Revised Standard Grade Technological Studies Applied Electronics Contents Introduction Structure Resources Assessment Detailed resource list Component Electronic Systems Electricity Simple Circuits Integrated Circuits: 555 timer Modular Electronic Systems Introduction: Electronics – a systematic approach Modular boards Analogue and digital signals Problem solving in electronics Switches Truth tables The comparator NAND and NOR gate boards Logic in Electronics Switching logic Binary numbers Combinational logic Pin-out diagrams Practical tasks Electronics Mini-Project Introduction Application of Technology Example: Remote Controlled Buggy with Light and Sound Computer simulation Appendix 1: Infrared Remote Control Remote controlled toy ii iii iii iv iv vi 1 3 14 77 81 85 86 88 95 98 101 115 117 119 121 130 132 147 150 157 157 158 159 161 165 169 Standard Grade Technological Studies: Applied Electronics Introduction Electronics is a key influence in today’s society and is therefore a key area of study in Technological Studies. This component unit should be studied early in the course after pupils have some knowledge of systems. Structure This unit is split into three distinct sections: Component Electronic Systems Modular Electronic Systems Logic in Electronics. These sections can be delivered in any order, with each approach having its own advantages and disadvantages. Obviously there is some overlap between the units. For example, logic appears in the Modular Systems section in the form of the inverter, the OR, AND, NAND and NOR gates and as subsystem boards. Similarly, if the Modular Systems section is delivered first then some areas of Component Systems are mentioned. The advantage of delivering the Modular Systems first is that it gives an easy introduction to electronics; however, there is a danger that pupils will work through this section and solve the problems without picking up a real understanding of electronics. Logic Systems naturally follows on from the Modular Systems section. The advantage of delivering the Component Systems first is that the pupils gain a firm understanding of electronics, components and circuits. This gives them a deeper understanding, which helps in the subsequent sections. The disadvantage is that pupils may find the theory contained in this section difficult early in the course, although as they are General/Credit pupils the level should be well within their ability. By delivering the Component Systems first, pupils will cover the use of multimeters and prototype circuit boards that are used in the other sections. If the Component Systems section is to be delivered last, then it will be necessary to give the pupils some instruction in the use of multimeters, prototype circuit boards, simple electronic theory and components. The contents of this unit are set out comprehensively so that teachers do not require the use of additional notes or textbooks. Pupils can move at their own pace in many areas, but it must be stressed that these unit notes should not be used as an open learning pack and it will be necessary to deliver many important lessons at crucial times. These include an introduction to electrical theory (Ohm’s law, Kirchoff’s second law, etc.), series circuits, parallel circuits, and an introduction to components (recognition, use and characteristics). Standard Grade Technological Studies: Applied Electronics iii Resources The resources required to run this unit are the same as those being used in Technological Studies at present. Some equipment may differ in type (for example different meters, prototype boards and modular systems) and therefore the notes provided will have to be interpreted differently. The main resources are: a range of components prototype circuit boards (often referred to as breadboards) digital non-auto ranging multimeters a modular electronic system (for example E&L boards) circuit simulation software (for example, Crocodile Clips). Circuit simulation software can be used for many of the activities but pupils must also have experience of building physical circuits. This is necessary to experience the real components as well as the problem-solving attached to building real circuits. Teachers are encouraged to use other resources such as video and the interactive CDROMs that are available. Software that simulates Modular Systems is also available and could be used to aid classroom management problems that arise from faulty boards. A detailed list of resources is provided at the end of this introductory section. Assessment External This unit of work and the exercises within will prepare the pupils for any electronics questions that appear in the 90-minute exam at the end of the course. It will enable all pupils to gain the knowledge and understanding required and give them suitable practice in reasoning and numerical analysis. Internal The internal assessment of this unit requires pupils to carry out a structured assignment. The assignment should take approximately three hours to complete but in some circumstances this can be extended. The pupils will be expected to: complete a specification from a given brief create appropriate diagrams to illustrate the problem parameters produce a graphical representation of a proposed solution perform a computer simulation of the proposed solution build and test the proposed solution evaluate the solution against the original specification. It must be stressed that this is not like the existing main project report. iv Standard Grade Technological Studies: Applied Electronics Example The pump motor in an automatic heating system is designed to be on all the time, day or night, unless it gets too hot in the daytime. Design a system that drives the pump motor constantly except when it is hot during the day. For this assessment problem, pupils would be expected to produce: a limited specification from the information in the brief a system diagram illustrating the parameters diagram(s) showing a proposed solution using modular boards or a discrete component circuit a parts/component list from classroom resources a computer simulation using Crocodile Clips or other suitable simulation software a physical solution to the problem a small written evaluation comparing the performance of the solution to the specification. Further information on the internal assessment can be found in Appendix 1 of the Arrangement Documents: Guidelines for Internal Assessment. Standard Grade Technological Studies: Applied Electronics v Detailed resource list Relay Miniature 5 V DPDT (RS 376-981) Component electronics systems Low voltage power supply Integrated circuit 555 timer IC Prototype circuit boards Digital multimeter (non-auto-ranging) Resistors 100 R 220 R 270 R 390 R 1K Light-dependent (LDR) ORP 12 Thermistor: ntc (RS 256-102) Computer simulation software Crocodile Clips Modular electronic systems Modular circuit board systems E&L, or Alpha systems Simulation software Control Studio Potentiometers 10 K (RS 375-304) 100 K (RS 375-332) Logic in electronics Transistors BC 108 Modular circuit board system E&L, or Alpha systems Diodes Light-emitting 5mm red 1N4001 (RS 261-148) Computer simulation software Crocodile Clips Capacitors 100 F electrolytic 1 F bead Low-voltage power supply Switches Miniature push (RS 331-758) Miniature slide (RS 339-673) Prototype circuit board Logic probe Lamp Holder (RS 564-891) MES lamp 6 V (RS 586-172) MES lamp 12 V (RS 586-201) Buzzer Piezo flying lead (RS 203-0233) Motor 36 volt miniature vi Resistors 220 R Diodes Light-emitting 5 mm red Integrated circuits (TTL) 7400 7408 7432 7404 Standard Grade Technological Studies: Applied Electronics Component Electronic Systems Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems 1 Contents Electricity Simple Circuits Integrated Circuits: 555 timer 2 3 14 77 Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems Electricity Introduction Electricity is one of the most important forms of energy available to man. It affects everyone’s lives in many ways. If you take time to think about your everyday life you will realise that our lives are full of devices that depend upon electricity. These devices depend on the electrical circuits inside them to work. The circuits often change the electrical energy into other forms of energy such as heat, light and sound. In this area of study you will learn how these circuits work and about the different components within them. Electric circuits An electric circuit is a closed loop or network made up of electrical components such as batteries, bulbs, switches and wires. Switch Battery Lamp Electric current Electric current is the name given to the flow of negatively charged particles called electrons. e le c tr o n s Current is measured in amperes, usually referred to as ‘amps’ (A). Current is the rate of flow of electrical charges (called electrons) through a circuit. Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems 3 Voltage In most circuits a battery or voltage supply is used to drive the electrons through the components. Voltage is measured in volts (V). + V _ Current Flow R Resistance All materials conduct electricity. The materials that conduct electricity well are called conductors and those that are poor conductors are called insulators. Metals are good conductors while rubber and glass are good insulators. A good conductor offers very little resistance to the flow of electrical current. In other words, it lets currents flow with very little voltage being applied. Resistance is therefore a measure of how much voltage is required to let a current flow. Resistance is measured in ohms (). Electron flow conventional current Scientists in the early nineteenth century decided the direction of conventional current flow. It seemed to them that current flowed from the positive side of power supplies to the negative side. It was not until the twentieth century that electrons were discovered and the true direction of current flow was proved. As stated earlier, electric current is the flow of electrons but often it is more useful to consider electric current to flow in the opposite direction. This is called conventional current. So although it is technically wrong, for convenience ‘conventional current’ will be used in the circuits and calculations throughout this work. + V _ Conventional Current R Conventional current flows from positive to negative. One of the main reasons for maintaining this convention is that symbols and other data based on conventional current have become standard. 4 Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems Batteries and voltage supplies Batteries and voltage supplies are the source of power behind all electrical circuits. Without a power source, electrical circuits will not work. In your work (as in most electronic circuits) all power sources will be low-voltage this normally means everyday batteries or a low-voltage power supply. The low-voltage supplies and batteries will normally supply between three and 12 volts. Electronic components normally work on much lower voltages and so the circuits must be designed carefully. The symbols for batteries and voltage supplies are as follows. Single battery or cell Multiple batteries or cells Voltage supply 6 volts Note the positive and negative side of the battery: -v e +v e Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems 5 Direct current (d.c.) The voltage supplied by batteries or low-voltage supplies is direct current (d.c.). This is the normal type of supply to low-voltage circuits. Alternating current (a.c.) supplies are high-voltage usually 230 volts. This is the normal supply in homes and schools. Many portable electric power tools work from 110 volts for safety. Resistors Resistors are basic components in electrical and electronic circuits. They limit the amount of current flowing in circuits or parts of circuits. Resistors are roughly cylindrical and have coloured stripes. They also have connection wires sticking out of each end. The stripes indicate the value of the resistors. The colours represent numerical values according to a special code. 6 Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems Resistor colour code Resistors are marked with what is known as a resistor colour code. Each band that surrounds the body of the resistor helps identify the value (in ohms) and the tolerance (in per cent). In most resistors only four colour bands are used. The colour code chart for resistors is shown below. The colours are used to represent different numbers, and in this way we are able to tell the value for each digit. First and second colour band Digit Black 0 x1 Brown 1 x 10 Red 2 x 100 Orange 3 x 1000 or 1 K Yellow 4 x 10 000 or 10 K Green 5 x 100 000 or 100 K Blue 6 x 1 000 000 or 1 M Violet 7 Silver means divide by 100 Grey 8 Gold means divide by 10 9 Tolerances: brown 1% red 2% gold 5% silver 10% none 20% White Multiplier Standard values Resistors are supplied in a range of standard values: 1.0, 2.2, 3.3, 4.7, 5.6, 6.8, 7.5, 8.2 and 9.1. These standard values can then be multiplied by 10, 100, 1000, and so on. Typical values of resistors are 220 R, 100 K, 680 R, etc. Some other popular sizes are also available, such as 270 R and 390 R. Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems 7 4-band resistor colour code layout 4 Band Resistor Colour Code Layout 1st band 1st digit 4th band tolerance 2nd band 2nd digit 3rd band multiplier Example If the colours on the above resistor are: 1st band red 2nd band violet 3rd band brown 4th band gold then using the table on the previous page, the value of this resistor is 270 and its tolerance is 10 per cent. This is worked out as ‘2’ for the red first band, ‘7’ for the violet second band and ‘times 10’ for the brown third band. For most purposes you can ignore the tolerance. In the above example the manufacturers guarantee that the resistor will not vary from the marked resistance by more than 10 per cent. Symbol for resistance Although the symbol for ohms is ‘’ it is often shown as a capital R; that is, 270 ohms can be expressed as either 270 or 270 R. 8 Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems Using the resistor colour code Using the resistor colour code chart, record the resistance values of the following resistors. Write your answers in your normal report notes/jotter. 1. 100 R 10 blue – violet – brown – silver 2. 3 K9 2 orange – white – brown – gold 3. 100 K 10 brown – black – red – gold 4. M2 5 brown – black – green – brown Draw and note the colours of the resistors below. Use colour pencils to show the correct colour bands. Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems 9 Exercises 1. Using the colour-code chart, determine the colours of the first three bands of the following resistors. No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Value 270 R 1 K5 33 K 1 M2 330 R 150 R 82 K 560 R 6 K8 750 R 390 R 2 M1 82 R 4700 R 9 K1 Colour 2. Using the colour-coding code, calculate the values of the following resistors. No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 10 Value First three colour bands red red red yellow violet black grey red red yellow violet orange red red orange orange orange orange green blue brown red violet black grey red brown brown green green brown grey yellow brown black yellow green blue orange brown grey black brown grey green blue grey orange orange orange yellow red red brown grey red black violet brown orange Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems Diodes Diodes are devices that allow current to flow in one direction only. Current can pass this way only Anode Cathode Symbol for Diode Current will flow through the diode only when the anode (positive side) is connected to the positive side of the circuit and the cathode (negative side) is connected to the negative side of the circuit. Light-emitting diodes A light-emitting diode is a special diode that gives out light when current is flowing though it. LEDs are used as indicators to tell when a circuit (or part or a circuit) is working. You can tell the cathode of an LED as it is the short leg and there is a ‘flat’ on the plastic casing. -ve As with the normal diode, the current can only pass one way. Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems 11 Switches Switches are useful input devices (or transducers) that have metal contacts inside them to allow current to pass when then they are touching. There are several ways in which the contacts in mechanical switches can be operated. The main types are push-button, toggle, key, slide, magnetic (reed) and tilt. These switches are ‘digital’ input devices as they can only be on or off. Toggle Slide Key Tilt Rocker Reed The switches shown above are all single pole with single or double throws. These are known as SPST and SPDT switches. The symbols are shown below. 12 Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems 13 Microswitches Microswitches are small switches that are useful for detecting motion. They are especially good as sensors and limit switches. Typical systems that use microswitches are traffic barriers and lift systems. The microswitch above has a roller fixed to a lever that detects movement and throws the switch. It has three terminals: common, normally open (NO) and normally closed (NC). The microswitch below is commonly used in schools. 3 -- NO 1 -- C 2 -- NC Like most microswitches, this one can be wired in three ways. C and NO: this is a normal on/off switch. C and NC: this allows current to flow when the switch is not operated. C, NC and NO: when wired like this it acts as a changeover switch. These microswitches are single-pole double-throw (SPDT) switches. 14 Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems Simple Circuits Series circuits The diagram below shows a typical use for an LED circuit, where the LED indicates that the car radio/cassette is on. The diagram also shows a simplified series circuit layout for the LED indicator. The resistor is necessary to protect the LED from drawing too much current and ‘blowing’. The diagram below shows the above circuit using the component’s symbols. This is called the circuit diagram. Switch I 6V LED The components in this circuit are connected in series. This means that they are connected up in a line, one after the other (or end to end). Series circuits are the simplest to deal with as the same current flows through all of the components. The voltage, however, is divided up between the components – more of this later. Standard Grade Technological Studies: Applied Electronics – Component Electronic Systems 15