Saini Electrical

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A

PROJECT REPORT

PC BASED ELECTRICALOVER LOAD CONTROL

REPORT SUBMITTED IN PARTIAL FULFILLMENTOF THE REQUIREMENTS FOR THE AWARD OF

THE DEGREE OF

BACHELOR OF TECHNOLOGYIN

ELECTRONICS &TELECOMMUNICATION

ENGINEERING

SUBMITTED BYCHETAN OMPURI

B-TECH (FINAL YEAR)ELECTRONICS & TELECOMMUNICATION ENGINEERING

DEPARTMENT OF ELECTRONICS & TELECOMMUNICATION ENGINEERING

MAHATMA GANDHI COLLEGE OF ENGINEERING & TECHNOLOGYSECTOR-62, NOIDA,

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(2008-2009)

CERTIFICATE

This is to certify that the project titled PC BASED OVER

LOAD CONTROL is submitted by Mr. Chetan Ompuri

in the partial fulfillment of requirements for the award ofDegree of Bachelor of Technology in Electronics &

Telecommunication, is a record of candidates own work

carried under my supervision.

_______________Faculty Guide

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ACKNOWLEDGEMENT

It is my great pleasure in expressing sincere gratitude towards my guide

Mr. P.R. Bhattacharyya for his invaluable guidance in all phase of my project work.

He has always been a source of inspiration to me and I am highly indebted to him for his

kindness and help.

I avail this opportunity to place on record my deep sense of gratitude towards my

revered all those people who has been provided me support and current information

onwards my completion of project report. Their perpetual inspiration, several patient

discussions, constructive criticism and valuable guidance throughout, helped the

research work to materialize.

I take this opportunity to thankSunny Electricals, Ludhiana, for all kind of support. I

would also like to thank all those who have directly or indirectly helped me during my

project.

I am also grateful to my parents for constant inspiration and encouragement to carry on

with the project work.

CHETAN OMPURI

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CONTENTS

TOPIC

INTRODUCTION

OBJECTIVE

OVERVIEW

POWER SUPPLY

MAKING PRINTED CIRCUIT BOARD

PC PARALLEL PORT

COMPONENTS USED

(I) CAPACITOR

(II) DIODE

(III) RELAY

(IV) RESISTANCE

(V) TRANSFORMER

(VI) TRANSISTOR

PROGRAM

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INTRODUCTION

A given electrical generating station has a fixed installed

capacity i.e. it is capable of maintaining a stable operation

with the load on it not exceeding its installed capacity.

Hence, an electrical power system has fixed capacity to

supply loads, if loads exceeds the capacity it effects its

stability. Hence efforts should be made to ensure that theload does not exceed its capacity.

In presenting this report on Overload control we have kept

in mind this fact of the power system.

We have represented total eight loads , of which the four of

them are represented as VIP areas and the other four as non

VIP areas .Our aim is to keep the total load on the system to

be constant without making any changes in generating

station by shedding some of loads, which in our case is the

non VIP loads, as the VIP areas should get uninterrupted

power supply.

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OBJECTIVES

1) To design an overload sensing circuit that gives relay

switching while overloading for four outputs.

2) To interface these outputs to PC as inputs and get the

load connections for eight appliances at output port of

PC using driver circuit.

3) To write a program in C or C++, which controls theinputs for different load indication, and switch the

output loads for VIP and general categories area.

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BLOCK DIAGRAM

OVERVIEW

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The present circuit for overload control using PC

interface is based on Load sensing devices to be sensed and

interfaced using a software in C by graphical user interface

GUI.

In the circuit, 8 output loads are to be connected with

PC parallel port for actual electricity supply distribution to

the user end. Out of which four are V.I.P areas and rest four

are in general category. In the system we have four inputsensing devices that reads the overload at the supply end.

As all the eight outputs connected to the same phase and

single transformer distribution, the system reads the

overload if happens on the same phase. As it happen, the

first output relay from the general category is disconnected

automatically and further for the more load sensing

activation another general category output is going to be

disconnected. In any case our V.I.P area loads are to be

retained with continues supply.

UNDER/OVER VOLTAGE PROTECTION TO DEVICES

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Here is a simple solidstate circuit which provides both

under-voltage and over voltage protection to a household

device. Various types of commercial stabilizers available in

the market do not normally provide the cut-off at the

extreme voltage limits, which is very important for devices.

If the supply voltage varies within +10V, there is no harm

done to a device. But protection is absolutely essential if the

supply varies beyond these limits. The circuit described herecuts off the supply whenever it goes beyond the set limits.

The base voltage of transistor T1 should be adjusted to just

over 6V with preset VR1 so that the under-voltage relay RL1

just gets energized at the normal voltage. This relay should

get released at the lower voltage limit. At normal voltage,

RL1 should remain energized.

Similarly, the base voltage of T2 should be adjusted to just

under 6V by the corresponding preset VR2 such that RL2

just gets energized at the upper voltage limit and is

released at the normal voltage.

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Normally open contact (N/O) of RL1 normally-closed contact

(N/C) of RL2 are connected in series with the supply.

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POWER SUPPLY

In alternating current the electron flow is alternate, i.e. the

electron flow increases to maximum in one direction,

decreases back to zero. It then increases in the other

direction and then decreases to zero again. Direct current

flows in one direction only. Rectifier converts alternating

current to flow in one direction only. When the anode of the

diode is positive with respect to its cathode, it is forward

biased, allowing current to flow. But when its anode is

negative with respect to the cathode, it is reverse biased

and does not allow current to flow. This unidirectional

property of the diode is useful for rectification. A single

diode arranged back-to-back might allow the electrons to

flow during positive half cycles only and suppress the

negative half cycles. Double diodes arranged back-to-back

might act as full wave rectifiers as they may allow the

electron flow during both positive and negative half cycles.

Four diodes can be arranged to make a full wave bridge

rectifier. Different types of filter circuits are used to smooth

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out the pulsations in amplitude of the output voltage from a

rectifier. The property of capacitor to oppose any change in

the voltage applied across them by storing energy in the

electric field of the capacitor and of inductors to oppose any

change in the current flowing through them by storing

energy in the magnetic field of coil may be utilized. To

remove pulsation of the direct current obtained from the

rectifier, different types of combination of capacitor,

inductors and resistors may be also be used to increase to

action of filtering.

NEED OF POWER SUPPLY:

Perhaps all of you are aware that a power supply is a

primary requirement for the Test Bench of a home

experimenters mini lab. A battery eliminator can eliminate

or replace the batteries of solid-state electronic equipment

and the equipment thus can be operated by 230v A.C.

mains instead of the batteries or dry cells. Nowadays, the

use of commercial battery eliminator or power supply unit

has become increasingly popular as power source for

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household appliances like transreceivers, record player,

cassette players, digital clock etc.

THEORETICAL CONCEPT

USE OF DIODES IN RECTIFIERS:

Electric energy is available in homes and industries in

India, in the form of alternating voltage. The supply has a

voltage of 220V (rms) at a frequency of 50 Hz. In the USA, it

is 110V at 60 Hz. For the operation of most of the devices in

electronic equipment, a dc voltage is needed. For instance,

a transistor radio requires a dc supply for its operation.

Usually, this supply is provided by dry cells. But sometime

we use a battery eliminator in place of dry cells. The battery

eliminator converts the ac voltage into dc voltage and thus

eliminates the need for dry cells. Nowadays, almost all-

electronic equipment includes a circuit that converts ac

voltage of mains supply into dc voltage. This part of the

equipment is called Power Supply. In general, at the input of

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the power supply, there is a power transformer. It is

followed by a diode circuit called Rectifier.

The output of the rectifier goes to a smoothing filter, and

then to a voltage regulator circuit. The rectifier circuit is the

heart of a power supply.

RECTIFICATION

Rectification is a process of rendering an alternating

current or voltage into a unidirectional one. The component

used for rectification is called Rectifier. A rectifier permits

current to flow only during the positive half cycles of the

applied AC voltage by eliminating the negative half cycles or

alternations of the applied AC voltage. Thus pulsating DC is

obtained. To obtain smooth DC power, additional filter

circuits are required.

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A diode can be used as rectifier. There are various

types of diodes. But, semiconductor diodes are very

popularly used as rectifiers. A semiconductor diode is a

solid-state device consisting of two elements is being an

electron emitter or cathode, the other an electron collector

or anode. Since electrons in a semiconductor diode can flow

in one direction only-from emitter to collector- the diode

provides the unilateral conduction necessary for

rectification. Out of the semiconductor diodes, copper oxide

and selenium rectifier are also commonly used.

FULL WAVE RECTIFIER

It is possible to rectify both alternations of the input

voltage by using two diodes in the circuit arrangement.

Assume 6.3 V rms (18 V p-p) is applied to the circuit.

Assume further that two equal-valued series-connected

resistors R are placed in parallel with the ac source. The 18

V p-p appears across the two resistors connected between

points AC and CB, and point C is the electrical midpoint

between A and B. Hence 9 V p-p appears across each

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resistor. At any moment during a cycle of vin, if point A is

positive relative to C, point B is negative relative to C. When

A is negative to C, point B is positive relative to C. The

effective voltage in proper time phase which each diode

"sees" is in Fig. The voltage applied to the anode of each

diode is equal but opposite in polarity at any given instant.

When A is positive relative to C, the anode of D1 is

positive with respect to its cathode. Hence D1 will conduct

but D2 will not. During the second alternation, B is positive

relative to C. The anode of D2 is therefore positive with

respect to its cathode, and D2 conducts while D1 is cut off.

There is conduction then by either D1 or D2 during the

entire input-voltage cycle.

Since the two diodes have a common-cathode load

resistor R

L

, the output voltage across R

L

will result from the

alternate conduction of D1 and D2. The output waveform

vout across RL, therefore has no gaps as in the case of the

half-wave rectifier.

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The output of a full-wave rectifier is also pulsating

direct current. In the diagram, the two equal resistors R

across the input voltage are necessary to provide a voltage

midpoint C for circuit connection and zero reference. Note

that the load resistor RL is connected from the cathodes to

this center reference point C.

An interesting fact about the output waveform vout is

that its peak amplitude is not 9 V as in the case of the half-

wave rectifier using the same power source, but is less than

4 V. The reason, of course, is that the peak positive

voltage of A relative to C is 4 V, not 9 V, and part of the

4 V is lost across R.

Though the full wave rectifier fills in the conduction

gaps, it delivers less than half the peak output voltage that

results from half-wave rectification.

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BRIDGE RECTIFIER

A more widely used full-wave rectifier circuit is the

bridge rectifier. It requires four diodes instead of two, but

avoids the need for a centre-tapped transformer. During the

positive half-cycle of the secondary voltage, diodes D2 and

D4 are conducting and diodes D1 and D3 are non-

conducting. Therefore, current flows through the secondary

winding, diode D2, load resistor RL and diode D4. During

negative half-cycles of the secondary voltage, diodes D1

and D3 conduct, and the diodes D2 and D4 do not conduct.

The current therefore flows through the secondary winding,

diode D1, load resistor RL and diode D3. In both cases, the

current passes through the load resistor in the same

direction. Therefore, a fluctuating, unidirectional voltage is

developed across the load.

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FILTRATION

The rectifier circuits we have discussed above deliver

an output voltage that always has the same polarity: but

however, this output is not suitable as DC power supply for

solid-state circuits. This is due to the pulsation or ripples of

the output voltage. This should be removed out before the

output voltage can be supplied to any circuit. This

smoothing is done by incorporating filter networks. The filter

network consists of inductors and capacitors. The inductors

or choke coils are generally connected in series with the

rectifier output and the load. The inductors oppose any

change in the magnitude of a current flowing through them

by storing up energy in a magnetic field. An inductor offers

very low resistance for DC whereas; it offers very high

resistance to AC. Thus, a series connected choke coil in a

rectifier circuit helps to reduce the pulsations or ripples to a

great extent in the output voltage. The fitter capacitors are

usually connected in parallel with the rectifier output and

the load. As, AC can pass through a capacitor but DC

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cannot, the ripples are thus limited and the output becomes

smoothed. When the voltage across its plates tends to rise,

it stores up energy back into voltage and current. Thus, the

fluctuations in the output voltage are reduced considerable.

Filter network circuits may be of two types in general:

CHOKE INPUT FILTER

If a choke coil or an inductor is used as the first-

components in the filter network, the filter is called choke

input filter. The D.C. along with AC pulsation from the

rectifier circuit at first passes through the choke (L). It

opposes the AC pulsations but allows the DC to pass through

it freely. Thus AC pulsations are largely reduced. The further

ripples are by passed through the parallel capacitor C. But,

however, a little nipple remains unaffected, which are

considered negligible. This little ripple may be reduced by

incorporating a series a choke input filters.

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CAPACITOR INPUT FILTER

If a capacitor is placed before the inductors of a choke-

input filter network, the filter is called capacitor input filter.

The D.C. along with AC ripples from the rectifier circuit

starts charging the capacitor C. to about peak value. The AC

ripples are then diminished slightly. Now the capacitor C,

discharges through the inductor or choke coil, which

opposes the AC ripples, except the DC. The second

capacitor C by passes the further AC ripples. A small ripple

is still present in the output of DC, which may be reduced by

adding additional filter network in series.

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CIRCUIT DIAGRAM

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MAKING PRINTED

CIRCUIT BOARD (P.C.B.)

INTRODUCTION-

Making a Printed Circuit Board is the first step towards

building electronic equipment by any electronic

industry. A number of methods are available for

making P.C.B., the simplest method is of drawing

pattern on a copper clad board with acid resistant

(etchants) ink or paint or simple nail polish on a

copper clad board and do the etching process for

dissolving the rest of copper pattern in acid liquid.

MATERIAL REQUIRED

The apparatus needs for making a P.C.B. is :-

* Copper Clad Sheet

* Nail Polish or Paint

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* Ferric Chloride Powder. (Fecl)

* Plastic Tray

* Tap Water etc.

USES

Printed Circuit Board are used for housing components to

make a circuit for compactness, simplicity of servicing and

case of interconnection. Thus we can define the P.C.B. as :

Prinked Circuit Boards is actually a sheet of bakelite (an

insulating material) on the one side of which copper

patterns are made with holes and from another side, leads

of electronic components are inserted in the proper holes

and soldered to the copper points on the back. Thus leads of

electronic components terminals are joined to make

electronic circuit.

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In the boards copper cladding is done by pasting thin copper

foil on the boards during curing. The copper on the board is

about 2 mm thick and weights an ounce per square foot.

The process of making a Printed Circuit for any

application has the following steps (opted

professionally):

* Preparing the layout of the track.

* Transferring this layout photographically M the copper.

* Removing the copper in places which are not needed,

by the process of etching (chemical process)

* Drilling holes for components mounting.

PRINTED CIRCUIT BOARD

Printed circuit boards are used for housing components to

make a circuit, for comactness, simplicity of servicing and

ease of interconnection. Single sided, double sided and

double sided with plated-through-hold (PYH) types of p.c

boards are common today.

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Boards are of two types of material (1) phenolic paper

based material (2) Glass epoxy material. Both materials are

available as laminate sheets with copper cladding.

Printed circuit boards have a copper cladding on one or

both sides. In both boards, pasting thin copper foil on the

board during curing does this. Boards are prepared in sizes

of 1 to 5 metre wide and upto 2 metres long. The thickness

of the boards is 1.42 to 1.8mm. The copper on the boards is

about 0.2 thick and weighs and ounce per square foot.

PC PARALLEL PORT

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The standard LPT port was designed for a printer

connection, in cooperation with printer manufacturers.

Nobody expected a different use, so its design was kept

very simple. Standard parallel port (SPP) uses a 25-pin

female CANNON plug. There are eight data lines, four output

lines (control signals), and five input lines (status). Normally,

PC waits for the printer to send "I'm ready" signal (BUSY

pin), sets the data lines according to a next character to be

printed, sends "There's a new character for you" signal

(pulse on STROBE), and waits for the printer again. In this

worst case, the computer spends most of the time waiting. It

is possible for the PC to do something else while the printer

is busy, using a hardware interrupt - pin /ACK, IRQ 5 or IRQ 7

(interrupt has to be enabled via the appropriate register).

PC BIOS supports upto four printer ports (LPT's). However,

only two I/O addresses are reserved for LPT's, 378h and

278h. The HERCULES company distributed their (very

successful at that time) graphics adapters with a built-in

printer port, which used the 3BCh address. This one was

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later designated as a third I/O address for LPT; some

manufacturers don't support it, though. During computer

boot-up, BIOS looks for LPT ports on the above addresses in

the same order. If a LPT is found, a number from 1 to 3 is

assigned to it (so we get LPT1, LPT2 or LPT3). Usually, LPT1

uses IRQ7, and LPT2 use IRQ5, but don't rely on it. It should

be noted that all LPT's could share a single IRQ together

with a sound card or a modem. The problem is that some

software drivers don't support interrupt sharing, and the

above configuration won't work. Therefore, it's safer to

assign a dedicated IRQ for each device, or to have LPT and a

sound card share IRQ7 (works most of the time). LPT boards

that are 2 years old or newer can be configured for different

IRQ's and I/O addresses, either via jumpers on board or via

software (BIOS SETUP on most machines).

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Standards called EPP (Enhanced Parallel Port) and ECP

(Extended Capabilities Port) brought many enhancements.

The most important one is the possibility of bi-directional

communication over the data pins D0-D7, due to modified

hardware design of these pins. The SPP data pin is wired

according to picture 1 with 2 transistors, one pulling high &

the other pulling low, one of them conducting at any time.

Picture 2 shows the EPP or ECP data pin circuit. The only

difference between ECP/EPP and the "normal" SPP is, that

the transistor pulling high has been replaced by a resistor

(it's supposed to be 4700 Ohms, according to the

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standards). Therefore, an ECP/EPP pin can be set to "read

mode" by setting it to 1, so the transistor pulling low is open

(non-conducting) and the actual logical level on the pin can

be read. This system is backward compatible with SPP in

most cases; some difficulties do arise.

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It should be clear now, that this port could be used for direct

connection of two PC's without the need for network

adapters and expensive networking software. Parallel port

connection is generally 3 to 4 times faster than a serial port

connection. However, the length of the connection cable is

severely limited. Since all signaling uses 5V logical levels

instead of current loops, cables longer than 3ft (1 meter)

tend to be sensitive to interference. It is still possible to use

cables up to 10 meters (30ft) in length, as long as certain

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rules are observed. Unfortunately, software supporting ECP

and EPP ports is not widely available yet. Most programs,

like Laplink or Norton Commander, support only the SPP port

(cable sometimes called '4BIT', since only 4 data bits are

transferred at a time). Some software available on the

Internet (e.g. EASYNET) can emulate an IPX-compatible

network over a 4BIT cable. While this is ideal for occasional

data transfer between a notebook or a desktop PC, it's not

the best option for a stable network connection, as the price

of network adapters has dropped significantly.

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ECP, EPP or SPP?

While new parallel port standards are backward compatible

on the hardware level, it is possible, that they won't work in

all cases (e.g., when a long printer cable is used). More, few

printers take advantage of the bi-directional communication.

Still, the most compatibility problems arise from faulty

software for communication between the PC and the printer

- sometimes, it accidentally switches data flow due to

improper use of added control bits, etc. My experience with

various name-brand manufacturers shows that, if the port is

used for printer only, the best option is to switch the port to

SPP mode. You can experiment with the extended modes,

but the source of troubles is often here. However, EPP/ECP

port shows its strengths if a CD-ROM, JAZ or ZIP drive,

modem, or another such device is connected to it. The

transfer speed goes up rapidly.

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HOW TO MAKE GOOD COMMUNICATION CABLES?

Every data wire should be shielded, or separated from its

neighbor by a ground line to reduce echos between

neighboring wires. The cable can be longer and achieves

faster speeds. For ribbon cables, the pinout of the parallel

port connector suggests such wiring. Another good idea is to

use a cable, where each pair of wires is twisted together -

use one of them for "live" data, and the other for ground.

PAY ATTENTION TO MAINS CONNECTIONS

OF CONNECTED EQUIPMENT.

Every PC has its cover, as well as the ground pins,

connected to the center wire of the mains plug ("protective

earth"). Often, this one is connected to the neutral wire. If

you have two PCs connected to different mains plugs that

you intend to connect together, it is possible that each of

them is connected to a different branch of your home

electrical wiring. Although these are connected together at

the switchboard, they may have different voltages if a

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heavy load is connected to one of them (e.g. washer, dryer,

etc.) causing a voltage drop. Single pulse can reach the

order of tens of volts. This voltage difference then appears

at the inputs of the PC, EASILY DESTROYING the parallel or

serial port, hard drive controller, sometimes even the whole

mainboard. Therefore, it is a good idea to connect only PC's

powered from the same mains plug, or at least connected

by a single extension cord. The same applies to monitor,

printer, notebook, and other connections. With some

notebook computers, the safest thing to do is to run on

batteries while connected to a desktop PC; however, new

notebooks should have no problems. Please note that

communication cables are dangerous to notebooks; when

an external disk drive, etc. connects via the parallel port,

this port may not be fully compatible, and notebook damage

may occur.

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MORE PARALLEL PORT HINTS.

Always use either shielded wires, or connect remaining

wires in the cable to the ground. This applies especially

for long cables used for fast data transfer (over

100kbit/s).

When making devices connected to LPT, always

connect a pull-up resistor "ladder" to +5V to all data

wires, preferably at the connector itself. This should

reduce potential effect of RC networks in the cable.

Usually, resistors between 4 and 10 k-ohms work the

best.

For fast communication, always use D-type flip-flops

(triggered by edge) instead of latches (triggered by

logic level). The latter ones are sensitive to crosstalks,

which can cause data errors. (For example, D-type IO's

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are 74374, 574, 7474, ..., while latches are 74373, 573,

etc.)

When writing software, always keep in mind-enhanced

ports. For example, bits that are unused or "reserved"

in SPP mode may have assigned meaning in ECP or EPP

modes.

Don't try to power devices from the LPT, like a mouse

is powered from the serial port. Sometimes, the

voltage corresponding to logical 1 is about 3.5V, so,

after adding voltage on the diodes, you can't even rely

on circuits operating from 2.7V (due to current-carrying

capacity).

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COMPONENTS USED

The various components used in making the project are:

CAPACITORS

It is an electronic component whose function is to

accumulate charges and then release it.

To understand the

concept of capacitance,

consider a pair of metal plates which all are placed near to

each other without touching. If a battery is connected to

these plates the positive pole to one and the negative pole

to the other, electrons from the battery will be attracted

from the plate connected to the positive terminal of the

battery. If the battery is then disconnected, one plate will be

left with an excess of

electrons, the other with

a shortage, and a

potential or voltage

difference will exists

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between them. These plates will be acting as capacitors.

Capacitors are of two types: - (1) fixed type like ceramic,

polyester, electrolytic capacitors-these names refer to the

material they are made of aluminium foil. (2) Variable type

like gang condenser in radio or trimmer. In fixed type

capacitors, it has two leads and its value is written over its

body and variable type has three leads. Unit of

measurement of a capacitor is farad denoted by the symbol

F. It is a very big unit of capacitance. Small unit capacitor

are pico-farad denoted by pf (Ipf=1/1000,000,000,000 f)

Above all, in case of electrolytic capacitors, it's two terminal

are marked as (-) and (+) so check it while using capacitors

in the circuit in right direction. Mistake can destroy the

capacitor or entire circuit in operational.

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DIODE

The simplest semiconductor device is made up of a

sandwich of P-type semiconducting material, with contacts

provided to connect the p-and n-type layers to an external

circuit. This is a junction Diode. If the positive terminal of

the battery is connected to the p-type material (cathode)

and the negative terminal to the N-type material (Anode), a

large current will flow. This is called forward current or

forward biased.

If the connections are reversed, a very little current will

flow. This is because under this condition, the p-type

material will accept the electrons from the negative terminal

of the battery and the N-type material will give up its free

electrons to the battery, resulting in the state of electrical

equilibrium since the N-type material has no more electrons.

Thus there will be a small current to flow and the diode is

called Reverse biased.

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Thus the Diode allows direct current to pass only in one

direction while blocking it in the other direction. Power

diodes are used in concerting AC into DC. In this, current will

flow freely during the first half cycle (forward biased) and

practically not at all during the other half cycle (reverse

biased). This makes the diode an effective rectifier, which

convert ac into pulsating dc. Signal diodes are used in radio

circuits for detection. Zener diodes are used in the circuit to

control the voltage.

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SOME COMMON DIODES ARE:-

1. Zener diode.

2. Photo diode.

3. Light Emitting diode.

1. ZENER DIODE:-A zener diode is specially designed junction diode,

which can operate continuously without being damaged in

the region of reverse break down voltage. One of the most

important applications of zener diode is the design of

constant voltage power supply. The zener diode is joined in

reverse bias to d.c. through a resistance R of suitable value.

2. PHOTO DIODE:-

A photo diode is a junction diode made from photo-

sensitive semiconductor or material. In such a diode, there

is a provision to allow the light of suitable frequency to fall

on the p-n junction. It is reverse biased, but the voltage

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applied is less than the break down voltage. As the intensity

of incident light is increased, current goes on increasing till

it becomes maximum. The maximum current is called

saturation current.

3. LIGHT EMITTING DIODE (LED):-

When a junction diode is forward biased, energy is

released at the junction diode is forward biased, energy is

released at the junction due to recombination of electrons

and holes. In case of silicon and germanium diodes, the

energy released is in infrared region. In the junction diode

made of gallium arsenate or indium phosphide, the energy

is released in visible region. Such a junction diode is called a

light emitting diode or LED.

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RELAY

Relay is a common, simple application of

electromagnetism. It uses an electromagnet made from an

iron rod wound with hundreds of fine copper wire. When

electricity is applied to the wire, the rod becomes magnetic.

A movable contact arm above the rod is then pulled toward

the rod until it closes a switch contact. When the electricity

is removed, a small spring pulls the contract arm away from

the rod until it closes a second switch contact. By means of

relay, a current circuit can be broken or closed in one circuit

as a result of a current in another circuit.

Relays can have several poles and contacts. The types

of contacts could be normally open and normally closed.

One closure of the relay can turn on the same normally

open contacts; can turn off the other normally closed

contacts.

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Relay requires a current through their coils, for which a

voltage is applied. This voltage for a relay can be D.C. low

voltages upto 24V or could be 240V a.c.

A relay is an electrical switch that opens and closes under

control of another electrical circuit. In the original form, the

switch is operated by an electromagnet to open or close one

or many sets of contacts. It was invented byJoseph Henry in

1835. Because a relay is able to control an output circuit of

higher power than the input circuit, it can be considered, in

a broad sense, to be a form of electrical amplifier.

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These contacts can be either Normally Open (NO) ,

Normally Closed (NC) , or change-over contacts.

Normally-open contacts connect the circuit when the

relay is activated; the circuit is disconnected when the

relay is inactive. It is also called Form A contact or

"make" contact. Form A contact is ideal for applications

that require to switch a high-current power source from

a remote device.

Normally-closed contacts disconnect the circuit when

the relay is activated; the circuit is connected when the

relay is inactive. It is also called Form B contact or

"break" contact. Form B contact is ideal for applications

that require the circuit to remain closed until the relay

is activated.

Change-over contacts control two circuits: one

normally-open contact and one normally-closed contact

with a common terminal. It is also called Form C

contact.

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OPERATION

When a current flows through the coil, the resulting

magnetic field attracts an armature that is mechanically

linked to a moving contact. The movement either makes or

breaks a connection with a fixed contact. When the current

to the coil is switched off, the armature is returned by a

force that is half as strong as the magnetic force to its

relaxed position. Usually this is a spring, but gravity is also

used commonly in industrial motor starters. Relays are

manufactured to operate quickly. In a low voltage

application, this is to reduce noise. In a high voltage or high

current application, this is to reduce arcing.

If the coil is energized with DC, a diode is frequently

installed across the coil, to dissipate the energy from the

collapsing magnetic field at deactivation, which would

otherwise generate a spike of voltage and might cause

damage to circuit components. If the coil is designed to be

energized with AC, a small copper ring can be crimped to

the end of the solenoid. This "shading ring" creates a small

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out-of-phase current, which increases the minimum pull on

the armature during the AC cycle. [1]

By analogy with the functions of the original

electromagnetic device, a solid-state relay is made with a

thyristor or other solid-state switching device. To achieve

electrical isolation, a light-emitting diode (LED) is used with

a photo transistor.

Relays are used

To control a high-voltage circuit with a low-voltage

signal, as in some types ofmodems,

To control a high-current circuit with a low-current

signal, as in the startersolenoid of an automobile,

To detect and isolate faults on transmission and

distribution lines by opening and closing circuit

breakers (protection relays),

To isolate the controlling circuit from the controlled

circuit when the two are at different potentials, for

example when controlling a mains-powered device

from a low-voltage switch. The latter is often applied to

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control office lighting as the low voltage wires are

easily installed in partitions, which may be often

moved as needs change. They may also be controlled

by room occupancy detectors in an effort to conserve

energy,

To perform logic functions. For example, the boolean

AND function is realised by connecting NO relay

contacts in series, the OR function by connecting NO

contacts in parallel. The change-over or Form C

contacts perform the XOR (exclusive or) function.

Similar functions for NAND and NOR are accomplished

using NC contacts. Due to the failure modes of a relay

compared with a semiconductor, they are widely used

in safety critical logic, such as the control panels of

radioactive waste handling machinery.

To perform time delay functions. Relays can be

modified to delay opening or delay closing a set of

contacts. A very short (a fraction of a second) delay

would use a copper disk between the armature and

moving blade assembly. Current flowing in the disk

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maintains magnetic field for a short time, lengthening

release time. For a slightly longer (up to a minute)

delay, a dashpot is used. A dashpot is a piston filled

with fluid that is allowed to escape slowly. The time

period can be varied by increasing or decreasing the

flow rate. For longer time periods, a mechanical

clockwork timer is installed.

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CIRCUIT DIAGRAM

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CIRCUIT DESCRIPTION

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The circuit is simple NPN transistor common emitter

switching circuit. The transistor T-1 is supplied through

negative at emitter. The base is conducted through the port

output from computer and collector gives output to energies

the relay commonly connected to +ve supply. The diode

prevents back emf produced by relay while working.

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RESISTANCE

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Resistance is the opposition of a material to the current. It is

measured in Ohms ( ). All conductors represent a certain

amount of resistance, since no conductor is 100% efficient.

To control the electron flow (current) in a predictable

manner, we use resistors. Electronic circuits use calibrated

lumped resistance to control the flow of current. Broadly

speaking, resistor can be divided into two groups viz. fixed

& adjustable (variable) resistors. In fixed resistors, the value

is fixed & cannot be varied. In variable resistors, the

resistance value can be varied by an adjuster knob. It canbe divided into (a) Carbon composition (b) Wire wound (c)

Special type.

The most common type of resistors used in our projects is

carbon type. The resistance value is normally indicated by

colour bands. Each resistance has four colours, one of the

band on either side will be gold or silver, this is called fourth

band and indicates the tolerance, others three band will give

the value of resistance.

For example if a resistor has the following marking on it say

red, violet, gold. Comparing these coloured rings with the

colour code, its value is 27000 ohms or 27 kilo ohms and its

tolerance is 5%. Resistor comes in various sizes (Power

rating). The bigger, the size, the more power rating of 1/4

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watts. The four colour rings on its body tells us the value of

resistor value as given below.

COLOURS CODE:

Black----------------------------------------0

Brown--------------------------------------1

Red------------------------------------------2

Orange-------------------------------------3

Yellow--------------------------------------4

Green---------------------------------------5

Blue-----------------------------------------6

Violet---------------------------------------7

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Grey-----------------------------------------8

White---------------------------------------9

The first rings give the first digit. The second ring gives

the second digit. The third ring indicates the number of

zeroes to be placed after the digits. The fourth ring gives

tolerance (gold 5%, silver 10%, No colour 20%).

In variable resistors, we have the dial type of

resistance boxes. There is a knob with a metal pointer. This

presses over brass pieces placed along a circle with some

space b/w each of them.

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Resistance coils of different values are connected b/w

the gaps. When the knob is rotated, the pointer also moves

over the brass pieces. If a gap is skipped over, its resistance

is included in the circuit. If two gaps are skipped over, the

resistances of both together are included in the circuit and

so on.

A dial type of resistance box contains many dials

depending upon the range, which it has to cover. If a

resistance box has to read upto 10,000 , it will have three

dials each having ten gaps i.e. ten resistance coils each of

resistance 10 . The third dial will have ten resistances

each of 100 .

The dial type of resistance boxes is better because the

contact resistance in this case is small & constant.

TRANSFORMER

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PRINCIPLE OF THE TRANSFORMER:-

Two coils are wound over a Core such that they are

magnetically coupled. The two coils are known as the

primary and secondary windings.

In a Transformer, an iron core is used. The coupling

between the coils is source of making a path for themagnetic flux to link both the coils. A core as in fig.2 is used

and the coils are wound on the limbs of the core. Because of

high permeability of iron, the flux path for the flux is only in

the iron and hence the flux links both windings. Hence there

is very little leakage flux. This term leakage flux denotes

the part of the flux, which does not link both the coils, i.e.,

when coupling is not perfect. In the high frequency

transformers, ferrite core is used. The transformers may be

step-up, step-down, frequency matching, sound output,

amplifier driver etc. The basic principles of all the

transformers are same.

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MINIATURE TRANSFORMER

CONVENTIONAL POWER TRANSFORMER

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TRANSISTOR

The name is transistor derived from transfer resistors

indicating a solid state Semiconductor device. In addition to

conductor and insulators, there is a third class of material

that exhibits proportion of both. Under some conditions, it

acts as an insulator, and under other conditions its a

conductor. This phenomenon is called Semi-conducting and

allows a variable control over electron flow. So, the

transistor is semi conductor device used in electronics for

amplitude. Transistor has three terminals, one is the

collector, one is the base and other is the emitter, (each

lead must be connected in the circuit correctly and only

then the transistor will function). Electrons are emitted via

one terminal and collected on another terminal, while the

third terminal acts as a control element. Each transistor has

a number marked on its body. Every number has its own

specifications.

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There are mainly two types of transistor (i) NPN & (ii)

PNP

NPN Transistors:

When a positive voltage is applied to the base, the

transistor begins to conduct by allowing current to flow

through the collector to emitter circuit. The relatively small

current flowing through the base circuit causes a much

greater current to pass through the emitter / collector

circuit. The phenomenon is called current gain and it is

measure in beta.

PNP Transistor:

It also does exactly same thing as above except that it

has a negative voltage on its collector and a positive voltage

on its emitter.

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Transistor is a combination of semi-conductor elements

allowing a controlled current flow. Germanium and Silicon is

the two semi-conductor elements used for making it. There

are two types of transistors such as POINT CONTACT and

JUNCTION TRANSISTORS. Point contact construction is

defective so is now out of use. Junction triode transistors are

in many respects analogous to triode electron tube.

A junction transistor can function as an amplifier or

oscillator as can a triode tube, but has the additional

advantage of long life, small size, ruggedness and absence

of cathode heating power.

Junction transistors are of two types which can be

obtained while manufacturing.

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THE TWO TYPES ARE: -

1) PNP TYPE: This is formed by joining a layer of P

type of germanium to an N-P Junction

2) NPN TYPE: This is formed byjoining a layer of N type germanium

to a P-N Junction.

Both types are shown in figure,

with their symbols for representation. The centre section is

called the base, one of the outside sections-the emitter and

the other outside section-the collector. The direction of the

arrowhead gives the direction of the conventional current

with the forward bias on the emitter. The conventional flow

is opposite in direction to the electron flow.

OPERATION OF PNP TRANSISTOR:-

P N P

N P N

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A PNP transistor is made by sand witching two PN

germanium or silicon diodes, placed back to back. The

centre of N-type portion is extremely thin in comparison to P

region. The P region of the left is connected to the positive

terminal and N-region to the negative terminal i.e. PN is

biased in the forward direction while P region of right is

biased negatively i.e. in the reverse direction as shown in

Fig. The P region in the forward biased circuit is called the

emitter and P region on the right, biased negatively is called

collector. The centre is called base.

The majority carriers (holes) of P region (known as

emitter) move to N region as they are repelled by the

positive terminal of battery while the electrons of N region

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are attracted by the positive terminal. The holes overcome

the barrier and cross the emitter junction into N region. As

the width of base region is extremely thin, two to five

percent of holes recombine with the free electrons of N-

region which result in a small base current while the

remaining holes (95% to 98%) reach the collector junction.

The collector is biased negatively and the negative collector

voltage aids in sweeping the hole into collector region.

As the P region at the right is biased negatively, a very

small current should flow but the following facts are

observed:-

1) A substantial current flows through it when the emitter

junction is biased in a forward direction.

2) The current flowing across the collector is slightly less

than that of the emitter, and

3) The collector current is a function of emitter current i.e.

with the decrease or increase in the emitter current a

corresponding change in the collector current is

observed.

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The facts can be explained as follows:-

1. As already discussed that 2 to 5% of the holes are lost

in recombination with the electron n base region, which

result in a small base current and hence the collector

current is slightly less than the emitter current.

2. The collector current increases as the holes reaching

the collector junction are attracted by negative

potential applied to the collector.

3. When the emitter current increases, most holes are

injected into the base region, which is attracted by

the negative potential of the collector and hence

results in increasing the collector current. In this way

emitter is analogous to the control of plate current by

small grid voltage in a vacuum triode.

Hence we can say that when the emitter is forward biased

and collector is negatively biased, a substantial current

flows in both the circuits. Since a small emitter voltage of

about 0.1 to 0.5 volts permits the flow of an appreciable

emitter current the input power is very small. The collector

voltage can be as high as 45 volts.

APPENDIX

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A program in C which controls the inputs for different load indication,

and switch the output loads for VIP and general categories area.

#include

#include

#include

void main()

{

unsigned char c;int i;

textmode(C40);

_setcursortype(_NOCURSOR);

gotoxy(9,2);

printf("OVER LOAD CONTROL SYSTEM");

gotoxy(7,24);

printf("PRESS INPUTS AND SEE RESULTS");

gotoxy(1,9);

printf("OUTPUTS");

gotoxy(12,8);

printf("%c",218);

gotoxy(12,9);

printf("%c",179);

gotoxy(12,10);

printf("%c",192);

for(i=0;i


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{

gotoxy(13+i,8);

printf("%c",196);

gotoxy(13+i,10);

printf("%c",196);

gotoxy(14+i,8);

printf("%c",194);

gotoxy(14+i,9);

printf("%c",179);

gotoxy(14+i,10);printf("%c",193);

}

gotoxy(13+i,8);

printf("%c",196);

gotoxy(13+i,10);

printf("%c",196);

gotoxy(14+i,8);

printf("%c",191);

gotoxy(14+i,9);

printf("%c",179);

gotoxy(14+i,10);

printf("%c",217);

gotoxy(13,7);

printf("2 3 4 5 6 7 8 9");

gotoxy(13,11);

printf(" V I P 4 3 2 1 - Blk");

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gotoxy(1,17);

printf("OVERLOAD SWITCH");

gotoxy(16,16);

printf("%c",218);

gotoxy(16,17);

printf("%c",179);

gotoxy(16,18);

printf("%c",192);

for(i=0;i


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printf("%c",191);

gotoxy(18+i,17);

printf("%c",179);

gotoxy(18+i,18);

printf("%c",217);

gotoxy(15,15);

printf("10 11 12 13");

gotoxy(15,19);

printf("1K 2K 3K 4K");

while(!kbhit()){

c=inportb(0x379);

i=c;

switch(i)

{

case 127:

for(i=0;i


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outportb(0x378,255);

break;

case 63:

gotoxy(13+14,9);

printf(" ");

gotoxy(17,17);

printf("%c",219);

outportb(0x378,127);

break;

case 95:gotoxy(13+12,9);

printf(" ");

// gotoxy(13+14,9);

// printf(" ");

gotoxy(17+2,17);

printf("%c",219);

outportb(0x378,63);

break;

case 111:

gotoxy(13+10,9);

printf(" ");

// gotoxy(13+12,9);

// printf(" ");

// gotoxy(13+14,9);

// printf(" ");

gotoxy(17+4,17);

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printf("%c",219);

outportb(0x378,31);

break;

case 119:

gotoxy(13+8,9);

printf(" ");

// gotoxy(13+10,9);

// printf(" ");

// gotoxy(13+12,9);

// printf(" ");// gotoxy(13+14,9);

// printf(" ");

gotoxy(17+6,17);

printf("%c",219);

outportb(0x378,15);

break;

}

delay(125);

}

outportb(0x378,0);

_setcursortype(_NORMALCURSOR);

textmode(C80);

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