CONTENTS

1. Why a Project?

2. Introduction

3. Principle

4. Chronology

5. Circuit Detail

- Circuit Description & Working

- Circuit Layout

- Component List

6. PCB Details

- PCB Description

- PCB Layout

7. Assembling

8. Conclusion

9. Reference

10. Ideas which could not be implemented

WHY A PROJECT?

A student specially technical student is expected to do some experimentation

and research work on the subject, which he thought in the class textbook during the

course of his studies. Such an effort when well organized with a definite aim or

purpose is called a project.

The object of a project is to envelope technical thinking and induced the

student to make an ordinary analysis to the situation following at hand so as to

search a definite conclusion.

By doing project student display’s his spirit of inquiring creating & criticizing

way of solving a problem through understanding of existing situation, independent

thinking and ability to understand basic fact.

INTRODUCTION

In an automobile headlight, a 'meeting' beam (dip beam) is provided in addition to

the driving beam (high beam) so as to reduce the dazzle for those approaching

head-on to the vehicle.

The Auto Dipping Device for a head light is intended to automatically change the

Headlight Circuit to either driving beam or dip beam given a particular set of road

conditions, without the intervention of the driver. The present practice is to operate

the dip switch manually.

The function of the headlight is to illuminate the road ahead of the automobile so as

to reveal objects ahead from a safe distance; at the same time it should cause

minimum discomfort and glare for drivers coming from the opposite side.

Manual dipping is not being done satisfactorily in India due to a variety of reasons,

which includes sheer physical strain involved in operation of the dipper switch

hundreds of times every night. (The total for a single night will be 1000 if we consider

8 hours of traveling and one encounter every one-minute and could exceed this

number if one travels on roads with dense traffic). The other reason includes a

general tendency of paying more attention to steering control at the cost of dipping

during a critical vehicle meeting situation especially in the case of heavy loaded

vehicles. More reasons are the physiological and psychological state of a driver,

which is influenced by a variety of factors like working hours, economic issues and

social factors etc. Another major cause is 'ego problem', which makes each one wait

till the other person initiates dipping, which may not happen.

A frequent cause of accidents at nights is the glare caused by oncoming vehicles

which momentarily blinds the driver's vision. It takes three to eight seconds for a

person with good eyesight to recover from the glare and during this time the vehicle

will have covered a long distance in utter darkness and it will be sheer luck if it

escapes an accident.

The observations of the study group on road safety (Constituted by Government of

India vide Resolution No.19 (14) 68, June 3, 1969) regarding the conditions of our

national highways are:

“The Indian roads are all essentially very narrow, tortuous in their alignment

and suffer from many inadequacies, vis-à-vis the present day motor traffic

which has registered a phenomenal increase during the post-Independence

period. The other conditions of the roads like poor shoulders, narrow culverts

and bridges, sharp and numerous curves and steep gradients which limit the

sight distance, numerous low level causeways and submersible bridges are

perennial hazards. All the above tell on the nerves of the driver, causing

fatigue and leading to errors and misjudgment while driving”.

All the above indicate the importance of dipping of headlights in a country like India,

so as to avoid the problem of glare which impairs the visibility which is vital for safe

driving in a meeting situation during the night. This leads to the conclusion that an

Auto Dipping Device can go a long way towards safety enhancement.

WHAT IS AN AUTO DIPPER?

An Auto Dipper is a device capable of changing over the circuit of head light without

the intervention of the driver given a particular set of objective road conditions. Its

primary aim is to reduce the dazzle for the observer approaching ahead of the

vehicle while ensuring that the user will not be put to inconvenience.

THE FUNCTIONAL REQUIREMENTS ON A DARK ROAD

The basic function of an auto dipper is to maintain the head lamps in either driving

beam or meeting beam automatically depending on the opposing traffic.

AUTOMATIC DRIVING BEAM

It has to bring into operation the driving beam if there is no oncoming vehicle.

Necessarily this means the auto dipper must be immune to the signals from; street

lamps, moonlight, road reflectance, solar radiation during the late dusk and early

dawn.

AUTOMATIC DIP BEAM

It has to bring into operation the meeting beam from both headlights whenever an

oncoming vehicle approaches to within about say 250 meters with its headlights in

driving beam until the vehicle is about to pass. The auto dipper, after bringing into

operation the dip beam, should logically be capable of continuing the operation of the

headlights in dip beam, if the headlights of the oncoming vehicle were also shifted to

the dip beam.

Our project is designed based on the above conceptual framework and is believed to

cater to the actual road conditions in a way convenient to the user and is expected to

relieve him from the repetitive task of operating the dipper switch. The auto dipper is

not to replace the human judgment but only to assist the user and the ultimate

control is left with the user.

PRINCIPLE

A circuit is designed which uses a LDR(light dependent resistor) to sense the light

emitted by the vehicle coming from the opposite direction. This light sensed by the

LDR is used to send signals to the circuit to trigger the command to a upper or the

dipper circuit depending on the amount of light emitted by the vehicle coming from

opposite direction.

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 to 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.

CIRCUIT DETAILS

CIRCUIT DESCRIPTION & WORKING:-

This project is very useful in car head light automatically. During night time, car head

light upper dipper changes automatically. The 9 Volt supply is fed in a controlling

circuit of IC 555. In this project IC 555 is used as a switch. One light dependent

resistance (LDR) is also used to act with light intensity. The resistance of the L.D.R

increases or decreases on the intensity of light. When light falls on L.D.R its

resistance decreases and in darkness the resistance increases. In the circuit IC 555

is used as a timer. Pin No.2 of the IC is earthed through 10 k preset which keeps the

flip-flop system of the IC at a high state. Pin No. 3 of the IC is the output pin and

remains at a low state. The IC does not operate until light falls on the LDR. When

light falls on L.D.R., the resistance of the L.D.R. decreases, as a result of

which, Pin No. 2 of the IC gets positive voltage, the Pin No.2 is trigger pin which

can trigger the required circuit ON. When light falls on the LDR the Upper circuit

gets switched OFF while the Dipper circuit gets switched ON and the vice- versa

CIRCUIT LAYOUT:-

COMPONENT LIST:-

Components Total Qty. Details

Battery 1 9V

IC 1 555 Timer

Capacitor 1 4.7Kohm

Resistance 1 100 Kohm

Variable resistance 1 10 Kohm

LDR 1 Light dependent resistance

Wire - -

Other misc 1 Board, Wire, Socket For U1, Case, Mains Plug, Socket

9 VOLT BATTERY:-

A nine-volt battery, sometimes referred to as a PP3 battery, is shaped as a rounded

rectangular prism and has a nominal output of nine volts. Its nominal dimensions are

48 mm × 25 mm × 15 mm (ANSI standard 1604A). PP3 actually refers to the type of

connection or snap that is on top of the battery . The PP3 connector (snap) consists

of two connectors: one smaller circular (male) and one larger, typically either

hexagonal or octagonal (female). The connectors on the battery are the same as on

the connector itself -- the smaller one connects to the larger one and vice versa.

The battery has both the positive and negative terminals on one end. The negative

terminal is fashioned into a snap fitting which mechanically and electrically connects

to a mating terminal on the power connector. The power connector has a similar

snap fitting on its positive terminal which mates to the battery. This makes battery

polarization obvious since mechanical connection is only possible in one

configuration. The clips on the 9-volt battery can be used to connect several 9-volt

batteries in series. One problem with this style of connection is that it is very easy to

connect two batteries together in a short circuit, which quickly discharges both

batteries, generating heat and possibly a fire. While this is a danger, the same thing

can be done with multiple 9 volt batteries to create higher voltage (they can snap

together). The wiring usually uses black and red wires, red for positive, and black for

negative.

Inside a PP3 there are ordinarily six alkaline or carbon-zinc 1.5 volt (nominal) cells

arranged in series. These are either AAAA cells, or special flat, rectangular cells.

The exact size of the constituent cells varies from brand to brand -- some brands are

slightly longer than others -- as does the manner in which they are joined together.

Some brands use soldered tabs on the battery, others press foil strips against the

ends of the cells.

Very cheap versions may contain only five 1.5 volt cells. Rechargeable NiCd and

NiMH batteries have various numbers of 1.2 volt cells. Lithium versions use three 3.2

V cells - there is a rechargeable lithium polymer version. There is also a Hybrio

NiMH version that has a very low discharge rate (85% of capacity after 1 year of

storage). .

555 TIMER IC:-

One of the most versatile linear integrated circuit is the 555 timer. The IC was

designed and invented by Hans R. Camenzind. It was designed in 1970 and

introduced in 1971 by Signetics (later acquired by Philips). The original name was

the SE555/NE555 and was called "The IC Time Machine".[1] The 555 gets its name

from the three 5-kohm resistors used in typical early implementations. Depending on

the manufacturer, it includes over 20 transistors, 2 diodes and 15 resistors on a

silicon chip installed in an 8-pin mini dual-in-line package. Since its debut the device

has been used in a number of novel an useful application. A sample of these

application includes monostable and stable multivbratores dc-dc converters digital

logic probes waveform generators analog frequency meters and tachometer

temperature measurement and control infrared transmitter burglar and toxic gas

alarms, voltage regulator, electric eyes and may other The 555 is monolithic timing

circuit that can produced accrued and highly stable time delays an oscillation. The

timer basically operated in one of et two modes either as monostable (one

shot)multivibrotor or as an stable (free running )multivibrator. The device is available

as an 8 pin metal can an mini DIP of 14 pin DIP. The SE555 is designed for the

operation temperature renege from 55 degree to +5 to 18 v supply voltage in both

free running (astable ) and onset (monostable) modes; it has an adjustable duty

cycle; timing is from microseconds through hours; it has ha high current output; it can

source of sink 2000mA;the output can drive TTL and has a temperature stability of

50 parts per million(ppm) per degree Celsius change in temperature of equivalently

0.005% per degree Celsius. Like general-purpose op-amps the 555 timer is reliable

easy to use and low cost.

Internal Schematics:

Schematic Symbol:

Nr. Name Purpose

1 GND Ground, low level (0V)

2 TR A short pulse high → low on the trigger starts the timer

3 Q During a timing interval, the output stays at +VCC

4 RA timing interval can be interrupted by applying a reset

pulse to low (0V)

5 CVControl voltage allows access to the internal voltage

divider (2/3 VCC)

6 THRThe threshold at which the interval ends (it ends if U.thr

→ 2/3 VCC)

7 DISConnected to a capacitor whose discharge time will

influence the timing interval

8V+, VCC

The positive supply voltage which must be between 3 and 15 V

Specifications:

Supply voltage (VCC)4.5 to 15

V

Supply current (VCC = +5 V)

3 to 6 mA

Supply current (VCC = +15 V)

10 to 15 mA

Output current (maximum)

200 mA

Power dissipation 600 mW

Operating temperature0 to 70

°C

CAPACITOR:-

A capacitor or condenser is a passive electronic component consisting of a pair of

conductors separated by a dielectric. When a voltage potential difference exists

between the conductors, an electric field is present in the dielectric. This field stores

energy and produces a mechanical force between the plates. The effect is greatest

between wide, flat, parallel, narrowly separated conductors.

An ideal capacitor is characterized by a single constant value, capacitance, which is

measured in farads. This is the ratio of the electric charge on each conductor to the

potential difference between them. In practice, the dielectric between the plates

passes a small amount of leakage current. The conductors and leads introduce an

equivalent series resistance and the dielectric has an electric field strength limit

resulting in a breakdown voltage.

The fundamental relation for the capacitance between two flat plates separate be a

dielectric materiel is given by C=0.08854KA where

C= capacitance in p:f.

K= dielectric constant

A=Area per plate in square cm.

D=Distance between two plates in cm

Design of capacitor is connected with the relation of the proper dielectric

material with particular type of application. The dielectric material used for capacitors

may be grouped in the various classed like Mica Glass air ceramic paper Aluminum

electrolytic etc. The value of capacitance never remains constant except under

certain filed condition it changed with temperature frequency and aging. The

capacitance value marked on the capacitor strictly applies only at specified room

temperature and at low frequencies.

RESISTORS:-

A resistor is a two-terminal electronic component that produces a voltage across its

terminals that is proportional to the electric current through it in accordance with

Ohm's law:

V = IR

Resistors are elements of electrical networks and electronic circuits and are

ubiquitous in most electronic equipment. Practical resistors can be made of various

compounds and films, as well as resistance wire (wire made of a high-resistivity

alloy, such as nickel/chrome).The resistance are heat dissipating elements and in

the electronic circuits they are mostly used for either controling the currents in the

circuit or developing a voltage drop across it which could be utilized for so

application There are various types of resistance’s which can be classified according

to a number of factors depending upon (I0) Material used for fabrication a resistance

(II) Wattage an physical size (III) Intended application (iv) Ambient temperature

rating (v) Cost basically the resistor can be splinted in to the following four parts with

the construction view point (1) Base(2) Resistance element (3) Terminals (4)

Protective means. The following characteristics are inherent in all resistance’s an

may be controlled by design considerations and choice of material I.e. Temperature

co–efficient Voltage co–efficient of resistance high frequency characteristics power

rating and reseating tolerance voltage retting of Resistors Resistance’s may be

classified as (1) Fixed (2) semivariable (3) Variable resistance’s We have used

carbon resistance’s. Resistors can be integrated into hybrid and printed circuits, as

well as integrated circuits. Size, and position of leads (or terminals) are relevant to

equipment designers; resistors must be physically large enough not to overheat

when dissipating their power.

Colour Code:

VARIABLE RESISTORS:-

Variable resistors consist of a resistance track with connections at both ends and a wiper which moves along the track as you turn the spindle. The track may be made from carbon, cermet (ceramic and metal mixture) or a coil of wire (for low resistances). The track is usually rotary but straight track versions, usually called sliders, are also available.

Variable resistors may be used as a rheostat with two connections (the wiper and just one end of the track) or as a potentiometer with all three connections in use. Miniature versions called presets are made for setting up circuits which will not require further adjustment.

Variable resistors are often called potentiometers in books and catalogues. They are specified by their maximum resistance, linear or logarithmic track, and their physical size. The standard spindle diameter is 6mm.

The resistance and type of track are marked on the body:    4K7 LIN means 4.7 k linear track.    1M LOG means 1 M logarithmic track.

Some variable resistors are designed to be mounted directly on the circuit board, but most are for mounting through a hole drilled in the case containing the circuit with stranded wire connecting their terminals to the circuit board.

Standard Variable Resistor:

Open Style Preset:

Closed Style Preset:

Multiturn Preset:

LDR(LIGHT DEPENDENT RESISTOR):-

A photo resistor or light dependent resistor or cadmium sulfide (CdS) cell is a resistor

whose resistance decreases with increasing incident light intensity. It can also be

referenced as a photoconductor.

A photo resistor is made of a high resistance semiconductor. If light falling on the

device is of high enough frequency, photons absorbed by the semiconductor give

bound electrons enough energy to jump into the conduction band. The resulting free

electron (and its hole partner) conduct electricity, thereby lowering resistance.

A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor

has its own charge carriers and is not an efficient semiconductor, e.g. silicon. In

intrinsic devices the only available electrons are in the valence band, and hence the

photon must have enough energy to excite the electron across the entire band gap.

Extrinsic devices have impurities, also called dopants, added whose ground state

energy is closer to the conduction band; since the electrons do not have as far to

jump, lower energy photons (i.e., longer wavelengths and lower frequencies) are

sufficient to trigger the device. If a sample of silicon has some of its atoms replaced

by phosphorus atoms (impurities), there will be extra electrons available for

conduction. This is an example of an extrinsic semiconductor.

Photo resistors come in many different types. Inexpensive cadmium sulfide cells can

be found in many consumer items such as camera light meters, street lights, clock

radios, alarms, and outdoor clocks.

They are also used in some dynamic compressors together with a small

incandescent lamp or light emitting diode to control gain reduction.

Lead sulfide and indium antimonite LDRs are used for the mid infrared spectral

region. Ge:Cu photoconductors are among the best far-infrared detectors available,

and are used for infrared astronomy and infrared spectroscopy.

LED(LIGHT EMITTING DIODE):-

As there name indicated it is a forward biased P-N junction which emits visible

light when energized. Charge carrier recombination tacked place when elections

from the N- side cross the junction and recombine with the heeds on the P side Now

electrons are in the higher conduction hand on the N side whereas holes are in the

lower valance band on the P side During recombination some of the energy

difference is given up in the form of heat and light (i.e.proton) in the case of

semiconductor materials like gallium arsenate (Ga As) Gallium phoshide (Gap) and

Gallium arsenate phoshide (GaAsP) a greater percentage of energy is released

during recombination and is given out in the form of light LED’s emit no light when

the are reverse biased.

A light-emitting diode (LED) is an electronic light source. The LED was first invented

in Russia in the 1920s, and introduced in America as a practical electronic

component in 1962. Oleg Vladimirovich Losev was a radio technician who noticed

that diodes used in radio receivers emitted light when current was passed through

them. In 1927, he published details in a Russian journal of the first ever LED.

All early devices emitted low-intensity red light, but modern LEDs are available

across the visible, ultraviolet and infra red wavelengths, with very high brightness.

LEDs are based on the semiconductor diode. When the diode is forward biased

(switched on), electrons are able to recombine with holes and energy is released in

the form of light. This effect is called electroluminescence and the color of the light is

determined by the energy gap of the semiconductor. The LED is usually small in

area (less than 1 mm2) with integrated optical components to shape its radiation

pattern and assist in reflection.[2]

LEDs present many advantages over traditional light sources including lower energy

consumption, longer lifetime, improved robustness, smaller size and faster switching.

However, they are relatively expensive and require more precise current and heat

management than traditional light sources.

Applications of LEDs are diverse. They are used as low-energy indicators but also

for replacements for traditional light sources in general lighting and automotive

lighting. The compact size of LEDs has allowed new text and video displays and

sensors to be developed, while their high switching rates are useful in

communications technology.

SWITCHES:-

In electronics, a switch is an electrical component that can break an electrical circuit,

interrupting the current or diverting it from one conductor to another.[1][2] The most

familiar form of switch is a manually operated electromechanical device with one or

more sets of electrical contacts. Each set of contacts can be in one of two states:

either 'closed' meaning the contacts are touching and electricity can flow between

them, or 'open', meaning the contacts are separated and no conducting.

Since the advent of digital logic in the 1900s, the term has spread to a variety of

digital active devices such as transistors and logic gates whose function is to change

their output state between two logic levels or connect different signal lines, and even

computers, network switches, whose function is to provide connections between

different ports in a computer network. The term 'switched' is also applied to

telecommunications networks, and signifies a network that is circuit switched,

providing dedicated circuits for communication between end nodes, such as the

public switched telephone network. The common feature of all these usages is they

refer to devices that control a binary state: they are either on or off, closed or open,

connected or not connected.

PCB DETAILS

PCB DESCRITION:-

A printed circuit board, or PCB, is used to mechanically support and electrically

connect electronic components using conductive pathways, or traces, etched from

copper sheets laminated onto a non-conductive substrate. It is also referred to as

printed wiring board (PWB) or etched wiring board. A PCB populated with electronic

components is a printed circuit assembly (PCA), also known as a printed circuit

board assembly (PCBA).

PCBs are rugged, inexpensive, and can be highly reliable. They require much more

layout effort and higher initial cost than either wire-wrapped or point-to-point

constructed circuits, but are much cheaper and faster for high-volume production.

Much of the electronics industry's PCB design, assembly, and quality control needs

are set by standards that are published by the IPC organization.

Conducting layers are typically made of thin copper foil. Insulating layers dielectric

are typically laminated together with epoxy resin prepreg. The board is typically

coated with a solder mask that is green in color. Other colors that are normally

available are blue, and red.

PCB LAYOUT:-

ASSEMBLING

There are a few steps followed before really starting the assembling process. These

steps consists of,

PCB layout preparation

Screen Printing

PCB Etching

Drilling

Soldering

PCB LAYOUT PREPARATION:-

There are various softwares available for designing of the PCB layout. Some of them

are listed below:

Dip trace

Altium

E-CAD Pro

Adobe Page Maker

The steps followed in creating this layout is as follow:

1. Various components are available in any software you choose. Select the

components which are contained in your circuit.

2. Make sure that the components selected are of same specifications as used.

3. Similarly select the other components from the component library of the

software being used.

4. Arrange the components in such a way to create a design which looks like

your circuit.

5. Check the connections once more to ensure any discrepancy.

6. When the circuit is completely ready follow the procedure to convert this

circuit layout into the PCB layout (this process differs from one software to

other software).

7. Check the PCB layout once more comparing it with your circuit.

8. Print the desired PCB layout on a simple paper or a butter paper or a gelatin

paper.

SCREEN PRINTING:-

Screen printing is a printing technique that uses a woven mesh to support an ink-

blocking stencil. The attached stencil forms open areas of mesh that transfer ink as a

sharp-edged image onto a substrate. A roller or squeegee is moved across the

screen stencil, forcing or pumping ink past the threads of the woven mesh in the

open areas.

Screen printing is also a stencil method of print making in which a design is imposed

on a screen of silk or other fine mesh, with blank areas coated with an impermeable

substance, and ink is forced through the mesh onto the printing surface. It is also

known as "silk screening" or "serigraphy".

Line art and text may be printed onto the outer surfaces of a PCB by screen printing.

When space permits, the screen print text can indicate component designators,

switch setting requirements, test points, and other features helpful in assembling,

testing, and servicing the circuit board.

Screen print is also known as the silk screen, or, in one sided PCBs, the red print.

Lately some digital printing solutions have been developed to substitute the

traditional screen printing process. This technology allows printing variable data onto

the PCB, including serialization and barcode information for traceability purposes.

PCB ETCHING:-

Etching, also known as chemical milling, is the process of using acids, bases or

other chemicals to dissolve unwanted materials such as metals, semiconductor

materials or glass. This process has been used on a wide variety of metals with

depths of metal removal as large as 12mm (0.5 in). Selective attack by the chemical

reagent on different areas of the workpiece surfaces is controlled by removable

layers of material called masking or by partial immersion in the reagent. It has

applications in the printed circuit board and semiconductor fabrication industries. It is

also used in the aerospace industry to remove shallow layers of material from large

aircraft components, missile skin panels, and extruded parts for airframes.

The process is known to have been used by craftsmen in Europe in the middle ages,

where it was applied to the decoration of armour. One such craftsman, Daniel Hopfer

(circa 1470-1536) of Augsburg, Germany, is credited with being the first person to

apply the method to printmaking.

The vast majority of printed circuit boards are made by bonding a layer of copper

over the entire substrate, sometimes on both sides, (creating a "blank PCB") then

removing unwanted copper after applying a temporary mask (eg. by etching), leaving

only the desired copper traces. A few PCBs are made by adding traces to the bare

substrate (or a substrate with a very thin layer of copper) usually by a complex

process of multiple electroplating steps.

There are three common "subtractive" methods (methods that remove copper) used

for the production of printed circuit boards:

1. Silk screen printing uses etch-resistant inks to protect the copper foil.

Subsequent etching removes the unwanted copper. Alternatively, the ink may

be conductive, printed on a blank (non-conductive) board. The latter

technique is also used in the manufacture of hybrid circuits.

2. Photoengraving uses a photomask and chemical etching to remove the

copper foil from the substrate. The photomask is usually prepared with a

photoplotter from data produced by a technician using CAM, or computer-

aided manufacturing software. Laser-printed transparencies are typically

employed for phototools; however, direct laser imaging techniques are being

employed to replace phototools for high-resolution requirements.

3. PCB milling uses a two or three-axis mechanical milling system to mill away

the copper foil from the substrate. A PCB milling machine (referred to as a

'PCB Prototyper') operates in a similar way to a plotter, receiving commands

from the host software that control the position of the milling head in the x, y,

and (if relevant) z axis. Data to drive the Prototyper is extracted from files

generated in PCB design software and stored in HPGL or Gerber file format.

"Additive" processes also exist. The most common is the "semi-additive" process. In

this version, the unpatterned board has a thin layer of copper already on it. A reverse

mask is then applied. (Unlike a subtractive process mask, this mask exposes those

parts of the substrate that will eventually become the traces.) Additional copper is

then plated onto the board in the unmasked areas; copper may be plated to any

desired weight. Tin-lead or other surface platings are then applied. The mask is

stripped away and a brief etching step removes the now-exposed original copper

laminate from the board, isolating the individual traces.

The additive process is commonly used for multi-layer boards as it facilitates the

plating-through of the holes (to produce conductive vias) in the circuit board.

DRILLING:-

Holes through a PCB are typically drilled with tiny drill bits made of solid tungsten

carbide. The drilling is performed by automated drilling machines with placement

controlled by a drill tape or drill file. These computer-generated files are also called

numerically controlled drill (NCD) files or "Excellon files". The drill file describes the

location and size of each drilled hole. These holes are often filled with annular rings

to create vias. Vias allow the electrical and thermal connection of conductors on

opposite sides of the PCB.

When very small vias are required, drilling with mechanical bits is costly because of

high rates of wear and breakage. In this case, the vias may be evaporated by lasers.

Laser-drilled vias typically have an inferior surface finish inside the hole. These holes

are called micro vias.

It is also possible with controlled-depth drilling, laser drilling, or by pre-drilling the

individual sheets of the PCB before lamination, to produce holes that connect only

some of the copper layers, rather than passing through the entire board. These holes

are called blind vias when they connect an internal copper layer to an outer layer, or

buried vias when they connect two or more internal copper layers and no outer

layers.

The walls of the holes, for boards with 2 or more layers, are plated with copper to

form plated-through holes that electrically connect the conducting layers of the PCB.

For multilayer boards, those with 4 layers or more, drilling typically produces a smear

comprised of the bonding agent in the laminate system. Before the holes can be

plated through, this smear must be removed by a chemical de-smear process, or by

plasma-etch.

SOLDERING:-

Soldering is a process in which two or more metal items are joined together by

melting and flowing a filler metal into the joint, the filler metal having a relatively low

melting point. Soft soldering is characterized by the melting point of the filler metal,

which is below 400 °C (752 °F).[1] The filler metal used in the process is called solder.

Soldering is distinguished from brazing by use of a lower melting-temperature filler

metal; it is distinguished from welding by the base metals not being melted during

the joining process. In a soldering process, heat is applied to the parts to be joined,

causing the solder to melt and be drawn into the joint by capillary action and to bond

to the materials to be joined by wetting action. After the metal cools, the resulting

joints are not as strong as the base metal, but have adequate strength, electrical

conductivity, and water-tightness for many uses. Soldering is an ancient technique

mentioned in the Bible[2] and there is evidence that it was employed up to 5000 years

ago in Mesopotamia

One of the most frequent applications of soldering is assembling electronic

components to printed circuit boards (PCBs). Another common application is making

permanent but reversible connections between copper pipes in plumbing systems.

Joints in sheet metal objects such as food cans, roof flashing, rain gutters and

automobile radiators have also historically been soldered, and occasionally still are.

Jewelry components are assembled and repaired by soldering. Small mechanical

parts are often soldered as well. Soldering is also used to join lead came and copper

foil in stained glass work. Soldering can also be used to effect a semi-permanent

patch for a leak in a container cooking vessel.

Guidelines to consider when soldering is that since soldering temperatures are so

low a soldered joint has limited service at elevated temperatures. Solders generally

do not have much strength so the process should not be used for load bearing

members.

Some examples of solder types and their applications are tin-lead (general purpose),

tin-zinc for joining aluminium, lead-silver for strength at higher than room

temperature, cadmium-silver for strength at high temperatures, zinc-aluminium for

aluminium and corrosion resistance, and tin-silver and tin-bismuth for electronics.

There are two main components used while soldering. These are explained below.

SOLDER:

A solder is a fusible metal alloy with a melting point or melting range of 90 to 450 °C

(200 to 840 °F), used in a process called soldering where it is melted to join metallic

surfaces. It is especially useful in electronics and plumbing. Alloys that melt between

180 and 190 °C are the most commonly used.

The word solder comes from the Middle English word soudur, via Old French

solduree and soulder, from the Latin solidare, meaning '‘to make solid’'. Solder can

contain lead and or flux but in many applications solder is now lead free.

SOLDER IRON:

A soldering iron is a tool used for applying heat to two adjoining metal parts such that

solder may melt and flow between those parts, binding them securely and

conductively.

A soldering iron is composed of a heated metal tip and an insulated handle. Heating

is often achieved electrically, by passing a current, supplied through an electrical

cord or a battery, through a heating element. Another heating method includes

combustion of a suitable gas, which can either be delivered through a tank mounted

on the iron (flameless), or through an external flame.

Some heat up and cool down in a few seconds, but others take minutes.

The soldering process is as described below:

Good soldering is a skill that is learnt by practice. The most important point in

soldering is that both parts of the joint to be made must be at the same temperature.

The solder will flow evenly and make a good electrical and mechanical joint only if

both parts of the joint are at an equal high temperature. Even though it appears that

there is a metal to metal contact in a joint to be made, very often there exists a film of

oxide on the surface that insulates the two parts. For this reason it is no good

applying the soldering iron tip to one half of the joint only and expecting this to heat

the other half of the joint as well.

When the iron is hot, apply some solder to the flattened working end at the end of

the bit, and wipe it on a piece of damp cloth or sponge so that the solder forms a thin

film on the bit. This is tinning the bit.

Melt a little more solder on to the tip of the soldering iron, and put the tip so it

contacts both parts of the joint. It is the molten solder on the tip of the iron that allows

the heat to flow quickly from the iron into both parts of the joint. If the iron has the

right amount of solder on it and is positioned correctly, then the two parts to be

joined will reach the solder's melting temperature in a couple of seconds. Now apply

the end of the solder to the point where both parts of the joint and the soldering iron

are all touching one another. The solder will melt immediately and flow around all the

parts that are at, or over, the melting part temperature. After a few seconds remove

the iron from the joint. Make sure that no parts of the joint move after the soldering

iron is removed until the solder is completely hard. This can take quite a few seconds

with large joints. If the joint is disturbed during this cooling period it may become

seriously weakened.

The hard cold solder on a properly made joint should have a smooth shiny

appearance and if the wire is pulled it should not pull out of the joint. In a properly

made joint the solder will bond the components very strongly indeed, since the

process of soldering is similarly to brazing, and to a lesser degree welding, in that

the solder actually forms a molecular bond with the surfaces of the joint.

It is important to use the right amount of solder, both on the iron and on the joint. Too

little solder on the iron will result in poor heat transfer to the joint, too much and you

will suffer from the solder forming strings as the iron is removed, causing splashes

and bridges to other contacts. Too little solder applied to the joint will give the joint a

half finished appearance: a good bond where the soldering iron has been, and no

solder at all on the other part of the joint.

Remember it is much more difficult to correct a poorly made joint than it is to make

the joint properly in the first place. Anyone can learn to solder, it just takes practice.

PRINTED CIRCUIT ASSEMBLY:-

After the printed circuit board (PCB) is completed, electronic components must be

attached to form a functional printed circuit assembly, or PCA (sometimes called a

"printed circuit board assembly" PCBA). In through-hole construction, component

leads are inserted in holes. In surface-mount construction, the components are

placed on pads or lands on the outer surfaces of the PCB. In both kinds of

construction, component leads are electrically and mechanically fixed to the board

with a molten metal solder.

There are a variety of soldering techniques used to attach components to a PCB.

High volume production is usually done with machine placement and bulk wave

soldering or reflow ovens, but skilled technicians are able to solder very tiny parts

(for instance 0201 packages which are 0.02" by 0.01") by hand under a microscope,

using tweezers and a fine tip soldering iron for small volume prototypes. Some parts

are impossible to solder by hand, such as ball grid array (BGA) packages.

Often, through-hole and surface-mount construction must be combined in a single

PCA because some required components are available only in surface-mount

packages, while others are available only in through-hole packages. Another reason

to use both methods is that through-hole mounting can provide needed strength for

components likely to endure physical stress, while components that are expected to

go untouched will take up less space using surface-mount techniques.

After the board has been populated it may be tested in a variety of ways:

While the power is off, visual inspection, automated optical inspection. JEDEC

guidelines for PCB component placement, soldering, and inspection are

commonly used to maintain quality control in this stage of PCB manufacturing.

While the power is off, analog signature analysis, power-off testing.

While the power is on, in-circuit tests, where physical measurements (i.e.

voltage, frequency) can be done.

While the power is on, functional test, just checking if the PCB does what it

had been designed for.

To facilitate these tests, PCBs may be designed with extra pads to make temporary

connections. Sometimes these pads must be isolated with resistors. The in-circuit

test may also exercise boundary scan test features of some components. In-circuit

test systems may also be used to program nonvolatile memory components on the

board.

In boundary scan testing, test circuits integrated into various ICs on the board form

temporary connections between the PCB traces to test that the ICs are mounted

correctly. Boundary scan testing requires that all the ICs to be tested use a standard

test configuration procedure, the most common one being the Joint Test Action

Group (JTAG) standard.

When boards fail the test, technicians may desolder and replace failed components,

a task known as "rework".

CONCLUSION

The reliability and accuracy of equipment is inversely proportional to the

number of components being used. The less number of the components more

reliability and accuracy can be achieved almost of the electronic components are

temperature and voltage variation dependent. So more number of component more

the problem, you have also it increase the maintenance cost.

Our equipment has been designed using the most modern LSI chips available

in the market which can take the voltage fluctuation of greater degree.

REFERENCE

www.aaroncake.net/circuits

www.wikepedia.com

www.circuitstoday.com

Op-Amp and their linear integrated circuit- By R.A.Gaikward

Electronic Devices And Circuits- By Nashelsky & Boysted

Network Analysis- By Van Valkenburg

Power Electronics- By P.C. Sen

www.alldatasheet.com

IDEAS WHICH COULD NOT BE IMPLEMENTED

A circuit which would give details about the vehicle coming from the opposite

side. The detail like it is at what distance from the driver, his speed of

approaching and the intensity of the light.

A circuit which would automatically trigger the upper headlight circuit even if

the vehicle is approaching him from opposite side in case the other driver

does not give response to our generosity.

A circuit which would send signals to the driver when he takes reverse his

vehicle and is about to hit something.