DIPLOMA IN ELECTRICAL AND ELECTRONICS

Autonomous under Directorate of Technical Education

HRD Department, Govt. of Sikkim

Approved by AICTE, An ISO 9000:2000 certified Institute

NAME OF PROJECT

Automatic Emergency Light

PROJECT REPORT

(2009-2011)

Submitted by

Name Reg. No

GANGADHAR YADAV C09DEE12

Under the guidance of

(Miss kabita Nepal)

Submitted as part of the curriculum of the first year diploma in …Electrical and Electronics…… discipline of CCCT, Chisopani, carried out successfully during the Academic year

2010

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Autonomous under Directorate of Technical Education

HRD Department, Govt. of Sikkim

Approved by AICTE, An ISO 9000:2000 certified Institute

CERTIFICATE

This is to certify that the project work entitled

(automatic emergency light) is a bonafide

work carried out by Gangadhar Yadav bearing

registration number C09d-EE12 during the

academic year <2010>. It is certified that all the

project report has been approved as it satisfies

the academic requirements in respect of project

work prescribed for the Diploma in …Electrical

and Electronic….

Signature of Guide Signature of Course In-charge Signature of Principal

External Examiner

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Signature with Date

Examiner’s Certificate

The project report of

1. Gangadhar Yadav

Titled AUTOMATIC EMERGENCY LIGHT

is approved and is accepted in quality and form.

Internal Guide (Name and Signature) External Examiner (Name and Signature)

Name :Miss.Kabita Nepal 1. Name:

2. Name:

DIPLOMA IN ELECTRICAL AND ELECTRONICS

STUDENTS DECLARATION

We hereby declare that the project report entitled

AUTOMATIC EMERGENCY LIGHTsubmitted to Centre for Computers and Communication Technology

in partial fulfillment for award of Diploma in electrical & electronics

during the academic period January 2010 to June 2010 is our

original work and not submitted for the award of any other degree,

diploma, fellowship, or any other similar title or prizes.

SL.NO Name Reg.NO signature

01 Gangadhar Yadav C09D-EE12

Place: C.C.C.T

Date:

DIPLOMA IN ELECTRICAL AND ELECTRONICS

ACKNOWLEDGEMENT

The completion of any inter-disciplinary project depends upon the co-operation,Coordination and combined effort of several sources of knowledge, energy and time for us. It is difficult task to pretend to know who helped us the most. Therefore, we approach this matter of acknowledgement through these lines trying best giving full credit where it is due.

We have a great pleasure in submitting the micro project document. The project successful completion would be incomplete without mentioning the name of people who really helped us in accomplishing this project to successful one.

We are taken this opportunity to express our deep sense of obligation and gratitude to the help given by our project co-ordinator Miss.Kabita nepal for his guidance, supervision and constructive criticism in the successful completion of the project.

We also express sincere gratitude to Mr. Mukesh sharma for providing the inspiration required for taking the project to its completion we are very grateful to him for providing us the required lab facilities. The successful presentation of this project is in itself acknowledgement of the immense blessing of our parents and support and encouragement extended to us by our teachers. So after the completion of the project, we feel very obliged to express.Our gratitude towards all those who make valuable contribution throughout the duration of the project.

Finally we thank all the staff members, teaching and non-teaching staff and our friends for helping us either directly or indirectly during the conduction period of the project.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

CONTENTS

1. INTRODUCTION (SYNOPSIS)

1.1 Introduction

2. DESIGN AND DEVELOPMENT

2.1 Block Diagram

2.2 Block Description

2.3 Circuit Diagram

2.4 Circuit Description

3. ESTIMATION AND COSTING

4. IMPLEMENTATION

4.1 Resistor

4.2 Diodes

4.3 Capacitor

4.4 Transistor

4.5 Transformer

4.6 LEDs

4.7 Switches

4.8 Battery

5. APPLICATION

5.1 Advantages

5.2 Disadvantage

6. CONCLUSION

6.1 Drawing

6.2 Appendices

6.3 Reference

DIPLOMA IN ELECTRICAL AND ELECTRONICS

DIPLOMA IN ELECTRICAL AND ELECTRONICS

AIM:-To design the circuit of AUTOMATIC EMERGENCY LIGHT

INTRODUCTION:-

This is automatic emergency light used in night at emergency time when the power cut or off by some region. This emergency light takes 230V AC and it converts it in 12V DC and charge the battery which is used in this circuit. The power of the battery is used that time when the power is cut off or we need to use it. This light is used mostly in villages because there is the lack of electricity is provided. In this circuit I use BD 140 transistor the advantage of this emergency light is that if we Use this emergency light in a room no other light source is required but in other emergency light we use another light source when the power is available.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

BLOCK DIAGRAM

DIPLOMA IN ELECTRICAL AND ELECTRONICS

BLOCK DISCRIPTION

First the power supply is given 230 through the step down transformer, the transformer convert it into 12V 1A but it is not gives dc so rectifier is used in it to convert it into dc. For filter the signals in the circuit a capacitor is used on it which filter the signals and convert it into pure DC. It also charged the battery when the power is given in the circuit. A transistor is used to maintain the power supply regularly and the control units (Zener diode) it maintain the zener voltage and also used it as a switch in reverse biased condition after that battery is the second power supplier which charged first and give backup power when the main power is cut off.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

CIRCUIT DIAGRAM

DIPLOMA IN ELECTRICAL AND ELECTRONICS

C IRCUIT DESCRIPTION

This is the circuit diagram of low cost emergency light based on white LED. The white led provides very bright light which turns on when the mains supply is not there. The circuit has an automatic charger which stops charging when the battery is fully charged. Here 230v is converted into 12v using step down transformer. Bridge rectifier is used to convert AC input to DC supply. Capacitor is used to filter the input AC supply. When the main supply is ON the charged capacitor voltage is much greater than the battery voltage which keeps the transistor T1 & T2 in reversed biased. As soon as the main supply fails or removed the capacitor voltage becomes lesser as compared to battery voltage. This puts both transistor T1 and T2 in forward biased and the LEDs will glow with the battery voltage.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Uses1. Convert 120V-230V Ac into 12V Dc and charge the

battery.2. Use in that places where the power doesn’t supply

properly.

Advantages

Saves fuel. Pollution free. Easy to use. Very low cost under Rs(200-300) Easy to install anywhere.

Disadvantages

It can be used only for short period.

Delectated circuit. IMPLEMENTATION

This project is useful to us. It is used in emergency.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Equipment cost list

Components Quantit

y

cost

Diode in4007 05 002.5

Resistor 100Ω 11 005

Resistor 16Ω, 5w 01 005

Led (white) 10 005

Transformer 12 v 01 080

Battery 6v 5 amp. 01 150

LM 317 01 012

Transistor BD140, BC547 01 each 025

Variable Resistor 01 015

Switch board 01 030

Capacitor 25v 1000µF 01 015

Total cost --------- 344.5

only/-

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Resistors

Example: Circuit symbol:

Function

Resistors restrict the flow of electric current, for example a resistor is placed in series with a light-emitting diode (LED) to limit the current passing through the LED.

Connecting and soldering

Resistors may be connected either way round. They are not damaged by heat when soldering.

The ResistorColour Code

Colour Number

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Grey 8

White 9

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Resistor values - the resistor colour code

Resistance is measured in ohms, the symbol for ohm is an omega .

1 is quite small so resistor values are often given in k and M . 1 k = 1000 1 M = 1000000 .

Resistor values are normally shown using coloured bands. Each colour represents a number as shown in the table.

Most resistors have 4 bands:

The first band gives the first digit. The second band gives the second digit. The third band indicates the number of zeros. The fourth band is used to shows the tolerance (precision) of the

resistor, this may be ignored for almost all circuits but further details are given below.

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

So its value is 270000 = 270 k . On circuit diagrams the is usually omitted and the value is written 270K.

A special colour code is used for the fourth band tolerance:silver ±10%, gold ±5%, red ±2%, brown ±1%. If no fourth band is shown the tolerance is ±20%.

Tolerance may be ignored for almost all circuits because precise resistor values are rarely required.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Resistor shorthand

Resistor values are often written on circuit diagrams using a code system which avoids using a decimal point because it is easy to miss the small dot. Instead the letters R, K and M are used in place of the decimal point. To read the code: replace the letter with a decimal point, then multiply the value by 1000 if the letter was K, or 1000000 if the letter was M. The letter R means multiply by 1.

For example:

560R means 560 2K7 means 2.7 k = 2700 39K means 39 k 1M0 means 1.0 M = 1000 k

Resistors in Series and Parallel

For information on resistors connected in series and parallel please see the Resistance page,

Power Ratings of Resistors

Electrical energy is converted to heat when current flows through a resistor. Usually the effect is negligible, but if the resistance is low (or the voltage across the resistor high) a large current may pass making the resistor become noticeably warm. The resistor must be able to withstand the heating effect and resistors have power ratings to show this.

Power ratings of resistors are rarely quoted in parts lists because for most circuits the standard power ratings of 0.25W or 0.5W are suitable. For the rare cases where a higher power is required it should be clearly specified in the parts list, these will be circuits using low value resistors (less than about 300 ) or high voltages (more than 15V).

DIPLOMA IN ELECTRICAL AND ELECTRONICS

The power, P, developed in a resistor is given by:

P = I² × Ror P = V² / R

Where-

P = power developed in the resistor in watts (W) I = current through the resistor in amps (A) R = resistance of the resistor in ohms ( ) V = voltage across the resistor in volts (V)

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Diodes

Example: Circuit symbol:

Function

Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows the direction in which the current can flow. Diodes are the electrical version of a valve and early diodes were actually called valves.

Forward Voltage Drop

Electricity uses up a little energy pushing its way through the diode, rather like a person pushing through a door with a spring. This means that there is a small voltage across a conducting diode, it is called the forward voltage drop and is about 0.7V for all normal diodes which are made from silicon. The forward voltage drop of a diode is almost constant whatever the current passing through the diode so they have a very steep characteristic (current-voltage graph).

Reverse Voltage

When a reverse voltage is applied a perfect diode does not conduct, but all real diodes leak a very tiny current of a few µA or less. This can be ignored in most circuits because it will be very much smaller than the current flowing in the forward direction. However, all diodes have a maximum reverse voltage (usually 50V or more) and if this is exceeded the diode will fail and pass a large current in the reverse direction, this is called breakdown.

Ordinary diodes can be split into two types: Signal diodes which pass small currents of 100mA or less and Rectifier diodes which can pass large currents. In addition there are LEDs (which have their own page) and Zener diodes (at the bottom of this page).

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Connecting and soldering

Diodes must be connected the correct way round, the diagram may be labelled a or + for anode and k or - for cathode (yes, it really is k, not c, for cathode!). The cathode is marked by a line painted on the body. Diodes are labelled with their code in small print, you may need a magnifying glass to read this on small signal diodes!

Small signal diodes can be damaged by heat when soldering, but the risk is small unless you are using a germanium diode (codes beginning OA...) in which case you should use a heat sink clipped to the lead between the joint and the diode body. A standard crocodile clip can be used as a heat sink.

Rectifier diodes are quite robust and no special precautions are needed for soldering them.

Testing diodes

You can use a multimeter or a simple tester (battery, resistor and LED) to check that a diode conducts in one direction but not the other. A lamp may be used to test a rectifier diode , but do NOT use a lamp to test a signal diode because the large current passed by the lamp will destroy the diode!

Signal diodes (small current)

Signal diodes are used to process information (electrical signals) in circuits, so they are only required to pass small currents of up to 100mA.

General purpose signal diodes such as the 1N4148 are made from silicon and have a forward voltage drop of 0.7V.

Germanium diodes such as the OA90 have a lower forward voltage drop of 0.2V and this makes them suitable to use in radio circuits as detectors which extract the audio signal from the weak radio signal.

For general use, where the size of the forward voltage drop is less important, silicon diodes are better because they are less easily damaged by heat when soldering, they have a lower resistance

DIPLOMA IN ELECTRICAL AND ELECTRONICS

when conducting, and they have very low leakage currents when a reverse voltage is applied.

Protection diodes for relays

Signal diodes are also used to protect transistors and ICs from the brief high voltage produced when a relay coil is switched off. The diagram shows how a protection diode is connected 'backwards' across the relay coil.

Current flowing through a relay coil creates a magnetic field which collapses suddenly when the current is switched off. The sudden collapse of the magnetic field induces a brief high voltage across the relay coil which is very likely to damage transistors and ICs. The protection diode allows the induced voltage to drive a brief current through the coil (and diode) so the magnetic field dies away quickly rather than instantly. This prevents the induced voltage becoming high enough to cause damage to transistors and ICs.

DiodeMaximumCurrent

MaximumReverseVoltage

1N4001 1A 50V

1N4002 1A 100V

1N4007 1A 1000V

1N5401 3A 100V

1N5408 3A 1000V

Rectifier diodes (large current)

Rectifier diodes are used in power supplies to convert alternating current (AC) to direct current (DC), a process called rectification. They are also used elsewhere in circuits where a large current must pass through the diode.

All rectifier diodes are made from silicon and therefore have a forward voltage drop of 0.7V. The table shows maximum current and maximum reverse voltage for some popular rectifier diodes. The 1N4001 is suitable for most low voltage circuits with a current of less than 1A.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Bridge rectifiers

There are several ways of connecting diodes to make a rectifier to convert AC to DC. The bridge rectifier is one of them and it is available in special packages containing the four diodes required. Bridge rectifiers are rated by their maximum current and maximum reverse voltage. They have four leads or terminals: the two DC outputs are labelled + and -, the two AC inputs are labelled

.

The diagram shows the operation of a bridge rectifier as it converts AC to DC. Notice how alternate pairs of diodes conduct.

Various types of Bridge Rectifiers

Zener diodes

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Example: Circuit symbol:

a = anode, k = cathode

Zener diodes are used to maintain a fixed voltage. They are designed to 'breakdown' in a reliable and non-destructive way so that they can be used in reverse to maintain a fixed voltage across their terminals. The diagram shows how they are connected, with a resistor in series to limit the current.

Zener diodes can be distinguished from ordinary diodes by their code and breakdown voltage which are printed on them. Zener diode codes begin BZX... or BZY... Their breakdown voltage is printed with V in place of a decimal point, so 4V7 means 4.7V for example.

Zener diodes are rated by their breakdown voltage and maximum power:

The minimum voltage available is 2.4V. Power ratings of 400mW and 1.3W are common.

Capacitors

Function

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Capacitors store electric charge. They are used with resistors in timing circuits because it takes time for a capacitor to fill with charge. They are used to smooth varying DC supplies by acting as a reservoir of charge. They are also used in filter circuits because capacitors easily pass AC (changing) signals but they block DC (constant) signals.

Capacitance

This is a measure of a capacitor's ability to store charge. A large capacitance means that more charge can be stored. Capacitance is measured in farads, symbol F. However 1F is very large, so prefixes are used to show the smaller values.

Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico):

µ means 10-6 (millionth), so 1000000µF = 1F n means 10-9 (thousand-millionth), so 1000nF = 1µF p means 10-12 (million-millionth), so 1000pF = 1nF

Capacitor values can be very difficult to find because there are many types of capacitor with different labelling systems!

There are many types of capacitor but they can be split into two groups, polarised and unpolarised. Each group has its own circuit symbol.

Polarised capacitors (large values, 1µF +)

Examples: Circuit symbol:

Electrolytic Capacitors

Electrolytic capacitors are polarised and they must be connected the correct way round, at least one of their leads will be marked + or -. They are not damaged by heat when soldering.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

There are two designs of electrolytic capacitors; axial where the leads are attached to each end (220µF in picture) and radial where both leads are at the same end (10µF in picture). Radial capacitors tend to be a little smaller and they stand upright on the circuit board.

It is easy to find the value of electrolytic capacitors because they are clearly printed with their capacitance and voltage rating. The voltage rating can be quite low (6V for example) and it should always be checked when selecting an electrolytic capacitor. If the project parts list does not specify a voltage, choose a capacitor with a rating which is greater than the project's power supply voltage. 25V is a sensible minimum for most battery circuits.

Tantalum Bead Capacitors

Tantalum bead capacitors are polarised and have low voltage ratings like electrolytic capacitors. They are expensive but very small, so they are used where a large capacitance is needed in a small size.

Modern tantalum bead capacitors are printed with their capacitance, voltage and polarity in full. However older ones use a colour-code system which has two stripes (for the two digits) and a spot of colour for the number of zeros to give the value in µF. The standard colour code is used, but for the spot, grey is used to mean × 0.01 and white means × 0.1 so that values of less than 10µF can be shown. A third colour stripe near the leads shows the voltage (yellow 6.3V, black 10V, green 16V, blue 20V, grey 25V, white 30V, pink 35V). The positive (+) lead is to the right when the spot is facing you: 'when the spot is in sight, the positive is to the right'.

For example: blue, grey, black spot means 68µF For example: blue, grey, white spot means 6.8µF For example: blue, grey, grey spot means 0.68µF

Unpolarised capacitors (small values, up to 1µF)

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Examples: Circuit symbol:

Small value capacitors are unpolarised and may be connected either way round. They are not damaged by heat when soldering, except for one unusual type (polystyrene). They have high voltage ratings of at least 50V, usually 250V or so. It can be difficult to find the values of these small capacitors because there are many types of them and several different labelling systems!

Many small value capacitors have their value printed but without a multiplier, so you need to use experience to work out what the multiplier should be!

For example 0.1 means 0.1µF = 100nF.

Sometimes the multiplier is used in place of the decimal point: For example: 4n7 means 4.7nF.

Capacitor Number Code

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

the 1st number is the 1st digit, the 2nd number is the 2nd digit, the 3rd number is the number of zeros to give the capacitance in

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

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

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

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Capacitor Colour Code

A colour code was used on polyester capacitors for many years. It is now obsolete, but of course there are many still around. The colours should be read like the resistor code, the top three colour bands giving the value in pF. Ignore the 4th band (tolerance) and 5th band (voltage rating).

For example:

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

Note that there are no gaps between the colour bands, so 2 identical bands actually appear as a wide band.

For example:

wide red, yellow means 220nF = 0.22µF.

Polystyrene Capacitors

This type is rarely used now. Their value (in pF) is normally printed without units. Polystyrene capacitors can be damaged by heat when soldering (it melts the polystyrene!) so you should use a heat sink (such as a crocodile clip). Clip the heat sink to the lead between the capacitor and the joint.

Colour Code

Colour Number

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Grey 8

White 9

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Real capacitor values (the E3 and E6 series)

You may have noticed that capacitors are not available with every possible value, for example 22µF and 47µF are readily available, but 25µF and 50µF are not!

Why is this? Imagine that you decided to make capacitors every 10µF giving 10, 20, 30, 40, 50 and so on. That seems fine, but what happens when you reach 1000? It would be pointless to make 1000, 1010, 1020, 1030 and so on because for these values 10 is a very small difference, too small to be noticeable in most circuits and capacitors cannot be made with that accuracy.

To produce a sensible range of capacitor values you need to increase the size of the 'step' as the value increases. The standard capacitor values are based on this idea and they form a series which follows the same pattern for every multiple of ten.

The E3 series (3 values for each multiple of ten) 10, 22, 47, ... then it continues 100, 220, 470, 1000, 2200, 4700, 10000 etc. Notice how the step size increases as the value increases (values roughly double each time).

The E6 series (6 values for each multiple of ten) 10, 15, 22, 33, 47, 68, ... then it continues 100, 150, 220, 330, 470, 680, 1000 etc. Notice how this is the E3 series with an extra value in the gaps.

The E3 series is the one most frequently used for capacitors because many types cannot be made with very accurate values.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Transistors

This page covers practical matters such as precautions when soldering and identifying leads. The operation and use of transistors is covered by the Transistor Circuits page.

Function

Transistors amplify current, for example they can be used to amplify the small output current from a logic IC so that it can operate a lamp, relay or other high current device. In many circuits a resistor is used to convert the changing current to a changing voltage, so the transistor is being used to amplify voltage.

A transistor may be used as a switch (either fully on with maximum current, or fully off with no current) and as an amplifier (always partly on).

The amount of current amplification is called the current gain, symbol hFE.

For further information

Types of transistor

There are two types of standard transistors, NPN and PNP, with different circuit symbols. The letters refer to the layers of semiconductor material used to make the transistor. Most transistors used today are NPN because this is the easiest type to make from silicon. If you are new to electronics it is best to start by learning how to use NPN transistors.

The leads are labelled base (B), collector (C) and emitter (E).These terms refer to the internal operation of a transistor but they are not much help in understanding how a transistor is used, so just treat them as labels!

Transistor circuit symbols

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A Darlington pair is two transistors connected together to give a very high current gain.

In addition to standard (bipolar junction) transistors, there are field-effect transistors which are usually referred to as FETs. They have different circuit symbols and properties and they are not (yet) covered by this page.

Connecting

TransistoTransistors have three leads which must be connected the correct way round. Please take care with this because a wrongly connected transistor may be damaged instantly when you switch on.

If you are lucky the orientation of the transistor will be clear from the PCB or stripboard layout diagram, otherwise you will need to refer to a supplier's catalogue to identify the leads.

The drawings on the right show the leads for some of the most common case styles.

Soldering

Transistors can be damaged by heat when soldering so if you are not an expert it is wise to use a heat sink clipped to the lead between the joint and the transistor body. A standard crocodile clip can be used as a heat sink.

Do not confuse this temporary heat sink with the permanent heat sink (described below) which may be required for a power transistor to prevent it overheating during operation.

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Heat sinks

Waste heat is produced in transistors due to the current flowing through them. Heat sinks are needed for power transistors because they pass large currents. If you find that a transistor is becoming too hot to touch it certainly needs a heat sink! The heat sink helps to dissipate (remove) the heat by transferring it to the surrounding air.

Testing a transistor

Transistors can be damaged by heat when soldering or by misuse in a circuit. If you suspect that a transistor may be damaged there are two easy ways to test it:

1. Testing with a multimeter

Use a multimeter or a simple tester (battery, resistor and LED) to check each pair of leads for conduction. Set a digital multimeter to diode test and an analogue multimeter to a low resistance range.

Test each pair of leads both ways (six tests in total):

The base-emitter (BE) junction should behave like a diode and conduct one way only.

Testing an NPN transistor

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The base-collector (BC) junction should behave like a diode and conduct one way only.

The collector-emitter (CE) should not conduct either way.

The diagram shows how the junctions behave in an NPN transistor. The diodes are reversed in a PNP transistor but the same test procedure can be used.

2. Testing in a simple switching circuit

Connect the transistor into the circuit shown on the right which uses the transistor as a switch. The supply voltage is not critical, anything between 5 and 12V is suitable. This circuit can be quickly built on breadboard for example. Take care to include the 10k resistor in the base connection or you will destroy the transistor as you test it!

If the transistor is OK the LED should light when the switch is pressed and not light when the switch is released.

To test a PNP transistor use the same circuit but reverse the LED and the supply voltage.

Some multimeters have a 'transistor test' function which provides a known base current and measures the collector current so as to display the transistor's DC current gain hFE.

Transistor codes

There are three main series of transistor codes used in the UK:

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Codes beginning with B (or A), for example BC108, BC478 The first letter B is for silicon, A is for germanium (rarely used now). The second letter indicates the type; for example C means low power audio frequency; D means high power audio frequency; F means low power high frequency. The rest of the code identifies the particular transistor. There is no obvious logic to the numbering system. Sometimes a letter is added to the end (eg BC108C) to identify a special version of the main type, for example a higher current gain or a different case style. If a project specifies a higher gain version (BC108C) it must be used, but if the general code is given (BC108) any transistor with that code is suitable.

Transformer

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the secondary winding. This effect is called mutual induction.

If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (VS) is in proportion to the primary voltage (VP), and is given by the ratio of the number of turns in the secondary (NS) to the number of turns in the primary (NP) as follows:

By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be "stepped up" by making NS greater than NP, or "stepped down" by making NS less than NP.

Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate with the same basic principles, although the range of designs is wide. While new technologies have eliminated the

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need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household ("mains") voltage. Transformers are essential for high voltage power transmission, which makes long distance transmission economically practical.

Basic principles

The transformer is based on two principles: firstly, that an electric current can produce a magnetic field (electromagnetism) and secondly that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing the current in the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil.

An ideal transformer

An ideal transformer is shown in the adjacent figure. Current passing through the primary coil creates a magnetic field. The primary and secondary coils are wrapped around a core of very high magnetic permeability, such as iron, so that most of the magnetic flux passes through both the primary and secondary coils.

Induction law

The voltage induced across the secondary coil may be calculated from Faraday's law of induction, which states that:

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where VS is the instantaneous voltage, NS is the number of turns in the secondary coil and Φ equals the magnetic flux through one turn of the coil. If the turns of the coil are oriented perpendicular to the magnetic field lines, the flux is the product of the magnetic flux density B and the area A through which it cuts. The area is constant, being equal to the cross-sectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary. Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer,[26] the instantaneous voltage across the primary winding equals

Taking the ratio of the two equations for VS and VP gives the basic equation[27] for stepping up or stepping down the voltage

[edit] Ideal power equation

The ideal transformer as a circuit element

If the secondary coil is attached to a load that allows current to flow, electrical power is transmitted from the primary circuit to the secondary circuit. Ideally, the transformer is perfectly efficient; all the incoming energy is transformed from the primary circuit to the magnetic field and into the secondary circuit. If this condition is met, the incoming electric power must equal the outgoing power.

Pincoming = IPVP = Poutgoing = ISVS

giving the ideal transformer equation

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Transformers normally have high efficiency, so this formula is a reasonable approximation.

Winding resistance

Current flowing through the windings causes resistive heating of the conductors. At higher frequencies, skin effect and proximity effect create additional winding resistance and losses. Hysteresis losses

Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core. For a given core material, the loss is proportional to the frequency, and is a function of the peak flux density to which it is subjected.[39] Eddy currents

Ferromagnetic materials are also good conductors, and a solid core made from such a material also constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore circulate within the core in a plane normal to the flux, and are responsible for resistive heating of the core material. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness.[39] Mechanical losses

In addition to magnetostriction, the alternating magnetic field causes fluctuating electromagnetic forces between the primary and secondary windings. These incite vibrations within nearby metalwork, adding to the buzzing noise, and consuming a small amount of power.[40] Stray losses

Leakage inductance is by itself largely lossless, since energy supplied to its magnetic fields is returned to the supply with the next half-cycle.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Light Emitting Diodes (LEDs)

Example: Circuit symbol:

Function

LEDs emit light when an electric current passes through them.

Connecting and soldering

LEDs must be connected the correct way round, the diagram may be labelled a or + for anode and k or - for cathode (yes, it really is k, not c, for cathode!). The cathode is the short lead and there may be a slight flat on the body of round LEDs. If you can see inside the LED the cathode is the larger electrode (but this is not an official identification method).

LEDs can be damaged by heat when soldering, but the risk is small unless you are very slow. No special precautions are needed for soldering most LEDs.

Testing an LED

Never connect an LED directly to a battery or power supply! It will be destroyed almost instantly because too much current will pass through and burn it out.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

LEDs must have a resistor in series to limit the current to a safe value, for quick testing purposes a 1k resistor is suitable for most LEDs if your supply voltage is 12V or less. Remember to connect the LED the correct way round!

Colours of LEDs

LEDs are available in red, orange, amber, yellow, green, blue and white. Blue and white LEDs are much more expensive than the other colours.

The colour of an LED is determined by the semiconductor material, not by the colouring of the 'package' (the plastic body). LEDs of all colours are available in uncoloured packages which may be diffused (milky) or clear (often described as 'water clear'). The coloured packages are also available as diffused (the standard type) or transparent.

Tri-colour LEDs

The most popular type of tri-colour LED has a red and a green LED combined in one package with three leads. They are called tri-colour because mixed red and green light appears to be yellow and this is produced when both the red and green LEDs are on.

The diagram shows the construction of a tri-colour LED. Note the different lengths of the three leads. The centre lead (k) is the common cathode for both LEDs, the outer leads (a1 and a2) are the anodes to the LEDs allowing each one to be lit separately, or both together to give the third colour.

Bi-colour LEDs

A bi-colour LED has two LEDs wired in 'inverse parallel' (one forwards, one backwards) combined in one package with two leads. Only one of the LEDs can be lit at one time and they are less useful than the tri-colour LEDs described above.

Sizes, Shapes and Viewing angles of LEDs

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Calculating an LED resistor value

An LED must have a resistor connected in series to limit the current through the LED, otherwise it will burn out almost instantly.

The resistor value, R is given by:

R = (VS - VL) / I

VS = supply voltage VL = LED voltage (usually 2V, but 4V for blue and white LEDs) I = LED current (e.g. 10mA = 0.01A, or 20mA = 0.02A) Make sure the LED current you choose is less than the maximum permitted and convert the current to amps (A) so the calculation will give the resistor value in ohms ( ). To convert mA to A divide the current in mA by 1000 because 1mA = 0.001A.

If the calculated value is not available choose the nearest standard resistor value which is greater, so that the current will be a little less than you chose. In fact you may wish to choose a greater resistor value to reduce the current (to increase battery life for example) but this will make the LED less bright.

Connecting LEDs in series

If you wish to have several LEDs on at the same time it may be possible to connect them in series. This prolongs battery life by lighting several LEDs with the same current as just one LED.

All the LEDs connected in series pass the same current so it is best if they are all the same type. The power supply must have sufficient voltage to provide about 2V for each LED (4V for blue and white) plus at least another 2V for the resistor. To work out a value for the resistor you must add up all the LED voltages and use this for VL.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Switches

Switch Contacts

Several terms are used to describe switch contacts: Pole - number of switch contact sets. Throw - number of conducting positions, single or double. Way - number of conducting positions, three or more. Momentary - switch returns to its normal position when released. Open - off position, contacts not conducting. Closed - on position, contacts conducting, there may be several on

positions.

For example: the simplest on-off switch has one set of contacts (single pole) and one switching position which conducts (single throw). The switch mechanism has two positions: open (off) and closed (on), but it is called 'single throw' because only one position conducts.

Switch Contact Ratings

Switch contacts are rated with a maximum voltage and current, and there may be different ratings for AC and DC. The AC values are higher because the current falls to zero many times each second and an arc is less likely to form across the switch contacts.

For low voltage electronics projects the voltage rating will not matter, but you may need to check the current rating. The maximum

DIPLOMA IN ELECTRICAL AND ELECTRONICS

current is less for inductive loads (coils and motors) because they cause more sparking at the contacts when switched off.

Standard Switches

Type of Switch Circuit Symbol Example

ON-OFFSingle Pole, Single Throw = SPST

A simple on-off switch. This type can be used to switch the power supply to a circuit.

When used with mains electricity this type of switch must be in the live wire, but it is better to use a DPST switch to isolate both live and neutral.

Photograph © Rapid ElectronicsSPST toggle switch

(ON)-OFFPush-to-make = SPST Momentary

A push-to-make switch returns to its normally open (off) position when you release the button, this is shown by the brackets around ON. This is the standard doorbell switch.

Photograph © Rapid Electronics

Push-to-make switch

ON-(OFF)Push-to-break = SPST Momentary

A push-to-break switch returns to its normally closed (on) position when you release the button.

Push-to-break switch

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Photograph © Rapid Electronics

ON-ONSingle Pole, Double Throw = SPDT

This switch can be on in both positions, switching on a separate device in each case. It is often called a changeover switch. For example, a SPDT switch can be used to switch on a red lamp in one position and a green lamp in the other position.

A SPDT toggle switch may be used as a simple on-off switch by connecting to COM and one of the A or B terminals shown in the diagram. A and B are interchangeable so switches are usually not labelled.

ON-OFF-ONSPDT Centre OffA special version of the standard SPDT switch. It has a third switching position in the centre which is off. Momentary (ON)-OFF-(ON) versions are also available where the switch returns to the central off position when released.

Photographs © Rapid Electronics

SPDT toggle switch

SPDT slide switch(PCB mounting)

SPDT rocker switch

Dual ON-OFFDouble Pole, Single Throw = DPST

A pair of on-off switches which operate together (shown by the dotted line in the circuit symbol).

A DPST switch is often used to switch mains electricity because it can isolate both the live and neutral connections.

Photograph © Rapid ElectronicsDPST rocker switch

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Battery (electricity)

Various batteries (top-left to bottom-right): two AA, one D, one

handheld ham radio battery, two 9-volt PP3, two AAA, one C, one

camcorder battery, one cordless phone battery.

An electrical battery is a combination of one or more

electrochemical cells, used to convert stored chemical energy into

electrical energy. Since the invention of the first Voltaic pile in 1800

by Alessandro Volta, the battery has become a common power

source for many household and industrial applications. According to

a 2005 estimate, the worldwide battery industry generates US$48

billion in sales each year,[1] with 6% annual growth.[2]

There are two types of batteries: primary batteries (disposable

batteries), which are designed to be used once and discarded when

they are exhausted, and secondary batteries (rechargeable

batteries), which are designed to be recharged and used multiple

times. Miniature cells are used to power devices such as hearing

aids and wristwatches; larger batteries provide standby power for

telephone exchanges or computer data centers.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

How batteries work

Main article: Electrochemical cell

A voltaic cell for demonstration purposes. In this example the two

half-cells are linked by a salt bridge separator that permits the

transfer of ions, but not water molecules.

A battery is a device that converts chemical energy directly to

electrical energy.[21] It consists of a number of voltaic cells; each

voltaic cell consists of two half cells connected in series by a

conductive electrolyte containing anions and cations. One half-cell

includes electrolyte and the electrode to which anions (negatively-

charged ions) migrate, i.e., the anode or negative electrode; the

other half-cell includes electrolyte and the electrode to which

cations (positively-charged ions) migrate, i.e., the cathode or

positive electrode. In the redox reaction that powers the battery,

reduction (addition of electrons) occurs to cations at the cathode,

while oxidation (removal of electrons) occurs to anions at the

anode.[22] The electrodes do not touch each other but are

electrically connected by the electrolyte. Many cells use two half-

cells with different electrolytes. In that case each half-cell is

enclosed in a container, and a separator that is porous to ions but

not the bulk of the electrolytes prevents mixing.

Dry cell

Line art drawing of a dry cell.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

1. Brass cap, 2. Plastic seal, 3. Expansion space, 4. Porous

cardboard, 5. Zinc can, 6. Carbon rod, 7. Chemical mixture

A dry cell has the electrolyte immobilized as a paste, with only

enough moisture in the paste to allow current to flow. As opposed

to a wet cell, the battery can be operated in any random position,

and will not spill its electrolyte if inverted.

While a dry cell's electrolyte is not truly completely free of moisture

and must contain some moisture to function, it has the advantage of

containing no sloshing liquid that might leak or drip out when

inverted or handled roughly, making it highly suitable for small

portable electric devices. By comparison, the first wet cells were

typically fragile glass containers with lead rods hanging from the

open top, and needed careful handling to avoid spillage. An

inverted wet cell would leak, while a dry cell would not. Lead-acid

batteries would not achieve the safety and portability of the dry cell,

until the development of the gel battery.

A common dry cell battery is the zinc-carbon battery, using a cell

sometimes called the dry Leclanché cell, with a nominal voltage of

1.5 volts, the same nominal voltage as the alkaline battery (since

both use the same zinc-manganese dioxide combination).

The makeup of a standard dry cell is a zinc anode (negative pole),

usually in the form of a cylindrical pot, with a carbon cathode

(positive pole) in the form of a central rod. The electrolyte is

ammonium chloride in the form of a paste next to the zinc anode.

The remaining space between the electrolyte and carbon cathode is

taken up by a second paste consisting of ammonium chloride and

manganese dioxide, the latter acting as a depolariser. In some

more modern types of so called 'high power' batteries, the

ammonium chloride has been replaced by zinc chloride.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

Advantages

Saves fuel. Pollution free. Easy to use. Very low cost under Rs(200-300) Easy to handle anywhere. Simple design. Construction is easy.

Disadvantages

It can be used only for short period.

Delectated circuit. This circuit required a constant dc voltage.

DIPLOMA IN ELECTRICAL AND ELECTRONICS

CONCLUSION

Hence we conclude that this is a electrical based project. This is

one of simple projects.

This can be used in emergency when the power is cut off or when

the voltage is low.

DRAWING

I got this circuit from efymag. And my project coordinator helps

me to design this circuit.

REFERENCE

WEBSITE

http://www.electronicslab.com

http://www.wikipedia.org

http://www.efymag.com

BOOKS

Basic Electrical Engineering.

Principle of Electronics.