Basic Electronics
Objective and outcomes
The Objective of this short Basic electronic course is to get the learners toe have a basic understanding of electronics and to
get them interested in electronics. The Basics can be applied in the learners school work for thoughts that study Science,
Electricity, Digital electronics and Programming.
Prerequisites
Learners must have completed Grad 9 (St7) with any of the following subjects Science, Electricity, Digital electronics and
Programming
Introduction
This training is developed to give learners the basic understanding of electronics to have just enough knowledge to let them
understand what is needed to become part of the Secunda Radio Armature Clubs BACAR project. After this course the Lerner
will still have to do self-study and more study’s to become professional in the field of Electronics.
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Index
Chapter
Description
Chapter 1
Ohm’s Law
Page
2
Chapter 2
Resistor Basics
6
Chapter 3
Light-emitting Diodes (LEDs)
9
Chapter 4
Capacitor
12
Chapter 5
Logic gates
15
Chapter 6
AND gate Astable
17
Chapter 7
How to Solder
20
Chapter 8
First Aid for Burns
23
Acknowledgement
24
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Chapter 1
Ohm’s Law
Georg Ohm Published in 1827 that :
“That the current through a conductor between two points is directly proportional to the potential difference across the two
points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that
describes this relationship”
I=Current measured in Amperes (A)
V=Potential measured in Volt (V)
R= Resistance measured in Ohm (Ω)
Voltage
We define voltage as the amount of potential energy between two points on a circuit. One point has more charge than another. This difference in
charge between the two points is called voltage. It is measured in volts, which, technically, is the potential energy difference between two points
that will impart one joule of energy per coulomb of charge that passes through it (don’t panic if this makes no sense, all will be explained). The
unit “volt” is named after the Italian physicist Alessandro Volta who invented what is considered the first chemical battery. Voltage is represented
in equations and schematics by the letter “V”.
When describing voltage, current, and resistance, a common analogy is a water tank. In this analogy, charge is represented by
the water amount, voltage is represented by the water pressure, and current is represented by the water flow. So for this
analogy, remember:



Water = Charge
Pressure = Voltage
Flow = Current
Consider a water tank at a certain height above the ground. At the bottom of this tank there is a hose.
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The pressure at the end of the hose can represent voltage. The water in the tank represents charge. The more water in the
tank, the higher the charge, the more pressure is measured at the end of the hose.
We can think of this tank as a battery, a place where we store a certain amount of energy and then release it. If we drain our
tank a certain amount, the pressure created at the end of the hose goes down. We can think of this as decreasing voltage, like
when a flashlight gets dimmer as the batteries run down. There is also a decrease in the amount of water that will flow
through the hose. Less pressure means less water is flowing, which brings us to current.
Current
We can think of the amount of water flowing through the hose from the tank as current. The higher the pressure, the higher
the flow, and vice-versa. With water, we would measure the volume of the water flowing through the hose over a certain
period of time. With electricity, we measure the amount of charge flowing through the circuit over a period of time. Current is
measured in Amperes (usually just referred to as “Amps”). An ampere is defined as 6.241*1018 electrons (1 Coulomb) per
second passing through a point in a circuit. Amps are represented in equations by the letter “I”.
Let’s say now that we have two tanks, each with a hose coming from the bottom. Each tank has the exact same amount of
water, but the hose on one tank is narrower than the hose on the other.
We measure the same amount of pressure at the end of either hose, but when the water begins to flow, the flow rate of the water in the tank
with the narrower hose will be less than the flow rate of the water in the tank with the wider hose. In electrical terms, the current through the
narrower hose is less than the current through the wider hose. If we want the flow to be the same through both hoses, we have to increase the
amount of water (charge) in the tank with the narrower hose.
This increases the pressure (voltage) at the end of the narrower hose, pushing more water through the tank. This is analogous
to an increase in voltage that causes an increase in current.
Now we’re starting to see the relationship between voltage and current. But there is a third factor to be considered here: the
width of the hose. In this analogy, the width of the hose is the resistance. This means we need to add another term to our
model:




Water = Charge (measured in Coulombs)
Pressure = Voltage (measured in Volts)
Flow = Current (measured in Amperes, or “Amps” for short)
Hose Width = Resistance
Resistance
Consider again our two water tanks, one with a narrow pipe and one with a wide pipe
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It stands to reason that we can’t fit as much volume through a narrow pipe than a wider one at the same
pressure. This is resistance. The narrow pipe “resists” the flow of water through it even though the water is at
the same pressure as the tank with the wider pipe.
In electrical terms, this is represented by two circuits with equal voltages and different resistances. The circuit with the higher
resistance will allow less charge to flow, meaning the circuit with higher resistance has less current flowing through it.
This brings us back to Georg Ohm. Ohm defines the unit of resistance of “1 Ohm” as the resistance between two points in a
conductor where the application of 1 volt will push 1 ampere, or 6.241×1018 electrons. This value is usually represented in
schematics with the greek letter “Ω”, which is called omega, and pronounced “ohm”.
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Chapter
2
Resistor Basics
Resistors are electronic components which have a specific, never-changing electrical resistance. The resistor’s resistance limits
the flow of electrons through a circuit.
They are passive components, meaning they only consume power (and can’t generate it). Resistors are usually added to
circuits where they complement active components like op-amps, microcontrollers, and other integrated circuits. Commonly
resistors are used to limit current, divide voltages, and pull-up I/O lines.
Resistor units
The electrical resistance of a resistor is measured in ohms. The symbol for an ohm is the greek capital-omega: Ω. The
(somewhat roundabout) definition of 1Ω is the resistance between two points where 1 volt (1V) of applied potential energy will
push 1 ampere (1A) of current.
Schematic symbol
All resistors have two terminals, one connection on each end of the resistor. When modeled on a schematic, a resistor will
show up as one of these two symbols:
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Two common resistor schematic symbols. R1 is an American-style 1kΩ resistor, and R2 is an international-style 47kΩ resistor.
Types of Resistors
Resistors come in a variety of shapes and sizes. They might be through-hole or surface-mount. They might be a standard,
static resistor, a pack of resistors, or a special variable resistor.
Decoding the color bands
Through-hole, axial resistors usually use the color-band system to display their value. Most of these resistors will have four
bands of color circling the resistor.
The first two bands indicate the two most-significant digits of the resistor’s value. The third band is a weight value, which
multiplies the two significant digits by a power of ten.
The final band indicates the tolerance of the resistor. The tolerance explains how much more or less the actual resistance of
the resistor can be compared to what its nominal value is. No resistor is made to perfection, and different manufacturing
processes will result in better or worse tolerances. For example, a 1kΩ resistor with 5% tolerance could actually be anywhere
between 0.95kΩ and 1.05kΩ.
How do you tell which band is first and last? The last, tolerance band is often clearly separated from the value bands, and
usually it’ll either be silver or gold.
Here’s a table of each of the colors and which value, multiplier or tolerance they represent:
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Here’s an example of a 4.7kΩ resistor with four color bands:
When decoding the resistor color bands, consult a resistor color code table like the one above. For the first two bands, find that
color’s corresponding digit value. The 4.7kΩ resistor has color bands of yellow and violet to begin - which have digit values of 4
and 7 (47). The third band of the 4.7kΩ is red, which indicates that the 47 should be multiplied by 102 (or 100). 47 times 100
is 4,700!
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Chapter 3
Light-emitting Diodes (LEDs)
LEDs are all around us: In our phones, our cars and even our homes. Any time something electronic lights up, there’s a
good chance that an LED is behind it. They come in a huge variety of sizes, shapes, and colors, but no matter what they look
like they have one thing in common: they’re the bacon of electronics. They’re widely purported to make any project better and
they’re often added to unlikely things (to everyone’s delight).
Unlike bacon, however, they’re no good once you’ve cooked them. This guide will help you avoid any accidental LED
barbecues! First things first, though. What exactly is this LED thing everyone’s talking about?
LEDs (that’s “ell-ee-dees”) are a particular type of diode that convert electrical energy into light. In fact, LED stands for “Light
Emitting Diode.” (It does what it says on the tin!) And this is reflected in the similarity between the diode and LED schematic
symbols:
In short, LEDs are like tiny light bulbs. However, LEDs require a lot less power to light up by comparison. They’re also more
energy efficient, so they don’t tend to get hot like conventional light bulbs do (unless you’re really pumping power into them).
This makes them ideal for mobile devices and other low-power applications. Don’t count them out of the high-power game,
though. High-intensity LEDs have found their way into accent lighting, spotlights and even automotive headlights!
How to Use LED’s
1) Polarity Matters
In electronics, polarity indicates whether a circuit component is symmetric or not. LEDs, being diodes, will only allow current to
flow in one direction. And when there’s no current-flow, there’s no light. Luckily, this also means that you can’t break an LED
by plugging it in backwards. Rather, it just won’t work.
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The positive side of the LED is called the “anode” and is marked by having a longer “lead,” or leg. The other, negative side of
the LED is called the “cathode.” Current flows from the anode to the cathode and never the opposite direction. A reversed
LED can keep an entire circuit from operating properly by blocking current flow. So don’t freak out if adding an LED breaks
your circuit. Try flipping it around.
2) More Current Equals More Light
The brightness of an LED is directly dependent on how much current it draws. That means two things. The first being that
super bright LEDs drain batteries more quickly, because the extra brightness comes from the extra power being used. The
second is that you can control the brightness of an LED by controlling the amount of current across it. But, setting the mood
isn’t the only reason to cut back your current.
3) There is Such a Thing as Too Much Power
If you connect an LED directly to a current source it will try to dissipate as much power as it’s allowed to draw, and, like the
tragic heroes of olde, it will destroy itself. That’s why it’s important to limit the amount of current flowing across the LED.
For this, we employ resistors. Resistors limit the flow of electrons in the circuit and protect the LED from trying to draw too
much current. Don’t worry, it only takes a little basic math to determine the best resistor value to use.
The basic template for an LED circuit is pretty simple, just connect your battery, resistor and LED in series. Like this:
You can use the information from the last section to help you determine the exact value you need
A standard LED needs a about of 20mA to light up and it need 1.5V to operate if the Battery is 9V what is the Resistor value?
Apply Ohm’ Law
R=V/I where V over the resistor is the Battery Voltage – the LED Voltage
R=(9V-1.5V)/0.02A
= 375 Ohm
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Chapter 4
Capacitor
Capacitors are short term charge stores that hold electrical energy in the form of an electric field. They are used widely in
electronic circuits. They are at the heart of all electronic timing devices. They also can act as back up power supplies to
memory chips. Another use is to smooth out the ripples from a power supply; in effect they are electrical springs. They are
also found in oscillators, signal generators, tone controls (filter circuits) to name a few. A variable capacitor is used to tune
radios.
At its simplest a capacitor consists of two metal plates separated by a layer of insulating material called a dielectric.
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Capacitance is measured in units called farads (F). A farad is a very big unit, and we are much more likely to use
microfarads
nanofarads (nF). You may even see picofarads (pF)
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
F

1 nF = 1 × 10-9 F

1 pF = 1 × 10-12 F
The symbol for a capacitor is shown below:
There are two types of capacitor, electrolytic and non-electrolytic.
 Electrolytic capacitors hold much more charge
 Electrolytic capacitors have to be connected with the correct polarity, otherwise they can explode.

Electrolytic
Non electrolytic
Advantages:
 High capacitance
 Can have high
working voltages.
Advantages:
 Do not lose charge
 Polarity does not
matter
 Stable up to 106 Hz
(or more)
Disadvantages:
 Low capacitance
Disadvantages:
 Polarity important
 High leakage current
 Not stable above 10
kHz
 Can be damaged by
AC
RC Network
At its simplest the RC network is a series circuit consisting of a capacitor and a resistor connected to a source.
If we discharge a capacitor, we find that the charge decreases by the same fraction for each time interval. If it takes time t for
the charge to decay to 50 % of its original level, we find that the charge after another t seconds is 25 % of the original (50 %
of 50 %). This time interval is called the half-life of the decay. The decay curve against time is called an exponential
decay.
Discharging a Capacitor
The voltage, current, and charge all decay exponentially during the capacitor discharge.
We can note the voltage and current at time intervals and plot the data, which gives us the exponential graph, using a circuit
like this.
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The graph is like this:
We should note the following about the graph:
 Its shape is unaffected by the voltage.
 The half life of the decay is independent of the voltage.
The product RC (capacitance × resistance) is called the time constant. The units for the time constant are seconds. We can
go back to base units to show that ohms × farads are seconds.
After RC seconds the voltage is 37 % of the original.
 Increase the resistance.
 Increase the capacitance.
The half-life is 69 % of the time constant.
To increase the time taken for a discharge we can:
t1/2 = 0.69 RC
Electronic engineers use the time constant in preference to the half-life. In theory the exponential decay should never allow a
capacitor to discharge completely, but in practice, a rule of thumb is that the capacitor is discharged completely after 5 RC
seconds.
Worked example
A 5000
(a)
What is the time constant?
(b)
What is the half-life of the decay?
Answer
-6 F = 10 s.
(b) t1/2 = 0.693 × RC = 0.693 × 10 = 6.93 s.
_______________________________________________________________
Chapter 5
Logic gates
Logic gates are at the heart of digital electronics. In digital electronics, we need to know nothing about electricity, other
than the difference between on (1) and off (0).
Digital electronics is widely used in telecommunications, computers, and sound recording. All digital devices are based on
these simple building blocks. In a digital camera, there are millions of these gates
.
The NOT gate
The simplest of all the logic gates is the NOT gate. Notice that when we write the name of a logic gate, we always write it
in UPPER CASE letters. Truth tables summarise the output condition for a variety of input conditions.
For the NOT gate the truth table looks like this:
INPUT
OUTPUT
0
1
1
0
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The NOT gate is often called an inverter.
The AND gate
For the AND gate the truth table looks like this:
A
B
OUTPUT
0
0
0
1
0
0
0
1
0
1
1
1
We can show the AND gate as a simple circuit of two switches in series. When both switches are closed, the bulb lights up.
The NAND gate
For the NAND gate the truth table looks like this:
A
B
OUTPUT
0
0
1
1
0
1
0
1
1
1
1
0
The NAND gate gets its name from the contraction of NOT and AND. The small circle on the output line tell us that it has an
inverting function. NAND gates are particularly easy to make, and other gates are actually made up of combinations of NAND
gates. We will look at this later.
_______________________________________________________________
Chapter 6
NAND gate Astable
We can make an astable circuit the output of which oscillates at a frequency determined by the value of the time
constant of a capacitor and a resistor.
If you look carefully at the arrangements of the NAND gates, it does not take a genius to see that the two NAND
gates are wired as NOT gates, so this set up is also called a NOT gate astable. Let’s have a look at how the
circuit works:
 Suppose the output of Y is high.
 This means that the input to Y is low.
 The capacitor will charge up.
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





A current flows through the resistor R which means there will be a voltage across it.
This raises the input to Y to high and it will trigger to the output being low.
Since X is connected to the feedback loop, its output will be low.
The low output of X will cause the capacitor to discharge.
This makes the input to Y low, hence the output to go to high.
And so on…
We can summaries this in the timing diagram:
We can show that the mark time is given by the relationship:
tH =1.1 RC
Similarly the space time is given by:
tL 1.1 RC
Therefore the period:
T = tH + tL = 2.2 RC
So the frequency:
f = 1/T = 1/2.2 RC
NAND gate Astable Practical Project
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Chapter 7
How to Solder
First a few safety precautions:





Never touch the element or tip of the soldering iron.
They are very hot (about 400°C) and will give you a nasty burn.
Take great care to avoid touching the mains flex with the tip of the iron.
The iron should have a heatproof flex for extra protection. An ordinary plastic flex will melt immediately
if touched by a hot iron and there is a serious risk of burns and electric shock.
Always return the soldering iron to its stand when not in use.
Never put it down on your workbench, even for a moment!
Work in a well-ventilated area.
The smoke formed as you melt solder is mostly from the flux and quite irritating. Avoid breathing it by
keeping you head to the side of, not above, your work.
Wash your hands after using solder.
Traditional solder contains lead which is a poisonous metal.
If you are unlucky (or careless!) enough to burn yourself please read the First Aid section.
Preparing the soldering iron:





Place the soldering iron in its stand and plug in.
The iron will take a few minutes to reach its operating temperature of about 400°C.
Dampen the sponge in the stand.
The best way to do this is to lift it out the stand and hold it under a cold tap for a moment, then
squeeze to remove excess water. It should be damp, not dripping wet.
Wait a few minutes for the soldering iron to warm up.
You can check if it is ready by trying to melt a little solder on the tip.
Wipe the tip of the iron on the damp sponge.
This will clean the tip.
Melt a little solder on the tip of the iron.
This is called 'tinning' and it will help the heat to flow from the iron's tip to the joint. It only needs to be
done when you plug in the iron, and occasionally while soldering if you need to wipe the tip clean on
the sponge.
You are now ready to start soldering:





Hold the soldering iron like a pen, near the base of the handle.
Imagine you are going to write your name! Remember to never touch the
hot element or tip.
Touch the soldering iron onto the joint to be made.
Make sure it touches both the component lead and the track. Hold the tip
there for a few seconds and...
Feed a little solder onto the joint.
It should flow smoothly onto the lead and track to form a volcano shape as shown in the diagram. Apply the solder to
the joint, not the iron.
Remove the solder, then the iron, while keeping the joint still.
Allow the joint a few seconds to cool before you move the circuit board.
Inspect the joint closely.
It should look shiny and have a 'volcano' shape. If not, you will need to reheat it and feed in a little more solder. This
time ensure that both the lead and track are heated fully before applying solder.
What is solder?
Traditional solder is an alloy (mixture) of tin and lead, typically 60% tin and 40% lead. It melts at a temperature of about 200°C.
Modern lead-free solder is an alloy of tin with other metals including copper and silver. It melts at a temperature of about
220°C.
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Coating a surface with solder is called 'tinning' because of the tin content of solder.
Always wash your hands after using solder, this is especially important with traditional solder because it contains lead
which is toxic.
The best size of solder for electronics is 22swg (swg = standard wire gauge). I recommend buying lead-free solder such as the
reel shown on the right.
Solder for electronics use contains tiny cores of flux, like the wires inside a mains flex. The flux is corrosive, like an acid, and it
cleans the metal surfaces as the solder melts. This is why you must melt the solder actually on the joint, not on the iron tip.
Without flux most joints would fail because metals quickly oxidise and the solder itself will not flow properly onto a dirty,
oxidised, metal surface.
Desoldering
At some stage you will probably need to desolder a joint to remove or re-position a wire or component. There are two ways to
remove the solder:
1. With a desoldering pump (solder sucker)






Set the pump by pushing the spring-loaded plunger down until it locks.
Apply both the pump nozzle and the tip of your soldering iron to the joint.
Wait a second or two for the solder to melt.
Then press the button on the pump to release the plunger and suck the
molten solder into the tool.
Repeat if necessary to remove as much solder as possible.
The pump will need emptying occasionally by unscrewing the nozzle.
Using a desoldering pump (solder sucker)
_________________________________________________
Chapter8
First Aid for Burns
Most burns from soldering are likely to be minor and treatment is simple:



Immediately cool the affected area under gently running cold water.
Keep the burn in the cold water for at least 5 minutes (15 minutes is recommended). If ice is readily available this
can be helpful too, but do not delay the initial cooling with cold water.
Do not apply any creams or ointments.
The burn will heal better without them. A dry dressing, such as a clean handkerchief, may be applied if you wish to
protect the area from dirt.
Seek medical attention if the burn covers an area bigger than your hand.
To reduce the risk of burns:



Always return your soldering iron to its stand immediately after use.
Allow joints and components a minute or so to cool down before you touch them.
Never touch the element or tip of a soldering iron unless you are certain it is cold.
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Acknowledgement
Thanks to the following web pages for information that was used to build this module.
http://en.wikipedia.org/wiki/Ohm's_law
https://learn.sparkfun.com/tutorials
http://www.antonine-education.co.uk/index.htm
http://electronicsclub.info/soldering.htm
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