Gleniffer High School. Practical Electronics. National 4 / 5. Introductory Course Book

Transcription

1 Gleniffer High School Practical Electronics National 4 / 5 Introductory Course Book

2 Index Contents Page Impact of electronics 3-9 Basic Electronics National 5 Calculations The 555 timer chip Appendices: Appendix 1 National 4 / 5 Logic gate pin out diagrams

3 The Impact of Electronics Today we are surrounded by a world of electronic devices such as mobile phones and computers. Many of the electronic systems are embedded into more familiar objects such as cars that we sometimes don t realise or forget about the electronics that make the device or machinery function so well. Looking at cars for example How many electronic systems do you think are in this car which was put on sale in 2013? Now have a quick read at the manufacturer s technical specifications This model has:- Now try and complete the list? Automotive Electronic Systems Climate control Traction control Advanced Braking System SIPS Airbags. 3

4 The picture below shows you some idea of the complexity of modern cars. 4

5 Electronic devices are everywhere in modern Western societies. Can you name these electronic or electronically controlled devices:- Clue Device personal communication system can play these in the house laptops netbooks and tablets are all types of these you watch this you listen to this these devices can be blue fast food heater make the dinner on this keeps your clothes clean keeps you clean controls your day and it can be portable keeps you warm this communication device is going nowhere personal transport takes you far away on holiday not a book but a library portable music device these are very cool keeps you safe variable borer a right tool 5

6 Computers (and mobile phones) use a number of different materials in their construction many of which are toxic but some of the materials are valuable when they are extracted from older unwanted devices. Recycling is an important aspect of the electronics industry with companies specialising in recycling electronic waste. The rate of development in the field of electronics is increasing with each technical advance making a range of older machines obsolete. In addition to this the consumer society we live in has developed a cycle of artificial obsolescence the most obvious example of this is the mobile phone industry with new styles of models being produced annually accompanied by aggressive advertising and mobile phone contracts targeted at specific ages to encourage an annual change over to newer models. This creates an unnecessary increase in unwanted phones which have to be recycled. As much as 4,000 tonnes of toxic e-waste is discarded every hour. The demand for raw materials in the electronics industry is rising and the need for recycling is increasing as the Earth s natural resources decrease. All electronic devices are connected by either copper strips on a board or by plastic coated copper wires. Copper extraction uses a great deal of the world s resources and modern methods of extraction scar the landscape. The natural resources used today in the extraction of copper are:- Up to 500 gallons of fresh water per second Copper mining also has a bad reputation because of the sulphuric acid produced when its solid waste are exposed to air and water. Combined with metals such as lead, arsenic, and cadmium, the solid waste is highly toxic to plants, wildlife and people. 6

7 There are 19 elements which make up an average computer and 11 of these are toxic. Toxic materials Antimony Arsenic Barium Beryllium Cadmium Chromium Cobalt Gallium Lead Mercury Palladium Non toxic materials Aluminium Copper Gold Iron Platinum Silver Tin Zinc The average life time of a mobile phone if it is not recycled in some way is only 12 to 18 months (contract length). For the average computer it is 3 to 5 years before replaced. being The requirement for recycling of electronic devices means that specialised companies have developed to extract the valuable materials from the waste devices. However gangs of criminals, posing as computer recycling firms, are dumping hundreds of containers full of broken computer equipment in the developing world and China every week where the methods of recycling are not only primitive but also very dangerous to the workers extracting the materials from the electronic devices. 7

8 To recover copper from e-waste, for instance, wires are pulled out, piled up and burned to remove the insulation covering the copper. This emits dioxins and other pollutants. Toxic cyanide and acids used to remove gold from circuit boards of junked computers also are released into the environment. Essential reading 8

9 After reading and completing further research about recycling and the handling of e-waste one of your assessment tasks in the course will be: At National 4 level: You are to give a presentation to the directors of your electronics company about: safe disposal of your waste electronic devices increasing use of electronic devices and where your company could get involved in expanding markets Use the internet and other sources to research these two topics. Sources must be retrievable. You must include: at least 2 specific examples of appropriate disposal methods for used electronic devices at least 2 specific examples of increasing uses of electronic devices You may present your findings in any format, such as a poster, slideshow, podcast or video. At National 5 level You are to give a presentation to the directors of your electronics company about: recycling pathways for electronic devices. social, environmental and economic impacts of the increasing use and miniaturisation of electronic devices Use the internet and other sources to research these two topics. You must include: at least two specific examples of recycling pathways for used electronic devices at least one specific example of increasing uses and miniaturisations of electronic devices, and at least one social impact at least one environmental impact, and at least one economic impact You may present your findings in any format, such as a poster, slideshow, podcast or video. 9

10 Basic Electronics In electronics we use 4 basic quantities:- Voltage which is the energy given to charge to move through the circuit and is measured in volts (V). Current which is the amount of charge passing a point in 1 second and is measured in Amperes (A). In this course the currents we use in electronics are small and we use the milliampere (ma) as the unit of current. There are 1000mA in 1 A. Resistance which is a measure of how difficult it is to move charge through a component (how much energy is used moving charge thorough the component. Resistance can be calculated from the voltage across a component and the current passing through the component. In the National 5 course we also study: Power is rate at which energy is transferred per second and is measured in Watts (W). Resistors dissipate or lose energy in the form of heat. As current passes through a resistor the resistor will become warm. With small currents this heating effect is not noticeable however as the current increases there comes a point at which the resistor begins to degrade. All resistors are rated according to a limiting power value. The resistors you will use in the course are rated at ¼ Watt this can also be written as 0.25W. We use a multimeter to measure all these quantities except power. 10

11 The Multi-meter. You will be using a digital multimeter similar to the one shown below: Insert pic of yellow multimeter here The digital multimeter has an internal battery to power its circuitry and an internal fuse to protect its circuits from excessive current. Basic multimeters can measure a variety of electrical quantities such as:- voltage current resistance More expensive and elaborate multimeters can measure more electrical quantities such as AC Current, capacitance and frequency and the hfe of transistors. The multimeter has 3 input sockets:- Com or common socket is always connected regardless of which quantity or range has been selected. 10 A should only be used to measure currents up to a maximum of 10 Amperes (commonly referred to as Amps). V Ω ma for small currents of less than 200 milliamperes, voltage and resistance. The maximum DC current which can be measured using the V A Ω socket is 200 milliamperes or 200 ma or 200 m. If you exceed this maximum value the internal fuse will blow and the meter will cease to measure the current in this set of ranges. However it will still measure the current on the 10 Ampere scale. The direct current or DC settings are marked by the symbol 11

12 Colours 1st colour band 2nd colour band 3rd colurnn No of zero's 4th colour band tolerance black 0 0 none brown 1 1 O brown 1% red 2 2 OO red 2% orange 3 3 OOO orange 3% yellow 4 4 OOOO yellow 4% green 5 5 OOOOO gold 5% blue 6 6 OOOOOO silver 10% violet 7 7 grey 8 8 white 9 9 Look at the resistor below the colour bands are Red violet brown gold The value of this resistor is /- 5% 270 Ω +/- 13 Ω So although you use the resistor at its stated (or nominal) value of 270 Ω in reality it can have any value between 257 Ω and 283 Ω This resistor has brown / black / orange and gold band Resistance value is Ω +/- 5% Stated value is 10,000 Ω 12

13 In electronics, resistor values are written slightly differently this is to reduce the chance of an incorrect value of resistor being inserted and causing damage the rest of the circuit. Resistor Resistance value (Ω) 100R R R 680 1K K K K K K M Now using the table above as a guide, copy and complete the table below: Resistor Resistance Value (Ω)

14 Measuring resistance When you make a resistance measurement you are using the internal battery of the multimeter to pass a small current through the resistor or component being tested. The display on basic models is usually only three or four digits, so you have to think about selecting the most suitable range on the multimeter. If the multimeter shown above was connected to a 1K2 resistor the display would show the following reading at each of these settings: Resistance range selected Resistance value displayed 200k k The final reading displayed indicates that the resistance value is higher than the range selected so the most accurate range to use would be the 2000 Ω range and the reading would be 1200 Ω. When measuring an unknown resistor you would always start with the largest range and then move the range dial until the display shows you then go up a range and this is the most accurate range /reading. 1 14

15 Imagine you have been given a resistor which is nominally 1K5 and you are asked to measure its actual resistance value then the multimeter would display the following readings as you selected lower ranges on the meter. Actual value is 1524 Ω You will be provided with a set of five resistors of unknown value. Using your multimeter: Resistance range selected Resistance value displayed 200k k always start at the highest resistance range work your way down the ranges until you have the correct value. measure the resistance value of each resistor noting the most accurate resistance in the table below. resistor Resistor range selected actual resistance Ω Note. The display on the meter will indicate if your range setting is too low! 1 15

16 Measuring Voltages Before making a voltage measurement you have to select from one of two ranges: AC voltage or DC voltage. In this unit you are measuring DC voltage only. So the correct set of ranges has to be selected. Remember that the common symbol used for DC voltage on multimeters is so you must select the ranges marked V The test leads should be connected to the common (COM) and the socket marked for current voltage and resistance (VΩ ma). Do not use the 10A socket! The multimeter display on basic models is usually only three or four digits and so you always have to think when you are using the multimeter. For example when you are measuring a voltage on a multimeter with a set of voltage ranges as shown above. If the multimeter shown above was connected to a 1.253V DC supply the display would show the following reading at each of these settings: On the voltage ranges there are 2 ranges which display the voltage in millivolts (mv). 1 volt = 1000 mv On the last range the voltage under test is greater than the maximum value on this range so the meter indicates this by the display multimeter range selected voltage displayed on multimeter OO1 200 OO mV mV 1 16

17 Connect the multimeter to the power supply unit ( PSU ) select the highest voltage range, Now switch on the PSU select the most accurate voltage range and measure the actual voltage output from the PSU entering it in the table below Repeat for different PSU voltage settings. PSU voltage multimeter range selected voltage displayed on multimeter When you test or measure voltage across components or at various points in a circuit you must remember that the circuit is live! You must always take great care when working with a multimeter on a live circuit. Select the correct voltage range. Do not touch the circuit under test with your hands. Use suitable size and types of test leads or connectors so that you do not shortcircuit components or wiring. If you are measuring the voltage near to a capacitor be careful that you do not short out the legs of the capacitor and discharge it. Never test circuits which involve either mains voltage or high voltages Remember you are only using power supplies up to a maximum of 12 volts DC. 17

18 Measuring current The circuitry in your multimeter is protected from large currents by an internal fuse, usually a 500mA fuse. This means that as soon as the current flowing through the meter reaches 500mA or 0.5A, the fuse will break protecting the sensitive circuitry inside the multimeter. As soon as the fuse has blown, the DC ranges will cease to function with the exception of the 10A circuit. You will then have to replace the fuse before continuing to use the multimeter to measure current in all the scales below 10 amperes. With many types of multimeters it is not easy or quick to change an internal fuse! In some meters you have to undo four screws and remove part of the casing before you can access the fuse. This is very important to remember, as a current of only just over 500mA is not uncommon in some circuits. Current ranges: 10A connect to 10A socket and common socket. All the ranges listed below are connected to the V ma socket and the common socket. These ranges are protected by the internal fuse. 200mA 20mA 2mA 200μA Note 0 to 200mA range 0 to 20mA range 0 to 2mA range 0 to 200μA range 2000μ is only 2mA 200μ is only 0.2mA So you must be very careful when using current scales to avoid blowing the fuse. 18

19 How current, voltage and resistance are related. Set up the circuit shown below: Now add in the battery and an ammeter and voltmeter as shown in the picture and circuit diagram. The meters have been labelled to make the layout easier to understand. 19

20 The circuit diagram looks like this Now take your screwdriver as shown and turn the adjuster on the variable resistor fully to the left (anticlockwise) and record the voltage and current readings in the table below. Re-adjust the variable resistor and record the meter readings. Repeat this 6 more times. (Remember your current is in milliamperes) Voltage Current Current (volts) (ma) (A) Voltage / Current 1 Your current readings have been measured in ma so to convert to amperes you must divide by 1000 and enter your answer in the Current (A) column. 2 Now divide the voltage by the current (A) and put the answer in the end column. 3 Repeat for all your readings. What do you notice about the values in the end column? Now measure the value of the resistor with a multimeter and write the answer in the box. How does the measured value of the resistor compare with the values calculated in the end column? 20

21 National 5 You have now shown that Voltage Current = Resistance Voltage must be measured in volts (V) Current must be measured in amperes (A) This will give a resistance which is measured in Ohms (Ω) This relationship can be written as R = V / I In science or engineering this is known as Ohm s Law and is usually written as V = I R Now calculate the resistance of the following circuits. Voltage = Current = Current = V ma A R = V / I Voltage = Current = Current = V ma A R = V / I 21

22 When you use more than one resistor in a circuit they can be connected in 2 different ways Series or Parallel Measuring the resistance value of resistors in series Measure the resistance of resistor 1 as shown being careful about your selection of resistance range to get the most accurate value. Record the resistance value of R1 in the table below. Repeat for resistor R2 and record the resistance in the table below. Connect the two resistors in series as shown and record the combined resistance of R1 and R2 in the third column of your table. Resistance R1 Resistance R2 Resistance R1 and R2 R1 + R2 ( ) ( ) ( ) ( ). In the fourth column headed R1+R2 add up the resistance values you have measured for R1 and R2 then put the total in this column. Repeat the above measurements for four more sets of resistors. Do you notice anything about the size of the resistances in the third and fourth columns? This can be written as R total = 22

23 Measuring the resistance value of resistors in parallel Measure the resistance of resistor 1 as shown below (being careful about your selection of resistance range to get the most accurate value). Record the resistance value of R1 in the table below. Repeat for resistor R2 and record the resistance in the table below. Connect the two resistors in parallel as shown in the diagram and record the combined resistance of R1 and R2 in the third column of your table. Resistance R1 (Ω) Resistance R2 (Ω) Resistance R1 and R2 in parallel (Ω) What conclusion can you make about total resistance of two resistors in parallel? You should have noticed two patterns or trends in your results if you have measured the resistances correctly! The patterns are: The total resistance is always smaller than the smallest value of resistor used in the parallel circuit. If two resistors of the same value are used then the total resistance is half the value of one of the resistors. However you can calculate the total resistance of resistors connected in parallel using this formula 1 / RTotal = 1 / R1 + 1 / R2 23

24 The 555 Timer You may wonder what is inside the 555 timer chip or what makes it work. Well, the 555 timer chip an Integrated Circuit (IC) and therefore it contains a miniaturised circuit surrounded by silicon. Each of the pins is connected to the circuit which consists of over 20 transistors, 2 diodes and 15 resistors. Do you notice the three (5k) resistors? This is how the chip got its name. An Overview of the 555 Timer The 555 Integrated Circuit (IC) is an easy to use timer that has many applications. It is widely used in electronic circuits. A 'dual' version called the 556 is also available which includes two independent 555 ICs in one package. The following illustration shows both the 555 (8-pin) and the 556 (14-pin). 24

25 In a circuit diagram the 555 timer chip is often drawn like the illustration below. Notice how the pins are not in the same order as the actual chip, this is because it is much easier to recognize the function of each pin, and makes drawing circuit diagrams much easier. The power supply can have a value from 4.5 to 15v, with 18v the absolute maximum which can be used. Using the Output of a 555 Timer The output (Pin 3) of the 555 can be in one of two states at any time, which means it is a digital output. It can be connected directly to the inputs of other digital ICs, or it can control other devices with the help of a few extra components. The first state is the 'low' state, which is the voltage 0V at the power supply. The second state is the 'high' state, which is the voltage Vcc at the power supply. Sinking and Sourcing When the Output goes low, current will flow through the device and switch it on. This is called 'sinking' current because the current is sourced from Vcc (pin 8) and flows through the device and the 555 to 0V. When the Output goes high, current will flow through the device and switch it on. This is called 'sourcing' current because the current is sourced from the 555 and flows through the device to 0V (pin 1). Sinking and sourcing can also be used together so that two devices can be alternately switched on and off. 25

26 The device(s) could be anything that can be switched on and off, such as LEDs, lamps, relays, motors or electromagnets. Unfortunately, these devices have to be connected to the Output in different ways because the Output of the 555 can only source or sink a current of up to 200mA. Make sure your power supply can provide enough current for both the device and the 555; otherwise the timing of the 555 will be affected. In the simulated circuits below the LED flashes on and off A typical sinking circuit simulation A typical sourcing circuit simulation A typical sinking and sourcing circuit The LEDs flash alternately (this means the when the top LED is on the bottom LED is off and vice versa). The 555 has three main operating modes, one of which is the Astable, mode. 26

27 Astable mode An Astable Circuit has no stable state - hence the name "astable". The output continually switches state between high and low without any intervention from the user, producing what is called a 'square' wave. This type of circuit could be used to give a mechanism intermittent motion by switching a motor on and off at regular intervals. It can also be used to flash lamps and LEDs, and is useful as a 'clock' pulse for other digital ICs and circuits. We will use a version of this circuit this in our flashing lights circuit in National 4 assessment task 3 and in the Practical Activity Cycle lights at National 5 level 27

28 Pin Configuration of the 555 Timer Here is the identification for each pin: Pin 1 (Ground): Connects to the 0v power supply. Pin 2 (Trigger): Detects 1/3 of rail voltage to make output HIGH. Pin 2 has control over pin 6. If pin 2 is LOW, and pin 6 LOW, output goes and stays HIGH. If pin 6 HIGH, and pin 2 goes LOW, output goes LOW while pin 2 LOW. This pin has a very high impedance (about 10M) and will trigger with about 1uA. Pin 3 (Output): (Pins 3 and 7 are "in phase.") Goes HIGH (about 2v less than rail) and LOW (about 0.5v less than 0v) and will deliver up to 200mA. Pin 4 (Reset): Internally connected HIGH via 100k. Must be taken below 0.8v to reset the chip. Pin 5 (Control): A voltage applied to this pin will vary the timing of the RC network (quite considerably). Pin 6 (Threshold): Detects 2/3 of rail voltage to make output LOW only if pin 2 is HIGH. This pin has a very high resistance (about 10M) and will trigger with about 0.2uA. 28

29 Pin 7 (Discharge): Goes LOW when pin 6 detects 2/3 rail voltage but pin 2 must be HIGH. If pin 2 is HIGH, pin 6 can be HIGH or LOW and pin 7 remains LOW. Goes OPEN (HIGH) and stays HIGH when pin 2 detects 1/3 rail voltage (even as a LOW pulse) when pin 6 is LOW. (Pins 7 and 3 are "in phase.") Pin 7 is equal to pin 3 but pin 7 does not go high - it goes OPEN. But it goes LOW and will sink about 200mA. Pin 8 (Supply): Connects to the positive power supply (Vcc). This can be any voltage between 4.5V and 15V DC, but is commonly 5V DC when working with digital ICs. 29

30 Appendix 1 National 4 / 5 Logic gate pin out diagrams Both National 4 and 5 will use these three gates Quad 2-input OR Gate 7432 Key: A1 inputa to first gate A2 input B to first gate Q1 output from first gate Inverter or NOT Gate 7404 Quad 2-input AND Gate

31 Quad 2-input NAND Gate 7400 / These 3 gates are used only in the National 5 course Quad 2-input NOR Gate 7402 Quad 2-input XOR Gate