automatic street light changer

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AUTOMATIC STREET LIGHT CHANGER

COMPONENT LIST

1. IC’s

Number Quantity Rate/P.

555 IC 1 10.00

BEL187 1 3.00

2. Light Emitting Diodes (LED’s)

Red 1 2.00

3. Diodes

1N4007 1 10.50

4. Sensors

LDR 1 45.00

5. Electrolytic Capacitors

10F/25V 1 10.00

6. Variable ResistorsPreset 4k7 (pot) 21 30.00

GLOBUS ENGG. COLLEGE,BHOPAL

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7. Carbon Resistors (0.25W)

100K 1 0.25

330E 1 0.25

8. battery

0-9v, 500mA 1 20.00

9. PCB

2” X 3” 2 120

10. Meslenious

IC Base (4 pin) 2 10.00

Mains Cable 2 30.00

Battery clamp 1 10.00

Ferric Cloride 100gms. 40.00

Soldering Wire 20gms. 30.00

Connecting wires 3mtrs. 10.00

Soldering Paste 10gms. 5.00

11 Buzzer 1 15.00


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STREET LIGHT CHANGER

WORKING

This project can be used as morning alarm. It can be fitted inside the room to inform you the entry of stranger, thieves etc. Also it can be fitted in treasuries.

This project is such a project which can astonish you and your family and also the people who are not acquainted with electronics. For example, there are some people who go to the bed late but unable to wake-up in the morning. This project gives a bell as soon as there is morning light. As such this project only works when where is light. In this project an IC555, transistor BEL 187 & a 12Volt.

Relay have been used. Also one light dependent resistance [LDR] is used to act with light intensity. The resistance of the LDR increases or decreases on the intensity of light, when light falls on LDR its resistance decreases and in darkness the resistance increases. In this circuit IC 555 is used as a timer. Pin no. 4 of the IC is earthed through a 2.2K preset which keeps the Flip-Flop system of the IC at a high state in darkness. Pin no. 3 of the IC is the output pin & remains at a low state. The IC does not operate in this condition of darkness. But when light falls on LDR, the resistance of the LDR decreases, as a result of which, pin no. 4 of the IC gets positive voltage, the Flip-Flop system of the IC comes to low state and internal inverting amplifier of the IC comes to high state resulting a voltage develop at pin no. 3. This pin no. 3 voltage biases the transistor BEL 187 and the transistor operates the relay. When the relay is ON, the bell starts ringing.


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NOTE:- Readers may note that the LDR is mounted in such a way that morning sun light directly falls on the LDR.

DIODES

It is two terminal device consisting of a P-N junction formed either in GE or SI crystal. The P and N type regions are referred to as anode and cathode respectively. Commercially available diodes usually have some means to indicate which lead is P and which lead is N. Standard notations consists the number proceeded by IN such as In 240& 250. Here 240 and 250 correspond to color band.

RESISTANCE

The resistance are heat dissipating elements and in the electronic circuits

they are mostly used for either controlling the currents in the circuit or developing

a voltage drop across it which could be utilized for many application there are

various types of resistance's which can be classified according to a number of

factors depending upon:-

(I) Material used for fabrication of 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 or 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 rating

of Resistors Resistance's may be classified as :-


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(1) Fixed (2) Semivariable and (3) Variable resistance We have used

carbon resistance.

Resistors and resistive networks are extensively used in electronic

circuits and measurement work. The foremost properties of material used in the

construction of resistors meant for precision work are stability or performance

with time temperature co efficient, low thermoelectric emf. With copper high

resistively resistance to oxidation corrosion and moisture case of manufacture

and low cost.

MATERIAL USED FOR RESISTORS:-

The most widely used material for precision resistors are:

MANAGING:-

It is an alloy of copper manganese and nickel and is universally used

as resistance material for precision resistors and for resistance measuring

apparatus. It has a normal composition of 84% copper 12% manganese and 4%

nickel. The foremost property of managing is that it has almost a zero

temperature coefficient of resistance near about room temperature.

CONSTANTINE:-

These are series of alloy of nickel & copper containing 40 to 60 percent

nickels, with a small amount of manganese to improve their mechanical properties.

Constantine has a resistively at ordinary temperature of about 2 times that of


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copper is corrosion resistant inexpensive & easy to work. It also finds application

is resistors of 1000 -- & above as in voltmeter multipliers.

NICKEL CHROMIUM ALLOYS:-

These alloy have a somewhat higher temperature coefficient of

resistance than that of managing and Constantine these alloys cannot be uses in

precision resistance Nichimo has a very high resistively and resists corrosion

even at very high temperature.

GOLD CHROMIUM:-

It is an alloy of recent introduction which appears to be very promising for some application it is made with slightly over 2 percent of


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chromium. For many application the extremely small temperature coefficient of gold chromium alloys make their use desirable especially for heat resistant standard.

RESISTANCE WIRES:-

The resistance wire is generally double silk of silk and cotton covered.

The wire is enameled before these coating are applied. High quality resistors

are wound with only layer of wire although this requires use of smaller wire

than for multi layer coils. Resistance with a wide range of values are

extensively used in electrical and electronic circuits. A colour code is used to

indicate the resistance value and its percentage reliability. The resistor has a set

of concentric rings to tit with their significance. The first two bands from the

end indicate the first two significant figures of resistance is ohms the third band

indicates the decimals multiplies and the last band stands for the tolerance in

about the indicated value.

Resistance Designation

A number of methods are available to mark the resistance values on the body

of a resistor. some of the important methods are as discussed below:

1. The resistance values are discussed on the body of the resistor. This method is widely used for marking industrial or consumer resistors.

2. The resistance values are printed on the body of the resistor as a series of number or number and the letter R. This method is used for marking MIL- spec (Military specification resistor)

3. The resistance values are printed on the body of a resistance as a code using coloured bands. This method is used for both industrial or


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consumer and MIL-space resistars, to designate resistance as well as tolerance percentage.

Colour Code Resistance Designation :-

The resistance and tolerance specifications for fixed resistors are usually

printed on the body of a resistor. Most wire-wound resistor specifications

(including power rating) are also printed on the resistor. However, carbon-

composition carbon film some metal film resistance are designated by a colour

code system. In this systems the bands of different colours are used to identify the


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resistance value and tolerance rating of the resistor. The power rating is determined

from the physical size of a resistor. There are tow common systems of colour code

designed namely a four band system and a five band system. But the four band

colour code system is more common. In the four band system, the first two bands

represent the significant figures, while the third band is the multiplier (essentially

the number of zeros) as shown if Fig. 7.13 The fourth band represents the tolerance

band.

Table 7.1 gives code for different colours. It may be noted from this table

that the black band represents value (0) and white the maximum value (9). The red

band represents a tolerance of + 2%, gold + 5%, silever + 10% and a plain (or no

colour band) represents a tolerance of + 20%. The following examples illustrate the

use of colour code system.

For example suppose we have to specify the code for 10 +10% resistor.

Look at table 7.1 and check that the first significant figure (or first digit) of the

specified value (10 ) is 1. Therefore the first band will be of a brown colour. The

second significant figure of the specified value (10) is 0. Therefore the second

band will be of a black colour. The third band will again be of a black colour,

because we need a multiplier of 1 (1) for 10 resistance. Finally + 10% is

represented by a silver colour band. Therefore 10 + 10% will have a colour code

designation as shown in Fig. 7.14 (a).

Now consider a colout code resistor as shown in Fig. 7.14 (b). The gray

corresponds to first band its value is 8. Similarly, red corresponds to second band

its value is 2. Therefore the first tow significant figure of the resistance values is

82. The third band is of orange colour. Therefore the multiplier (number of zero) is

1000. Hence the resistance value is 82.000 . The tolerance band is of gold colour


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which corresponds to a tolerance of + 5%. Therefore the resistance value can lie

anywhere between 82 000 + 5% i.e. 73 000 and 90 200 .

Sometimes the resistance values less than 10 are also used. For such resistors the third band is either of gold or silver. It serves as a fractional multiplier. If the third band is gold, multiply the first two digits of the resistance value by 0.1. If it is silver, then multiply by 0.01 However the fourth band represents the tolerance value as discussed earlier. Thus we can check that the resistance value of the resistor shown in Fig. 7.14 © is 0.47 + 10%.

RESISTORS

A resistor is an electrical component, which has been manufacture with a

specified amodnt of resistance. The resistors can conduct current in both the

directions. The resistors may be connected in an electric circuit without concern

for lead polarisation. The resistors are used mainly for two purposes, namely

controlling the flow of electric current and providing desired amounts of voltage in

electric in electric or electronic circuits.

Resistor specifications

The resistors are specified in terms of their resistance values, tolerance

power rating and thermal stability. By tolerance, we mean the allowed variation

permitted in the normal or marded value or the resistor. It means that the actual

value of the resistor may be either greater or smaller than that of the indicated

value, by a factor given by the specified tolerance. Thus resistors are manufactured

with a specified tolerance. For example, a 5000 resistor with a tolerance of +

10% will have an actual resistance value anywhere between 4500 and 5500 or

in other words 500 greater or smaller them the rated value.

The power rating of a resistor is given by the maximum wattage it can

dissipate, without excessive heating. Since the power rating is proportional to the


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square of a current, there fore current must not be higher than its safe value. If the

current exceeds the safe value, the resistance will burn out. Usually, carbon

composition resistors will fail, if operated at near the rated power values. In this

case, the resistor will not burn out. But the failure is gradual, which takes many

months. It changes gradually to a much lower amount of resistance. This causes an

improper operation of an electronic of an electronic circuit particularly in

amplifier. Thus in order to increase the life of use a power dissipation of about half

of the rating of the resistor.

The thermal stability of a resistor is indicated by the temperature coefficient

specification, which is usually expressed in parts per million per degree centigrade

(+ ppm/C). The smaller value of temperature coefficient will have less variation in

the resistance value. Therefore, smaller value of temperature coefficient means a

higher thermal stability of a resistor.

CLASSIFICATION OF RESISTORS

Shows the classification of resistors in the from of a family tree. The

resistors are basically of two types, namely linear resistors and non- linear

resistors. Each type is further subdivided into many types as shown in the figure.

1. Linear resistors. The resistors through which the current is directly

proportional to the applied voltage, are called linear resistors. Such resistors

have a property that their resistance value do not change with the variation in

applied voltage, temperature or light intensity. The linear resistors are of two

types namely fixed resistors and variable resistors.


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2. Non-linear. The resistors through which the current is not directly

proportional to the applied voltage, are called non-linear resistors. Such

resistors have a property that their resistance values change with variation in

applied voltage, temperature of light intensity. The non-linear resistors are of

three namely thermistor, photo resistor and varistor.

Carbon Composition Resistors:-

These resistors are made by mixing carbon powder and insulating binders to

produce the desired value of resistance. The resulting resistance values are within +

10% of the desired value. However, the resistors with + 5% tolerance are also

obtained through special techniques. Usually, the resistance element is a simple rod

of carbon powder, which is enclosed in a plastic case for insulation and mechanical

strength as shown in Fig.7.3.(a). The two ends of the carbon resistance element are

joined to metal caps with leads of tinned wire. The leads are provided for soldering

the resistor into a circuit.

The carbon composition resistors are available in resistance values ranging 1

to 22 M and power ratings of 1/8, 1/4,1/2,1 and 2 watts. The size of these

resistors varies with the power ratings as shown in Fig.7.3(b). These days, the

carbon composition resistors with power rating of 1 W of less are widely used in

electronic equipments.

CAPACITORS

The fundamental relation for the capacitance between two flat plates

separate be a dielectric materiel is given by C=0.08854KA where


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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 caterial with particular type of application. The dielectric material used foe capacitors may be grouped in the carious classed like Mica Glass air ceramic paper Aluminum eletrolytic etc. The value of capacitance never remains constant except under certain field 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 some of the capacitor use din circuits are impregnated paper dielectric capacitor Glass dielectric capacitors vitreous enamel dielectric capacitors etc.

Classification of Capacitors

The capacitors are commonly classified on the basis of dielectric material used for their manufacturing. it is because of the fact that characteristics of a capacitor are mainly due to the properties of a dielectic. Figure 7.23 shows different types of capacitors manufactured these days.

The capactiors may be divided into two classes, namely fixed capacitors and variable capactors. Each type is further subdivided in to many types as shown in the figure.

Electrolytic Capacitors

These capacitors are made up of metal plates, which have a difinite polarity separated by a thin metal oxide dielectric as shown in Fig. 7.24. The metal oxide is


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a conductive compound having dielectric constant between 8 and 25. Usually, it is in a paste form, though it can be in a liquid form also. The plate acts as a positive electrode or anode. The capacitor is formed by using either a conducting electrolyte as a second electrode or a semiconductor such as manganese dioxide. The electrolyte used is either in a liquid form or in the form of a paste, which saturates a paper or a gauge. The capacitor is packed in metal cylinder. The cathode is connected to the cylinder. The cylinder is usually, enclosed in a paper tube or cardboard tube, in order to insulate it form outside.

When a voltage of correct polarity is applied to a capacitor, a very thin insulating layer of oxygen atoms forms between the anode and the oxide layer. A reversal of polarity removes the insulating layer, thereby allowing very high currents. Thus electrolytic capacitors are known as polarised capacitors. They must be connected in a circuit according to the 'plus' (+) and 'minus' (-) markings on the body of a capacitor. If the capacitor is connected with a reverse polarity, it will act as a short circuit and get overheated, due to excessive leakage current, and it can explode also.

Some electrolytic capacitors are made with two capacitors in one cylinder. These oapacitors are internally connected in series in an inverse arrangement, so that one of them is always working as a capacitor. This prevents the high leakage current, when operated with reverse polarity. Such capactitors are known as non-polarized electrolytic capacitors.

The electrolytic capacitors possess a large value of capacitance ranging form 1 uF ot 10000 uF in very compact sizes. The electrolytic capacitors are used in a variety of specialised applications. Such application include their uses in starting motors, blocking d.c. current, passing a.c. current, filtering unwanted signals, tuning currents to a specific frequency, coupling and bypassing signals etc.

Types of Electrolytic Capacitors:-

The metal electrolytic capacitor, as discussed in last article, can be either of an aluminum or tantalum metal. Accordingly, the electrolytic capacitors can be divided into two types namely aluminum and tantalum electrolytic capacitors.


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1. Aluminum electrolytic capacitors. These capacitors have higher working voltage and low clost as compared to other capacitors of similar capacity. But they are susceptible to certain compounds like freon, trichloroethylene and carbon terachloride etc.

2. Tantalum electrolytic capacitors. These capacitors are superior to the aluminum electrolytics. They have a longer life, temperature range, frequency range, low leakage current etc. The have a high resistance to mechanical shock and virations. The tantalum electrolytic capacitors are available in a variety of sizes and shapes.

Disadvantages of Electrolytic Capacitors:-We have already discussed that electrolytic capacitors have a large

capacitances values ranging form 1 uF to 10000 uF. They have a large number of applications both in electrical and electronic circuits. But they have certain disadvantages, which can not be ignored. Following are some of important ones:

1. They have lower working voltages than other capacitors of similar capacity.

2. They have much higher leakage current and leakage resistance.

3. They have poor storage life, as their dielectric loses its properties over long periods of service.Variable Capacitors

The capacitors, in which the capacitance value may be changed by some means, are called variable capacitors. The capacitance value is, usually, changed either by varying the area between the plates or by adjusting the spacing between them. The variable capacitors have capacitance in picofarad (pF) range. These capacitors are made by using air, mica, ceramic or plastic as a dielectric. The variable capacitors, using air as a dielectric, are used as ganged capacitors in radio receivers. The variable capacitors, using other dielectrics, are called trimmers or padders.

LED

As there name indicated it is a forward biased P-N junction which emits visible Light when energized. Charge carrier recombination tacked place when electrons from the N-side cross the junction and recombine with the heeds on the P


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side. Now electrons are in the higher conduction band 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) Gellium phosphide (Gap) and Gallium arsenate phosphide (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 they are reverse biased.

LDR

The abbreviation LDR stands for light dependent resistance. The resistance

of an LDR(photoreceptor) depends on the amount of light falling on LDR. The

Claris CL 905 is an example of LDR its resistance is about 15 M ohms in the dark

and bout 15 K ohms in a bright light. An LDR contains a Zig Zag pattern of

cadmium sulphide of cadmium solenoid whose resistance varies as the intensity to

the light A glass window is provided to allow light to fall on the photoreceptor.

They are also not stable with temperature. Due to these reason they can be used

where precise measurement of light is not necessary.

They can be used to switch precise measurement of light is not necessary. They can be used to switch on street lights when it gets dark. For switching operation a photoreceptor a transistor driver and a relay can be used.

RELAY

Relay is electrical device and it functions as an electrically operated switch. Most are operated Electro-magnetically. When current flower through a coil. Electromagnetic field is generated. The generated electrical field attracts the armature in turn opens or close the electrical contacts. The time taken by relay for is in milli-second range.


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A Common type of relay having open and otherwise a closed contacts shown in figure. The normally closed contact provides a continuity between the armature and the upper contact. The spring holds the armature as shown in fig. When a desired voltage is applied to the coil, the armature is attracted to the coil and it is drawn downwards.

This breaks the normally closed and makes the contact open. Now the continuity exists between the armature and the normally open contact.

RELAY CONSTRUCTION

The relay consists of three basic elements.

1. An actuating or exciting coil2. Mechanical linkage to transfer the exciting /de-excitation of the coil output.3. Contact switching.

It consists of a coil wound over a magnetic core or rod. One face of the core

is attached to a base plate that is extenuated to the other face of the coil. A movable

plate extending to the open face of the core is attached to the base plate such that a

small gap remains between the movable plate and the core. The movable contacts

are attached to this plate. The fixed contacts constructed opposite to the moving

contacts. Suitable gap is maintained between the two contacts. The contact

arrangement is such that when the movable plate is in contact with the core face

the contact get closed. the coil when energized products magnetic field in the core.

The open face becomes a pole of the electromagnet and attracts the movable

plate. The movable place comes in contact of the pole face and is held firmly there

as the magnetic circuit remains close through the base plate. The contact attached


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to the movable plate are now firmly held to the fixed contacts. Thus actuation of

the coil causes the normally open contacts to close.

The normally closes contacts are placed in such a way that they remain

closed when the coil is not energized and get open upon actuation of the coil. A

spring is fitted to the movable plate that brings the movable plate and the contacts

back to their original position when the coil is deactuated.

TRANSISTOR:-

A transistor consists of two junctions by sandwiching either p-type of 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

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. These 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.

3. The middle section is a very thin layer. This is the most important factor in

the function of a transistor.

4. Transistor as an Amplifier.

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

amplifier. The weak signal is applied between emitter base junction and output is


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taken across the load Rc connected in the collector circuit in order achieve faithful

amplification the input circuit should always remain forward biased. This d.c.

Voltage V EE is applied in the input in addition to the signal.

This d.c. Voltage is known as bias voltage and magnitude is such that is

always keeps the input circuit forward besides regardless of the polarity to the

signal.

7.11 VARISTORS

The word varistor in an acronym from variable resistor. The varistors are voltage dependent resistance (VDR's). These are used to protect circuit from high energy voltage transients (also called surges) by rapidly changing from high stand by resistance to low conducting resistance. This action of a varistor clamps the voltage to a safe level. A high-energy voltage transient is an abnormal short living disturbance in the circuit, which is produced by switching operation, a sudden fault in electrical equipment or lightning stroke.

A typical volt ampere (V-I) characteristic of a varistor is shown in Fig. 7.12 (a).In this figure, the solid curve represents region for continuous, while the dashed curve represents surges respones. It may be noted from the characteristic curve that if a transient changes a voltage in a circuit from 120 to 170 volts, the current suddenly jumps from 100 mA to 400 mA. It means a 300% increase of current in the circuit. This sudden increase in the current may damage the circuit. The varistor protects the circuit from destructive energy by dissipating energy in its body. Figure 7.12 (b) shows a schematic symbol of a varistor.

The varistor are available in a variety of packages. These are capable of handling instaneous currents up to 2000 A with ac operating voltage ranging from 12 V to 660 V and at temperature from - 40C to + 85C.

7.12 VARISTOR APPLICATIONS


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Though the varistors have a number of application these days, yet the

following are important from the subject point of view.

1. Transient suppression in inductive and transformer switching circuits.

2. Switch contact are suppression.

3. Protection of circuits.

SWITCHES

An electrical switch is a device usually used to open or close an electrical

circuit. Mostly switches are manually operated devices. Switches play important

role in electronics, to stop the flow of current or send the current.

TYPES OF SWITCHES:-

(1) Single Pole Single Throw (SPST) : This type of switch can contact or

disconnected only a single wire circuit. These are of two types-slide type and

toggle type. Its current rating is from 0.5 to 6 and voltage from 6 volt to 30

volt. It is primarily used as an On-Off switch in small electrical appliances.

(2) Single Pole Double Throw (SPDT) Switch : This type of switch has on

position. SPDT are also of two types- (1) Slide Type (2) Toggle switch. The

slide type SPDT is used for PCB mounting but toggle SPDT is used in low

current devices as in SPST. Slide type is available in 1 A.4A for a voltage

range of 30v to 6v. Toggle type SPDT has a current rating of 1A, 1.5A for a

voltage range of 330 V and 30 V.


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(3) Double Pole Single Throw (DPST) Switch : Such a type of switch has only

one position of closure but two contacts simultaneously. It is similar to a

SPST switch. The major difference in DPST switch is that both side of a

two-wire line are switched at once.

(4) Double Pole Double Throw (DPDT) Switch : This type of switch has two

poles and can be moved on either side that is to the right or to the left. Two

DPST switches connected together can also be used a DPDT switch. There

are two types of DPDT switches.

(1) Toggle type (2) Slide type DPDT

(5) Micro Switches : Micro switches are various types. Basically they can be

classified as illuminated rocker switches and subminiature rocker switch.

But all the switches discussed above are toggle micro-switches.

They are suitable for both low level and high level (power switching)

applications. Normally these switches are enclosed in a nylon case. This

nylon construction provides a double insulation for extra safety. This

insulation resistance is generally grater than 10M ohm. The temperature

rating of micro-switches is between 25C to 70C.

(6) Band Switches : These switches are used in instrument such as Radio, TV

and Tape recorder to select a desired circuit. Mostly a three-band radio

receiver set requires a three-position band switch. These switches are of

different types slide type or rotary type.

(7) Push Button Switches : Both locking a latching (contacts remaining

operated after the button is pressed) and non locking (contacts release after

removal of the finger) designs are available. Other design variations have

multiple contacts, snap action and wiper action. In most design, state of the


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switch (operated or not) is determined by visual observation only. Some

designs have an indication light either self-contained or separate.

(8) Keyboards : A wide variety of keyboards or key pads are used for providing

manual input to electronic instrument such as telephone sets and adding

machines. The most commonly available keyboard has a 12 button (4 rows

and 3 columns) arrangement identical to the telephone instruments although

keyboards with 16 and 20 button arrangement are also available.

MANUFACTURING PROCESS

PCB LAYOUT

Lay out of the desired circuit is the most important in any circuit board manufacturing process. The following points are to be observed while performing the layout of the PCB

Sufficient space should be maintained between two components. High heat dissipation components like high voltage resistors should be mounted

at a sufficient distance from the semiconductors and electrolytic capacitors. Components layout should make proper combination with copper side circuit

layout. Circuit copper line thickness should be decided taking into account the current

drain in the circuit.


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PREPARATION OF SCREEN :

Nylon bolting cloth (Silk screen cloth) is stretched and attached to a wooden

frame. Photosensitive chemical (silcot-6) and ammonium bicarbonate is spread on

cloth and dried in total darkness.

The screen is exposed to UV light and is developed in water.

PRINTING :

The screen is placed on suitable copper laminated sheet on copper side and

circuit black printing ink (acid resistant paint) is spread on it. After printing the

PCB should be allowed to dry for at least 10 hrs. in a dust proof chamber.


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ETCHING :

The removal of excess copper on the copper laminated PCB apart from the

printed circuit is known as etching. Generally PCB is placed in F3C13 solution and

kept for one hour.

DRILLING :

Under this operation drilling should be done as per circuit lay with the

suitable drill and high speed machine. Drilling should always be done from copper

side to avoid possibility of coming out of copper circuit and chipping out of

Bakelite.

GREEN MAKING :

It is done with special epoxy paint and special thinner is requited for

cleaning the screen. It provides as better and also prevents frequency overlapping

between the tacks at high frequency operation.

THINNING :

It is an electroplating process (tin plating) done to increases the conductivity

of the conducting medium and to avoid oxidizing effect.


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COMPONENT MOUNTING :

All components are mounted at their respective position as per the components

layout. proper precautions should be taken during mounting process.

ETCHING PROCESS :

Etching process requires the use of chemicals acid resistant dishes and running water supply Ferric chloride is maximum used solution but other enchants such as ammonium per sulfate 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 use a very sharp knife to cut round the pattern carefully a remove the paper corresponding to the required copper pattern areas. Then apply the resist solutions, which can be kind of ink proportion fort the purpose maintaining smoothing clean outlines as far as possible. While the board is drying test all the components.

Before going to next stage, check the whole gotten and cross cheek against the circuit diagram check for any freeing matte on the copper. The etching bath should be in a galls or enamels disc. If using crystal of ferric-chloride these should be thoroughly dissolved in water to the proportional suggested. There should be 0.5 Lt. Of water for 125 Gm. of crystal.

Water liquid should be thoroughly deflated and druid in water land ; never pour down the drain. To prevent particles of copper hindering further etching, agitate the solutions carefully be 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. In spite of there being a resist coating there is no protection against etching away through exposed copper edges; this leads to


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over etching. Have running water ready so that etched board can be removed properly and rinsed ; this will hall etching immediately.

Drilling is one of those operations that calls for great care because most of the holes will be made a very small drill. For most purposes a 1 mm drill is used Drill all holes with this size first those that need to be larger can be easily drilled again with the appropriate lager size.

COMPONENT ASSEMBLE :

From the greatest variety of electronic components available today, which

runs into tent of thousands of different types it is often a perplexing task to know

which is the right task for a given job.

There should be damage such as hair line crack intuit opera on PCB that

could age a seriousfiec on the operational ability to the completed assemble. If

there are than they can and should be repaired fiesta bye soldering a short link of

bare copper wire over the affected part.

The most popular method of holding all the items is to been the wires future

apart after they even been indebted in the appropriate holes. This will hold the

component in position ready for soldering.

Some components will be considerably larger than other occupying and

possible partially obscuring neighboring components. Because of this best to start

by mounting the smallest first and progressing through to the largest. Before

starting make certain that no further drilling I likely to be necessary because access

may be impossible later.


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Next will probably be the resistor small signal diodes of other similar size

components some capacitor are very small but it would be best to fit these after

words when fitting each group of components marks of each one on the

components its as it is fitted and if we have to leave the job we know where to

recommence.

Although transistor & integrated circuit are small items there are good

reasons for leaving the soldering of these until the last step the main pint is that

these components are sensitive to heart and is subjected to prolonged application to

the soldering iron they could be internally damaged.

All the components before mounting are rubbed with sandpaper so that

oxide layer is removed from their tips. Now they are mounted according to the

components layout.

SOLDERING TECHNIQUES :

A soldered connection ensure metal continuity. The soldering process

involves :

(1) Melting of the flux which in turn removes the oxide films on the metal

to be soldered.

(2) Melting the solder which removes the impurities.


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(3) The solder partially dissolve of the metal in the connection.

(4) The solder cools and fuses wit the metal.

The soldering techniques involves knowledge of :

(1) Soldering iron

(2) Soldering wire

(3) Soldering procedure

(4) Replacing components

(5) Prosecutions of when using C-MOS, devices

(6) Knowledge of good and bad soldering joints.

(7) Disordering techniques

1. SOLDERING & SOLDERING TECHNIQUES

(1) Soldering Iron : Soldering iron is an essential tool for soldering. A.

Soldering iron should give sufficient heat a melt solder by heat

transfer when the iron tip is applied to a connection to be soldered.

The selection of the soldering iron can be made as regard to its tips

size shape and wattage. Soldering iron temperature is selected and

controlled according to the work to be performed. Generally two types

of soldering irons are available: Soldering Pencil and Soldering Gun.


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(2) Soldering Pencils : These are light weight soldering iron which can

generate around 12 watts to 50 watts of heat. Modular soldering.

2. SOLDERING ALLOY

Soldering Materials :

The soldering material is used to join together two or more metals at temperatures below their melting point. The solder alloy consists of Lead (37%) and Tin (63%). The continuous connection between two metal joint is made by solder materials.

Most commonly used solder wire consists of 60% of Tin 40% Lead. This is in the from of a hollow wire whose center is filled with an organic paste like material called rosin. Its melting temperature is 190 degree centigrade.

FLUX :

Flux is a material used to aid soldering process. Flux is needed to

scratch away the small film of oxide on the surface of metals to be soldered.

This flux forms a protective film that prevents reoxiadation while the

connection is heated to the point at which the solder melts. Flux is very

helpful on old dusty, eroded joint.

3. SOLDERING PROCEDURE


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(a) The soldering procedure involves selection of soldering iron

cleaning of components to be soldered and cleaning of the PCB

to be soldered.

(b) The soldering iron should be selected according to the job and

should be powerful enough to provide heat. The tip of the

soldering iron should be selected as per the space available for

soldering.

(c) The component that has to be soldered should be properly bent

and its leads should properly inserted in the PCB. Before.

(d) If one has already identified the fault component, then one

should not try to remove or desolder the component. The

components should simply be cut and taken out.

PRECAUTIONS WHEN USING C-MOS DEVICES :

CMOS Devices are sensitive to static charges. So care has to be taken

while handling these device. Static charge is generated by rubbing cloth with

human body or by any other friction of human body.

(1) Before string or handling CMOS Devices touching the ground or

metallic chassis of the equipment.

(2) One can wear a metallic band in hand which is connected to ground.

(3) The working table should be either of wood or should have rubber

sheet.

(4) The soldering iron tip should be static charge free.


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DESOLDERING TECHNIQUES

(a) By using a desoldering wick(b) By using a desoldering pump

Desoldering wick is made of fine copper wire mesh. When this is applied to the heated components, the molten solder gets attached to the wire mesh by capillary action.

Desoldering pump has a suction pump. The nozzle of the desoldering pump is kept to the heated component. The molten solder is sucked by a spring action.

Insertion in the PCB, the lead should be properly cleaned. After component has been inserted it can be soldered.

(d) The oxide on the PCB can be removed by using flux, sandpaper. The tip of

the soldering iron should be clean and should have proper shape. The shape

of the tip normally gets bad over a period of time. The shape can be made

proper by filling.

(e) During soldering excessive heat is generated at the soldering iron tip. If the

soldering iron tip is in contact with component for a longer time then there is

possibility of damaged or may loose its characteristics.

(f) Place iron tip at 45 degree to the PCB and component joint.

(g) Place the solder near the iron and let it flow.

(h) Smoothen the area of joint by the soldering iron tip. By doing this, the

molten solder alloy flows into the PCB hole.

(i) Soldering should be done when the equipment is off.


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REPLACEMENT OF COMPONENT

(a) In case of single sided PCB, the component to be removed can be disordered with the help of iron and flux. The only precaution that has to be taken is that track should not break while removing.

(b) In case of Through Hole PCB, care has the to be taken so that component while removing does not damaged the Through Hole.

(c) In this case the component is soldered on one side and the lead flows through the hole to the other sides, so disordering and removing becomes very difficult and required practice.

DIODES :-

It is s two terminal device consisting of a P-N junction formed either in GE

or SI crystal. The P and N type regions are referred to as anode and cathode

respectively. Commercially available diodes usually have some means to indicate

which lead is P and which lead is N. Standard notations consists the number

proceeded by IN such as In 240 & 250. Here 240 and 250 correspond to color

band.

COMPONENT TESTING

DIODE TESTING:

The condition of the semiconductor diode can be determined quickly using

the ohmmeter section of the multimeter. The forward - bias resistance of a

semiconductor diode is quite low compared to the reverse-bias level.

Therefore, if we measure the resistance of a diode using forward-bias connections,

we can expect a relatively low level. The resulting ohmmeter indication will be a


37


function of current established through the diode by the internal battery (often 1.5)

of the ohmmeter circuit. The higher the current, the lower the resistance level. For

the reverse-bias situation the reading should be quite high, requiring a high

resistance scale on the meter.

A high resistance reading in both the directions obviously indicates an open

condition i.e. defective device, while a very low resistance in both the directions

will probably indicate a shorted device.

TRANSISTOR TESTING:

The ohmmeter or the resistance scales of a digital multimeter can be used to

check state of a transistor. For a transistor in the active region the base-to-emmiter

junction is forward-biased and the bade-to-collector junction is reverse-biased.

Essentially. Therefore, the forward-biased junction should register a relatively low

resistance, while the reverse-biased junction shows a much higher resistance. For

an npn transistor, the forward-biased junction from base to emmiter should result

in a reading that will typically fall in the range of 100 to a few kilohms. The

reverse-biaded base-to-collector junction should result in a reading typically

exceeding 100k. For a pnp transistor the lead are reversed for each junction.

Obviouldy, a large or small resistance in both directions for either junction of an

npn or npn transistor indicates a faulty device.

If both junctions of a transistor result in the expected reading the type of

transistor can also be determined by simply noting the polarity of the leads as

applied to the base emmiter junction. If the positive lead is connected to the base


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and the negative lead to the emmiter a low resistance reading would indicate an

npn transistor. A high resistance reading would indicate an pnp transistor.

Although an ohmmeter can also be used to determined the leads of a transistor, it is

assumed that this determination can be made by simply looking at the orientation

of the leads on the casing.

CAPACITOR TETSTING:

The voltmeter section of the digital multimeter can be used to check the state

of electrolytic capacitor. When the leads of the multimeter are connected to the

capacitor the reading of the voltmeter increases from zero to a maximum value and

then from maximum to zero. Now when the leads of the multimeter are connected

in reverse direction again the voltage increases from zero to a maximum value and

then decreases to zero.

IC TESTING :

IC L200 is an analog IC. The condition of the IC can be determined Quickly

by using analog IC tester.

CITCUIT TESTING:


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The best way to check that the circuit is working is to monitor the current as

it flows into the battery. As all the current goes through the parallel

Combination of resistor R2 & R3. So we can get a good estimate of the current

going into your battery by measuring the voltage drop across the resistor. Use the

formula I = V/R (where I = current in amps, V = voltage in volts, R = resistance in

ohms) to get the current flowing through the resistor (since we know the value of

R2 & R3 )

Initially, if the battery is discharged, the maximum current (Imax as

described above) should be flowing through the combination of R2 & R3, and

voltage drop should be.

45 volts.

As the battery fills up, the voltage (and hence current) will drop, until eventually

the calculation gives us only a few tens of milliamps flowing into the battery.

Steps of project making

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


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5) and procure them after carrying out market survey.

6) Plan and prepare PCB for mounting all the components.

7) Fix the components on the solder them.

8) Test the circuit for the desired performance.

9) Trace and rectify faults if any.

10) Give good finish to the unit.

11) Prepare the project report.

Application

1) Morning alarm2) Automatic hi-way light3) Automatic house light4) Security system


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BIBLOGRAPHY

BOOKS :

1) Electronic devices and circuit theory

2) Electronic projects.

3) Microelectronic circuits.


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4) Electronic for you.

WEBSITES:

1) www.efy.com

2) www.nationalsemiconductor .com

3) www.icdiscriptiion .com


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