsible for
its performance.
a. Luminous flux – It is the light energy radiating from the LED. It is
measured in terms of Lumen ( lm ) or Milli lumen ( mlm )
b. Luminous intensity – is the luminous flux covering a large area. It is
measured as Candela ( cd ) or milli candela ( mcd ) Brightness of LED is
directly related to its luminous intensity.
c.Luminous efficacy - is the emitted light energy relative to the input power.
It is measured in terms of lumen per watt ( lm w).
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Forward current, Forward voltage, Viewing angle and Speed of response are
the factors affecting the brightness and performance of LEDs. Forward
current ( IF ) is the current flowing through the LED when it is forward
biases and it should be restricted to 10 to 30 milli amperes other wise LED
will die. Viewing angle is the off – axis angle at which the luminous
intensity fall to half its axial value. This is why the LED becomes brighter in
full on condition. High bright LEDs have narrow viewing angle so that light
is focused into a beam. Forward voltage ( VF ) is the voltage drop across the
LED when it conducts. The forward voltage drop range from 1.8 V to 2.6
Volts in ordinary LEDs and in Blue and White it will go up to 5 volts. Speed
of response denotes how fast an LED switch on and off. This is an important
factor if LEDs are used in communication systems.
LED is a current dependent device. Minimum 20 mA current is required to
get sufficient brightness. If excess current is flowing through the LED, its
semiconductor heats up and gradually deteriorate. This leads to poor
performance and finally LED will be destroyed. Wattage of the LED is the
forward voltage multiplied by the forward current. In high current LEDs,
forward current can go up to 350 mA. In these devices the wattage depends
on the forward voltage drop ranging from 1.8 volts to 4 volts. Therefore an
average of 1 watt is found in high current LEDs
LED is always connected to the power supply through a series resistor. This
resistor is called as” Ballast resistor” which protects LED from damage due to
excess current. It regulates the forward current to the LED to a safer limit and
protects it from burning. Value of the resistor determines the forward current
and hence the brightness of LED. The simple equation Vs – Vf / If is used to
select the resistor value. Vs represent input voltage of the circuit, Vf the
forward voltage drop of LED and If, the allowable current through the LED.
The resulting value will be in Ohms. It is better to restrict the current to a
safer limit of 20 mA.
5. Condenser MIC
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6. Piezo Buzzer
7. Common PCB ( Perf Board )
Most experimenters are familiar with "Perf board" which is a pre-drilled
circuit for creating prototypes of simple circuits. It's not too expensive and for
more easier to get started with than etching PCB's. The components are
mounted by inserting the leads through the most appropriate holes then are
wired on the back side, usually by bending the leads over to the desired
connection point.
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CIRCUIT DESCRIPTION
The Noise meter is designed to measure the sound level in the room in terms
of decibel. The circuit has three sections – A sound detector, Inverting
amplifier and an analogue display driver. The input section has a sound
detector comprising a condenser Micro phone and associated components like
R1, C4 and R2. Resistor R1 regulates the current flowing into the mic, and
determines its gain Capacitor C4 is the DC blocking capacitor to remove DC
fraction from the sound signals generated by the mic. Resistor R4 (12K) along
with feed back resistor R5 (10M) determines the gain of the amplifier built
around IC 1.
Operational amplifier CA 3130 (IC 1) is designed as a mic amplifier using
some discrete components. Resistor R3 (10K) and R4 (10K) provides half
supply voltage (4.5V) to the Non-inverting input (pin 3) of IC 1. The sound
signals from the Micro phone are fed to the Inverting input (pin 2) of IC 1
through capacitor C4 and resistor R2. Capacitor C4 blocks the DC entering
into the OP Amp since it may affects the functioning of the OP Amp. The
output of IC 1 (pin 6) is connected to the inverting input (pin 2) through the
feed back resister R5 (10M). Since the input impedance of IC 1 i.e. very high,
even a small current can activate the OP Amp.
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CIRCUIT DIAGRAM
Prototype of Electronic Noise Meter
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The output of IC 1 is given to the preset VR 1 via capacitor C5 which is used
to control the volume. Capacitor C5 blocks the DC fractions from the
amplified sound and allows only AC signals to pass through the preset VR 1.
The AC signal from the wiper of VR 1 is rectified through a diode pump
comprising D1, D2 and C6 and R6. The diode pump rectifies the AC signals
from the wiper of preset VR 1 and maintains it at the output level of IC 1.
Capacitor C6 acts as a reservoir capacitor for DC and resistor R6 act as the
discharge path for its charge.
The display section is built around the monolithic display driver IC LM 3914
(IC2). It senses the analogue voltage and drives ten LEDs to provide a
logarithmic analogue display. Current through the LEDs is regulated by the
internal resistor of IC2 eliminating the need of external resistors. The output
pins of LM 3914, 18 to 10 sinks current and turns low one by one from 18 to
10, as the input pin 5 receives an increment of 125 mV. DC. Pin 9 of IC2 is
connected to the supply line to set a dot mode’ display.
When the input of IC2 gets 125 mV from the diode pump, first LED (pin 18)
lights and the remaining LEDs at pins 17 to 11 lights or the input signal
increases with 125 mV increments. When the LED at pin 10 lights, PNP
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transistor conducts due to negative base bias (Normally remains positive
through R7) and it conducts. This activates the buzzer.
Here in the circuits each LED represents 3 dB sound level. That is, LED 1
indicates 3 dB and LED 10 indicates 30 dB. Present VR1 can be used to
adjust the input signal to 1C2 around 125 mV so that the first LED lights to
indicate 3dB. Then with each increment of 125 mV at the input of 1C2, LEDs
light one by one showing the sound levels, 6 dB, 9 dB, 12 dB, 15 dB, 18 dB,
21 dB, 24 dB, 27 dB and 30 dB. When the sound level crosses 30 dB, buzzer
sounds, indicating that the noise level is increasing above the normal limit.
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COMPONENTS
RESISTORS
R1
=
10 K
R2
=
12 K
R3
=
10 K
R4
=
10 K
R5
=
10 M
R6
=
27 K
R7
=
10 K
R8
=
4.7 K
R9
=
1K
R10
=
5K
CAPACITORS
C1
=
1000 uF, 26V
C2
=
0.1uF
C3
=
0.1uF
C4
=
0.22 uF
C5
=
4.7 uF, 25 V
C6
=
1 uF , 16 V
C7
=
2.2 uF , 16V
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TRANSISTOR (T1)
BC 558
IC CHIPS
IC 1
7809
IC 2
CA 3130
IC 3
LM 3914
DIODES
D1
IN 4148
D2
IN 4148
D3
IN 4001
MICROPHONE
PRESET VR 1- 1K
LED
LED I - LED 4 - Green
LED 5 - LED 7 - Yellow
LED 8 - LED 10 – Red
BATTERY SNAP
9 V PP3 BATTERY
COMMON PCB
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WORKING OF THE CIRCUIT
The circuit comprises a sound intensity sensor and a display unit.
The sound intensity sensor is built around a condenser microphone. Op amp
IC CA 3130 (IC2) and associated components Op amp IC2 is configured as a
high gain inverting amplifier. The voltage supply to IC2 at its non inverting
Pin 3 is divided to half by resistors R3 and R4, which is also used as the
reference voltage. Resistor R1 determines the sensitivity of the condenser
microphone.
The microphone picks up sound vibrations and converts them into the
corresponding electric pulses, which are fed to the inverting input of IC 2 (Pin
2) via capacitor C4 and resistor R2 Capacitor C4 blocks any DC entering the
op-amp, Since it may affect the functioning of the op-amp. The output of IC 2
is connected to the inverting input through resistor R5 (10 M) for negative
feed back. Since the input impedance of IC2 is very high even a small current
can activate the op-amp.
The output of IC2 is given to preset VR1 via capacitor C5, which is used to
control the volume. Capacitor C5 blocks DC, allowing only AC to pass
through preset VR 1. The AC signals from the wiper of VR 1 are fed to a
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diode pump comprising diodes D1 & D2. The diode pump rectifies the AC
and maintains it at the output level of IC2. Capacitor C6 acts as a reservoir
capacitor for DC and resistor R6 provides the path for its discharge.
The display circuit is built around monolithic IC LM 3914 (IC3), which
senses the analogue voltage and drives ten LEDs to provide a logarithmic
analogue display. Current through the LEDs is regulated by the internal
resistor of IC3, eliminating the need for external resistors. The built in low
bias input buffer of IC3 accepts signals down to ground potential and drives
ten individual comparators inside IC3. The outputs of IC3 go low in a
descending order from 18 to 10 as the input voltage increases.
Each LED connected to the output to IC3 represents the sound level of 3 dB,
so when all the 10 LEDs glow it means the sound level intensity is 30 dB.
Pin 9 of IC 3 is connected to 9V to get the dot-mode display. In the dot-mode
display, there is a small amount of overlap between segments. This assures
that at no time will all the LEDs be ‘off’.
When output pin 10 of IC 3 goes low, pnp transistor T1 gets base bias
(normally cut – off due to resistor or R7) to the sound piezobuzzer (PZ 1)
connected to its collector.
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The circuit can be constructed on any general purpose PCB. Condenser
microphone should be connected using a shield wire and enclosed in a tube to
increase its sensitivity. For audiovisual indicators, use a small DC Piezo
buzzer and transparent LEDs. Adjust preset VR 1 until only the first LED
light up keep the circuit near the audio equipment or TV set to monitor the
audio level.
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CONCLUSION
This ‘Electronic Noise meter’ is made from the basic components like.
Transistors, resistors, capacitors, diodes IC chips etc is meant to display the
noise level in a room. The basic advantage of this Noise meter is that it woks
in a 9-V battery and hence would work even at the time of power failure.
This device can be placed at hospitals, libraries, laboratories, Silent Zones
etc to monitor the sound levels.
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REFERENCES
 Electronic principles- Albert Paul Malvino
 Principles of electronics- V.K.Mehta
 Electronic fundamentals and applications - Millman & Halkias
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WEBSITES
www.electronicsforu.com
www.electroschematics.com
www.dmohankumar.wordpress.com
www.electroskan.wordpresscom
www.alldatasheets.com
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