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. ResistorsA 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. CapacitorsThe 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

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

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If the value is obtained in PF, it is easy to convert it into KPF or uFPF / 1000 = KPF or nPF / 10, 00000 = uFFor example, if the capacitor is 104, then it is 10-0000 PF or 100 KPF or n or 0.1 uF

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 CircuitsOp 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

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to 1907 when Captain Henry Joseph observed the property of electro-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 = 1 K

R10 = 5 K

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 558IC CHIPSIC 17809IC 2CA 3130IC 3LM 3914DIODESD1IN 4148D2IN 4148 D3IN 4001MICROPHONEPRESET VR 1- 1KLED LED I - LED 4 - GreenLED 5 - LED 7 - YellowLED 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

WEBSITES www.electronicsforu.com www.electroschematics.com www.dmohankumar.wordpress.com www.electroskan.wordpresscom www.alldatasheets.com

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