bridgwater college electrical and electronics - the basics tmc

Bridgwater College

Electrical and Electronics - The Basics

tmc

ELECTRONICS - Today and Yesterday

The Electronic Age

Electronics is about using things such as transistors and silicon chips to make electricity work for us.

The Transistor was invented in the late 1940’s followed by silicon chips in the 1960’s. A silicon chip (or integrated circuit), maycontain up to several thousand transistors and other devices, allformed on a sliver of silicon so small you could lose it on yourfingernail. Miniaturising electronic circuits in this way is calledMicroelectronics and it has far reaching effects on nearly all aspectsof life.


Today we take for granted the way in which electronics makes ourlife easier and more enjoyable - lets look at some of it’s benefits.

• Consumer goods - washing machines, T.V. and video, stereo system alarms, cameras, video/digital cameras, P.C.’s,

vehicle systems, the list is endless.• Communications - man made satellites have been put into orbit

around our planet, to provide world wide communication.

• Medical Electronics - use of ECG, X-rays and bio-electronics.• Control Electronics - used in motor vehicle systems.• Computer Electronics - fully integrated into out society.


The Compact Disc

Lets use this one piece of technology as an example. The compact disc has revolutionised the way in which we store and record anyinformation, whether it is sound, video, DVD or both.This is a plastic disc about 120 mm in diameter and 1.2 mm thick,which stores sound/picture in the form of microscopically small pitsalong a track that spirals out from the centre of the disc. Each pitis about 1000th of a mm long and about a 10th as deep. The track isso narrow that thirty tracks are about as wide as a human hair.Sixty minutes of sound requires about ten million such pits.


The Compact Disc

The compact disc is then coated in a thin layer of Aluminium overwhich is paced a thin layer of transparent plastic.The disc is then rotated at high speed, where a laser beam reads theinformation on the disc. The stream of on/off pulses of laser light is converted to electrical signals which are processed into sound.


Looking Back - what was it like before?

Less than 100 years ago, electronicswas unknown. There were no radios,no televisions, computers, robots orartificial satellites and none of theproducts and services we take forgranted today. In such a short space of time there has been a revolution in theway we communicate, control, measure, take care of people andenjoy ourselves.


Looking Back - what was it like before?

This revolution came naturally out of thestudy of electricity, an old science notunknown to the Greeks over 2000years ago. Electricity was a subject of great interest to Victorianscientists and to Sir William Crookes inparticular.


A Snap Shot of History

1897 - Sir J. J. Thomson stated that Cathode Rays were rapidlymoving electrical charges. This marked the discovery of theelectron (named after the Greek word for Amber).

1904 - Sir John A. Fleming invents the thermionic valve. This was anearly diode, where electrons would only flow in one direction.

1907 - Lee de Forest invents the triode. This was used on the firstcommunication devices, such as the system fitted to the Titanic.



1922 -The use of Thermionic valves for the BBC transmitter. Firmssuch as Marconi, HMV made radio sets with parts and valvessupplied from Mazda and Ozram.

1936 - The start of regular television broadcasts.

1939-45 - Invention of Radar.

1948 - Invention of the Transistor by, Shockley at the Bell telephonelaboratories.



1960’s - First integrated circuits are used on a silicon chip. This takes man to the Moon.

1970 - NOW - The electronics industry is one of the fastest evolving and changing in the world. Technology is ever makingadvances which can be seen in the world around usboth at work and in the home.


The Apollo Space Programs

The space race in which JFK took the U.S.A. was responsible for one of the

biggest steps forward in the developmentof electronics. The computers which

were developed using the new I.C. chipswere known as 3rd generation computers.

They were responsible for navigation and theguidance control of all Apollo spacecraft.

Today the computers on motor vehicles havefar superior power and accuracy.


How much has the Motor Vehicle been affected?

A LOT!!!

ELECTRONICS - The Basics

Electrons in Atoms

Atoms are extremely small bits of material - millions lie side by sideon the dot at the end of this sentence. All atoms have a nucleus inwhich particles called protons and neutrons live. Electrons howevermake up an electron cloud outside the nucleus. The nucleus is verysmall compared with the overall size of the atom - say the size of anorange compared with the size of a cathedral. Using this model youcan imagine electrons to be flies in the cathedral.

From the point of electronics the 2 most important properties of anelectron are its electrical charge and its small mass.


Electrons in Atoms

An electron carries a negative charge and the proton an equal positive charge. Since these charges are opposite, protons and theelectrons attract each other. The neutron carries no electrical chargethat is to say it is neutral.


Atomic Structure

electrons

nucleus

protons

neutrons


Atomic Structure

Hydrogen and oxygen are 2 very common substances since theiratoms go to make up that very useful substance called water.

A Hydrogen Atom electron shell proton

As you can see it has just 1 proton and 1 electron. It is this singleproton that tells us it is Hydrogen since it is the number of protonsin the nucleus of an atom that determines its properties.


Atomic Structure

The electrical charge of on a proton is equal and opposite to the charge of an electron, making the hydrogen atom electrically neutral.

An Oxygen atom is more complicated. It has a nucleus of 8 protonsand 8 neutrons. thus the electrically neutral oxygen atom has 8electrons in the space surrounding the nucleus.


Atomic Structure

Neutrons combine with protons to make up the nuclei of all atoms,but they do not carry an electrical charge. In spite of the neutronszero charge, neutrons and protons do attract each other stronglywhen they are close together in the nucleus of an atom. when thisforce is overcome, as in the case when uranium atoms are split,in nuclear reactors and atomic bombs, an enormous amount ofenergy is released.However, electrons are held much more weakly to atoms, and it isthis weakness upon which electronics is based.


Atomic Structure - some information about atoms

Atoms Number of Protons Number of neutrons Number of electronsin the nucleus in the nucleus in shells

Hydrogen 1 0 1Oxygen 8 8 8Copper 29 34 29Silver 47 61 47Silicon 14 14 14Germanium 32 40 32Carbon 6 6 6Iron 26 30 26


Conductors, insulators and semiconductors

The reason why some materials, such as copper, are good electricalconductors is that they contain “free electrons” which are quite weakly bound to the nuclei of the atoms of the material. Theseelectrons can be moved easily by connecting the material across abattery. Copper and Aluminium are good electrical conductorsand are used in electronics to allow electrons to flow easily betweenone device and another. Electrons are more strongly attracted totheir parent nuclei in electrical insulators, which therefore donot have any free electrons. Thus electrical insulators such as glass,polythene and mica are used to resist the flow of electrons.



Electronics is to with the use of semiconductors as well as the use ofconductors and insulators. Semiconductors are the basis of devicessuch as transistors and diodes, heat sensors and light emitters,integrated circuits and many other devices. as its name suggests, asemiconductor has an electrical resistance that falls somewherebetween that of a conductor and an insulator.Two of the most common semiconductors are Silicon and Germanium. They are important in electronics because theirresistance can be controlled to good effect. There are 2 ways ofdoing this.



First there is applying heat on a semiconductor. At very lowtemperatures semiconductors happen to be good electrical insulatorsbut as their temperature increases they become increasingly betterelectrical conductors. This means at every day temperatures theyallow some current to pass through them.The second way of controlling the resistance of a semiconductor isby adding minute amounts of substances to them.


Silicon Atoms

Germanium is now rarely used in electronics, which is mostly basedon silicon. The picture below shows a silicon atom that has 14

` electrons surrounding a nucleus of 14protons and 14 neutrons. The part ofthe structure that makes silicon usefulto electronics is the way in which theelectrons are arranged in the shellssurrounding the nucleus. There are 2in the inner shell, 8 in the next and 4 inthe outer shell.


Silicon Atoms

The outer shell is known as the Valency Shell, which makes silicona pure crystalline material. In a crystal of pure silicon, each of the

4 outer electrons forms a covalentbond with a neighboring electron.The picture shows how the pairing usesup every one of the outer electrons.There are no free electrons to allow electricity to flow so silicon is aninsulator. At least at -273 deg/c.


Silicon Atoms

But at everyday temperatures Silicon conducts electricity a little,not much but enough to make silicon a bit of a problem when usedin transistors.


Silicon Atoms - n type and p type semi conductors

Once a very pure Crystal of silicon has been manufactured, it is“doped” with impurity atoms! These atoms are chosen so that theymake a bad fit in the Crystal structure of silicon, due to the impurityatoms having to many or too few electrons in their outer shells.Depending on the impurity their are 2 types of semiconductor.

N- type and P - type semiconductors.


Silicon Atoms - n type semi conductors (negative).

This type of semiconductor is produced by doping silicon with forexample phosphorous. A phosphorous atom has 5 electrons in itsouter shell. The picture below shows what happens when an atomof phosphorous is embedded in the Crystal structure of silicon.

4 of the 5 outer phosphorous electronsform covalent bonds with neighboringsilicon atoms, leaving a fifth free towander about. Phosphorous is said to bea donor impurity since each atom ofphosphorous can donate an electron.

p


Silicon Atoms - p type semi conductors (positive).

This is produced by doping silicon with atoms such as Boron whichhave 3 electrons in their outer shell. As you can see from the picture3 of its outer electrons have paired with silicon leaving an unpaired

silicon electron. This electron is not ableto conduct but will allow anotherelectron to pair with it. The vacancy created by the electron is called a holeand since it attracts electrons it behavesas if it had a positive charge. Boron is said to be an acceptor impurity.

b

Consider electricity as water, it will behave in a similar manner. Consider a garden hose with water flowing out. The pressure of the water will determine how far the water will travel out of the hose.

High pressure will cause the water to go a long way. The spark plugs in a petrol engine work when the voltage supplied to the plug has a

high voltage (1,000’s of volts) and then the spark will jump from the centre electrode to the earth electrode.


Electricity - Voltage (V).

A small garden hose will only allow a small flow of water. A fireman’s hose will allow a greater flow of water due to the fact that the bore of the hose is greater. A tap at either end of the hose could

reduce the flow of water.


Electricity - Amperage (A).

Consider a water wheel, it will have a great deal of power when thewater pressure is high i.e.. after rainfall. If the flow of water or

pressure is reduced then the amount the water wheel turns will be reduced also.


Electricity - Wattage (W).

Consider a garden hose that has a kink in it. This will cause a resistance that will reduce the flow and the pressure. Battery terminals often develop corrosion that causes resistance to the

electrical flow. As a result of the resistance the starter may not turnas fast or not at all.


Electricity - Ohms .

- +

Switch Lampis open

Battery

Voltageis electrical pressure

The lamp actsas a resistancein the circuitmeasured inohms.

Chemical action to produce electricity


- +

Switch Lampis now closed

Voltageis electrical pressureThe flow

of electricitymeasured inAmperes

The lamp actsas a resistancein the circuitmeasured inohms.

Chemical action to produce electricity

Battery


TECH 2000

Please identify these symbols. Use Crocodile Clips to help you.

Exercise

Using crocodile clips please design a circuit containing thefollowing:-

A batteryA bulbA bulb holderA Switch

To activate crocodile clips click on the icon.

Crocodile Clips Circuit


Resistors control current and are usually found between a goodconductor and a good insulator.

Their resistance is rated in ohms and heat-withstanding rating isexpressed in watts. Low wattage resistors, are small, high wattage

resistors, normally called power resistors, are larger.

Unit of resistance = ohm 1 Kilohm = 1000 ohms 1 Megohm= 1,000,000 ohms Types: Fixed and Variable

Before wiring into a circuit, check: 1. Resistance in ohms 2. Tolerance as a percentage. 3. Power rating in Watts.


Fixed Variable

or or


Symbols - resistors

CARBON RESISTORS

2W

1W 0.5W

WIRE WOUND RESISTORS

8.2 OHM 100 W


Most resistors you see have four colouredbands to indicate their resistance andtolerance. How do you know which wayround to read the resistor? The gold orsilver band features last in the code.


BANDS 1 2 3 TOLERANCE


COLOUR NUMERAL MULTIPLIER

TOLERANCE

1st and 2nd multiplier toleranceBLACK 0 *1 GOLD 5%BROWN 1 10 SILVER 10%RED 2 100 NO BAND 20%ORANGE 3 1000YELLOW 4 10000 GREEN 5 100000BLUE 6 1000000VIOLET 7 10000000GREY 8 100000000WHITE 9 1000000000



BAND 1 = GREEN = 5 2 = RED = 2 3 = RED = 00RESISTANCE IS 5200 Ohms




To convert into Kilo Ohms.Take the 5 2 0 0 Ohms and movethe decimal point three places to the left.




To convert into Kilo Ohms.Take the 5 2 0 0 Ohms into KiloOhms, move the decimal pointthree places to the left.

EXAMPLE

5 2 0 0. Ohms





EXAMPLE

5 2 0 . 0





EXAMPLE

5 2. 0 0





EXAMPLE

5 . 2 0 0 = 5.2Kilo Ohms





EXAMPLE

5 . 2 0 0 = 5.2Kilo Ohms

The forth band the tolerance band is Silver. The resistor has aTolerance of + or - 10%



If you are asked to calculate the minimumand maximum resistance this is how it isdone.The resistance is 5.2 K Ohms + or - 10 %




1st work out 10% of 5.2 K Ohms.Use your calculator.5.2 * 10 then press the % button on yourcalculator =.52 K Ohms





Now work out the MINIMUM value of the5.2 K Ohm resistor.5.2 - 0.52 = 4.68 K Ohms





The MAXIMUM value of the 5.2 K Ohmresistance is5.2 + 0.52 = 5.72 K Ohms



R=5.2K Ohms min = 4.68 max 5.72


bridgwater college electrical and electronics - the basics tmc

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