Chapter 1

INTRODUCTION

1.1 STRESS METER

Stress is the very common condition of every human being. Stress is nothing more than a

socially acceptable form of mental illness. This Stress meter allows to assess the emotional

pain. If the stress is very high, it gives visual indication on a LED display along with a beep.

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 warning beep. The

gadget is small enough to be worn around the wrist. The LM3915 is a monolithic integrated

circuit that senses analog voltage levels and drives ten LED’s, LCD’s or vacuum fluorescent

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

The gadget is based on the principle that the resistance of the 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 the stress meter sense the voltage

variations 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.

1.2 EVOLUTION

In an article “Stress and Mind Control”, 21/03/2008, Roberto Bonomi stated that “When we

speak of the fabulous relaxation capacity that mind control gives us, the first thing that comes

to our mind, is that we will be able to take off, the excesses of nervous tension, the stress; and

1

this is a great benefit. Because suppose that you could measure stress in inches, and that you

have stress zero when the meter is located in zero.”

Neuroscientists have begun to learn that even acute, everyday stress can turn off the brain’s

command-and-control center, the prefrontal cortex. Without our mental executive, we feel

helpless and out of control.The more we learn about stress, the more we realize that

monitoring stress and taking steps to keep it under control is an important preventive health

measure.

1.3 PURPOSE OF THE PROJECT

The purpose of stress meter is to assess the emotional pain of human being. The stress can

cause hair to fall, acne to break out and many other problems. These manifestations of stress

can cause even more anxiety. Stress causes cortical levels to increase within the body, which

increases oil production, which causes acne breakouts.

So this stress meter is to solve all the problems caused due to stress by checking the stress of

an individual and taking care before any serious problem occurs.

2

Chapter 2

BLOCK DIAGRAM AND PROJECT OVERVIEW

2.1 PRINCIPLE OF STRESS METER:

The stress meter is based on the principle that the variations in the resistance of the skin due

to blood pressure of one’s body can be directly converted and transmitted into analog voltage

levels to give the visual indication of human stress using a proper circuitry.

2.2 BLOCK DIAGRAM:

Fig: 2.1 Block diagram of stress meter

3

TOUCH PADSTRANSISTOR

(BC548)

IC LM3915LED’S (OUTPUT)

INPUT (FROM FINGERS)

2.2.1 BLOCK DIAGRAM DESCRIPTION:

Figure above shows a block diagram of the Stress Indicator device. The touch pads of the

stress meter sense the voltage variations across the touch pads and convey it to the signal

amplifier, followed by LED display for visual indication and a warning beep. The circuit is

very sensitive and detects even a minute voltage variation across the touch pads.

Touch pad- detects the changes on the skin resistance.

Transistor BC548- amplify the signal produced at skin surface obtain

from the touch pad.

IC LM3915- is use to sense the analogue voltage level at pin 5 obtain

from the transistor.

LED- indicates the level of pain produce from the galvanic skin

response.

2.3 APPLICATION:

Each LED in stress meter operates with a 3dB difference from the previous one, and a jumper

is provided to allow dot or bar mode. This project is an essential part of the expandable

analyzer and one meter circuit is used for each frequency band. There are many other uses for

a simple LED meter. They are ideal as power meters on amplifiers, can be used with mixers

(including the high quality mixer), preamps and any other application where it is important to

know the signal level.

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.

4

Chapter 3

COMPONENTS OVERVIEW

The components required for stress meter are as follows:

1. IC LM3915 (1 nos.)

2. Touch Pads

3. 9V Battery (1 nos.)

4. LEDs (5 red)

5. Transistor BC548 (1 nos.)

6. Zener Diode 5.1V, 0.5W (1 nos.)

7. Switch (1 nos.)

8. Piezo Buzzer (1 nos.)

9. Diode 1N4148 (1 nos.)

10.Variable Resistor (1MΩ, 47KΩ)

11.Resistors (47KΩ,1.2KΩ,560Ω,1KΩ,470Ω,470Ω)

12.Capacitor 100uF, 16v (2 nos.)

13.Capacitor 10uF,16v (1 nos.)

14.Zero PCB

3.1 IC LM3915:

The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives

ten 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 for current limiting resistors. The

whole display system can operate from a single supply as low as 3V or as high as 25V.

Features

3 dB/step, 30 dB Range

Drives LEDs, LCDs, or Vacuum Fluorescents

5

Bar or Dot Display Mode Externally Selectable by User

Expandable to Displays of 90 Db

Internal Voltage Reference from 1.2V to 12V

3.2 TOUCH PADS:

The touch pads are the two copper strips tied on two

fingers of the left hand. This provides the input in terms

of skin resistance. Skin resistance is primarily affected

by sweat, as salty water is an excellent conductor. So

essentially the machine is measuring how sweaty your

palms are.

3.3 BATTERY:

It has a rectangular prism shape with rounded edges

and a polarized snap connector at the top. The battery

has both terminals in a snap connector on one end.

The smaller circular (male) terminal is positive, and

the larger hexagonal or octagonal (female) terminal is

the negative contact. The connectors on the battery are

the same as on the connector itself; the smaller one

connects to the larger one and vice versa.

3.4 LED (light emitting diode):

A light emitting diode (LED) is a PN junction

semiconductor diode that emits photons when

electrical current passes through the junction

in the forward direction, the electrical carriers

6

FIG 3.1 IC LM3915

FIG 3.3 9v battery

Fig 3.4 Light Emitting Diode

FIG 3.4 Touch Pads

give up energy proportional to the forward voltage drop across the diode junction, this energy

is emitted in the form of light.

LED’s are used in numerical displays such as those

on electronic digital watches and pocket

calculators. By definition, it is a solid-state device

that controls current without heated filaments and

is therefore very reliable. LED’s are highly

monochromatic, emitting a pure color in a narrow

frequency range. The color emitted from an LED is

identified by peak wavelength and measured in

nanometers. LEDs are made from gallium-based

crystals that contain one or more additional materials

such as phosphorous to produce a distinct color. LED light output varies with the type of

chip, encapsulation, efficiency of individual wafer lots and other variables. Several LED

manufacturers use terms such as "super-bright," and "ultra-bright" to describe LED intensity.

Because LED’s are solid-state devices they are not

subject to catastrophic failure when operated within

design parameters. LED’s are current-driven

devices, not voltage driven. Although drive current

and light output are directly related, exceeding the

maximum current rating will produce excessive heat

within the LED chip due to excessive power

dissipation. The color of an LED is determined by

the semiconductor material, not by the coloring of

the 'package' (the plastic body). LEDs are available

in red, orange, amber, yellow, green, and blue and

white colors.

LED’s are specially constructed to release a large number of photons outward. Additionally,

they are housed in a plastic bulb that concentrates the light in a particular direction.

7

Fig 3.5 inside a Light Emitting

Diode

Table 3.1: LED color vs. potential difference

Diode

LED Color Potential Difference

Infrared 1.6V

red 1.8 to 2.1V

orange 2.2V

yellow 2.4V

green 2.6V

blue 3.0V to 3.5V

white 3.0V to 3.5V

ultraviolet 3.5V

3.5 TRANSISTOR (BC548):

BC548 is general purpose silicon, NPN,

bipolar junction transistor. It is used for

amplification and switching purposes. The

current gain may vary between 110 and 800.

The maximum DC current gain is 800.

Its equivalent transistors are 2N3904 and

2SC1815. These equivalent transistors

however have different lead assignments.

The variants of BC548 are 548A, 548B and

548C which vary in range of current gain and

other characteristics.

The transistor terminals require a fixed DC

voltage to

operate in the desired region of its characteristic

curves. This is known as the biasing. For

amplification applications, the transistor is

biased such that it is partly on for all input

conditions. The input signal at base is amplified

and taken at the emitter. BC548 is used in

common emitter configuration for amplifiers.

The voltage divider is the commonly used

biasing mode. For switching applications,

transistor is biased so that it remains fully on if

there is a signal at its base. In the absence of

base signal, it gets completely off.

8

Fig 3.6 Pins showing the terminals

Fig 3.7 Actual view of BC548

Diode

3.6 ZENER DIODE :

The Zener diode is like a general-purpose signal diode

consisting of a silicon PN junction. When biased in the

forward direction it behaves just like a normal signal

diode passing the rated current, but as soon as a reverse

voltage applied across the Zener Diode exceeds the

rated voltage of the device, the diodes breakdown

voltage is reached at which point a process

called Avalanche Breakdown occurs in the

semiconductor depletion layer and a current starts to

flow through the diode to limit this increase in voltage.

The current now flowing through the zener diode increases dramatically to the maximum

circuit value (which is usually limited by a series resistor) and once achieved this reverse

saturation current remains fairly constant over a wide range of applied voltages. The voltage

point at which the voltage across the zener diode becomes stable is called the “zener voltage”

for zener diodes this voltage can range from less than one volt to hundreds of volts.

The point at which the zener voltage triggers the current to flow through the diode can be

very accurately controlled (to less than 1% tolerance) in the doping stage of the diodes

semiconductor construction giving the diode a specific zener breakdown voltage, ( Vz ) for

example, 4.3V or 7.5V. This zener breakdown voltage on the I-V curve is almost a vertical

straight line.

9

Fig 3.8 Zener Diode

fig 3.9 VI characteristics of zener diode

3.8 SWITCH:

The switch used is a single pole double throw type switch. It performs the ON/OFF operation.

3.9 PIEZO-BUZZER:

Piezo buzzer is an electronic device commonly used to produce sound. Light weight, simple

construction and low price make it usable in various applications like car/truck reversing

indicator, computers, call bells etc. Piezo buzzer is based on the inverse principle of piezo

electricity discovered in 1880 by Jacques and Pierre Curie. It is the phenomena of generating

electricity when mechanical pressure is applied to certain materials and the vice versa is also

true. Such materials are called piezo electric materials. Piezo electric materials are either

naturally available or manmade. Piezoceramic is class of manmade material, which poses

piezo electric effect and is widely used to make disc, the heart of piezo buzzer. When

subjected to an alternating electric field they stretch or compress, in accordance with the

frequency of the signal thereby producing sound.

3.10 DIODE 1N4148:

10

fig 3.10 SPDT switch

fig 3.11Piezobuzzer

Switching diodes are a single p-n diode in a discrete package. A switching diode provides the

same functionality as a switch. It has high resistance below the specified applied voltage

similar to an open switch, whereas above that voltage it changes in a sudden way to the low

resistance of a closed switch. Switching diodes are used in devices such as ring modulation.

The 1N4148 is a standard silicon switching diode. It is one of the most popular and long-

lived switching diodes because of its dependable specifications and low cost. Its name

follows the JEDEC nomenclature.

The 1N4148 is useful in switching applications up to about 100 MHz with a reverse-recovery

time of no more than 4 ns. The 1N4148 comes in a DO-35 glass package for through-

hole mounting. This is useful for bread boarding of circuits.

SPECIFICATIONS:

VRRM = 75-100 V — maximum repetitive reverse voltage IO = 75-200 mA — average rectified forward current IF = 300 mA — maximum direct forward current VF = 1.0 V at 10 mA. IFSM = 1.0 A (pulse width = 1 s), 4.0 A (pulse width = 1 µs) — non-repetitive peak

forward surge current PD = 500 mW — power dissipation TRR < 4 ns — reverse-recovery time

3.11 VARIABLE RESISTOR (1MΩ, 47KΩ):

A potentiometer, informally a pot, is a three-

terminal resistor with a sliding or rotating contact

that forms an adjustable voltage divider. If only two

terminals are used, one end and the wiper, it acts as

a variable resistor or rheostat.

The measuring instrument called a potentiometer is

essentially a voltage divider used for measuring electric potential (voltage); the component is

an implementation of the same principle, hence its name.

11

fig 3.12 Diode 1N4148

fig 3.14 Potentiometer

Potentiometers are commonly used to control electrical devices such as volume controls on

audio equipment. Potentiometers operated by a mechanism can be used as

position transducers, for example, in a joystick. Potentiometers are rarely used to directly

control significant power (more than a watt), since the power dissipated in the potentiometer

would be comparable to the power in the controlled load.

3.12 RESISTORS (47KΩ, 1.2KΩ, 560Ω, 1KΩ, 470Ω,

470Ω):

A resistor is a passive two-terminal electrical component that

implements electrical resistance as a circuit element. Resistors

act to reduce current flow, and, at the same time, act to lower

voltage levels within circuits. In electronic circuits, resistors

are used to limit current flow, to adjust signal

levels, bias active elements, and terminate transmission

lines among other uses. High-power resistors,

that can dissipate many watts of electrical power as heat, may

be used

as part of motor controls, in power distribution systems,

or as test loads for generators.

Fixed resistors have resistances that only change slightly with

temperature, time or operating voltage.

Variable resistors can be used to adjust circuit elements

(such as a volume control or a lamp dimmer), or as sensing

devices for heat, light, humidity, force, or chemical

activity.

Resistors are common elements of electrical networks and electronic circuits and are

ubiquitous in electronic equipment. Practical resistors as discrete components can be

12

fig 3.15 47KΩ RESISTOR

fig 3.16 1.2KΩ RESISTOR

fig 3.17 560Ω RESISTOR

fig 3.18 1KΩ RESISTOR

fig 3.19 470Ω RESISTOR

composed of various compounds and forms. Resistors are also implemented within integrated

circuits.

The electrical function of a resistor is specified by its resistance: common commercial

resistors are manufactured over a range of more than nine orders of magnitude. The nominal

value of the resistance will fall within a manufacturing tolerance.

3.13 CAPACITOR 100uF, 10uf:

A capacitor is a passive two-

terminal electrical component used to store

electrical energy temporarily in an electric

field. The forms of practical capacitors vary

widely, but all contain at least two electrical

conductors (plates) separated by

a dielectric (i.e. an insulator that can store

energy by becoming polarized). The

conductors can be thin films, foils or sintered

beads of metal or conductive electrolyte, etc.

The non conducting dielectric acts to increase the capacitor's charge capacity. A dielectric can

be glass, ceramic, plastic film, air, vacuum, paper, mica, oxide layer etc. Capacitors are

widely used as parts of electrical circuits in many common electrical devices. Unlike

a resistor, an ideal capacitor does not dissipate energy. Instead, a capacitor stores energy in

the form of an electrostatic field between its plates.

When there is a potential difference across the conductors (e.g., when a capacitor is attached

across a battery), an electric field develops across the dielectric, causing

positive charge +Q to collect on one plate and negative charge −Q to collect on the other

plate. If a battery has been attached to a capacitor for a sufficient amount of time, no current

can flow through the capacitor. However, if a time-varying voltage is applied across the leads

of the capacitor, a displacement current can flow.

An ideal capacitor is characterized by a single constant value, its capacitance. Capacitance is

defined as the ratio of the electric charge Q on each conductor to the potential

13

fig 3.20 100uF Capacitor

difference V between them. The SI unit of capacitance is the farad (F), which is equal to

one coulomb per volt (1 C/V). Typical capacitance values range from about 1 pF (10−12 F) to

about 1 mF (10−3 F).

The larger the surface area of the "plates" (conductors) and the narrower the gap between

them, the greater the capacitance is. In practice, the dielectric between the plates passes a

small amount of leakage current and also has an electric field strength limit, known as

the breakdown voltage. The conductors and leads introduce an

undesired inductance and resistance.

Capacitors are widely used in electronic circuits for blocking direct current while

allowing alternating current to pass. In analog filter networks, they smooth the output

ofpower supplies. In resonant circuits they tune radios to particular frequencies. In electric

power transmission systems, they stabilize voltage and power flow.

3.14 PERFORATED CIRCUIT BOARD (PCB):

A circuit in zero PCB (Printed Circuit Board) is one that uses individual components on a

breadboard or circuit board rather than a PCB to design an electronic circuit. This method is

cheaper compared to the use of PCB. The procedure used is:

* Place the components on the circuit board

* Plan the board’s wiring using the Perfboard layout planning sheet.

* Use the Kynar wire to connect the components.

Simplified procedure

1) Component list: Kynar wire, wire cutter, wire stripper, Rosin core solder, tweezers and

reading glasses or manual dexterity.

2) Place the components on the circuit board: Place the components to minimize the lengths

of wires required to reduce stray capacitance. Bend the pins to hold all the components place.

3) Make the wiring plan : Use a fine pencil in the holes for a socket pin and components

wires. Check the placement of the wires to ensure they are correctly placed. Always use the

circuit schematic.

14

4) Use the Kynar wire to connect the components: This procedure is repeated several times

until all the wires are connected. Sequentially, circuit board is placed to the helping hands

tool ready for soldering.

5) Measure and cut: Every wire is cut after referring to the planning sheet the loops are made

around the ends of wires. It is crucial to strip the insulation by 2mm from its end before

cutting a wire.

6) Crimps all the loops over pins and solder them : Crimping is done by tweezers and the

connection should last until the solder is applied.

7) Test the circuit board

Chapter 4

CIRCUIT DIAGRAM AND OPERATION

4.1 CIRCUIT DIAGRAM

15

Fig 3.21 perforated circuit board

4.2 CIRCUIT OPERATION:

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 gadget is small enough to be worn on the fingers.

The gadget is based on the principle that the resistance of the 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 the stress meter sense he

voltage variations 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

16

Fig 4.2 Display panel

touchpads.

The circuit comprises signal amplifier and analogue display sections. 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 the touch pads through resistor R1

and to the ground rail through potentiometer VR1.

By varying VR1, the sensitivity of T1 can be adjusted to the desired level. Diode D1

maintains proper biasing of T1 and capacitor C1 keeps the voltage from the emitter ofT1

steady.

The amplified signal from transistor T1 is given to the input of IC LM3915 (IC1) through

VR2. IC LM3915 is a monolithic integrated circuit that senses analogue voltage levels at its

pin 5 and displays them through LEDs providing a logarithmic analogue display. It can drive

up to ten LEDs one by one in the dot/bar mode for each increment of 125 mV in the

input. Here, we’ve used only five LEDs connected at pins 14 through 18 of IC1. LED1 glows

when input pin 5 of IC1 receives 150 mV. LED5 glows when the voltage rises to 650 mV and

LED5 flashes and piezobuzzer PZ1 beeps when the stress level is high.

Resistors R4 and R5 and capacitor C2 form the flashing elements. Resistor R3 maintains the

LED current at around 20 mA. Capacitor C3 should be placed close to pin 3 for proper

functioning of the IC. Zener diode ZD1 in series with resistor R6 provides regulated 5V to

the circuit.

The circuit can be assembled on a small piece of perforated board. Use transparent 3mm

LEDs and a small piezobuzzer for audio-visual indications. Enclose the circuit in a small

plastic case with touch pads on the back side. Two self-locking straps can be used to tie the

unit around your wrist.

After wearing touch pads on fingers (with touch pads in contact with the skin), slowly vary

17

VR1 until LED1 glows (assuming that you are in relaxed state). Adjust VR2 if the sensitivity

of IC1 is very high. The gadget is now ready for use.

Chapter 5

IMPLEMENTATION OF CIRCUIT

The circuit can be implemented in 2 ways:

18

1. Breadboard

2. PCB

5.1 BREADBOARD:

A breadboard is a construction base for prototyping of electronics. Originally it was literally

a bread board, a polished piece of wood used for slicing bread. In the 1970s the solderless

breadboard available and nowadays the term "breadboard" is commonly used to refer to

these. "Breadboard" is also a synonym for "prototype".

Because the solderless breadboard does not require soldering, it is reusable. This makes it

easy to use for creating temporary prototypes and experimenting with circuit design. For this

reason, solderless breadboards are also extremely popular with students and in technological

education. Older breadboard types did not have this property. A stripboard (veroboard) and

similar prototyping printed circuit boards, which are used to build semi-permanent soldered

prototypes or one-offs, cannot easily be reused. A variety of electronic systems may be

prototyped by using breadboards, from small analog and digital circuits to complete central

processing units (CPUs).

Typical specifications

A modern solder less breadboard consists of a perforated block of plastic with numerous tin

plated phosphor bronze or nickel silver alloy spring clips under the perforations. The clips are

19

Fig 5.1 Breadboard

often called tie points or contact points. The number of tie points is often given in the

specification of the breadboard.

The spacing between the clips (lead pitch) is typically 0.1 in (2.54 mm). Integrated

circuits (ICs) in dual in-line packages (DIPs) can be inserted to straddle the centerline of the

block. Interconnecting wires and the leads of discrete components (such

as capacitors, resistors, and inductors) can be inserted into the remaining free holes to

complete the circuit. Where ICs are not used, discrete components and connecting wires may

use any of the holes. Typically the spring clips are rated for 1 ampere at 5 volts and 0.333

amperes at 15 volts (5 watts).

Bus and terminal strips

Solderless breadboards are available from several

different manufacturers, but most share a similar

layout. The layout of a typical solderless breadboard is

made up from two types of areas, called strips. Strips

consist of interconnected electrical terminals.

Terminal strips

The main areas, to hold most of the electronic components.

In the middle of a terminal strip of a breadboard, one typically finds a notch running in

parallel to the long side. The notch is to mark the centerline of the terminal strip and provides

limited airflow (cooling) to DIP ICs straddling the centerline[citation needed]. The clips on the right

and left of the notch are each connected in a radial way; typically five clips (i.e., beneath five

holes) in a row on each side of the notch are electrically connected. The five clip columns on

the left of the notch are often marked as A, B, C, D, and E, while the ones on the right are

marked F, G, H, I and J. When a "skinny" dual in-line pin package (DIP) integrated circuit

(such as a typical DIP-14 or DIP-16, which have a 0.3-inch (7.6 mm) separation between the

pin rows) is plugged into a breadboard, the pins of one side of the chip are supposed to go

into column E while the pins of the other side go into column F on the other side of the notch.

Bus strips

To provide power to the electronic components.

A bus strip usually contains two columns: one for ground and one for a supply voltage.

However, some breadboards only provide a single-column power distributions bus strip on

20

Fig 5.2 Terminal and bus strips

each long side. Typically the column intended for a supply voltage is marked in red, while the

column for ground is marked in blue or black. Some manufacturers connect all terminals in a

column. Others just connect groups of, for example, 25 consecutive terminals in a column.

The latter design provides a circuit designer with some more control

over crosstalk (inductively coupled noise) on the power supply bus. Often the groups in a bus

strip are indicated by gaps in the color marking.

Bus strips typically run down one or both sides of a terminal strip or between terminal strips.

On large breadboards additional bus strips can often be found on the top and bottom of

terminal strips.

A "full size" terminal breadboard strip typically consists of around 56 to 65 rows of

connectors, each row containing the above-mentioned two sets of connected clips (A to E and

F to J). Together with bus strips on each side this makes up a typical 784 to 910 tie point

solderless breadboard. "Small size" strips typically come with around 30 rows. Miniature

solderless breadboards as small as 17 rows (no bus strips, 170 tie points) can be found, but

these are only suitable for small and simple designs.

Jump wires

Jump wires (also called jumper wires) for solderless

breadboarding can be obtained in ready-to-use jump

wire sets or can be manually manufactured. The latter

can become tedious work for larger circuits. Ready-to-

use jump wires come in different qualities, some even

with tiny plugs attached to the wire ends. Jump wire

material for ready-made or homemade wires should usually be 22 AWG (0.33 mm2) solid

copper, tin-plated wire - assuming no tiny plugs are to be attached to the wire ends. The wire

ends should be stripped 3⁄16 to 5⁄16 in (4.8 to 7.9 mm). Shorter stripped wires might result in

bad contact with the board's spring clips (insulation being caught in the springs). Longer

stripped wires increase the likelihood of short-circuits on the board. Needle-nose

pliers and tweezers are helpful when inserting or removing wires, particularly on crowded

boards.

Differently colored wires and color-coding discipline are often adhered to for consistency.

However, the number of available colors is typically far fewer than the number of signal

21

Fig 5.3 Jump wires

types or paths. Typically, a few wire colors are reserved for the supply voltages and ground

(e.g., red, blue, black), some are reserved for main signals, and the rest are simply used where

convenient. Some ready-to-use jump wire sets use the color to indicate the length of the

wires, but these sets do not allow a meaningful color-coding schema.

5.2 PERFORATED CIRCUIT BOARD (PCB):

Perfboard is a material for prototyping electronic

circuits (also called DOT PCB). It is a thin, rigid sheet

with holes pre-drilled at standard intervals across a

grid, usually a square grid of 2.54 mm (0.1 in)

spacing. These holes are ringed by round or square

copper pads. Inexpensive perfboard may have pads on

22

Fig 5.4 Stress meter on breadboard

Fig 5.5 PCB

only one side of the board, while better quality perfboard can have pads on both sides (plate-

through holes).

Since each pad is electrically isolated, the builder makes all connections with either wire

wrap or miniature point to point wiring techniques. Discrete components are soldered to the

prototype board such as resistors, capacitors, and integrated circuits. The substrate is typically

made of paper laminated with phenolic resin (such as FR-2) or a fiberglass-reinforced epoxy

laminate (FR-4).

The 0.1 in grid system accommodates integrated circuits in DIP packages and many other

types of through-hole components. Perfboard is not designed for prototyping surface mount

devices.

Before building a circuit on perfboard, the locations of the components and connections are

typically planned in detail on paper or with software tools. Small scale prototypes, however,

are often built ad hoc, using an oversized perfboard.

Software for PCB layout can often be used to generate perfboard layouts as well. In this case,

the designer positions the components so all leads fall on intersections of a 0.1 in grid. When

routing the connections more than 2 copper layers can be used, as multiple overlaps are not a

problem for insulated wires.

Once the layout is finalized, the components are soldered in their designated locations,

paying attention to orientation of polarized parts such as electrolytic capacitors, diodes, and

integrated circuits. Next, electrical connections are made as called for in the layout.

One school of thought is to make as many connections as possible without adding extra wire.

This is done by bending the existing leads on resistors, capacitors, etc. into position, trimming

off extra length, and soldering the lead to make the required electrical connection. Another

school of thought refuses to bend the excessive leads of components and use them for wiring,

on the ground that this makes removing a component later hard or impossible, e.g. when a

repair is needed.

If extra wires need to be used, or are used for principle reasons, they are typically routed

entirely on the copper side of perfboards. Because, as opposite to strip boards, nearby holes

aren't connected, and the only hole in a pad is already occupied by a component's lead. Wires

used range from isolated wires, including verowire (enameled copper wire with a

polyurethane insulation supposed to melt when soldered), to bare copper wire, depending on

individual preference, and often also on what is currently at hand in the workshop.

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For insulated wires thin solid core wire with temperature-resistant insulation such as Kynar or

Tefzel is preferred. The wire gauge is typically 24 - 30 AWG. A special stripping tool can be

used, incorporating a thin steel blade with a slit that the wire is simply inserted into and then

pulled loose, leaving a clean stripped end. This wire was developed initially for circuit

assembly by the wire wrap technique but also serves well for miniature point-to-point wiring

on perfboard. Bare copper wire is useful when merging a number of connections to form

an electrical bus such as the circuit's ground, and when there is enough space to properly

route connections, instead of wiring them rats-nest style.

Intentional solder bridges can be used to connect adjacent pads when necessary. Careful

hand–eye coordination is needed to avoid causing inadvertent short circuits.

Circuits assembled on perfboard are not necessarily fragile but may be less impact-resistant

than printed circuit boards.

Perfboard differs from stripboard in that each pad on perfboard is isolated. Stripboard is made

with rows of copper conductors that form default connections, which are broken into isolated

segments as required by scraping through the copper. This is similar to the pattern of default

connections on a solderless breadboard. However, the absence of default connectivity on

perfboard gives the designer more freedom in positioning components and lends itself more

readily to software-aided design than stripboard or breadboard.

5.3 SOLDERING PROCESS:

Soldering - a must skill for all electrical and electronic works. “Soldering” is defined as the

process of joining two pieces of metals using a filler metal, known as solder, having a low

melting point below the melting point of the work piece. It is often confused with welding but

the difference between them is, in soldering the work piece is not melted, they are joined

using a filler metal, but in welding work piece is joined by melting.

History

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Soldering was practiced as far back as 5000 years ago in Egypt. Soldering was widely

performed around 4000 years ago when tin was discovered as soldering metal. The process of

soldering was introduced in Mediterranean region, and was followed in the Roman Empire,

Swiss and Hungaria. Soldering has improved a lot from culture to culture and generation to

generation and in today’s scenario it is the best method for fabrication and assembly of

microelectronics.

Types of Soldering

Soldering is classified as shown in the image below:

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5.4 FINAL DESIGN OF STRESS METER ON PCB:

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Fig 5.8 SOLDERING ON PCB

Fig 5.9 STRESS METER ON PCB (FINAL DESIGN)

Chapter 6

CONCLUSIONS

6.1 RESULT:

The stress meter thus detects the resistance of skin which is according to one’s mental stress

and gives a visual indication on a LED display. The LED’s on the stress meter can be

observed as stress level indicators from zero to 5 stress levels on a scale of FIVE. The high

stress of a person is indicated through a warning beep.

6.2 ANALYSIS:

Resistance varies inverse proportional to the stress. If the stress level is high the skin offers

less resistance, and if relaxed 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.

The LED 1 glows by default when the circuit is on. When a person touches the touch pad of

the stress meter with his finger, it senses the skin resistance and hence the stress. On a scale

of ten, stress levels from 0 to 5 can be observed, where the LED 5 when on gives a warning

beep for high stress indication.

6.3 APPLICATIONS:

Person’s muscle tension changes can be seen (with their stress level

applied by the Muscle).

The mental state of a person can be known (based upon the

changes in skin (Resistance).

It can be used as a lie detector.

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It can be used in physical fitness programs. The circuit is

absolutely free from ambient light.

It is economical and a low budget project.

Not a complex circuit.

The components are easily available in the market and replaceable.

Noise pulse do not have any effect on the circuit.

LED’s can withstand the voltage even if no resistors are connected

across.

Can be used easily to regularly check one’s stress level.

6.4 ADVANTAGES:

1. Simple circuitry.

2. Easy to use.

3. Easy to transport.

4. Less power consumption.

5. Desired output.

6.5 DISADVANTAGES

1. Output is not measurable.

2. Output depends upon the

grip of the person.

6.6 FUTURE SCOPE

Stress meter can be further developed to design equipment like lie detectors; skin response

meters; skin resistance meters; fitness meters; grip scopes etc. therefore this model, if further

developed can be used in medical field, forensic department and it even helps in improving

the body fitness.

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APPENDIX

PIN DIAGRAM OF LM3915:

DEFINITION OF TERMS:

Absolute Accuracy: The difference between the observed threshold voltage and the ideal

threshold voltage for each comparator. Specified and tested with 10V across the internal

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voltage divider so that resistor ratio matching error predominates over comparator offset

voltage.

Adjust Pin Current: Current flowing out of the reference adjust pin when the reference

amplifier is in the linear region.

Comparator Gain: The ratio of the change in output current (ILED) to the change in input

voltage (VIN) required to produce it for a comparator in the linear region.

Dropout Voltage: The voltage measured at the current source outputs required to make the

output current fall by 10%.

Input Bias Current: Current flowing out of the signal input when the input buffer is in the

linear region.

LED Current Regulation: The change in output current over the specified range of LED

supply voltage (VLED) as measured at the current source outputs. As the forward voltage of

an LED does not change significantly with a small change in forward current, this is

equivalent to changing the voltage at the LED anodes by the same amount.

Line Regulation: The average change in reference output voltage (VREF) over the specified

range of supply voltage (V+).

Load Regulation: The change in reference output voltage over the specified range of load

current (IL (REF)).

Offset Voltage: The differential input voltage which must be applied to each comparator to

bias the output in the linear region. Most significant error when the voltage across the internal

voltage divider is small. Specified and tested with pin 6 voltage (VRHI) equal to pin 4

voltage (VRLO).

Relative Accuracy: The difference between any two adjacent threshold points. Specified and

tested with 10V across the internal voltage divider so that resistor ratio matching error

predominates over comparator offset voltage.

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LM3915 OUTPUT CHARACTERISTICS:

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REFERENCES

Journals:

Roberto Bonomi, “Stress and Mind Control”, dated 21/03/2008

Reference Books:

1. Joseph Edminster and Mahmood Nahvi, Electric circuits, Schaum’s Outline, 2003

2. Stanley G Burns and Paul R Bond, Principles of Electronic Circuits, International Thomson publishing, 1997

3. Richard C Jaegar and Travis N Blalock, Micro electronic circuit design, Third Edition Errata, 2008

Web:

1. http://www.engineersgarage.com/articles/soldering-tutorial-tips-types- processes

2. https://prezi.com/hnw7yesfjspu/stress-meter/ 3. https://en.wikipedia.org/wiki/Breadboard 4. https://en.wikipedia.org/wiki/Resistor

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