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Electrical and Electronics - The Basics Bridgwater College 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), may contain up to several thousand transistors and other devices, all formed on a sliver of silicon so small you could lose it on your fingernail. Miniaturising electronic circuits in this way is called Microelectronics and it has far reaching effects on nearly all aspects of life. ELECTRONICS - Today and Yesterday Today we take for granted the way in which electronics makes our life 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. ELECTRONICS - Today and Yesterday 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 any information, 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 pits along a track that spirals out from the centre of the disc. Each pit is about 1000th of a mm long and about a 10th as deep. The track is so narrow that thirty tracks are about as wide as a human hair. Sixty minutes of sound requires about ten million such pits. ELECTRONICS - Today and Yesterday The Compact Disc The compact disc is then coated in a thin layer of Aluminium over which is paced a thin layer of transparent plastic. The disc is then rotated at high speed, where a laser beam reads the information on the disc. The stream of on/off pulses of laser light is converted to electrical signals which are processed into sound. ELECTRONICS - Today and Yesterday Looking Back - what was it like before? Less than 100 years ago, electronics was unknown. There were no radios, no televisions, computers, robots or artificial satellites and none of the products and services we take for granted today. In such a short space of time there has been a revolution in the way we communicate, control, measure, take care of people and enjoy ourselves. ELECTRONICS - Today and Yesterday Looking Back - what was it like before? This revolution came naturally out of the study of electricity, an old science not unknown to the Greeks over 2000 years ago. Electricity was a subject of great interest to Victorian scientists and to Sir William Crookes in particular. ELECTRONICS - Today and Yesterday A Snap Shot of History 1897 - Sir J. J. Thomson stated that Cathode Rays were rapidly moving electrical charges. This marked the discovery of the electron (named after the Greek word for Amber). 1904 - Sir John A. Fleming invents the thermionic valve. This was an early diode, where electrons would only flow in one direction. 1907 - Lee de Forest invents the triode. This was used on the first communication devices, such as the system fitted to the Titanic. ELECTRONICS - Today and Yesterday A Snap Shot of History 1922 -The use of Thermionic valves for the BBC transmitter. Firms such as Marconi, HMV made radio sets with parts and valves supplied 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 telephone laboratories. ELECTRONICS - Today and Yesterday A Snap Shot of History 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 making advances which can be seen in the world around us both at work and in the home. ELECTRONICS - Today and Yesterday 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 development of electronics. The computers which were developed using the new I.C. chips were known as 3rd generation computers. They were responsible for navigation and the guidance control of all Apollo spacecraft. Today the computers on motor vehicles have far superior power and accuracy. ELECTRONICS - Today and Yesterday 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 side on the dot at the end of this sentence. All atoms have a nucleus in which particles called protons and neutrons live. Electrons however make up an electron cloud outside the nucleus. The nucleus is very small compared with the overall size of the atom - say the size of an orange compared with the size of a cathedral. Using this model you can imagine electrons to be flies in the cathedral. From the point of electronics the 2 most important properties of an electron are its electrical charge and its small mass. ELECTRONICS - The Basics Electrons in Atoms An electron carries a negative charge and the proton an equal positive charge. Since these charges are opposite, protons and the electrons attract each other. The neutron carries no electrical charge that is to say it is neutral. ELECTRONICS - The Basics Atomic Structure electrons protons nucleus neutrons ELECTRONICS - The Basics Atomic Structure Hydrogen and oxygen are 2 very common substances since their atoms 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 single proton that tells us it is Hydrogen since it is the number of protons in the nucleus of an atom that determines its properties. ELECTRONICS - The Basics 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 protons and 8 neutrons. thus the electrically neutral oxygen atom has 8 electrons in the space surrounding the nucleus. ELECTRONICS - The Basics 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 neutrons zero charge, neutrons and protons do attract each other strongly when they are close together in the nucleus of an atom. when this force is overcome, as in the case when uranium atoms are split, in nuclear reactors and atomic bombs, an enormous amount of energy is released. However, electrons are held much more weakly to atoms, and it is this weakness upon which electronics is based. ELECTRONICS - The Basics Atomic Structure - some information about atoms Atoms Hydrogen Oxygen Copper Silver Silicon Germanium Carbon Iron Number of Protons in the nucleus Number of neutrons in the nucleus 1 8 29 47 14 32 6 26 Number of electrons in shells 0 8 34 61 14 40 6 30 1 8 29 47 14 32 6 26 ELECTRONICS - The Basics Conductors, insulators and semiconductors The reason why some materials, such as copper, are good electrical conductors is that they contain “free electrons” which are quite weakly bound to the nuclei of the atoms of the material. These electrons can be moved easily by connecting the material across a battery. Copper and Aluminium are good electrical conductors and are used in electronics to allow electrons to flow easily between one device and another. Electrons are more strongly attracted to their parent nuclei in electrical insulators, which therefore do not have any free electrons. Thus electrical insulators such as glass, polythene and mica are used to resist the flow of electrons. ELECTRONICS - The Basics Conductors, insulators and semiconductors Electronics is to with the use of semiconductors as well as the use of conductors and insulators. Semiconductors are the basis of devices such as transistors and diodes, heat sensors and light emitters, integrated circuits and many other devices. as its name suggests, a semiconductor has an electrical resistance that falls somewhere between that of a conductor and an insulator. Two of the most common semiconductors are Silicon and Germanium. They are important in electronics because their resistance can be controlled to good effect. There are 2 ways of doing this. ELECTRONICS - The Basics Conductors, insulators and semiconductors First there is applying heat on a semiconductor. At very low temperatures semiconductors happen to be good electrical insulators but as their temperature increases they become increasingly better electrical conductors. This means at every day temperatures they allow some current to pass through them. The second way of controlling the resistance of a semiconductor is by adding minute amounts of substances to them. ELECTRONICS - The Basics Silicon Atoms Germanium is now rarely used in electronics, which is mostly based on silicon. The picture below shows a silicon atom that has 14 ` electrons surrounding a nucleus of 14 protons and 14 neutrons. The part of the structure that makes silicon useful to electronics is the way in which the electrons are arranged in the shells surrounding the nucleus. There are 2 in the inner shell, 8 in the next and 4 in the outer shell. ELECTRONICS - The Basics Silicon Atoms The outer shell is known as the Valency Shell, which makes silicon a pure crystalline material. In a crystal of pure silicon, each of the 4 outer electrons forms a covalent bond with a neighboring electron. The picture shows how the pairing uses up every one of the outer electrons. There are no free electrons to allow electricity to flow so silicon is an insulator. At least at -273 deg/c. ELECTRONICS - The Basics Silicon Atoms But at everyday temperatures Silicon conducts electricity a little, not much but enough to make silicon a bit of a problem when used in transistors. ELECTRONICS - The Basics 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 they make a bad fit in the Crystal structure of silicon, due to the impurity atoms 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. ELECTRONICS - The Basics Silicon Atoms - n type semi conductors (negative). This type of semiconductor is produced by doping silicon with for example phosphorous. A phosphorous atom has 5 electrons in its outer shell. The picture below shows what happens when an atom of phosphorous is embedded in the Crystal structure of silicon. 4 of the 5 outer phosphorous electrons form covalent bonds with neighboring silicon atoms, leaving a fifth free to wander about. Phosphorous is said to be p a donor impurity since each atom of phosphorous can donate an electron. ELECTRONICS - The Basics Silicon Atoms - p type semi conductors (positive). This is produced by doping silicon with atoms such as Boron which have 3 electrons in their outer shell. As you can see from the picture 3 of its outer electrons have paired with silicon leaving an unpaired silicon electron. This electron is not able to conduct but will allow another electron to pair with it. The vacancy created by the electron is called a hole and since it attracts electrons it behaves b as if it had a positive charge. Boron is said to be an acceptor impurity. ELECTRONICS - The Basics Electricity - Voltage (V). 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. ELECTRONICS - The Basics Electricity - Amperage (A). 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. ELECTRONICS - The Basics Electricity - Wattage (W). Consider a water wheel, it will have a great deal of power when the water 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. ELECTRONICS - The Basics Electricity - Ohms . 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 turn as fast or not at all. ELECTRONICS - The Basics Switch is open Lamp The lamp acts as a resistance in the circuit measured in ohms. Voltage is electrical pressure - + Battery Chemical action to produce electricity ELECTRONICS - The Basics Switch is now closed Lamp The lamp acts as a resistance in the circuit measured in ohms. Voltage is electrical pressure The flow of electricity measured in Amperes - + Battery Chemical action to produce electricity TECH 2000 Please identify these symbols. Use Crocodile Clips to help you. ELECTRONICS - The Basics Exercise Using crocodile clips please design a circuit containing the following:A battery A bulb A bulb holder A Switch To activate crocodile clips click on the icon. ELECTRONICS - The Basics Resistors control current and are usually found between a good conductor and a good insulator. Their resistance is rated in ohms and heat-withstanding rating is expressed 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. ELECTRONICS - The Basics Symbols - resistors Fixed or Variable or ELECTRONICS - The Basics CARBON RESISTORS 2W 1W 0.5W WIRE WOUND RESISTORS 8.2 OHM 100 W ELECTRONICS - The Basics Most resistors you see have four coloured bands to indicate their resistance and tolerance. How do you know which way round to read the resistor? The gold or silver band features last in the code. ELECTRONICS - The Basics BANDS 1 2 3 TOLERANCE ELECTRONICS - The Basics COLOUR NUMERAL MULTIPLIER TOLERANCE 1st and 2nd multiplier tolerance BLACK BROWN RED ORANGE YELLOW GREEN BLUE VIOLET GREY WHITE 0 1 2 3 4 5 6 7 8 9 *1 10 100 1000 10000 100000 1000000 10000000 100000000 1000000000 GOLD 5% SILVER 10% NO BAND 20% ELECTRONICS - The Basics BANDS 1 2 3 TOLERANCE BAND 1 = GREEN = 5 2 = RED =2 3 = RED = 00 RESISTANCE IS 5200 Ohms ELECTRONICS - The Basics BANDS 1 2 3 TOLERANCE BAND 1 = GREEN = 5 To convert into Kilo Ohms. 2 = RED =2 Take the 5 2 0 0 Ohms and move 3 = RED = 00 the decimal point three places to RESISTANCE IS 5200 Ohms the left. ELECTRONICS - The Basics BANDS 1 2 3 TOLERANCE BAND 1 = GREEN = 5 To convert into Kilo Ohms. EXAMPLE 2 = RED =2 Take the 5 2 0 0 Ohms into Kilo 3 = RED = 00 Ohms, move the decimal point 5 2 0 0. Ohms RESISTANCE IS 5200 Ohms three places to the left. ELECTRONICS - The Basics BANDS 1 2 3 TOLERANCE BAND 1 = GREEN = 5 To convert into Kilo Ohms. EXAMPLE 2 = RED =2 Take the 5 2 0 0 Ohms into Kilo 3 = RED = 00 Ohms, move the decimal point 5 2 0.0 RESISTANCE IS 5200 Ohms three places to the left. ELECTRONICS - The Basics BANDS 1 2 3 TOLERANCE BAND 1 = GREEN = 5 To convert into Kilo Ohms. EXAMPLE 2 = RED =2 Take the 5 2 0 0 Ohms into Kilo 3 = RED = 00 Ohms, move the decimal point 5 2. 0 0 IS 5200 Ohms RESISTANCE three places to the left. ELECTRONICS - The Basics BANDS 1 2 3 TOLERANCE BAND 1 = GREEN = 5 To convert into Kilo Ohms. EXAMPLE 2 = RED =2 Take the 5 2 0 0 Ohms into Kilo 3 = RED = 00 Ohms, move the decimal point 5 . 2 0 0 =IS5.2Kilo Ohms RESISTANCE 5200 Ohms three places to the left. ELECTRONICS - The Basics BANDS 1 2 3 TOLERANCE BAND 1 = GREEN = 5 To convert into Kilo Ohms. EXAMPLE 2 = RED = 2 Thethe forth the tolerance Take 5 2 band 0 0 Ohms into Kilo 3 = RED = 00 bandmove is Silver. The resistor Ohms, the decimal pointhas a 5 . 2 0 0 =IS5.2Kilo Ohms RESISTANCE 5200 Ohms Tolerance ofthe + orleft. - 10% three places to ELECTRONICS - The Basics BANDS 1 2 3 TOLERANCE If you are asked to calculate the minimum and maximum resistance this is how it is done. The resistance is 5.2 K Ohms + or - 10 % ELECTRONICS - The Basics BANDS 1 2 3 TOLERANCE If1st youwork are asked to calculate the minimum out 10% of 5.2 K Ohms. and resistance this is how it is Usemaximum your calculator. done. 5.2 * 10 then press the % button on your The resistance is K5.2 K Ohms + or - 10 % calculator =.52 Ohms ELECTRONICS - The Basics BANDS 1 2 3 TOLERANCE If1st youwork are asked to calculate the minimum out 10% of 5.2 K Ohms. Now work out the MINIMUM value of the and maximum resistance this is how it is Use your calculator. 5.2 K Ohm resistor. done. 5.2 *- 0.52 10 then press the % button on your 5.2 = 4.68 K Ohms The resistance is K5.2 K Ohms + or - 10 % calculator =.52 Ohms ELECTRONICS - The Basics BANDS 1 2 3 TOLERANCE If1st youwork are asked to calculate the minimum out 10% of 5.2 K Ohms. The MAXIMUM value this of the 5.2 KitOhm and maximum resistance is how is Use your calculator. resistance is done. 5.2 *+ 0.52 10 then press the % button on your 5.2 = 5.72 K Ohms The resistance is K5.2 K Ohms + or - 10 % calculator =.52 Ohms ELECTRONICS - The Basics BANDS 1 2 3 TOLERANCE R=5.2K Ohms min = 4.68 max 5.72