Practical Electronic Circuits: A Strong Foundation for Creating Electronic ProjectsPractical Electronic Circuits: A Strong Foundation for Creating Electronic Projects

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Practical Electronic Circuits A Strong Foundation for Creating Electronic Projects By A. B. Lawal Copyright © 2019 by AB Prominent Publisher All rights reserved. ISBN: 9788835341215 Published in the United States Limit of Liability/Disclaimer of Warranty All information given in this book is based on my own research and does not constitute technical or financial advice. The author and publisher cannot be held responsible for the consequences of actions taken, or any consequences through inaction, as a direct or indirect result of the information in this book. All information is used at your own risk. Whilst all content is checked for accuracy, no information contained within this book or in any of its links is to be used without taking technical, professional and marketing advice first. Anyone seeking advice should consult an Independent Advisor. The author of this book is not liable or responsible for any other websites or services linked to or from it. It is forbidden to reproduce any part of this book in any form or medium. Reselling is prohibited. Table of Contents Preface About the Author 1. Fundamentals of Electronic Circuits 1.1 Power Supplies & Electronic Signals 1.1.1 Power Supply 1.1.2 Electronic Signal 1.2 Electricity: Charges & Current 1.2.1 Electric Charge 1.2.2 Electric Current 1.2.3 Current Drawn By Common Electronic Devices 1.3 Electric Voltage, Grounds & Power 1.3.1 Electric Voltage 1.3.2 Grounds 1.3.3 Electric Power 1.3.4 Electric Heat 1.4 Conductors, Resistors & Semiconductors 1.4.1 Conductors, Insulators & Resistivity 1.4.2 Electrical Resistance & Resistivity

1.4.3 Conductivity 1.4.4 Good Conductors, Poor Conductors & Semiconductors 1.4.5 Semiconductors 1.5 Resistor Symbols, Types & Color Codes 1.5.1 Active & Passive Components 1.5.2 Resistor Symbols 1.5.3 Ohm’s Law 1.5.4 Types of Resistors 1.5.5 Thermistor 1.5.6 Varistor Resistor 1.5.7 LDR (Light Dependent Resistors) or Photo Resistor 1.5.8 Surface Mount Resistor (SMD) 1.5.9 Standard Resistors 1.5.10 Resistor Tolerance 1.5.11 The E-Series 1.5.12 How to Read Resistor Color Codes 1.5.13 How to Read 4-Color Coded Resistors 1.5.14 Zero-Ohm Resistor Practice Exercise 1: Reading Color Codes 1.5.15 How to Read 5-Color Coded Resistors 1.5.16 How to Read 5-Color Coded Resistors with Reliability Band 1.5.17 How to Read the Color Codes of Surface-Mount (SMD) Resistors 1.5.18 How to Read 6-Color Coded Resistors with TCR 1.5.19 How to Understand Resistor Power Ratings Practice Exercise 2: Building a Current-Limiting Circuit for an LED 1.6 Resistor Networks: Series & Parallel Combinations 1.6.1 The Series Combination 1.6.2 The Parallel Combination 1.6.3 The Voltage Divider Circuit: How to Use Resistors to Tap Voltages Practice Exercise 3: Building Resistor Networks & Divider Circuit 1.7 Open, Closed & Short Circuits 1.7.1 Difference Between Open & Closed Circuits 1.7.2 Short Circuits & Dangers of Overloading 1.8 Electrostatic Charge Protection

1.8.1 How to Protect Electronic Components from Static Discharges 1.9 Electronic Switches 1.9.1 Categories of Switches 1.9.2 Types of Switches Practice Exercise 4: Using DPDT Switch to Control Light & Alarm Circuits 1.10 Understanding Wires, Cables & Wire Gauges 1.10.1 Difference Between Wire & Cable 1.10.2 Wire Gauges 1.10.3 Types of Cables Used in Electronics & Telecommunication 1. How to Set up A Modest Workshop for Yourself 2.1 Where You Can Set up A Modest Workshop 2.1.1 The Essential Ingredients of a Good Workshop 2.2 The Basic Hand Tools for Your Workshop 2.3 Basic Electronic Components for Your Workshop 1. Workshop Safety: How to Stay Safe 3.1 General Workshop Safety 3.2 Personal Workshop Safety 3.2.1 Soldering Safety 3.3 Safety from Unexpected High Voltages 1. More Helpful Resources Conclusion Preface This book Practical Electronic Circuits: A Strong Foundation for Creating Electronic Projects is designed to provide skills and a hands-on practical experience for students of electronic engineering and computer science. It also provides a good foundation for anyone interested in learning how to create electronic projects. Electronics curricula are densely packed in many engineering and computer science colleges. This book therefore is a great help because it treats each topic thoroughly. So it is a great companion. The book will be of great help for your electronics education because it is filled with simple and moderately complex practical projects. Links to stores where you can get very cheap electronic parts to work with are also included. You will also learn how to be safe in your workspace, and how to develop the courage you need to carry out any electronic project. A step by step approach is used to explain the process of carrying out an electronic project. This book is also a great value for every electronics students undergoing technical training. It encourages them through providing useful technical advice needed in a highly practical environment, with a clearly defined problem so they do not get stuck while building even complex projects. About the Author A. B. Lawal is a control and instrumentation Engineer. He also has a master’s degree in computer science. He worked for a couple telecommunication companies for over 10 years before becoming a lecturer in a prestigious engineering college in the United States. He is currently involved in evaluation, revision, redesign, and expansion of electronic systems and technically related computer programs. 1. Fundamentals of Electronic Circuits

1.1 Power Supplies & Electronic Signals In this chapter, I lay some important groundwork that you need to make sense of the rest of the book. I examine the bits and pieces that make up the most common types of electronic devices, and that make electronic circuits in general to work. All electronic and electrical devices, from the simplest flashlight to the giant and complex control systems on a modern aircraft, all need one thing in common: power supply . 1.1.1 Power Supply A power supply is a source of electricity, or more precisely, a source of electrons . Without power supply, an electronic device is all just a pile of inactive plastic, metal or silicon (among other things). A few examples of power supplies are batteries, power adaptors for charging your mobile phones and laptop computers and so on. Fig. 1.1.1 shows a power supply built by assembling a few batteries. However, a power supply itself can be built with electronic devices, such as shown in Fig. 1.1.2 and Fig. 1.1.3 .

Fig. 1.1.1: 12V DC Battery Power Supply: Source:

Fig. 1.1.2: A Laptop Charger. Source:

Fig. 1.1.3: Power supply of a desktop computer. Source: Next, I take a look at the basic concept underlying all electronic circuits: signals . I’m not going to bore you with any complicated or tedious or physics concepts, but I want to warn you from the start. In order to learn how electronic circuits work and get to a level where you can design and build your own electronic devices, you need to have at least a basic idea of what a signal is. So put on your thinking cap and come with me. Fig. 1.1.4 shows various symbols used for representing DC and AC power sources in electronic circuits. The positive terminal of a DC power supply is usually represented by “ +” while the negative terminal is represented by “ ─‘’ .

Fig. 1.1.4. various symbols for circuit power supplies As shown in Fig. 1.1.4, the + terminal of bi-polar junction transistor circuits is often represented by V CC , while the + terminal of FET and MOSFET circuits is often represented by V DD . We will look at FET (field effect transistor) and MOSFET (metal-oxide-semiconductor transistor) circuits later. 1.1.2 Electronic Signal In the field of electronics, a signal is an electric current or electromagnetic field used to transmit data from one place to another. DC ( Direct Current ) is the simplest form of signal because it travels in only one direction so it can be switched on or off. It is the principle behind the working of the early telegraph . AC ( Alternating Current ) on the other hand is a type of current that pulsates or changes direction periodically. Electronic devices process AC signals very often. Such signals are electromagnetic carriers of one or more data streams. Fig. 1.1.5 shows graphical representations of DC and AC signals.

Fig. 1.1.5: DC signal (left) and AC signal (right). A very common source of alternating current is the mains , which is usually obtained from the electric sockets on the walls of your room or office. Mains is usually supplied by the electric power authority in your locality. Fig. 1.1.6 .

Fig. 1.1.6: Mains sockets. Source: Before I move on to the next section I must mention that the oscilloscope is a very good example of both DC and AC signal sources often used in electronics labs. See Fig. 1.1.7 . You will learn how to use the oscilloscope later.

Fig. 1.1.7: A 70MHz 2-Channel analogue oscilloscope. Source: 1.2 Electricity: Charges & Current Even though we don’t know exactly what electricity is, we do know a lot about what it does and how it behaves. You will find it easier to understand electricity if you avoid using the term electricity itself to describe it. The reason is very simple: The word electricity is not very precise. Scientists and engineers use the word electricity to refer to a few different but related things. The most common ones are rather precise names like electric charge, electric current, electric field, and electric energy . All these are what are commonly called electricity . 1.2.1 Electric Charge Electric charge, electrical charge, electrostatic charge, or simply charge, is the characteristic of a unit of matter that expresses the extent to which it has more or fewer electrons than protons. In an atom, it is the electron that carries a negative elementary or unit charge and the proton carries a positive charge. The two types of charge are equal and opposite. For practical purposes, the most important thing you should know about electric charge is that opposite charges attract and similar charges repel . In other words, negative charges attract positive charges

positive charges attract negative charges negative charges repel negative charges positive charges repel positive charges Therefore an electron and a proton attract each other, but an electron repels another electron and a proton repels another proton. The unit of electric charge is coulomb (symbol is C ). 1.2.2 Electric Current An electric current is defined as the rate of flow of electric charge past a given point or region. We say an electric current exists when there is a net flow of electric charge through a given point or region. In electric circuits this charge is often carried by electrons moving through a wire. In other words, electric current is the total charge that passes through a given cross-sectional area A per unit time. This cross-sectional area is frequently represented by a slice through a solid material, such as a conductor (for example, a copper wire).

Fig. 1.2.1: ΔQ Charge crosses a conductor of cross-sectional area A in Δt time. Supposing Δ Q represents the amount of charge that passes through an area in a given time interval Δ t as shown in Fig. 1.2.1 . , then the average current I ave is defined as: The SI unit (international system of units) of current is therefore coulombs per second or C/s, but the ampere (A) is often preferred. So 1 A = 1 C/s. The ampere is a rather too large a unit for practical uses in electronic circuits, so you will find it more convenient to express current in milliamps (mA), microamps (A) or nanoamps (A). 1 mA = 1 × 10 -3 A, 1 μA = 1 × 10 -6 A, 1 nA = 1 × 10 -9 A. 1.2.3 Current Drawn By Common Electronic Devices When tinkering with circuits in general, it is good to have idea of how much current common electronic and electrical devices (commonly called loads ) draw from their power supplies. Below are some examples: A 100-watt lightbulb (electrical device): about 1 A; A laptop computer (electronic gadget): between 2 to 3 A; A microwave oven (electrical device): about 10 A; A fluorescent light: 1 to 2 A; A radio or stereo set: (electronic): 0.5 to 3 A; A typical LED (a small electronic indicator light): 20 mA; A microchip (electronic): a few μA or even perhaps several pA

A current sufficient to induce a cardiac or respiratory arrest: about 100 mA to 1 A. A mobile (smart) phone: around 200 mA An electric fan (electrical device): about 1 A; A TV set (electronic gadget): 1 to 3 A; A toaster (electrical gadget): 7 to 10 A; An automobile starter: around 200 A; A lightning strike: about 1000 A. Electric current can be measured by a ammeter but a digital multimeter is often used in electronics because it has higher precision and can measure various ranges of current. We will look at the multimeter and how to use it in chapter 7. In electronic circuits, an ammeter is represented by

Fig. 1.2.2 shows an analogue DC ammeter and Fig. 1.2.3 shows a digital DC ammeter.

Fig. 1.2.2: An analogue DC ammeter, range 0 to 3A. Source: School Specialty Canada

Fig. 1.2.3: An digital DC ammeter, range 0 to 10A. Source: Arbor Scientific 1.3 Electric Voltage, Grounds & Power 1.3.1 Electric Voltage In their natural state, the electrons in a conductor such as a copper wire freely move from one point to another, but in a completely random way. To make them all move together in one and the same direction, all you have to do is give them a push . In other words, electric voltage can be thought of as a kind of “electrical pressure”. The technical term for this push is electromotive force , abbreviated EMF , or sometimes simply E . But it is more commonly known as voltage . Technically speaking the voltage is also referred to as a potential difference or just potential — they both mean the same thing. This means that potential difference or voltage is a relative word since you can only measure it across two points, one of which may the reference point called ground . For example, if we say that a point in a circuit has a voltage of 12 V it is meaningless unless we have another point in the circuit (which may be the ground) with which to compare it. Electric voltage can be measured by a voltmeter but a digital multimeter is often used in electronics because it has higher precision and can measure various ranges of voltage. In electronic circuits a voltmeter is represented by

Fig. 1.3.1 shows an analogue DC voltmeter and Fig. 1.3.2 shows a digital DC voltmeter.

Fig. 1.3.1: An analogue DC voltmeter having one ground or zero terminal (black) and 2 other positive terminals, 0 to 3V range and 0 to 5V range (red). Source: Alibaba

Fig. 1.3.2. A digital DC Voltmeter. Source: RobotShop 1.3.2 Grounds As we discussed in the last section voltage is a relativity game. Very often we have to define a ground. So a ground is a zero-volt (0-V) reference point in a circuit on which to base all other voltage measurements . The ground is frequently represented by one of the three symbols shown in Fig. 1.3.3 .

Fig. 1.3.3 Electrical ground symbols Note that we can have a point in a circuit that is below the ground, that is, that has a negative voltage . For example, Fig. 1.3.4 (connection of two cells in series ) shows one way in which we can define voltages by selecting a ground—which in this case is simply the middle GND (a 0-V reference marker). The upper point ( +4.5 V ) is above the ground so it is positive , while the lower point ( -4.5 V ) is below the ground so it is negative .

Fig. 1.3.4: A simple circuit showing three points: a positive point, a negative point and a ground 1.3.3 Electric Power Another important electrical quantity is power. Power is simply the work done by an electric circuit. Electric current itself is not all that useful. It becomes useful only when the energy it carries is converted into some other form of energy, such as heat, light, sound, or radio waves. Let us take an incandescent light bulb as an example. The voltage pushes current through the filament, which converts the energy carried by the current into heat and light. So we now have a kind of generalized power law , which says that if the current entering a device and the voltage across it can be measured, the power used by the device is given by: P = VI (Voltage multiplied by current) Power is measured in units called watts (abbreviated W ). 1.3.4 Electric Heat The power consumed or dissipated by an electronic device or an appliance can be converted to heat energy, as we saw in the previous example of an incandescent light bulb. In other words, power can be lost into heating in an electronic component or device. It is often a very important part of circuit design to know how to calculate the power dissipated by a circuit. That is because electronic components like transistors, resistors, capacitors and integrated circuits (which we will discuss later) all have some maximum power ratings. If you exceed the maximum power rating of an electronic component, you run the risk of burning it. For example using a 1/4 -watt resistor in a circuit that dissipates 2 watts will cause the damage of the resistor. 1.4 Conductors, Resistors & Semiconductors

1.4.1 Conductors, Insulators & Resistivity An electrical conductor is a material that conducts electricity. Electrical conductivity is the ability of a material to conduct electricity. An insulator is a material that does not conduct electricity. 1.4.2 Electrical Resistance & Resistivity Electronics is all about manipulation of the flow of electric current. One of the major ways of manipulating current is by using resistance to reducing it. If there was no resistance, flow of current would be unregulated and useless. The electrical resistance (R) of an object or material is a measure of how much it opposes the flow of electric current. The SI unit of resistance is ohm ( Ω ). The object or material is called a resistor . Conductance ( G ) is the inverse of resistance. The SI unit is Siemens , S although mho (ohm written in reverse) can also be used as an alternative unit. Resistivity ( ρ ) is the resistance of a conductor of a unit cross-sectional area and a unit length. Theoretically, resistivity is very useful for comparing the ability of various materials to conduct electric currents. Therefore a conductor with a high resistivity is a poor conductor. The SI unit of resistivity is ohm-meter ( Ωm ). The value of resistivity of a conductor depends on its temperature . For practical purposes, resistivity values are usually tabulated at a temperature of 20° C (68° F). The resistivity of a metallic conductor generally increases with a rise in temperature. However, for semiconductors like silicon and carbon, the resistivity generally decreases with temperature rise. For example, the resistivity of a very good electrical conductor like a hard-drawn copper wire is 1.77 × 10 -8 ohm-meter at 20° C. 1.4.3 Conductivity Conductivity ( σ ) is the reciprocal of resistivity , and is a measure of how much electric current flows in a conductor. The SI unit of conductivity is Siemens per meter (or mho per meter ). A good electrical conductor has high conductivity but a low resistivity. A good insulator (also known as a dielectric ), has a high resistivity but a low conductivity. Semiconductors have intermediate values of both. 1.4.4 Good Conductors, Poor Conductors & Semiconductors A good electrical conductor allows flow of electric current with little or negligible impediment. A Examples of good conductors are metals such as silver, copper and aluminum. Carbon is also a very good conductor. A poor or bad electrical conductor on the other hand is a material that does not readily conducts electric current. Steel, tungsten and bismuth are examples of poor conductors because it is an alloy. Insulators are materials that are poor conductors of electricity. Some examples of good insulators are plastic, glass and Teflon. The most important factor that determines if a material is a conductor or an insulator is how readily its atoms give up the electrons on their outermost shells. Many atoms are very possessive of their electrons, and are therefore good insulators. Table 1.4.1 shows values of conductivity and resistivity of various materials.

Table 1.4.1. Conductivities and resistivities of various materials 1.4.5 Semiconductors A semiconductor is material which has a conductivity between the conductivity of conductors and nonconductors or insulators. In other words, a semiconductor is neither a good conductor nor a good insulator. A semiconductor can be a pure element like silicon or germanium , or a compound like gallium arsenide or cadmium selenide . A pure semiconductor material is produced through a process called doping , that is, a small amount of impurity like arsenide is added to it, causing a significant change in its conductivity. A few examples of semiconductor devices are diodes, transistors, photocells, silicon-controlled rectifiers, thyristors and triacs. 1.5 Resistor Symbols, Types & Color Codes A resistor is a passive two-terminal electrical component that uses resistance as a circuit element. 1.5.1 Active & Passive Components A passive component such as a resistor cannot amplify voltage, current or signal, but it can only reduce them. An active component such as transistors, opamp (operational amplifiers) and transformers can amplify voltage, current or signal. 1.5.2 Resistor Symbols Resistors are the most widely used components in electronic circuits. There are two common electronic symbols used to represent a fixed resistor (a resistor with a fixed value of resistance). The first one ( IEC or US symbol) is a horizontal or vertical zig-zag line with 3 spikes at the top and 3 spikes at the bottom. See Fig. 1.5.1 where a resistor R 1 of value 150Ω is represented by a horizontal zig-zag line and a resistor R 2 of value 25Ω is represented by a vertical zig-zag line. IEC stands for International Electrotechnical Commission . It is an international standards organization where standards for all electronic, electrical and related technologies (collectively known as "electrotechnology") are prepared and published.

Fig. 1.5.1. IEC symbol is used to represent two fixed resistors R1 and R2 The second one ( European symbol) looks like a small box. See Fig. 1.5.2 .

Fig. 1.5.2. European symbol is used to represent two fixed resistors R1 and R2 It is left to you which symbol type you use (IEC or European). The most important thing is be consistent. Do not mix the two standards! The IEC standard is used in this book. 1.5.3 Ohm’s Law Ohm’s law gives us one of the fundamental relationships often found in the study of electronic circuits. Ohm’s law states that the current I flowing through a conductor is directly proportional to the voltage V applied across it, provided the temperature is constant. In other words, if you increase the voltage applied to a conductor whose resistance R is fixed, the current will increase linearly. Conversely, if you decrease the voltage, the current goes down. The circuit shown in Fig. 1.5.3 shows the three parameters ohm’s law refers to.

Fig. 1.5.3 Parameters of Ohm's law (V, I and R) Ohm’s law expresses this relationship with a simple mathematical formula below: V=IxR Where V = Voltage or potential difference (in volts),

I = Current (in amperes), and R = Resistance (in ohms). 1.5.4 Types of Resistors Fig. 1.5.4 shows common types of resistors used in electronic circuits.

Fig. 1.5.4: Various types of resistors used in electronic circuits. Source: Resistors can be broadly divided into linear and non-linear as shown in Fig. 1.5.4. Linear resistors are those that obey ohm’s law. Examples are carbon-film, metal-film and wire-wound resistors. They are also called ohmic resistors because they obey ohm’s law (have constant resistance). Non-ohmic resistors do not obey ohm’s law because their resistance vary with temperature. A few examples are diodes, thermistors, varistor resistors and LDR (light-dependent resistor or photo-resistor). 1.5.5 Thermistor A thermistor is a type of variable resistor that is sensitive to temperature changes. In other words, the resistance of a thermistor decreases with increase in temperature or increases with decrease in temperature. 1.5.6 Varistor Resistor A varistor resistor is a nonlinear device made from a semiconductor. In other words, there is a non-linear relationship between the current flowing through it and the voltage applied across it. A good example of the most commonly used form of varistor resistors is the MOV (metal oxide varistor).

1.5.7 LDR (Light Dependent Resistors) or Photo Resistor The LDR is a kind of photo conductive cell. It is a light-controlled variable resistor. Its resistance decreases with increase in light intensity. 1.5.8 Surface Mount Resistor (SMD) A SMD resistor is a rectangular shaped resistor. It is an electronic component that is used with SMT (Surface Mount Technology) in industrial electronics because of its considerable advantages in terms of space saving and automated manufacture of PCB (printed circuit boards). Fig. 1.5.5 shows some common resistors used in electronic circuits with their IEC (right) and European (left) symbols.

Fig. 1.5.5. Common resistors used in electronic circuits and their symbols The resistance of the rheostat, potentiometer or preset resistors can be varied using some kind of sliders, knobs or even a small screw driver, and that is why they fall into the class of variable resistors. 1.5.9 Standard Resistors In 1952 the IEC defined a standard for resistance and tolerance values. They did this to make the mass manufacturing of resistors easy. These resistors are referred to as preferred values or E-series , and they are published in IEC 60063:1963 standard. These standard values are also used for other components like inductors, capacitors and Zener diodes. There are important reasons for the standardization of resistor values. For example, when manufacturers make resistors of different resistance values, they end up nearly equally spaced on a logarithmic scale. This assists the supplier to limit the number of different resistor values that have to be produced. Using standard values ensures that resistors produced by different manufacturers are compatible for the same circuit design, which electrical engineers find favorable. Apart from the preferred values, there are many other standards relating to resistors. For example, there are standard sizes for resistors, and the marking of resistors with color codes or numerical codes. 1.5.10 Resistor Tolerance Tolerance is the percentage of error in the resistance of a resistor. It is a measure of how much more or less you can expect a resistor's actual value of resistance to be from the value stated by the manufacturer. For example, a 100KΩ resistor with a % tolerance actually has a value somewhere between 5 percent below and 5 percent above. This works out to somewhere between 95KΩ and 105 KΩ.

Here is another example. A 470Ω resistor with a % tolerance actually has a value somewhere between 10 percent below and 10 percent above. This works out to somewhere between 423Ω and 517Ω. 1.5.11 The E-Series In the E12 series, every decade (such as 0.1 to 1, 1 to 10, 10 to 100 and so on) is divided into 12 steps. In other words every value of resistor in the series is 21% or 1.21 times higher than the previous value rounded to a whole number. For example if the previous resistor value R 1 is 10 ohms, the next value R 2 is 10 x 1.21 rounded to a whole number. That is So in the E-series, there cannot be a resistor of 11 or 13 ohms. The series is expressed as follows: 1– 1.2 – 1.5 – 1.8 – 2.2 – 2.7 – 3.3 – 3.9 – 4.7 – 5.6 – 6.8 – 8.2 – 10 – 12 – 15 – 18 and so on. So in the series, resistor values can be represented with a power of ten: 1.2– 12 – 120 – 1200 ohms, and so on. See Fig. 1.5.6 .

Fig. 1.5.6. The E-12 series Aside the E12 series, there are other series in existence. Below is a list of the most common series and their tolerances: E6 , 20% tolerance E12 , 10% tolerance E24 , 5% tolerance (also available with 1% tolerance) E48 , 2% tolerance E96 , 1% tolerance E192 , 0.5% tolerance (also used for resistors with 0.25% and 0.1%). Table 1.5.1 gives the values in each E-series and the tolerances.

Table 1.5.1. Some E-series values and tolerances

1.5.12 How to Read Resistor Color Codes We can work out the resistance of a standard resistor by examining the little stripes of bright colors (called color codes or colored bands ) painted on it. These color codes indicate two important facts about the resistor: its resistance in ohms its tolerance, which, as already explained above, indicates how close to the indicated value the resistance of the resistor actually is. Four stripes or bands of color are painted on most resistors. The first three stripes indicate the resistance value of the resistor (the first two digits being the significant figures and the third being the multiplier) while the fourth stripe indicates its tolerance. There are precision resistors that have five bands of color, with the first four colors representing the resistance value and the last color representing the tolerance. 1.5.13 How to Read 4-Color Coded Resistors Table 1.5.2 shows the standard color codes used for reading the resistance of a resistor. You should know that some people use purple instead of violet to represent the digit 7 because these two colors look alike to them. Table 1.5.2. The standard color codes used for reading the resistance of a resistor Fig. 1.5.7 illustrates how to read the color codes of a 4-color coded resistor to arrive at the value and tolerance.

Fig. 1.5.7. How to read the color codes of a 4-color coded resistor If you are not sure from which side of a resistor you should read the colors, begin from the side that is closest to the color stripe. The first band is often but not always painted very close to the edge of the resistor and the last band is not so close to the edge. Another way to know from which side to read the colors is that the space between the third and the fourth band is wider than the others and is used to identify the fourth tolerance band (as shown in Fig. 1.5.7). If the fourth band is not present, then the tolerance is 20 percent. Follow this procedure to determine the value of a 4-color coded resistor: 1. Hold the resistor horizontally and always read the colors from left to right For many resistors, the first color should be the one that is closest to the left end of the resistor. If you notice this first color is on the right side of the resistor, turn the resistor counterclockwise so that the first color is on the left.

If you are unable to tell the color that is closest to the left end of the resistor, then ensure that when you hold the resistors horizontally the tolerance band (the band that has wider space from the others) is on the extreme right, as shown in Fig. 1.5.7. 1. Look up the color of the first band to determine the value of the first digit. Let us say the first stripe is yellow as shown in the example illustrated in Fig. 1.5.7, then first digit is 4 . 1. Look up the color of the second band to determine the value of the second digit. This means that if the first band is violet , then the second digit is 7 , as shown in Fig. 1.5.7. 1. Look up the color of the third band to determine the multiplier. So if the third band is brown , the multiplier is 10 . See Fig. 1.5.7. 1. Multiply the two-digit value you got from steps 2 and 3 by the multiplier you got from step 4 to determine the value of the resistor. So in our current example of Fig. 1.5.7, our two-digit value is 47. If we multiply this by 10 we have 470. Here is a summary of how resistor to read the resistor in Fig. 1.5.7. First digit = Yellow = 4 Second digit = Violet = 7 Third digit = Brown = x 10 Resistor Value = 47 x 10 = 470 ohms The 4th band has gold color, so tolerance = 5% . The indicated (estimated) value of this resistor = 470Ω This means that the real or actual value of this resistor lies somewhere between (470Ω ─ 5%) to (470Ω + 5%). Since 5% of 470Ω = 23.5Ω, then the real/actual value of the resistor is somewhere between (470 ─ 23.5) and (470 + 23.5). So the real value lies within the range 446.5Ω to 493.5Ω . If you use a multimeter to read this resistor you can confirm the real value is somewhere in the stated range, that is 446.5Ω to 493.5Ω. That was simple enough, wasn’t it? Let us look at another practical example in Fig. 1.5.8 :

Fig. 1.5.8. How to read the color codes of another 4-color coded resistor First digit = Brown = 1 Second digit = Red = 2 Third digit = Green = x 100k = x 100000 = x Resistor Vale = 12 x 100000 = 1200000 ohms = 1200kΩ Hints: 1000 ohms = 1k ohms. 1000,000 ohms = 1M ohms. Note that KΩ and MΩ are more often used in practice than Ω itself.

The 4th band has gold color, so tolerance = 5% . The indicated (estimated) value of this resistor = 1200kΩ or 1.2MΩ. This means that the real or actual value of this resistor lies somewhere between (1200kΩ ─ 5%) to (1200kΩ + 5%). Since 5% of 1200kΩ = 60kΩ, then the real/actual value of the resistor is somewhere between (1200kΩ ─ 60kΩ) and (1200kΩ + 60kΩ). So the real value lies within the range 1140kΩ to 1260kΩ . With the help of a multimeter you can read this resistor to confirm the real value is somewhere in the stated range, that is 1140kΩ to 1260kΩ. If the project or application you’re building demands a higher precision, you will need to spend a little more money to purchase higher-tolerance resistors. However and tolerance resistors are fine for all the circuits presented in this book (unless it is indicated otherwise). The tolerance of a resistor is indicated in its last color band, as listed in Table 1.5.3 . Table 1.5.3: The tolerance values of a resistor and their colors 1.5.14 Zero-Ohm Resistor A zero-ohm resistor is one that has a single black band. It has a resistance of approximately zero. It is often used to connect two points on a PCB (printed circuit board). Practice Exercise 1: Reading Color Codes A. Read the indicated value of the resistance of the resistor shown in Fig. E1 in KΩ and find out the range in which the real value of the resistance lies.

Fig. E1. Practice Exercise: Determine the value of the resistor B. Read the indicated value of the resistance of the resistor shown in Fig. E2 in ohms and find out the range in which the real value of the resistance lies.

Fig. E2. Second Practice Exercise: Determine the value of the resistor 1.5.15 How to Read 5-Color Coded Resistors For precision resistors, five color bands are often used. The first three bands are used as significant figures and the fourth band as the multiplier. There is usually a wider space between the fourth and fifth band. The fifth band is used to identify the tolerance of the resistor. Fig. 1.5.9 shows a 5-color coded resistor. We will read it to arrive at the value of its resistance and the tolerance.

Fig 1.5.9. A 5-color coded resistor First digit = Red = 2 Second digit = Violet = 7 Third Digit = Green = 5 Fourth digit = Red = x 100 = x Resistor Vale = 275 x 100 = 27500 ohms = 27.5kΩ The 5th band has brown color, so tolerance = 1% . See Table 1.5.3. The indicated (estimated) value of this resistor = 27.5kΩ . This means that the real or actual value of this resistor lies somewhere between (27.5kΩ ─ 1%) to (27.5kΩ + 1%). But 1% of 27.5kΩ = 0.275kΩ. Hence the real/actual value of the resistor is somewhere between (27.5kΩ ─ 0.275kΩ) and (27.5kΩ + 0.275kΩ). So the real value lies within the range 27.225kΩ to 27.775kΩ . With the help of a multimeter you can read this resistor to confirm the real value is somewhere in the stated range, that is 27.225kΩ to 27.775kΩ. 1.5.16 How to Read 5-Color Coded Resistors with Reliability Band There is another type of five-band labeling scheme that is rarely used in commercial electronics but is specially reserved for resistors that are produced with military specifications. In this scheme, the fifth band indicates a reliability level or failure rate . The reliability band gives us the percentage change in the value of the resistance over a certain time interval (for example, 1000 hours). In this scheme, brown =1%, red = 0.1%, orange = 0.01%, Yellow = 0.001%. 1.5.17 How to Read the Color Codes of Surface-Mount (SMD) Resistors For surface-mount resistors, a 3-digit or 4-digit labeling system is often used. In the 3-digit scheme, the first two digits indicates the significant figures, while the last digit indicates the multiplier. For example, 473 = 47 x 1000 = 47000 ohms. See Fig. 1.5.10 . If the value is less than 100 ohms, the capital letter R is substituted for one of the significant digits, representing a decimal point. For example, 27R5 = 27.5Ω, 1R0 = 1.0Ω, R10 = 0.10Ω and 33R = 33 Ω). In the 4-digit scheme the first 3 digits are used as the significant figures, while the last digit is used as the multiplier. Again, the letter R is used as a decimal point. See the examples in Fig. 1.60. For example, 4702 = 470 x 100 = 47000Ω = 47kΩ, 33R0 = 33Ω.

Fig. 1.5.10. 3-digit and 4-digit SMD resistor value calculator When tolerance levels is very important in the 4-digit scheme, an extra digit (a letter) is placed at the end of the third digit to indicate the tolerance (e.g., F = 1.0%). See examples in Fig. 1.5.11 .

Fig. 1.5.11. How tolerance level is indicated in the 4-digit scheme Fig. 1.5.12 is a picture of a PCB with some surface-mount resistors on it.

Fig. 1.5.12. Picture of a PCB showing some SMDs. Source

1.5.18 How to Read 6-Color Coded Resistors with TCR A resistor with 6 bands is usually used for high precision applications. In this scheme, an additional band (6th band) is used to specify the TCR (temperature co-efficient of resistance in ppm/K ). Brown is the most common color used for the sixth band (100 ppm/K). What this means is that when the temperature of the resistor changes by 10˚C, the value of the resistance can change by 0.1%. See Table 1.5.4 . Table 1.5.4. Temperature co-efficient values and colors of a 6-band resistor Fig. 1.5.13 illustrates the color code scheme of a 6-band resistor.

Fig. 1.5.13. How to read the color codes of a 6-band resistor We can use the color codes to read the value of the resistor. We start from the left end as follows: First band = Blue = 6 Second band = Red = 2 Third band = Violet = 7 Multiplier band = Black = x 1 = x Tolerance Band = Green = 0.5% . Temp. Co-efficient Band = Yellow = 25 ppm/k The value of the resistor = 627 x 1 = 627Ω Therefore, the indicated (estimated) value of this resistor 1.5.19 How to Understand Resistor Power Ratings However, there is no standard for resistor power ratings, hence there is often deviation from the above described series. In other words it is difficult

to tell a resistor’s power rating just by looking at it. Unlike resistance and tolerance, no color codes are used for reading wattage. Fortunately, the size of a resistor is a very good indicator of its power rating. Sometimes when you buy new resistors, you can find their power ratings written on their packaging. After you have worked with resistors for a while, you will learn how to quickly recognize the difference in sizes between various resistors of different power ratings. Resistors with high power ratings are usually called power resistors or high power resistors . Fig. 1.5.14 and Fig. 1.5.15 are good practical guides for learning common resistor with power ratings from ¼ watt to 10 watts.

Fig. 1.5.14. Some common resistors with their power ratings and physical dimensions

Fig. 1.5.15. Some power resistors Practice Exercise 2: Building a Current-Limiting Circuit for an LED One of the most common applications of resistors is for limiting the current flowing through an electronic component. An example of such a component is the LED ( L ight- E mitting D iode) which is commonly used for making indicator lights in mobile phones and other electronic devices. An LED is very sensitive to current. You only need a few milliamps of current to make an LED glow brightly. A few 100mA current is large enough to burn out and LED. In this project you want to build a simple circuit for learning how a resistor can be used to limit the current flowing through an LED. The schematic diagram you want to follow to build your circuit is shown in Fig. 1.5.16 .

Fig. 1.5.16. Schematic diagram for limiting current in an LED You will need the following parts which you can purchase very cheaply from your local electronic parts dealer or from an e-commerce store like RadioShark . Parts List: One 9 volt battery ( Vs ) such as Duracell or HIW One 820Ω resistor ( R ) (any resistor in the range 470Ω to 1kΩ resistor can be used instead) One solderless breadboard RadioShack 2760003 One 5mm red LED (green or blue LED can be used instead), RadioShack 2760209 One small Phillips-head screwdriver to remove the battery holder and packaging One stripper to cut and strip the battery wire One battery holder (some paper tape or masking tape can be used if you do not have a holder) Study Fig. 1.5.17 and follow the steps below to build your circuit.

Fig. 1.5.17. Circuit for limiting current in an LED 4 Steps to Build your Circuit Make sure you remove your battery from your If your battery cam 1. Connect the resistor Insert one lead (end) of the resistor into your breadboard in hole d2 , and then insert the other lead into any nearby hole in the top bus strip (positive voltage rail or the strip that is s connected to the red battery wire). 1. Connect the LED. If you look at the leads of the LED closely you will see they are not the same length. Insert the shorter lead (called the cathode ) into hole e7 . Insert the longer lead (called the anode ) into hole e2 (right below hole d2 where you inserted one lead on the resistor in step 1. Important : If you insert the leads backwards the LED will not light after the circuit is completed. 1. Connect the battery leads a. Insert the black lead (wire coming from the negative (-) terminal of the battery) into hole f7 right below the cathode of the LED. b. Insert the red lead (wire coming from the negative (+) terminal of the battery) into any nearby hole on the same line as the upper lead of the resistor in the top bus strip of the breadboard. 1. Connect the battery It’s time to test your circuit! Use the paper/masking tape to connect the black wire to the negative (-) terminal of the battery and connect the red wire to the positive (+) terminal of the battery. If you have the battery holder, it will make this easy and you do not need the tape. The LED should light up instantly. If it does not, double-check your connections to ensure the circuit is assembled correctly as shown in Fig. 1.67. If the LED still does not light up, your battery is probably flat. So try a different battery. Assuming you used a 820Ω resistor ( R ) and a 9V battery ( Vs ), the current that lights up the LED in this circuit can easily be calculated. First we need to work out the voltage drop across the resistor using the schematic diagram in Fig. 1.66. Since most LEDs need about 1.5V to work safely, the voltage drop across the resistor is therefore = 9V ─ 1.5V = 7.5V. Therefore I = 0.0091A (or 9mA) approximately. Repeat the above calculation with whatever value of resistor ( R ) and battery voltage ( Vs ) you actually used in your own circuit. As you can see from this result, an LED needs pretty small currents to light brightly indeed. In fact most LEDS need 5mA to 20mA to light up

brightly without fear of damaging them. 1.6 Resistor Networks: Series & Parallel Combinations Sometimes critical values of resistors are needed in electronic circuits. Let us say for example you need a 123Ω resistor in your circuit. Unfortunately you can not find it in your local store or favorite online supplier. You do not just give up or settle for a 100Ω resistor and hope it will work because you think it is close enough. That is not acceptable in practical electronics! When you are faced with such or a similar situation, all you have to do buy two or more resistors and combine them to create the overall resistance you need. In this example, you will need to buy and combine three resistors , namely 100Ω, 22Ω and 1Ω in series to form a resistor network. A resistor network is a combination of resistors in series or parallel which is a good substitute for a single resistor. In some cases we combine two or networks to form a more complex network of resistors (such as series-parallel and parallel-series). There are two basic ways of combining resistors. 1.6.1 The Series Combination The total resistance of a circuit with resistors wired in series (connected end to end) is the sum of the individual resistances. See an example in Fig. 1.6.1 where three resistors are connected in series to a 13V battery.

Fig. 1.6.1. Series combination of four resistors, 1Ω, 3Ω, 4Ω and 5Ω The same amount of current 1A flows through each resistor in any series connection like Fig. 1.6.1. In any series combination of resistors R 1 , R 2 , R 3 and so on, the total (effective) resistance R s is given by In the example shown in Fig. 1.6.1, R s = 1 + 3 + 4 + 5 = 13Ω . Can you use ohm’s law (V = I x R) to prove that the current flowing in each resistor is 1A? What is the conductance of the circuit? Answer: Remember that conductance G is the reciprocal of resistance. 1.6.2 The Parallel Combination The total resistance of a circuit with resistors R 1 , R 2 , R 3 and so on wired in parallel is always less than the resistance of any of the individual resistors, and is given by See an example in Fig. 1.6.2 where four resistors are connected in parallel to a 24V battery (V s ).

Fig. 1.6.2. Parallel combination of four resistors, 10Ω, 20Ω, 30Ω and 40Ω In the example shown in Fig. 1.6.1, . We can simplify this further. As you can see from this result, the total (effective) resistance (4.8 ohms) is less than the resistance of any of the individual resistors 10, 20, 30 or 40 ohms in the same circuit. Can you use ohm’s law to i. calculate the current supplied by the source (I T ) to all the resistors combined? ii. calculate the current flowing in each resistor individually, that is, I 1 , I 2 , I 3 and I 4 ? Results : I T = 5A, I 1 = 2.4A, I 2 = 1.2A, I 3 = 0.8A, I 4 = 0.6A. For parallel combination of two resistors you will find the following formula very fast for practical uses: 1.6.3 The Voltage Divider Circuit: How to Use Resistors to Tap Voltages One of the most useful and interesting applications of resistors is for dividing voltages. For example, if you connect two resistors together in series across a battery of voltage V in , you can tap a fraction of this voltage at the point where the two resistors are connected. Resistors used in this type of circuit are called a voltage divider . Voltage divider circuits are very common in practical electronics for reducing voltages, especially in circuits where variable resistors like potentiometers and preset resistors are employed. Fig. 1.6.3 shows a simple resistor network where two resistors R1 and R2 divide the voltage supplied by a battery into V 1 and V 2 .

Fig. 1.6.3. A simple voltage divider circuit example

In this example, we can simply use a multimeter to measure the values of V 1 and V 2 . However let us use the simple voltage divider formulas below to obtain a good approximation to what the multimeter will give us. Substituting the values of R 1 and R 2 (5Ω and 10Ω respectively) into (1) we have V 1 = 4V. Similarly substituting the values of R 1 and R 2 into (2) we have V 2 = 8V. We could have obtained V 2 by simply subtracting V 1 from V in as follows. V 2 = V in ─ V 1 = 12 ─ 4. V 2 = 8V (the same value we obtained earlier). The most important lesson to learn from this example is that we can use two resistor R 1 and R 2 to divide an input voltage V in into 4V and 8V. This technique can be extended to build a voltage divider circuit with more than 2 resistors. You will do this in practice exercise 3. Practice Exercise 3: Building Resistor Networks & Divider Circuit Here’s the parts list to use for this practice exercise. Parts List Six 1kΩ resistors One Breadboard One good multimeter that is enabled with ohm measurement A. Study the simple circuits in Fig. E3.1 . Connect the 1kΩ resistors in different ways on the breadboard as shown.

Fig. E3.1. Connecting some resistors in series and taking measurement with a multimeter Switch your multimeter to “ Ω ” (its ohm function) and use it to measure the total resistance in each of the three different ways shown. The results you get from your multimeter may be a little different because of the tolerance value of each resistor and the accuracy of the multimeter. Cross check your results by using the right formula to calculate the theoretical value of the total (effective) resistance of the resistors you combined in parallel. B. Study the simple circuits in Fig. E3.2 . Connect the 1kΩ resistors in different ways on the breadboard as shown.

Fig. E3.2. Connecting some resistors in parallel and taking measurement with a multimeter Ensure your multimeter is set to “ Ω ” (its ohm function). Use it to measure the total resistance in each of the three different ways shown in Fig. E3.2. The results you get from the multimeter may be a little different because each resistor has its own tolerance value, and also because of the accuracy of the multimeter. Cross check your results by using the right formula to calculate the theoretical value of the total (effective) resistance of the resistors you combined in parallel. C. Study the simple circuits in Fig. E3.3 . Connect three 1kΩ resistors (R1, R2 and R3) in series on your breadboard as shown.

Fig. E3.3. A simple voltage divider circuit with 3 resistors Use your multimeter or a voltmeter to find out how the 9V supply is divided. To do this measure the voltage across each resistor at a time. You should get about 3V for each output. This is because the three resistors have the same resistance of 1KΩ (ignoring their tolerances) so they divide the input voltage (9V) equally. 1.7 Open, Closed & Short Circuits 1.7.1 Difference Between Open & Closed Circuits

A closed circuit is a path through which electric current can flow. If a break is present anywhere in the circuit, we have an open circuit , and no current can flow. Sometimes we create open circuits entirely by accident. For example you may forget to connect a battery in one of your previous practice exercises, or may be there is a break in one of the wires in a circuit you were building. Another example is if when building your circuit on your solderless breadboard, you mistakenly plug one side of a component like an LED into the wrong hole in the breadboard. This leaves the LED unconnected and creating an open circuit. Very often open circuits are accidental but are usually harmless. However they can cause us a lot of frustration, especially when we try to figure out why the circuit we have built is not working the way we think it should. Fig. 1.7.1 is a comparison of a closed and open circuits.

Fig. 1.7.1. A Closed circuit (bulb lights) and an open circuit (bulb does not light). 1.7.2 Short Circuits & Dangers of Overloading A short circuit on the other hand is said to occur if a direct connection is made between two points in a circuit that are not supposed to be directly connected. An example is using a conductor like a wire to connect the two terminals of a power supply such as a car battery. This produces an effect called overloading on the wire, that is, the current capacity of the wire is exceeded, resulting in over heating. Important: Shorting car and truck battery terminals with wires or other conductors is very dangerous! Don’t try it! You may cause melting of the wire insulation, burning of the whole wire or huge sparks that may result in explosions o r even fire that can burn you. Electric current always seeks the path of the least resistance. This means that in a short circuit, the current always travels through the direct connection because there is no load to limit it so there is too little work to do. Fig. 1.7.2 illustrates a short circuit placed across the terminals of a 1.5V battery in a simple light bulb circuit.

Fig. 1.7.2. A short circuit does not allow the bulb to light. It only wastes electrical energy The green wire in the middle of the circuit diverts (shorts) the current away from the bulb. The current that is supposed to light the bulb is simply returned (shorted) to the battery in the direction of the arrows. Soon the battery will be exhausted and may become flat. Open and closed circuits have applications in switches which we will look at in section 1.9. 1.8 Electrostatic Charge Protection Electrostatic charge or static electricity is a build up of charges that allows current to flow in the absence of a circuit. Frequently the human body is the carrier of static charges, and it can be created in various ways. One of the most common ways your body can build up static charges is friction, such as when you walk across a nylon carpet. Even your clothes can pick up some static charges, for example when you rub a balloon on them, or when you toss them around in your clothes dryer. Although static charge that accumulated in your body will usually dissipate itself after some time but it can discharge more quickly if, for instance, you touch a conductor like a brass doorknob, and may give you a nasty shock. If the conductor you touched happens to be a sensitive electronic component like a transistor or an I.C (integrated circuit) the discharge can be destroy the innards of the component and render it useless for the circuit you want to use it for. 1.8.1 How to Protect Electronic Components from Static Discharges It is wise to protect your electronic components from static discharges before you start working on an electronic circuit project. One of the easiest ways you can do this is to ensure you discharge yourself by touching a large metal object like a metal workbench or a grinder before you begin your work. Another way to discharge your body is by wearing an antistatic wristband . See Fig. 1.8.1 . You must plug the alligator clip to a metal surface such as the frame of your workbench or a nearby drill press that is connected to a proper earth ground .

Fig. 1.8.1. Wear an antistatic wristband for static charge protection. 1.9 Electronic Switches Fundamentally, a switch is a mechanical device having two or more internally connected contacts , terminals or leads or simply a component for making (turning on) and breaking (turning off) a circuit. Switches are very important components of many electronic circuits. Very often in electronics, a switch is a solid state device (that is, a device made from semiconductors) used for interrupting electric current or diverting it from one conductor to another. 1.9.1 Categories of Switches There are basically two ways of categorizing switches. The first is the method we use to operate them. 1. Method used to open or close the contacts Slide switch - A knob is used to slide forth and back to open or close the contacts. Transistor radios use this switch. See Fig. 1.9.1 .

Fig. 1.9.1. A side switch

Toggle/Tumbler switch - A mechanical lever, handle or rocking mechanism is flipped up or down to open or close the switch contacts. This switch is found in common household light switches. Fig. 1.9.2 shows a common electronic toggle switch.

Fig. 1.9.2. A toggle switch Rotary switch - This has a knob that can be turned to open and close the contacts. It is often found in numerous table-top lamps and DC fans. An Example is shown in Fig. 1.9.3 .

Fig. 1.9.3. A rotary switch with 12 switch positions. Rocker switch - it uses a seesaw action. One side of the switch can be pressed down to close the contacts ( 1 or ON ), and the other side can be pressed down to open the contacts ( 0 or OFF ). Fig. 1.9.4 shows a common rocker switch.

Fig. 1.9.4. A rocker switch Knife switch - The contacts of a knife switch are usually exposed. It is made of a hinge that allows a metal conductor (the lever or knife) that can be inserted into or lifted from a slot or jaw. See Fig. 1.9.5 .

Fig. 1.9.5. A knife switch Push-button switch – The knob on this switch can be pushed to open or close the contacts of the switch. It has various applications such making the press buttons of a computer mouse.

In some makes of this switch, the switch can be pushed once to open the contacts and then pushed again to close them. In other words, each time the switch is pushed, the contacts alternate between open and close positions. See Fig. 1.9.6 .

Fig. 1.9.6. A push-button switch The contacts in some push-button switches can be either normally closed (NC) or normally open (NO). Magnetic Reed Switch – It is an electromagnetic switch. It consists of two leaf-like contacts (ferrous reeds) that are closely spaced and enclosed in a small air-tight glass tube. See Fig. 1.9.7 . In a normally open reed switch the two contacts will come together when you bring a magnetic field nearby, allowing current to flow. In a normally closed reed switch the two contacts will separate, interrupting flow of current, when you bring a magnetic field nearby. Unlike the mechanical switches discussed earlier, a reed switch does not require you to physically turn it on or off. It is controlled completely by a magnetic field.

Fig. 1.9.7. A reed switch with a nearby magnet to operate it Types of Contact Switches Normally open (NO) - The default state of the contacts of this switch is open. When the button is pushed, the contacts are closed. When the button is released the contacts open again. This implies that current can flow only when the button is pressed and held. Normally closed (NC) - The default state of the contacts of this switch is closed so current flows normally. When the button is pushed, the contacts are open and current does not flow. When the button is released the contacts close again and current flow resumes. 1. The type of connection they make with “poles” and “throws” The pole of a switch is the number of separate circuits that the switch can control. For example a single-pole switch controls only one circuit whereas a double-pole switch controls two separate circuits. In fact a double-pole switch is often made from two separate single-pole switches that are mechanically operated by the same button, lever or knob. The number of throws of a switch indicates the number of different output connections each pole of the switch can connect its input to. Fig. 1.9.8 and Fig. 1.9.9 illustrate how the most common types of throws, single-throw and double-throw work.

Fig. 1.9.8. A single throw switch schematic in (i) open state and (ii) closed state

Fig. 1.9.9. A double throw switch schematic in which (i) current flows through terminal A and (ii) current flows through terminal B As you can see from Fig. 1.9.8, in a double-throw switch the input terminal is connected to one of two available output terminals. In other words, a double-throw switch has three terminals. One of the terminals (the input ) is called the common terminal . The other two terminals (the outputs ) are often referred to as A and B . 1.9.2 Types of Switches The four common types of switches are illustrated in Fig. 1.9.10 .

Fig. 1.9.10. Four common types of switches: SPST, SPDT, DPST, DPDT S1 is a single pole, single throw switch ( SPST ). It is a basic on/off switch that you can use to turn only one circuit on or off. It has only two terminals: one for the input and one for the output. S2 is a single pole, double throw switch ( SPDT ). You can use this switch to route one input to one of two outputs. It is sometimes called an A/B switch because it allows you to choose between two outputs A and B. This switch has 3 terminals: one for the input and two for the outputs named A and B. S3 is a double-pole, single throw switch ( DPST ). This switch can turn on or off two circuits. There are 4 terminals in this switch: two inputs and two outputs. S4 is a double-pole, double throw switch ( DPDT ). This switch connects each of two separate inputs to one of two outputs A or B , that is, the combination of A1 and A2 or the combination of B1 and B2 . There are 6 terminals in this switch: two for the inputs, two for the A outputs, and two

for the B outputs. Practice Exercise 4: Using DPDT Switch to Control Light & Alarm Circuits Study the schematic diagram in Fig. E4.1 to do this exercise.

Fig. E4.1. using a DPDT switch to select a lamp-buzzer function or an LED-speaker function The schematic diagram is designed with the intention of producing a light and an alarm, using either the combination of a lamp and a buzzer or a combination of an LED and a speaker. Either of this combination should work depending on the position of the poles P1 and P2 of the DPDT switch. A specially designed electronic circuit A is used to supply the input signal needed for the Lamp-buzzer combination to function. Another specially designed electronic circuit B is used to supply the input signal needed for the LED-speaker combination to function. Use a pencil and paper to (i) redraw the schematic diagram to show how you would make only the lamp to light and only the buzzer to sound. (ii) redraw the schematic diagram to show how you would make only the LED to light and only the speaker to sound. 1.10 Understanding Wires, Cables & Wire Gauges 1.10.1 Difference Between Wire & Cable Wire and cable are two common terms used in the field of electronics and communication. Although they are often thought of as the same, they are not. A wire is a just single conductor that is usually made of copper or aluminium. On the other hand a cable refers to two or more insulated wires that are usually insulated and wrapped in one jacket. Multiple wires that have no insulation around them are classified as a single conductor. Most times, wires used in electronics are enclosed in some kind of insulation and cable jackets to protect and separate them from others adjacent to them. See Fig. 1.10.1 .

Fig. 1.10.1. Stripped wires inside insulations and a cable jacket. 1.10.2 Wire Gauges Wires are very important in electronics because they are used to carry electric currents and signals. For this reason we must choose the correct

sizes of wires . For example if too small a size of wire is used in a circuit, it could melt because it cannot handle the amount of current flowing through it. Similarly if too large a size of wire is used in a circuit, it would make the finished circuit cumbersome. So it is important to choose the appropriate wire size for an anticipated current level. Wire size is expressed in gauge number . The most common standard is the American Wire Gauge ( AWG ). In the AWG standard a smaller gauge number corresponds to a larger diameter wire (high current capacity) and vice versa. See Fig. 1.10.2 .

Fig. 1.10.2. Relative thickness of wire gauges and gauge numbers Table 1.10.1 shows a short list of some common AWG wire gauges, current capacities and resistance. You can learn more about AWG on wikipedia . Table 1.10.1. A list of some common AWG wire gauges. Note: 1 mil = 0.0254 mm (0.001 inch ) 1.10.3 Types of Cables Used in Electronics & Telecommunication The following are various types of cables used in practical electronics: Twisted pair cable – The two cables in a twisted pair cable are twisted across each other. Twisting of cables is used to minimize noise produced by magnetic couplings. That is why a twisted pair cable is very suitable for carrying signals in telecommunication and data communication. See Fig. 1.10.3 .

Fig. 1.10.3. Four twisted pair cables protected by a foil shield and a jacket Coaxial cable – It consists of an inner solid conductor (the center core ) with a surrounding paralleled outer foil conductor ( metallic shield ) and an outermost insulating layer ( jacket ) for the protection of the whole cable. Fig. 1.10.4 shows an example of a coaxial cable.

Fig. 1.10.4. A coaxial cable An insulating dielectric is used to separate the two conductors from each other. Most television cables are made of coaxial cables. Its performance is far more stable than that of a twisted pair cable. Multi conductor cable – A multi conductor cable contains two or more conductors that are insulated from each other. Its main purpose is to protect signal integrity, that is, to reduce hum, crosstalk and noise, hence they are called balanced line configuration cables. An example is shown in Fig. 1.10.5 .

Fig. 1.10.5. Three multi conductor cables Multi conductor cables are used in computers, instrumentation, control, communications, sound, audio, and data transmission. Fiber optic cable – A fiber optic cable uses a bundle of glass threads to transmit signals. It has a much greater bandwidth than ordinary metal cables, and therefore can carry more data. It is also less susceptible to interference. See Fig. 1.40.6 .

Fig. 1.10.6. An optic fiber cable For those reasons, fiber optic cables are preferred to traditional copper cables despite the fact that they are more expensive. 1. How to Set up A Modest Workshop for Yourself You do not need an elaborate workshop or laboratory to build basic electronic circuits. What you need is just a modest workplace that you can equip it with a set of basic tools as well as some basic electronic components to work with. So in this chapter, I will show you inexpensive tools you should acquire so you can be up and running quickly. Of course, you do not have to buy the tools all at once. You can just start with the simple collection of tools I recommend for you to work with in your small workspace. Later when you have acquired more advanced electronic skills, you can get a few more tools and equipment as your needs change. 2.1 Where You Can Set up A Modest Workshop To create a good place to work you can build a fancy workbench somewhere in your garage or in a spare room in your house. However if you are short of space you can set up your workshop just about anywhere. The two most import things you need are a small good workbench (preferably wooden) and a comfortable seat. See an example in Fig. 2.1.1 .

Fig. 2.1.1. An example of a modest workshop set up in a spare room. Source: Boing Boing 2.1.1 The Essential Ingredients of a Good Workshop The essential ingredients of any good workshop for creating electronic circuits are: An Adequate space: You should have adequate space for building your projects. If you are just getting started, a small work area – some 3 to 4 feet in the corner of your spare room or your garage – is ok. But as you develop more skills, you will certainly need more space. Warning : Ensure the location of your workshop is secure so that young children do not have access. Sooner or later your workshop will be filled with objects that can cause burns, shocks, or cuts, especially when ingested. Little children are very curious so it is very important to keep everything safely out of their reach. A comfortable seat: If you use a folding table or desk as your workbench a good office chair is the best seat. Since a workbench is about four to six inches taller than a desk, it will help to work comfortably while you are standing. A solid workbench: If you are just getting started, a simple card table or a small folding table should be adequate. As you develop more skills with time, you will want to go for a permanent and substantial workbench. For example, you ca use an old door set on top of a pair of old file cabinets to make an excellent workbench for yourself. Adequate lighting: Start with ambient light. The ideal lighting for building electronics circuits is overhead, in addition to proper ambient light. A light bulb from your side or behind you may not be adequate. If you can, but an inexpensive fluorescent shop light that you can suspend directly over your work area. See Fig. 2.1.2 .

Fig. 2.1.2. A suspended fluorescent fixture with two 4-foot tubes adapt well to most shop layouts and is easy to install If that is not possible in your workspace, another good lighting source is a desk lamp that swings overhead and throws light directly over your workbench. A constant supply of electricity: To build electronic circuits, you will certainly need a source of electricity nearby. One standard 13-amp or 15-amp electrical outlet has a sufficient current capacity, but you will need more electrical outlets with time. A very easy way to meet that need is to buy a multi-outlet power strip that you can place in convenient locations in your workspace, such as behind or on either side of your workbench. Tools storage: You need a good and safe place to store your tools and electronic parts (components). A very good storage you can use for your hand tools is a small sheet of pegboard mounted on the wall somewhere behind your workbench. You can use hooks to hang your tools as well so that they are within your reach. However, built-in cabinets are the best for larger tools like a drill or a saw. To store small electronic components, a multi-compartment storage box like the one shown in Fig. 2.1.3 is the best. I strongly advise you to purchase more than one storage boxes so that you will be able to store all your little components like resistors, capacitors, diodes, transistors, ICs and the likes.

Fig. 2.1.3. A Multicompartment storage box for storing small electronic components. Source: I also advise you keep at least two small shallow storage bins on your workbench. You need them for storing the components for the project you are currently working on. Such bins help you to keep your components together in one space instead of having them scattered all over your workbench. 2.2 The Basic Hand Tools for Your Workshop There are certain basic tools and supplies you need for building electronic projects. Fortunately, you do not need to purchase all of them at once. As you get more and more involved with your work, you will want to buy a wide variety of quality electronic tools and supplies. Fig. 2.2.1 shows some of the essential tools you will need at your disposal. We will look at a few more tools later in the book.

Fig. 2.2.1. Basic hand tools for electronic projects. Source: Screwdrivers: You do not need heavy-duty screwdrivers when building electronic projects. However, you should buy a good assortment of smalland medium-sized screwdrivers with both flat-blade and Phillips head. You will find the set of jeweler’s screwdrivers (also known as preset screwdrivers) shown inside a yellow box in Fig. 2.2.1 sometimes very useful. The swiveling knob on the top of each one helps in holding the screwdriver in a precise position while turning the blade.

Pliers: Occasionally you will use the standard flat-nosed pliers , but for most electronic projects, the needle-nose pliers (also called long-nose pliers) are more commonly used because they can be used for various types of work at such as bending and twisting wires, pushing wires through holes, picking up screws from crevices and so many more. See Fig. 2.2.1 Most needle-nose pliers I have seen also have a cutting edge that you can use to cut wire cutters. You need those with thin jaws for working with small electronic components. Wire cutters: Although the needle-nose pliers can be used to cut wires and component leads, a heavy-duty wire cutter is much better, especially for cutting thick wires. Wire/cable strippers: In Fig. 2.2.2 a set of wire/cable strippers was just used to strip some insulation off a small cable. When you use cable strippers, avoid applying too much pressure to prevent creation of weak spots in the cable that may eventually break it.

Fig. 2.2.2. A pair of wire/cable strippers. Source: Handheld magnifying glass: It is used to inspect soldered joints, read the codes and labels on small electronic components like diodes, resistors, and so on. See Fig. 2.2.1. Magnifying goggles: It is usually worn used to provide a completely hands-free magnification for small and delicate work. You will love those goggles that have lights mounted on them. See Fig. 2.2.3 .

Fig. 2.2.3. An engineer wearing magnifying googles. Source: Vise (also called third hand or circuit board holder): This is a common tool amongst engineers and hobbyists. It has a small stand and a couple of clips for holding the circuit you are working on, thereby freeing up your hands so you can do delicate work. See Fig. 2.2.4 .

Fig. 2.2.4. A vise for holding circuit boards while you work. Soldering Iron : This is a small hand-held tool used for heating up and melting solder for the purpose of making joints or connections between conductors on a circuit board. Since you will need this a lot, you can order an inexpensive soldering iron from or any other electronics parts dealer. See Fig. 2.2.5 . Soldering is the process of assembling electronic circuits using a soldering iron and solder. The main purpose of soldering is to create a permanent connection between two or more conductors such as two wires or between a conducting surface and a wire on a printed circuit board (PCB). Solder: It is the soft metal that can be melted with a soldering iron to join conductors together. A solder is a special alloy (mixture of two or more metals) of lead and tin and it usually has a low melting point. See Fig. 2.2.5 .

Fig. 2.2.5. A soldering iron (left) and a reel of solder (right). Source: Soldering iron stand/holder: It is used to hold and keep your hot soldering iron safely away from you and your work area when you are not soldering. Some soldering iron stands come with cleaning sponges. Ensure you damp your sponge (not soak) with water from time to time. The sponge can hold water because it is porous. When you rub the hot tip of your soldering iron on the wet sponge it makes globs of solder that may be clinging to it to fall off. You can order a soldering iron stand with a sponge on Amazon under $10. See Fig. 2.2.6 .

Fig. 2.2.6. A Soldering Iron stand with a sponge sold on Digital Multimeter: It is used to measure many electrical quantities like resistance, current, voltage and so on. Some of these measurements were discussed in chapter one. If you’re a beginner you can get an inexpensive multimeter similar to the one shown in Fig. 2.2.7 which I believe can help in most of the work you want to do for now.

Fig. 2.2.7. A digital multimeter with some of its functionalities labeled. Source: Rather than using various different meters, one good digital multimeter can be used to do various tests and identify component terminals, some of which are: 1. continuity test – to check if a wire or other conductor is not broken somewhere, that is, to test if it is electrically continuous . 2. open circuit test – to check if a wire or other conductor is broken somewhere, that is, to test if it is electrically open . 3. identifying the leads (or terminals) and polarity of a component like transistor, capacitor, diode, rectifiers, battery polarities (positive and negative poles), and so on.

Solderless Breadboard - A breadboard is a construction base or a plugboard that you can use to prototype your electronic circuits without soldering. Very often it is used for testing if a complete circuit, or a section of a circuit, can function before taking the pains to solder it. It can also be used as an instructional material for students of electronics. See Fig. 2.2.8 .

Fig. 2.2.8. A wired breadboard showing a few electronic components It has many holes in which you can insert/plug either wires or electronic components like resistors, transistors, capacitors, ICs and so on to create a complete electronic circuit without any soldering. It is a must-have because you want to experiment with various circuit layouts. When you are done with a circuit, you can take the components and the connection wires out of the breadboard, and then reuse them to wire a completely different circuit. Fig. 2.2.8 shows an inexpensive breadboard purchased from for only $6. You can still order a less expensive breadboards that is smaller than this, but this one (about 7 by 4 inches) is large enough for you to wire all the circuits I present in this book. Wires - A wire is a very important items to have in your workshop or lab. It is basically a length of a conductor like copper. Sometimes it is made of aluminum or other metals. As discussed in section 1.10, a conductor is usually covered with an outer layer of insulation usually made of polyethylene. There are two basic types of wires: Solid wire: It is made from a single piece of conductor like copper and is protected with an outer layer of insulation. Stranded wire: It is a bunch of smaller wires that are woven together and protected with an outer layer of insulation. See Fig. 2.2.9.

Fig. 2.2.9. Solid and stranded wires For the projects described in this book, you should use solid wires because they are easier to solder, insert into the holes in your breadboard holes, and are easy to use for making other types of terminal connections. One great disadvantage of stranded wires is they are a great potential for short circuits, especially where two or more bunches are used in the same circuit. For example, if one tiny strand gets separated from other wires in the bunch during soldering, it can go to touch a wire in a different bunch, creating a short circuit. This can cause problems when you power your circuit later. One advantage of stranded wires is they are more flexible than solid wires. A solid wire can be broken if it is bent too often, and this is why wires that are frequently bent and moved are usually made stranded.

For most of your electronics projects, you will want to use AWG of 20 to 22. Standard wire gauges were discussed in section 1.10.2 wire. Finally, you must know that wire insulations come with some color codes. The colors do not affect the electrical performance of wires inside. The colors are only used to indicate the purpose of the wire. Let us take a DC circuit as an example. It is common to see a red wire used to indicate positive ( + ) voltage connection and a black wire used to indicate negative ( − ) connections. To begin your electronic projects, I advise you order a flexible roll of wire as follows: One roll of AWG 20 (solid wire) One roll of AWG 20 (stranded wires) One roll of AWG 22 (solid wire) One roll of AWG 22 (stranded wires). Find a few different colors if you can. Flexible wires are very cheap and are readily available to ship on Amazon. You can order from your local dealer if you like. See a sample in Fig. 2.2.10 .

Fig. 2.2.10. AWG 20 colored electronics stranded wire. Source: Batteries: They are needed to power the circuits covered in this book. You will want to buy 12-volt and 9-volt batteries which are the ones you will need most. Alternatively you may want to get four to eight pieces 1.5-volt AA batteries with their holders. I suggest you buy the rechargeable ones. Although they cost more initially, they can easily be recharged when they lose their charges. Of course you will also need a battery charger to recharge them. In Fig. 2.2.11 , a few types of batteries used to power electronic circuits are shown.

Fig. 2.2.11. A few types of batteries used for powering electronic circuits Battery Holders: They can be used to connect your batteries to the circuit you have built. If you prefer AA batteries, you should get at least one AA battery holder like that shown in Fig. 2.2.12 .

Fig. 2.2.12. A battery holder that holds four 1.5-volt AA batteries. You should also order a couple 9-volt battery clips like the one shown in Fig. 2.2.13 .

Fig. 2.2.13. 9-volt battery clip Electrical tape: Get a few rolls of PVC or other electrician’s tape. See a few samples in Fig. 2.2.14 .

Fig. 2.2.14. A few electrical tapes You can use them to wrap and hold your temporary wire connections or joints together to keep them from shorting out. Air blower: You will this to blow dust off your old circuit board or project. See a common one Fig. 2.2.15 .

Fig. 2.2.15. Air blower Cable ties: They are little plastic ties, also called zip ties , that are often used for holding wires, cables and other insulated conductors temporarily (or permanently) together. See some of them in Fig. 2.2.16 .

Fig. 2.2.16. Four cable ties (the two upper ones are unused while the two lower ones are used to hold some cables together. Source: . Jumper clips: These are short wires with one alligator clip attached on each end. A jumper clip is typically 10 or 20 inches long and has an alligator clip attached on either end, as shown in Fig. 2.2.17 . They are often used to create quick connections between electronic components for testing purposes.

Fig. 2.2.17. Two sets of jumper clips 2.3 Basic Electronic Components for Your Workshop In addition to all the supplies and tools described in section 2.2, I suggest you also gather a few inexpensive electronic components to get you started with building your circuits. Like I said earlier, you do not need to buy all the components at once. Just gather at least the basic ones before going farther in this book. Try to buy these electronic components in person at much cheaper prices at the nearest RadioShack store (or online at ). Alternatively, you can buy them at a specialty electronics store or any other electronic parts distributor in your community. Resistors : I already discussed resistors, their color codes and power rating in section 1.5. A resistor is a passive two-terminal electrical component that is used to reduce the flow of electric current. You will find out that nearly all electronic circuits in this book have one or more resistors. In nearly all the circuits in this book, resistors of ¼ watt rating are used. You should purchase a wide variety of resistance values. I strongly recommend you purchase a minimum of 10 each of the 18 resistors in Table 2.3.1 : Table 2.3.1. Values of resistors to be purchased (10 of each) You can even save money by ordering a package containing a large assortment of carbon-film resistors. For example, you can order a pack of 500 different resistors at RadioShack for just 15 dollars. Capacitors : Capacitors are also very common electronic components. A capacitor (originally called a condenser) is a two-terminal device that temporarily stores electric charges. You will learn about capacitors in detail later in the book. Fig. 2.3.1 shows variety of capacitors:

Fig. 2.3.1. Varieties of capacitors There are several varieties of capacitors. The most common two are the electrolytic (or aluminum ) and ceramic disk . The capability of a capacitor to store charge is called the capacitance and is usually measured in a unit called farad ( F ). Since farad is a rather large unit of capacitance, the microfarad ( μF ) is often used. Start by ordering an assortment of capacitors such as 5 each of the values in Table 2.3.2 : Table 2.3.2. Values of capacitors to be purchased (5 of each) Diodes : A diode is a device that allows current to flow in only one direction (from the anode to cathode). It is found in many electronic circuits. Fig. 2.3.2 shows some of the most common types of diode, their identification numbers and the circuit symbol at the top.

Fig. 2.3.2: Three common types of diodes with their identification numbers. The circuit symbol is at the top Light-Emitting Diodes (LEDs) : An LED is a special type of diode that emits light when electric current flows through it. They come in various colors. See Fig. 2.3.3 . We will study diodes in greater detail later.

Fig. 2.3.3: Three most common types of LEDs: Red, Blue and Yellow

Transistors : A transistor is a three-terminal devices and is one of the most important electronic components. The terminals are called the base (B) , collector (C) and emitter (E) . This is how it works: when you apply the correct amount of voltage to the base, electric current then flows from the collector to the emitter. A transistor is bi-polar, that is, it is either NPN or PNP . See some commonly used transistors in Fig. 2.3.4 . The NPN type is the most commonly used for amplifying weak signals. We will study transistors in greater detail later.

Fig. 2.3.4. Some common types of transistors Integrated Circuit : A monolithic or integrated circuit (often simply referred to as an IC , a chip , or a microchip ) is a set of electronic circuits built on one small flat piece (the chip) of semiconductor material that is normally silicon. It is usually an integration of large number of other electronic components such as transistors, diodes, and so on. ICs are the building blocks of many modern electronic devices like your computer and cellphone. Fig. 2.3.5 . Shows a few integrated circuits.

Fig. 2.3.5. A few integrated circuits (ICs) 1. Workshop Safety: How to Stay Safe

Fig. 3.1.1. Electrical hazard sign you should put at the workshop/lab entrance or near your workbench In this chapter we will look at some important safety practices you must follow to avoid accidents in any electrical or electronic workshop , including yours, especially when you experiment with electronic components. When you follow these precautions and use the safety equipment recommended in this book, you, your friends and other people will be safe from the risks of spark, fire, electric shock and injury from electrical/electronic tools, equipment and instruments used in a workshop or laboratory. Before we proceed I want to ensure you that none of the electronic projects described in this book are dangerous . In fact none of them poses any threat at all. Still, I strongly advise you to take the precautions described below. 3.1 General Workshop Safety Before you start working on any electronic circuit, I strongly advise you follow the following basic safety precautions to minimize hazards: 1. Remove any electrical or electronic equipment from the power source (such socket outlets) when it is no longer in use or no longer needed. 2. Do not work on any electronic/electrical equipment or attempt repairs with high voltage on. 3. Never assume a power circuit is dead (off). Test and test again to confirm with a multimeter. 4. Ensure you have removed the power to a circuit before removing and replacing a fuse and replace. 5. Ensure that all your electronic equipment is properly grounded. If it is damaged, replace it. For example, replace the cable of the equipment instead of repairing it with an insulating tape. 6. Always use the right repair and maintenance tools. For example, use your pliers, not a cutter, to twist or bend cables. 7. Always return the cover of a circuit after removing it to reduce the risk of electric shock. 8. Avoid circuit overloading. An overloaded circuit is one that carries more current than it is designed to handle. This creates a risk of overheating that can make power cables to melt, resulting in fire outbreak. Overloading can happen for instance when you connect too many appliances, especially high-power appliances like heaters or power drills, to the same socket outlet. This causes drawing of a very large current from the socket. 1. Always have safety equipment like a fire extinguisher, a first-aid kit and even a mobile phone nearby so you can someone for assistance in a case of an accident. 2. Use an isolation transformer when you are working on an electronic circuit or equipment powered by AC. 3.2 Personal Workshop Safety To ensure that you are safe when working on electronic circuits, follow these personal safety precautions: 1. Always keep your work area dry. Presence of water or moisture in your work space can aid electric shock. So stay dry to stay safe . 2. Before you test or work on any new equipment always ensure you read the safety procedures that come with it. 3. Always work in a well-ventilated area. 4. Avoid wearing flappy or lose dresses like a gown when working in the workshop or lab. 5. Do not work with metal jewelries like rings, watches, long dangling necklaces, and bracelets on your hands.

6. Ensure you wear safety goggles whenever you are sawing, cutting or drilling. Some bits of blade or the object you are working on can easily break off and hit your face or even your eye. You certainly do not want bits of insulation, broken drill bits or copper wire in your eyes when you are working. 7. Wash your hands thoroughly before you touch your face, nose, mouth or eyes, especially after working with solder or other electronic components. Sometimes small bits of lead or other potentially toxic substances can get on your hands. 8. Always check for signs of defects, wear, tear and fraying on any electronic equipment cord, cable, and connectors. Also avoid knotting and binding of cables or routing them under the carpets. 9. Wear special safety rubber shoes and insulator gloves when working or carrying out repairs in your workshop or Lab. 10. Ensure that you check your work and confirm everything is okay (especially after a repair or maintenance work) before connecting power. 3.2.1 Soldering Safety Soldering is important in an electronic workshop but it can also be a source of fire hazard. You should make your soldering iron hot enough to melt your solder but you may also accidentally use it to ignite a combustible material like paper or burn the insulation of the soldering iron cord itself. For this reason: 1. Be constantly aware of a hot soldering iron in your workshop. Do not plug it in the electrical socket when you do not need it. Always unplug it when you finish your soldering. 2. Do not set your hot soldering iron directly down on the workbench. Instead make use of the holder or stand to safely hold it while it is hot. The soldering iron stand elevates the soldering iron safely away from your workbench. 3. Give your soldered joints and components some time (about 1 to 2 minutes) to cool down before you touch or handle them. 4. Ensure your soldering iron’s power cord is placed safely away from your work so that you do not accidentally bump it, knock it out of its stand and perhaps cause a burn. 3.3 Safety from Unexpected High Voltages One of the biggest risks of electric shock in electronics often comes from unexpected high voltages. It is easy to watch out for voltages that you know about, like those in your power supplies or batteries. However, there are some electronic circuits specially designed to amplify voltages. For example, your circuit may be running on a 6-volt battery, a much higher voltage may be present at certain points in the circuit. Furthermore, there are certain electronic devices that can store electric charge for hours or even days after you have disconnected electric power from them. The most notorious of such devices is the capacitor, which we discussed in section 2.3. A capacitor alternately stores and releases electrical charges. Therefore be wary of any circuit containing capacitors, especially large aluminum capacitors . Common small-size ceramic-disk capacitors like those shown in Fig. 2.3.1, store very little charge. Hence if a circuit you are building has one or more capacitors about the size of batteries, be very careful when you are working around them because they can hold large charges even hours after electric power has been cut off. Take the following safety precautions regarding capacitors: 1. A very common where large capacitors are found is in power-supply circuits such as that shown in Fig. 1.1.2 and Fig. 1.1.3. In fact, any electronic device that is plugged into a household electrical outlet may contain large capacitors in its power-supply. So work carefully around these capacitors. 2. The flash camera is another common equipment where you may find high-voltage capacitors. Although the battery of a flash camera may be a small 1.5 volt, the capacitor used to drive the flash unit may well be storing a charge of over 300 volts! Work carefully around these capacitors. 3. Always discharge the capacitor in a circuit first before you start working on it. You can use the blade of your screw driver to short out the leads and discharge small capacitors. Ensure you are touching only the insulated handle of the screwdriver as you do this and not touch any other part of the circuit with your bare hand. 4. To discharge a larger capacitor connect its leads to a large resistor or a lamp. A very easy way to do this is to wire a lamp holder to a pair of alligator clips. Then screw the lamp into the holder. Finally connect the clips carefully to the capacitor leads. If the capacitor is storing a

charge, you will see the lamp glow for a moment as the capacitor discharges through the lamp. 5. Stop working on a circuit where large capacitors are present and you are not completely confident in what you are doing. Refer to this document about workshop safety on IEEE’s website to learn more: . IEEE stands for Institute of Electrical and Electronics Engineers. 1. More Helpful Resources Below is a list of a few other books that I believe you will find very helpful. The first book in my list below, Getting Started with Electronics Projects ” will help you to build very powerful and educative electronic projects and it is free! 1. Getting Started with Electronics Projects ( )– Free pdf Book . 2a. Ladder Logic Programming Fundamentals 2019: Learn Ladder Logic Concepts Step By Step to Program PLC’s on The RS Logix 5000 Platform - ( ) – Kindle. 2b. Ladder Logic Programming Fundamentals 2019: Learn Ladder Logic Concepts Step By Step to Program PLC’s on The RS Logix 5000 Platform ( )- Paperback. 1. Artificial Intelligence Fundamentals: The Foundations & History of Intelligent Machines - ( ). 2. Fundamentals of Satellite Navigation Systems: How to Design GPS/GNSS Receivers Book 1 - The Principles, Applications & Markets – ( ). 3. Excel Pivot Tables & Charts: A Step By Step Visual Guide – ( ) 4. How to Study in USA on Scholarship: For Getting Financial Aids College Admissions & Visa Approval – ( ). 5. How to Study in Germany Tuition Free: Get Free Education, Admission & Visa Approval. Get Prepared for Studies at German Universities - ( ) 6. How to study in Australia on Scholarship: For Getting Financial Aids College Admissions & Visa Approval – ( ). 7. Cloud Computing Fundamentals: Learn the Latest Cloud Technology and Architecture with Real-World Examples and Applications - ( ). Conclusion Dear reader, I hope that you have found this book very helpful for learning the fundamentals of practical electronic circuits. You may find some of the concepts we have covered in this book confusing at first. However, with time and effort, you will be able to build simple and moderately complex circuits. So watch out for my next book on practical electronic circuits. Contact me through email if you have questions or a request. I wish you success! Regards, A. B. Lawal [email protected]