Mental Stress Identifier Project Report Electronics B.E.

GLOBUS ENGINEERING COLLEGE, BHOPAL

Table of Content

1. Project Introduction --------------------- 1

2. About Mental Stress --------------------- 2

3. Principle Used --------------------- 5

4. Circuit Description --------------------- 6

5. Circuit Diagram --------------------- 8

6. PCB Layout ----------------------9

7. Device Peripherals List ----------------------10

8. Peripherals’ Description ----------------------11

9. PCB Manufacturing process ----------------------37

10. Circuit Fabrication ----------------------39

11. Initializing & Working ----------------------47

12. Application ----------------------49

13. Farther Development ----------------------50

14. Chronology -----------------------51

15. Bibliography ----------------------52

GLOBUS ENGINEERING COLLEGE, BHOPAL

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PROJECT INTRODUCTION

Our project MENTAL STRESS IDENTIFIER is an instrument that

measures the mental stress or tension of human body. This stress

Monitor lets you assess your emotional pain. If the stress is very high, it

gives visual indication through a light emitting diode (LED) display along

with a warning beep. The device is small enough to be worn around the

wrist.

This device needs to initialize for person using it. We have to set device

in initial state which is for relaxed state, then it ready for use.

This is a low cost device may be useful in many areas where

psychological presence being tested. A set of component connected in

a manner so that the change of resistance of body can be detected,

which is key objective of device.

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ABOUT STRESS

'What is stress and how it affects the body' is a common query that is

heard everywhere nowadays. The stress definition is very simple. When

our body or mind cannot meet the demands made upon them, stress

arises! Let us explore more about what stress is...

WHAT IS STRESS: - Researchers view stress as the psychological and

physiological condition that a person experiences when a situation is

perceived as threatening, harmful or demanding.

DEFINITION: -

Hans Selye, the father of modern stress research,

defined Stress as "any event which may make demands upon the

organism, and set in motion a non-specific bodily response which leads

to a variety of temporary or permanent physiological or structural

changes".

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The three important clauses of definition:-

1. Demands upon the organism: Stress calls for action (response) from our body.

2. Non Specific Bodily Response: Whether the stress inducing event is negative/harmful (death of a dear friend), or positive/exciting (winning a 1 million lottery), the physiological response of our body will be same! Meaning, there is no specific response to a particular event. All events evoke the same type of response, though the emotional intensity may vary.

3. Temporary or permanent physiological or structural changes: The after effects of stress can cause either temporary or permanent changes in our body. What these changes are we will see later.

Definition of Stress by Richard S Lazarus

Stress is a condition or feeling experienced when a person perceives

that 'demands exceed the personal and social resources the individual

is able to mobilize.

STRESS MODEL & EFFECT ON BODY

General adaptation syndrome: It is a stress model. It has three stages which are defined by Dr. Selye.

Alarm

Resistance

Exhaustion

ALARM

When the threat or stressor is identified or realized, the body's stress response is a state of alarm. During this stage adrenaline will be produced in order to bring about the fight-or-flight response. There is also some activation of the HPA axis, producing cortisol.

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RESISTANCE

Resistance is the second stage. If the stressor persists, it becomes necessary to attempt some means of coping with the stress. Although the body begins to try to adapt to the strains or demands of the environment, the body cannot keep this up indefinitely, so its resources are gradually depleted.

EXHAUSTION

Exhaustion is the third and final stage in the GAS model. At this point, all of the body's resources are eventually depleted and the body is unable to maintain normal function. The initial autonomic nervous system symptoms may reappear (sweating, raised heart rate etc.). If stage three is extended, long term damage may result as the capacity of glands, especially the adrenal gland, and the immune system is exhausted and function is impaired resulting in decompensation.

The result can manifest itself in obvious illnesses such as ulcers, depression, diabetes, trouble with the system or even cardiovascular problems, along with other mental illnesses.

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PRINCIPLE USED

This Instrument is based on the principle that the resistance of skin

varies in accordance with your emotional states. If the stress level is

high the skin offers less resistance, and if the body is relaxed the, skin

resistance is high.

The low resistance of the skin during high stress is due to an increase

in the blood supply to the skin. This increases the permeability of the

skin and hence the conductivity for electric current.

This property of the skin is used here to measure the stress level. The

touch pads of stress meter sense the voltage across the touch pads and

convey the same to the circuit. The circuit is very sensitive and

detects even a minute voltage variation across the touch pads.

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CIRCUIT DESCRIPTION

The circuit comprises signal amplifier and analogue display

sections.

PARTS LIST

Semiconductors:

IC1 - LM3915 ,3-25V supply operated

T1 -BC548 CE amplifier mode

D1 - 1N4148 rectifier diode

ZD1 -5.1V, 0.5W

Resistors:

LED1-LED5 - 5mm light-emitting diode

R1 - 560E

R2 - 1.2 kilo ohm

R3,R4 - 470E

R5 -1 kilo ohm

R6 - 47 kilo ohm

VR1 -1M

VR2 -47 K

Capacitors:

C1 - 10µF, 16V

C2,C3 - 100µF, 16V

Miscellaneous:

PZ1 -piezo electric buzzer

B -9V battery

S -Switch

X -Touch Pads

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Voltage variations from the sensing pads are amplified by transistor

BC548 (T1), which is configured as a common-emitter amplifier. The

base of T1 is connected to one of touch pads through resistor R1 and to

ground rail through potmeter VR1.

Diode D1 maintains proper biasing of T1 and capacitor C1 keeps the

voltage from the emitter of T1 steady.

IC LM3915 is used as main component of the circuit. This is a monolithic

integrated circuit that senses analogue voltage levels at its pin 5 and

displays them through LEDs providing a logarithmic analogue display.

The circuit has 5 LEDs as visual indicator. The LEDs are connected to the

IC LM3915 from pin 14-18. Higher stress signals can be led out by pin

14, hence there is a piezo-electric buzzer PZ1 is connected between

LED5 & pin 14.

Resistors R4 and R5 and capacitor C2 form the flashing elements.

Resistor R3 maintains the LED current. Zener diode ZD1 in series with

resistor R6 provides regulated 5V to the circuit.

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CIRCUIT DIAGRAM

Fig: Stress Meter Circuit Using LM3915

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PCB LAYOUT

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DEVICE PERIPERAL LIST

Name Quantity

1. IC -LM3915 1 pc.

2. Transistor BC548 1 pc.

3. Diode 1N4148 1 pc.

4. Zener Diode 0.5W 1 pc.

5. LEDs (2 red, 2 green, 1 yellow) 5 pc.

6. Variable Resistor 1M 1pc.

7. Variable Resistor 47k 1pc.

8. Resistor 560E 1pc.

9. Resistor 1.2k 1pc.

10. Resistor 470E 2pc.

11. Resistor 1k 1pc.

12. Resistor 47k 1pc.

13. Capacitor 10µF, 16V 1pc.

14. Capacitor 100 µF, 16V 2pc.

15. Piezo Buzzer 1pc.

16. Switch 1pc.

17. Battery 9V 1pc.

18. Touch Pad 1pc.

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PERIPERAL DESCRIPTION

RESISTORS: -

A Resistor is a heat-dissipating element and in the electronic

circuits it is mostly used for either controlling the current in the circuit

or developing a voltage drop across it, which could be utilized for many

applications. There are various types of resistors, which can be

classified according to a number of factors depending upon:

(I) Material used for fabrication

(II) Wattage and physical size

(III) Intended application

(IV) Ambient temperature rating

(V) Cost

Basically the resistor can be split in to the following four parts from

the construction viewpoint.

(1) Base

(2) Resistance element

(3) Terminals

(4) Protective means.

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The following characteristics are inherent in all resistors and may be

controlled by design considerations and choice of material i.e.

Temperature co–efficient of resistance, Voltage co–efficient of

resistance, high frequency characteristics, power rating, tolerance &

voltage rating of resistors. Resistors may be classified as

(1) Fixed

(2) Semi variable

(3) Variable resistor.

In our project carbon resistors are being used.

A resistor is a block of material that limits the flow of current. The

greater the resistance, the lower the current will be. Since conductors

have an "electron cloud" around the atoms, they behave like a wide

pipe filled with water, and have low resistance to a flow of water.

Resistance can vary from very small to very large. A superconductor has

zero resistance, while something like the input to an op-amp can have a

resistance near 1012 Ω, and even higher resistances are possible. For

most materials, as temperature increases resistance tends to increase

as well. Resistance converts electrical energy into heat. Resistors which

dissipate large amounts of power are cooled so that they are not

destroyed, typically with finned heat sinks.

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Function

Resistors restrict the flow of electric current, for example a resistor is

placed in series with a light-emitting diode (LED) to limit the current

passing through the LED. Resistor values are normally shown using

coloured bands.

Each colour represents a number as shown in the table.

Most resistors have 4 bands:

The first band gives the first digit.

The second band gives the second digit.

The third band indicates the number of zeros.

The fourth band is used to shows the tolerance (precision) of the

resistor, this may be ignored for almost all circuits but further

details are given below.

Fig(3.5)

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This resistor has red (2), violet (7), yellow (4 zeros) and gold bands.

So its value is 270000 = 270 k .

On the circuit diagrams is usually omitted and the value is written 270K.

CAPACITORS:-

The fundamental relation for the capacitance between two flat plates

separated by a dielectric material is given by:-

C=0.08854KA/D

Where: -

C= capacitance in pf.

K= dielectric constant

A=Area per plate in square cm.

D=Distance between two plates in cm

Design of capacitor depends on the proper dielectric material with

particular type of application. The dielectric material used for

capacitors may be grouped in various classes like Mica, Glass, air,

ceramic, paper, Aluminum, electrolyte etc. The value of capacitance

never remains constant. It changes with temperature, frequency and

aging. The capacitance value marked on the capacitor strictly applies

only at specified temperature and at low frequencies.

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Function

Capacitors store electric charge. They are used with resistors in

timing circuits because it takes time for a capacitor to fill with charge.

They are used to smooth varying DC supplies by acting as a reservoir of

charge. They are also used in filter circuits because capacitors easily

pass AC (changing) signals but they block DC (constant) signals.

Capacitance

This is a measure of a capacitor's ability to store charge. A large

capacitance means that more charge can be stored. Capacitance is

measured in farads, symbol F. However 1F is very large, so prefixes are

used to show the smaller values.

Three prefixes (multipliers) are used, µ (micro), n (nana) and p (picot):

µ means 10-6 (millionth), so 1000000µF = 1F

n means 10-9 (thousand-millionth), so 1000nF = 1µF

p means 10-12 (million-millionth), so 1000pF = 1nF

Capacitor values can be very difficult to find because there are many

types of capacitor with different labeling systems!

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There are many types of capacitor but they can be split into two

groups, polarized and Unpolarised. Each group has its own circuit

symbol.

Electrolytic Capacitors

Electrolytic capacitors are polarized and they must be connected the

correct way round, at least one of their leads will be marked + or -.

They are not damaged by heat when soldering.

There are two designs of electrolytic capacitors; axial where the leads

are attached to each end (220µF in picture) and radial where both

leads are at the same end (10µF in picture). Radial capacitors tend to be

a little smaller and they stand upright on the circuit board.

It is easy to find the value of electrolytic capacitors because they are

clearly printed with their capacitance and voltage rating. The voltage

rating can be quite low (6V for example) and it should always be

checked when selecting an electrolytic capacitor. If the project parts list

does not specify a voltage, choose a capacitor with a rating which is

greater than the project's power supply voltage. 25V is a sensible

minimum for most battery circuits.

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Tantalum Bead Capacitors

Tantalum bead capacitors are polarized and have low voltage ratings

like electrolytic capacitors. They are expensive but very small, so they

are used where a large capacitance is needed in a small size.

Modern tantalum bead capacitors are printed with their capacitance,

voltage and polarity in full. However older ones use a colour-code

system which has two stripes (for the two digits) and a spot of colour

for the number of zeros to give the value in µF. The standard colour

code is used, but for the spot, grey is used to mean × 0.01 and white

means × 0.1 so that values of less than 10µF can be shown. A third

colour stripe near the leads shows the voltage (yellow 6.3V, black 10V,

green 16V, blue 20V, grey 25V, white 30V, pink 35V). The positive (+)

lead is to the right when the spot is facing you: 'when the spot is in

sight, the positive is to the right'.

For example: blue, grey, black spot means 68µF

For example: blue, grey, white spot means 6.8µF

For example: blue, grey, grey spot means 0.68µF

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Unpolarised capacitors (small values, up to 1µF)

Fig(3.12)

Circuit symbol:

Small value capacitors are Unpolarised and may be connected either

way round. They are not damaged by heat when soldering, except for

one unusual type (polystyrene). They have high voltage ratings of at

least 50V, usually 250V or so. It can be difficult to find the values of

these small capacitors because there are many types of them and

several different labeling systems!

Many small value capacitors have their value printed but without a

multiplier, so you need to use experience to work out what the

multiplier should be!

For example 0.1 means 0.1µF = 100nF.

Sometimes the multiplier is used in place of the decimal point:

For example: 4n7 means 4.7nF.

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Capacitor Number Code

A number code is often used on small capacitors where printing is

difficult:

the 1st number is the 1st digit,

the 2nd number is the 2nd digit,

The 3rd number is the number of zeros to give the capacitance in

pF.

Ignore any letters - they just indicate tolerance and voltage rating.

For example: 102 means 1000pF = 1nF (not 102pF!)

For example: 472J means 4700pF = 4.7nF (J means 5% tolerance).

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Capacitor Colour Code

Fig (3.13)

A colour code was used on polyester capacitors for many

years. It is now obsolete, but of course there are many

still around. The colours should be read like the resistor

code, the top three colour bands giving the value in pF.

Ignore the 4th band (tolerance) and 5th band (voltage

rating).

For example:

Brown, black, orange means 10000pF = 10nF = 0.01µF.

Note that there are no gaps between the colour bands, so

2 identical bands actually appear as a wide band.

For example: wide red, yellow means 220nF = 0.22µF.

Colour Code

Colour Number

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Grey 8

White 9

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DIODES:-

Circuit symbol

Function

Fig (3.6)

Diodes allow electricity to flow in only one direction. The arrow of the

circuit symbol shows the direction in which the current can flow.

Diodes are the electrical version of a valve and early diodes were

actually called valves.

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Forward Voltage Drop

Electricity uses up a little energy pushing its way through the diode,

rather like a person pushing through a door with a spring. This means

that there is a small voltage across a conducting diode, it is called the

forward voltage drop and is about 0.7V for all normal diodes which are

made from silicon. The forward voltage drop of a diode is almost

constant whatever the current passing through the diode so they have

a very steep characteristic (current-voltage graph).

Reverse Voltage

When a reverse voltage is applied a perfect diode does not conduct,

but all real diodes leak a very tiny current of a few µA or less. This can

be ignored in most circuits because it will be very much smaller than

the current flowing in the forward direction. However, all diodes have a

maximum reverse voltage (usually 50V or more) and if this is exceeded

the diode will fail and pass a large current in the reverse direction, this

is called breakdown.

Ordinary diodes can be split into two types: Signal diodes which pass

small currents of 100mA or less and Rectifier diodes which can pass

large currents.

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Zener diodes:-

Example:

Circuit symbol:

a = anode, k = cathode

Fig(3.9)

Zener diodes are used to maintain a fixed voltage. They are designed to

'breakdown' in a reliable and non-destructive way so that they can be

used in reverse to maintain a fixed voltage across their terminals. The

diagram shows how they are connected, with a resistor in series to limit

the current.

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Zener diodes can be distinguished from ordinary diodes by their code

and breakdown voltage which are printed on them. Zener diode codes

begin BZX... or BZY... Their breakdown voltage is printed with V in place

of a decimal point, so 4V7 means 4.7V for example.

Zener diodes are rated by their breakdown voltage and maximum

power:

The minimum voltage available is 2.7V.

Power ratings of 400mW and 1.3W are common.

Light Emitting Diodes (LEDs):-

Example:

Circuit symbol:

Fig(3.9)

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Function

LEDs emit light when an electric current passes through them.

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.

The LED is based on the semiconductor diode. When a diode is forward

biased (switched on), electrons are able to recombine with holes within

the device, releasing energy in the form of photons. This effect is called

electroluminescence and the color of the light (corresponding to the

energy of the photon) is determined by the energy gap of the

semiconductor. An LED is usually small in area (less than 1 mm2), and

integrated optical components are used to shape its radiation pattern

and assist in reflection. LEDs present many advantages over

incandescent light sources including lower energy consumption, longer

lifetime, improved robustness, smaller size, faster switching, and

greater durability and reliability. However, they are relatively expensive

and require more precise current and heat management than

traditional light sources. Current LED products for general lighting are

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more expensive to buy than fluorescent lamp sources of comparable

output.

Connecting and soldering

Fig(3.10)

LEDs must be connected in the correct way round, the diagram may be

labeled a or + for anode and k or - for cathode (yes, it really is k, not c,

for cathode!). The cathode is the short lead and there may be a slight

flat on the body of round LEDs. If you can see inside the LED the

cathode is the larger electrode (but this is not an official identification

method).

LEDs can be damaged by heat when soldering, but the risk is small

unless you are very slow. No special precautions are needed for

soldering most LEDs.

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Testing an LED

Never connect an LED directly to a battery or power supply!

It will be destroyed almost instantly because too much current will pass

through and burn it out.

LEDs must have a resistor in series to limit the current to a safe value,

for quick testing purposes a 1k resistor is suitable for most LEDs if

your supply voltage is 12V or less. Remember to connect the LED the

correct way round!

Colour of LEDs

LEDs are available in red, orange, amber, yellow, green, and blue and

white. Blue and white LEDs are much more expensive than the other

colours.

The colour of an LED is determined by the semiconductor material, not

by the colouring of the 'package' (the plastic body). LEDs of all colours

are available in uncolored packages which may be diffused (milky) or

clear (often described as 'water clear'). The coloured packages are also

available as diffused (the standard type) or transparent.

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Tri-colour LEDs

Fig (3.11) Tri-colour LEDs

The most popular type of tri-colour LED has a red and a green LED

combined in one package with three leads. They are called tri-colour

because mixed red and green light appears to be yellow and this is

produced when both the red and green LEDs are on.

The diagram shows the construction of a tri-colour LED. Note the

different lengths of the three leads. The centre lead (k) is the common

cathode for both LEDs; the outer leads (a1 and a2) are the anodes to

the LEDs allowing each one to be lit separately, or both together to give

the third colour.

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Bi-colour LEDs

A bi-colour LED has two LEDs wired in 'inverse parallel' (one forwards,

one backwards) combined in one package with two leads. Only one of

the LEDs can be lit at one time and they are less useful than the tri-

colour LEDs described above.

Sizes, Shapes and Viewing angles of LEDs

LEDs are available in a wide variety of sizes and shapes.

The 'standard' LED has a round cross-section of 5mm

diameter and this is probably the best type for general

use, but 3mm round LEDs are also popular.

Round cross-section LEDs are frequently used and they

are very easy to install on boxes by drilling a hole of the

LED diameter, adding a spot of glue will help to hold the LED if

necessary. LED clips are also available to secure LEDs in holes. Other

cross-section shapes include square, rectangular and triangular.

LED Clip

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TRANSISTOR: -

A transistor consists of two junctions formed by sandwiching

either p-type or n-type semiconductor between a pair of opposite

types. Accordingly, there are two types of transistors namely: -

(1) n-p-n transistor (2) p-n-p transistor

(NPN) (PNP)

An n-p-n transistor is composed of two n-type semiconductors

separated by a thin section of p type. However a p-n-p transistor is

formed by two p sections separated by a thin section of n-type. In each

type of transistor the following points may be noted.

1. There are two p-n junctions, therefore a transistor may be

regarded as combination of two diodes connected back to back.

2. There are three terminals taken from each type of semiconductor.

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3. The middle section is a very thin layer, which is the most

important factor in the functioning of a transistor.

4. Transistor can be used as an Amplifier also.

A transistor raises the strength of a weak signal and thus acts as

an amplifier. The weak signal is applied between emitter base junction

and output is taken across the load Rc connected in the collector circuit

(in common emitter configuration). In order to achieve faithful

amplification, the input circuit should always remain forward biased. To

do so, a dc voltage is applied in the input in addition to the signal. This

dc Voltage is known as biasing voltage and its magnitude and polarity

should be such that it always keeps the input circuit forward biased

regardless of the polarity to the signal to be amplified.

As the input circuit has low resistance a small change in signal

voltage causes an appreciable change in emitter current. This causes

change in collector current (by a factor called current gain of transistor)

due to transistor action. The collector current flowing through a high

load resistance Rc produces a large voltage across it. Thus a weak signal

applied to the input circuit appears in the amplified form in the

collector circuit. This is how a transistor acts as an amplifier. Transistor

may be used in different configuration like CB (common base) & CC

(common collector) according to requirements of amplifier (impedance

matching, buffer amplifier etc.).

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TRANSISTOR BC548-

In our project transistor BC 548 is used for amplifying purpose and

configured in CE (common emitter) mode.

Maximum Ratings

Rating Symbol Qty. Unit

Collector-Emitter Voltage VCEO 30 Vdc

Collector–Base Voltage VCBO 30 Vdc

Emitter–Base Voltage VEBO 6.0 Vdc

Collector Current — Continuous IC 100 mAdc

Total Device Dissipation @ TA = 25°C

Derate above 25°C

PD 625

5.0

mW

mW/°C

Total Device Dissipation @ TC = 25°C

Derate above 25°C

PD 1.5

1.2

mW

mW/°C

Operating and Storage Junction

Temperature Range

TJ , Tstg -55 to

+ 150

°C

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IC LM3915:-

The LM3915 is a monolithic integrated circuit that senses analog voltage

levels and drives at most 10 LEDs, LCDs or vacuum fluorescent

displays, providing a logarithmic 3 dB/step analog display.

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

LED current drive is regulated and programmable, eliminating the need

of current limiting resistors. The whole system can be 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 g35V. The input buffer drives 10

individual Comparators referenced to the precision divider. Accuracy is

typically batter than 1 dB.

The LM3915’s 3 dB/step display is suited for signals with wide dynamic

range, such as audio level, power, light intensity or vibration. Audio

applications include average or peak level indicators, power meters and

RF signal strength meters. Replacing conventional meters with an LED

bar graph, results in a faster responding, more rugged display with high

visibility that retains the ease of interpretation of an analog display.

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The LM3915 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 LM3915 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 with a

range of 60 or 90 dB. LM3915s can also be cascaded with LM3914s for a

linear/ log display or with LM3916s for an extended-range VU meter.

FEATURES:-

3 dB/step, 30 dB range.

Drives LEDs, LCDs, or vacuum fluorescents.

Bar or dot display mode externally selectable by user.

Expandable to displays of 90 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 g35V 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 LM3915 is rated for operation from 0°C to +70°C.

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P.C.B. MANUFACTURING PROCESS

It is an important process in the fabrication of electronic

equipment. The design of PCBs (Printed Circuit Boards) depends on

circuit requirements like noise immunity, working frequency and

voltage levels etc. High power PCBs requires a special design strategy.

The fabrication process to the printed circuit board will determine

to a large extent the price and reliability of the equipment. A common

target aimed is the fabrication of small series of highly reliable

professional quality PCBs with low investment. The target becomes

especially important for customer tailored equipments in the area of

industrial electronics.

The layout of a PCB has to incorporate all the information of the board

before one can go on the artwork preparation. This means that a

concept which clearly defines all the details of the circuit and partly

defines the final equipment, is prerequisite before the actual lay out

can start. The detailed circuit diagram is very important for the layout

designer but he must also be familiar with the design concept and with

the philosophy behind the equipment.

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BOARD TYPES:

The two most popular PCB types are:

1. Single Sided Boards

The single sided PCBs are mostly used in entertainment

electronics where manufacturing costs have to be kept at a

minimum. However in industrial electronics cost factors cannot be

neglected and single sided boards should be used wherever a

particular circuit can be accommodated on such boards.

2. Double Sided Boards

Double-sided PCBs can be made with or without plated through

holes. The production of boards with plated through holes is fairly

expensive. Therefore plated through hole boards are only chosen

where the circuit complexities and density of components does

not leave any other choice.

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CIRCUIT FABRICATION

Design Specification: -

(I) STEPS TAKEN WHILE PREPARING CIRCUIT

(A) PCB DESIGNING

The main purpose of printed circuit is in the routing of electric

currents and signal through a thin copper layer that is bounded firmly

to an insulating base material sometimes called the substrate. This base

is manufactured with integrally bounded layers of thin copper foil

which has to be partly etched or removed to arrive at a pre-designed

pattern to suit the circuit connections or other applications as required.

The term printed circuit board is derived from the original method

where a printed pattern is used as the mask over wanted areas of

copper. The PCB provides an ideal baseboard upon which to assemble

and hold firmly most of the small components.

From the constructor’s point of view, the main attraction of using PCB

is its role as the mechanical support for small components. There is less

need for complicated and time consuming metal work of chassis

contraception except perhaps in providing the final enclosure. Most

straight forward circuit designs can be easily converted in to printed

wiring layer the thought required to carry out the inversion cab footed

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high light an possible error that would otherwise be missed in

conventional point to point wiring .The finished project is usually neater

and truly a work of art.

Actual size PCB layout for the circuit shown is drawn on the

copper board. The board is then immersed in FeCl3 solution for 12

hours. In this process only the exposed copper portion is etched out by

the solution.

Now the petrol washes out the paint and the copper layout on

PCB is rubbed with a smooth sand paper slowly and lightly such that

only the oxide layers over the Cu are removed. Now the holes are

drilled at the respective places according to component layout as

shown in figure.

(B) LAYOUT DESIGN:

When designing the layout one should observe the

minimum size (component body length and weight). Before starting to

design the layout we need all the required components in hand so that

an accurate assessment of space can be made. Other space

considerations might also be included from case to case of mounted

components over the printed circuit board or to access path of present

components.

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It might be necessary to turn some components around to a

different angular position so that terminals are closer to the

connections of the components. The scale can be checked by

positioning the components on the squared paper. If any connection

crosses, then one can reroute to avoid such condition.

All common or earth lines should ideally be connected to a

common line routed around the perimeter of the layout. This will act as

the ground plane. If possible try to route the outer supply line to the

ground plane. If possible try to route the other supply lines around the

opposite edge of the layout through the center. The first set is tearing

the circuit to eliminate the crossover without altering the circuit detail

in any way.

Plan the layout looking at the topside to this board. First this

should be translated inversely; later for the etching pattern large areas

are recommended to maintain good copper adhesion. It is important to

bear in mind always that copper track width must be according to the

recommended minimum dimensions and allowance must be made for

increased width where termination holes are needed. From this aspect,

it can become little tricky to negotiate the route to connect small

transistors.

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There are basically two ways of copper interconnection patterns

underside the board. The first is the removal of only the amount of

copper necessary to isolate the junctions of the components to one

another. The second is to make the interconnection pattern looking

more like conventional point wiring by routing uniform width of copper

from component to component.

(C) ETCHING PROCESS:

Etching process requires the use of chemicals. Acid resistant

dishes and running water supply. Ferric chloride is mostly used solution

but other etching materials such as ammonium per sulphate can be

used. Nitric acid can be used but in general it is not used due to

poisonous fumes.

The pattern prepared is glued to the copper surface of the board

using a latex type of adhesive that can be cubed after use. The pattern

is laid firmly on the copper using a very sharp knife to cut round the

pattern carefully to remove the paper corresponding to the required

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copper pattern areas. Then apply the resistant solution, which can be a

kind of ink solution for the purpose of maintaining smooth clean

outlines as far as possible. While the board is drying, test all the

components.

Before going to next stage, check the whole pattern and cross

check with the circuit diagram. Check for any free metal on the copper.

The etching bath should be in a glass or enamel disc. If using crystal of

ferric- chloride these should be thoroughly dissolved in water to the

proportion suggested. There should be 0.5 lt. of water for 125 gm of

crystal.

To prevent particles of copper hindering further etching, agitate

the solutions carefully by gently twisting or rocking the tray.

The board should not be left in the bath a moment longer than is

needed to remove just the right amount of copper. Inspite of there

being a resistive coating there is no protection against etching away

through exposed copper edges. This leads to over etching. Have

running water ready so that etched board can be removed properly and

rinsed. This will halt etching immediately.

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Drilling is one of those operations that call for great care. For most

purposes a 0.5mm drill is used. Drill all holes with this size first those

that need to be larger can be easily drilled again with the appropriate

larger size.

(D) COMPONENT ASSEMBLY: -

From the greatest variety of electronic components available,

which runs into thousands of different types it, is often a perplexing

task to know which is right for a given job.

There could be damage such as hairline crack on PCB. If there are,

then they can be repaired by soldering a short link of bare copper wire

over the affected part.

The most popular method of holding all the items is to bring the

wires far apart after they have been inserted in the appropriate holes.

This will hold the component in position ready for soldering.

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Some components will be considerably larger .So it is best to start

mounting the smallest first and progressing through to the largest.

Before starting, be certain that no further drilling is likely to be

necessary because access may be impossible later.

Next will probably be the resistor, small signal diodes or other

similar size components. Some capacitors are also very small but it

would be best to fit these afterwards. When fitting each group of

components mark off each one on the circuit as it is fitted so that if we

have to leave the job we know where to recommence.

Although transistors and integrated circuits are small items there

are good reasons for leaving the soldering of these until the last step.

The main point is that these components are very sensitive to heat and

if subjected to prolonged application of the soldering iron, they could

be internally damaged.

All the components before mounting are rubbed with sand paper

so that oxide layer is removed from the tips. Now they are mounted

according to the component layout.

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(E) SOLDERING: -

This is the operation of joining the components with PCB after this

operation the circuit will be ready to use to avoid any damage or fault during

this operation following care must be taken.

A longer duration contact between soldering iron bit &

components lead can exceed the temperature rating of device &

cause partial or total damage of the device. Hence before

soldering we must carefully read the maximum soldering

temperature & soldering time for device.

The wattage of soldering iron should be selected as minimum as

permissible for that soldering place.

To protect the devices by leakage current of iron its bit should be

earthed properly.

We should select the soldering wire with proper ratio of Pb & Tn

to provide the suitable melting temperature.

Proper amount of good quality flux must be applied on the

soldering point to avoid dry soldering.

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INITALIZATION & WORKING

Our Mental Stress Identifier needs to initialize before use.

INITIALIZATION: -

The device is first taking the reference resistance from the body of

the user. There are two self locking straps provided with the touch pad.

Two self locking straps can be used to tie the unit around your wrist.

After tying the unit around user’s wrist (with touch pads in contact

with the skin), we check the battery connection. The device power

supply should ON & slowly very variable resistor VR1 until LED1 glows.

In this condition we assume that the user is in relaxed state. After that

adjust VR2 if the sensitivity of IC LM3915 i.e. IC1 is very high. Now the

device is ready to use.

HOW TO USE ?

We have to maintain the Wrist contact still bond with the pads in

power switch ON mode and keep body relaxed. Adjust VR1 until the

green LED (LED1) lights up and the device is ready. Adjust VR2 in case

he sensitivity of IC LM3915 i.e. IC1 is very high. This indicates normal

resistance of the skin, provided the body is fully relaxed.

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If user stressed or has ill feeling, skin resistance is decreases and the

green LED lights up followed by the red LED. In short, the red LED

indicate you are stressed, and the green LED indicate you are relaxed.

Now practice some relaxation technique and observe how much your

body is relaxed.

WORKING: -

When the metal plates come in contact of the body the transistor

amplify the voltage variations from the sensing pads. Since the base of

T1 is connected to VR1 through resistor R1 hence we can adjust the T1

by varying VR1.

The amplified signal from transistor T1 is given to the input of IC1 (IC

LM3915) through VR2. LEDs are directly connected to the IC1. IC1

senses the analog voltage level at pin 5 and displays them through LEDs

providing a logarithmic display. Every variation of input resistance is

sensed and by its voltage the respective LED glows which help us to

determine the stress level of the user.

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APPLICATIONS

The mental stress identifier can be very useful device in medical

application, psychological treatments, Crime application such as

Narcotic Test etc.

1. Psychological Observation of Patients.

2. Observing Behavior of patient during given time.

3. In Interviews where we can test the stability of the candidates in

stressed conditions.

4. Military & Intelligence operations.

5. It helps to doctors to monitor the current mental and physical state

of patient.

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FURTHAR DEVELOPEMENT

The device can be used in very advance manner. We can develop the

device as data saving facility, remote applications with infrared

transceiver & micro-controller based modern designs.

The micro-controller based design can be shown in fig.

Atmel 89C51

16x4 LCD display

Stress Meter Circuit

Operating Panel

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CHRONOLOGY

The following steps have been followed in carrying out the

project.

1. Study the books on the relevant topic.

2. Understand the working of the circuit.

3. Prepare the circuit diagram.

4. Prepare the list of components along with their specification.

Estimate the cost and procure them after carrying out market

survey.

5. Plan and prepare PCB for mounting all the components.

6. Fix the components on the PCB and solder them.

7. Test the circuit for the desired performance.

8. Trace and rectify faults if any.

9. Give good finish to the unit.

10. Prepare the project report.

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BIBILIOGRAPHY

REFERENCE FOR TECHNICAL INFORMATION FROM FOLLOWING BOOKS:

1. Electronics For You – September 2005 2. Integrated Electronics by Millman & Hawlkiwas. 3. Basic Electronics by J. B. Gupta

REFERENCE FOR ARTICLES & TECHNICAL INFORMATION ON REMOTE

ACCESS TERMINAL FROM FOLLOWING SITES:

http://www.google.co.in (google search engine)

http://www.whereisdoc.com

http://www.electronicsforu.com

http://www.lesstress.net/what-is-stress.htm

http://www.plugtek.com/morearticles.shtml

http://www.electronicprojects.com

http://www.datasheetcatalog.org/datasheets/150/128424_DS.pdf