Analog Electronics

Circuit design for the absolute beginner and kids

Introduction

Have you ever imagined how a cellphone works, how you will just speak into a cellphone while in your country and someone in another country will hear you? What actually happens inside the cellphone that makes such long-distance communication possible? How are we able to realize such a device like a cellphone by merely putting some pieces of components together? Well, the pieces of components we put together to realize the cellphone are called electronic components. Arranging the electronic components in such a way that electrons will move through them in a controlled manner to do what you want, is called electronics. It is simply the manipulation of the flow of electrons in a setup called electronic circuit, using the various electronic components.

 If you have ever imagined an electronic gadget or device that can perform a task like turning on a light bulb in the night and turning it off in the day, but you do not know how to start building such device, don’t worry, this tutorial will give you the knowledge you need to start building things from scratch like the gadget mentioned above and other fun experiments without having to surf the web for already made circuits.

The aim of this tutorial and the others that will come after it, is to give you an intuitive understanding of how to design electronic circuit from scratch, and at the same time assist you with designing different projects. So, if you like getting your hands to work, if you like practical, if you like tinkering, doing fun experiments and building things, then this tutorial is for you, because there are tons of projects to do. This tutorial is a practical hands-on text, simplified for kids and the absolute beginner in electronics, but serves as a good reference material for a professional.

Method of presentation

The tutorial uses a somewhat unconventional approach to make what would otherwise seem very difficult so easy. Every chapter begins with a project. This is to make the tutorial fun-filled and interesting. Once the reader has built a circuit and it works, it gives them the urge to read on, the next thing to read after each project design is explanation of how the design works. This in turn makes the learning more interesting.

On the other hand, if the reader built the circuit, tested it and it did not work, it will prompt the reader to find where they have gone wrong, the only way the reader can solve the problem is by reading the explanation of how the circuit works. This will necessitate further reading, and by reading further, they will be forced to keep reading so as to solve the problem.

 This is a very unconventional way of learning but has proven to be very effective. It eliminates obstacles that long theories and calculations present to beginners and kids that are keen to learning how to design electronic circuits from scratch.

The tutorial is project based, in the sense that every chapter begins with a project organized into three, as basic, intermediate and advanced, hence, if you follow the book sequentially working your way up from the first project, your journey through the tutorial will be a smooth ride.

However, there are rules and concepts in electronics that need to be categorically stated and internalized, these concepts are rules of thumb that cannot be overemphasized in the design of electronic circuits from scratch. These rules of thumb are clearly and boldly bulleted for emphasis’s sake in any chapter they are written. This means that every chapter has vital design rule information to convey. This tutorial is a must read for every electronic circuit design enthusiast.

Project 1:

Design a circuit that can turn on a light bulb (light emitting diode) when you press a switch, and turn off the bulb when you press the switch the second time.

Project description:

This is a very simple circuit that has the ability to turn on a light emitting diode abbreviated as LED when a switch is closed, and turns off the LED when the switch is opened.

 Closing a switch means causing a switch to close its metallic contact so that current can flow across it. At the other hand, opening a circuit means causing a switch to open its metallic contacts so that no current will flow across it.

Design components:

  1. 9 volts battery [1]
  2. Battery cap [1]
  3. 1KΩ resistor [1]
  4. Single pole single pole (SPST) pushbutton switch [1]
  5. Light emitting diode (LED) [1]

9 Volts battery

Volts battery
Figure 1.1: 9 volts battery

The battery supplies the electrical energy that powers the circuit. Here, we are using the general purpose 9v transistor radio battery made of carbon-zinc and alkaline chemistry. For this circuit, you can use any battery that can supply at least 3volts energy. However, using the 9v transistor radio battery gives you the convenience of connecting the battery to a breadboard via the battery cap.

Battery cap

battery cap
Figure 1.2: Battery cap

The 9v battery is plug into this cap, then the wires that extend out of the cap is then connected to other parts of the circuit the battery is used. The wires are red and black, the red one is connected to the positive terminal of the cap that plugs into the positive terminal of the battery, while the black one is connected to the negative terminal of the cap that plugs into the negative terminal of the battery.

1KΩ resistor

1 k resistor
Figure 1.3: 1 K resistor

The resistor is a ubiquitous electronic component in electronic circuit design. The work of a resistor is to reduce the rate of current in an electronic circuit. A resistor can be likened to a speed breaker. The higher the speed breaker, the greater resistance it will offer to vehicles crossing. Same thing is applicable to a resistor, the greater the resistance of a resistor measured in a unit called ohm (abbreviated as Ω), the greater the resistance it will offer to the flow of current in a circuit.

If the resistor is not used in the circuit, the 9v electrical energy supplied by the transistor radio battery will exert all its electrical energy unto the light emitting diode. If the light emitting diode is not designed to handle such amount of voltage (like the type we used in this project), it will damage the LED. Hence, a resistor is always necessary when we are connecting some voltage to an LED. In the next project, we will discuss how to calculate the resistance of current limiting resistors.

SPST pushbutton Switch

Figure 1.4: SPSP push button switch

The “single pole single throw” (SPST) pushbutton switch is a type of switch that has only one pole and one throw to make close contact. When you press the switch the first time, it closes the gap that will enable current to flow in the circuit, and when you press the switch the second time, it opens a gap that will disable current to flow. 

Closed circuit means there is “no gap” in the path of current flow in the circuit, this will enable current to flow in the circuit, while open circuit means that there is “a gap” in the path of current flow in the circuit, hence, current will not flow in the circuit.

Light emitting diode (LED)

Figure 1.5: LED

The light emitting diode is a type of diode that emits visible light when it is properly connected in a circuit. The light emitting diode comes in different sizes and colors. LED’s of different colors take different amount of voltages. An LED is always connected in series with a current limiting resistor, the work of the resistor is to allow only the right amount of current and voltage to enter the LED in other not to get it damaged by excess current and voltage. A light emitting diode is polarized. This means that is has a positive leg and a negative leg. The positive leg is the long leg, while the negative leg is the short leg. See figure 1.5. A diode generally is an electronic component that allows current to flow only in one direction, this means that when connecting any type of diode in a circuit, care should be taken not to connect them wrongly, else they will not work as expected.

Physical diagram of project 1

For our first project, we have listed and explained the various electronic components we will use to realize the circuit. Once you have these electronic components, you can proceed to making the circuit connection. Figure 1.6 below is a physical diagram of what your connection should look like.

Figure 1.6: Physical diagram of project 1

The figure above shows a picture of what your design should look like after you have done the connection. This is called a physical diagram because the diagram shows the images of the various electronic components used in the design.

The circuit symbols of the electronic components and their corresponding physical symbols are shown below. the circuit symbols are in turn used to design the circuit. As we proceed in the learning, we will be using more of the circuit symbols, because, it is what professionals use. And I bet you want to become a professional in this field of learning.

Figure 1.7 Electronic symbols and their corresponding physical symbols
Figure 1.8: Circuit diagram of project 1 using electronic symbols

I would discuss how to identify the various terminals of the electronic component symbols in later in the tutorial, like knowing the positive and negative terminals of an LED, but in the meantime let’s continue with connecting the components guided by the physical diagrams.

If you connected the electronic components exactly as shown in figure 1.6, if the switch was not already pressed, when you press the switch the first time, the LED will come on and it will remain on. If you press the switch the second time, the LED will go off. If you succeeded in carrying out this design and you obtained the result as stated; congratulations! You have designed your first electronic circuit from scratch. This is like programming Hello World! In computer programming.

FACTS ABOUT DESIGNING ELECTRONIC CIRCUIT FROM SCRATCH

Designing electronic circuits from scratch is an art, it requires you know the following:

1.Knowing exactly what you want to design

Here, you have to define without ambiguity what exactly you want to realize from the circuit, you have to give yourself clear information of what you want the circuit to do for you. This information will enable you chose the right electronic components for the design. Take cooking as an example, let’s say you want to prepare pizza, you have to categorically state the type of pizza you want, you have to state whether it is Cheese, Veggie, Pepperoni, Meat, Margherita, BBQ chicken, Hawaiian, Buffalo, Supreme, etc. Once you have clearly stated what you want, you can then proceed to the next step, which is selecting the various materials to prepare the pizza, such is also the case in electronic circuit design, once you have clearly stated what you want to achieve with your design, you can then proceed to selecting the appropriate electronic components to carry out your design.

2.Master to a reasonable length the various electronic components and how the behave in a circuit.

Like we stated earlier, circuit design is an art, let’s take the art of making pizza like we used above as an example, you need to know the various pizza making ingredients that can be used to make the type of pizza you have chosen to make. Your mastery of these ingredients and how to use them to prepare the pizza will enable you know when and how to use them to realize your aim. And it is this your knowledge of these various ingredients that will enable you come up with a good pizza.

Also, once you have mastered the ingredients and how to use them, you can write a recipe. Same thing is applicable to electronic circuit design, you need to know the various electronic components and how they behave in a circuit, this will enable you be able to design your circuit from scratch. Again, it will enable you be able to draw a circuit diagram for your design, which serves as a recipe for your design. hence, to be a good electronic circuit designer, you need to master to a reasonable extent, how the various electronic components behave and how to use them in a circuit.

3.Know some electronic circuit design rules

Still on the pizza making illustration, if you know the type of pizza you want to prepare and the various items needed to prepare it, the next thing you need to know is the guide on how to prepare the pizza, this guide is more like the rules in the recipe. The rules will tell you when to add what to add, and what will happen if you add the right ingredient at the wrong time or otherwise. There are rules governing electronic circuit design that every circuit designer must know. These rules are very common but vital and they cannot be overemphasized in electronic circuit design. they include but not limited to the following four rules listed below:

  1. More Current tend to flow through the least resistive path in a circuit
  2. Current flows from a region of high potential (voltage) to a region of low potential (voltage)
  3. Current will always flow in a circuit to return to ground
  4. Current will only flow in a circuit only when it sees a path to ground

As a beginner in electronics, do not panic if you do not understand what these rules are talking about, we shall explain them as we go deeper into the design of more projects.

4.Know some basic electronic engineering mathematics

Mathematics is one of the things that deter people from doing science and engineering. In this tutorial, we tried to keep the mathematics to bare minimum, however, there are occasions where we must do some math, basic math to be precise. The formula we might encounter most often is the ohm’s law formula that gives the relationship between current, voltage and resistance.  Once you’ve mastered the basic mathematics used in circuit parameter calculations and you have taking the other rules listed above into consideration, you are then on the right track to mastering how to design electronic circuit from scratch.

Circuit design tools used in project 1

SOLDERLESS BREADBOARD

To enable us make swift connection of the electronic components utilized in designing project 1, we can use a common electronic circuit prototyping tool called Breadboard. A breadboard or technically a solderless breadboard is a cuboid shaped plastic board that contains holes for fixing and connecting the leads and pins of electronic components while designing circuits. With a breadboard, you can always and easily connect electronic components. When you are done prototyping with a breadboard, you can easily remove the components and re-use them.

A breadboard is always used with jumper wires. It is not advisable to put stranded wires into the holes of a breadboard, because the wires may snap while being forced into the holes, which could render the breadboard useless. The jumper wires are used to connect legs of components on a breadboard that are not close enough to be connected on same strip.

Breadboards come in different sizes and colors, below are two different kinds of breadboards.

Figure 1.9a: Breadboard
Figure 1.9b: Breadboard

Inside a breadboard

A breadboard is made with metallic strips which are connected in a certain way in the board. The way the metallic strips are connected determine how the legs of electronic components are connected on the board. Below is image of the backing of the breadboard removed to reveal the metallic strips.

Figure 1.10: Breadboards with their backings removed
Figure 1.11: Sticky backing, partly removed to clearly show the metallic strips
Figure 1.12: 3D view of the breadboard

Figure 1.12 is a labeled diagram of a breadboard with integrated circuits affixed on it. You can cascade two or more breadboards by fixing the tabs into the notches, when you do that, you will get something like what we have in figure 1.13.

Figure 1.13: Three breadboards cascaded together

CONNECTION OF A BREADOARD

Figure 1.14: Top view of a breadboard, showing its holes

Figure 1.14 above shows the top view of a typical breadboard showing all the holes. Knowing how to use a breadboard means knowing how these holes are linked internally. Do not forget that these holes end on the metallic strip covered by the sticky backing. Some holes are linked together by a strip to give a continuous line of holes.

Here is how the breadboard is connected inside, looking at the image in figure 1.14, hole 1 is continuous up to hole 2, but not continuous to hole 3, then hole 3 is continuous up to hole 4. Line 1-4 is not continuous with the line underneath it.

Again, the holes under the line beneath line1-4 are continuous vertically and not horizontally. The crevasse is a line cutting our breadboard into two equal halves, so what we have above the crevasse is exactly what we have beneath the crevasse.

JUMPER WIRES

Jumper wires are the wires used on a breadboard to loop the legs of two or more components that are not close enough to fit into the same hole on a breadboard.

TYPES OF JUMPER WIRES  

There are just three types of jumper wires, Male-male, Male-female and Female-female jumper wires, they are shown below.

Figure 1.15: Jumper wires
Figure 1.16: Jumper wires used to loop holes on a breadboard

Connecting electronic components with a breadboard

Now we’ve known how to use a solderless breadboard, let us use it to connect our components in project 1 above

Figure 1.17: Circuit connection with a breadboard and jumper wires

Circuit connection explanation

From figure 1.17 above, current from the battery enters the switch, but because the switch is open (i.e. the switch is not pressed yet) current will not pass through the switch to enter other parts of the components in the circuit. However, once the switch is closed, i.e. the switch is pressed, current can pass through the switch and enter the resistor. The resistor slows down the rate at which current enters the LED. As current enters the LED, it moves from it and goes straight down to the negative leg of the Battery. It is only when the current returns to the negative leg of the battery that the LED will come ON. This conforms with the rule that current will always want to return to its source in a circuit. The current left from the positive terminal of the battery and returned at the negative terminal. As long as there is no path for current to return to its source in the circuit (i.e. when the switch was not pressed) the LED will never come ON. But once the switch is pressed and we have a closed circuit, current will flow and return to the negative terminal of the battery. Now, let’s talk about loops in electronic circuit design.

LOOPS (CIRCUITS) IN ELECTRONICS

A loop in electronics can also be called circuit. It describes a path that current flows through in a circuit. When we say loop, we are not referring to a circle, rather, we are referring to a path of current flow, from a power source and back to the power source (i.e. from the positive terminal of battery to the negative terminal of battery).  So, in a circuit, if all the components were connected in such a way that current would see a path to move from the positive terminal of the battery down to the negative terminal, such path constitutes a loop or circuit.

In figure 1 above (project 1 circuit) we can see that the electronic components are connected in such a way that there is a path for current to flow from the positive terminal of the battery to the negative terminal. From the image, you can see that the battery is connected to the switch, then to the resistor, then to the LED and back to the battery. That is an electronic loop or circuit.

Now we have understood what an electronic loop is, let’s discuss the various types of loops or circuits. As we

  1. Open circuit
  2. Closed circuit
  3. Short circuit

 Open circuit: This is a type of electronic circuit where there is no complete path of current flow from the positive terminal of the power source to the negative terminal. This can also be regarded as open loop. It is basically created in a circuit by the switch. It is a circuit with infinite resistance. When a circuit switch is turned off, the circuit automatically becomes an open circuit. Open circuit is a major problem in electronics, once current cannot move from its source, and return back to its source we have open loop or open circuit. Also, when some components fail or damage in a circuit, they create open circuit. Hence, the switch might still be in the ON state but a component somewhere in the circuit could create an open circuit.

Figure 1.18: Open circuit

In the figure above, you can see the arrow pointing at the gap on the switch where open circuit has been created in the circuit. Here, current cannot flow from the positive terminal of the battery to the negative terminal, because there is no complete path of current flow. In such a circuit shown above, it is the switch that created the open circuit, once the switch is closed, the open circuit will vanish and becomes closed circuit.

Closed circuit: Closed circuit is a type of electronic circuit or loop, where there is complete path of current flow.  A closed circuit is a type of circuit with finite amount of resistance but not zero resistance.  Once the switch is closed in a circuit, we have a closed circuit, it is as simple as that. Even if there is no switch in the circuit, as long as there is a complete path of current flow from the positive terminal of the battery to the negative terminal, through some other electronic component(s), we have a closed circuit. Unless the current in the power source has run down, else, every closed circuit has current circulating through it.

Figure 1.19: Closed circuit

The arrow in this circuit points to a closed switch in the circuit. The switch creates a closed circuit. In this kind of circuit, current can flow from the positive terminal of the battery to the negative terminal of the battery. A closed circuit means that current now has a path to flow through in a circuit.

Short circuit: As the name implies, it is a type of electronic circuit or loop where there is a short path of current flow from the positive terminal of the battery or power source to the negative terminal. Short path of current flow means that there is zero resistance in the circuit. Hence, the only resistance will be that of the connecting wires. (please note that wires themselves constitutes electrical resistance, very little, if not negligible with respect to the electronics discussed in this tutorial.) Short circuit is very dangerous. As a beginner in electronics, if there is anything you should and must avoid when designing a circuit, it is short circuit. Short circuit is what you get when you connect the positive terminal of a battery to its negative terminal without connecting any other component(s) in the circuit. It is a terrible thing to do in electronics. You have to avoid it at all cost. It causes batteries to heat up extraordinarily and can lead to explosions. Short circuit is a NO, NO. please avoid it.

Figure 1.20: Short circuit

In the figure above, we can see a short circuit. To understand short circuit better, let us explain the circuit. In the circuit above, current from the battery has to choose from the two paths:

  1. The part it will meet resistance, which is the path that contains all the electronic components in the circuit
  2. The part from A to B.

The path from A to B has little or no resistance across it, hence, all the current from the battery will meet little or no electrical resistance as they travel from the positive terminal of the battery to the negative terminal. This negligible resistance in the path of current flow in the circuit creates a short circuit or loop for the current to travel, hence, the name “short circuit”. Because the path from A to B is a short circuit with least resistance, all the current in the battery will follow that direction, because, current will always tend to follow the least resistive path in a circuit. And this is a rule we mentioned earlier that must be known by every electronic circuit designer. This least resistive path causes all current in the battery to flow back to the battery, this is very dangerous, as it can cause overheating of the battery and in some cases unavoidable explosion.

CURRENT AND VOLTAGE, RESISTANCE, OHM’S LAW AND POWER

Before you become very good at electronic circuit design, there are three electronic circuit design concepts you must know, they are:

  1. Current
  2. Voltage
  3. Resistance

CURRENT

Current is simply the number of charges that cross a boundary in one second. It is otherwise known as charges in motion. If a charge is stationary, it is not current. But when a charge moves, it makes a current. The number of electrical charges that move across a boundary at any given moment gives the current. If a unit charge moves across a boundary in a second unit, the movement of such a charge will bring about a unit current. So, if a charge of one coulomb passes across a boundary in one second, that constitutes a current of one ampere (Amp or A) the unit of current is Ampere, abbreviated as Amp or A. Current can be measured directly using a tool called Ammeter, or, it can be calculated using a simple formula.

As a circuit designer, you must know the amount of current the electronic components you are working with need and how to make that amount of current get to the electronic components. Supplying an amount of current larger than required to an electronic component, you risk damaging the electronic component. Again, supplying an amount of current less than needed to an electronic component, the device may not work properly, so, as a designer, you have to make sure that you supply the right amount of current to the various electronic components you use in your design.

VOLTAGE

Voltage is the work done in moving charge from one place to another. It is the energy involved when charges move. It is the force with which charges or current move in a circuit. We know that it is the charges from a power source like battery that supplies the electrical energy that operates our electronic devices. The force with which these charges move with, gives us the voltage of the charges. The unit of voltage is volts, abbreviated as V.  If the charges are moving faster, it means that the charges have high voltage, and if the charges are moving slower, it means that the voltage is low.

Just like current, we can either measure or calculate voltage. The tool used to calculate voltage is called a voltmeter. On the other hand, we can calculate the value of voltage using a simple formula. Knowing the amount of voltage you are working with is very vital in electronic circuit design. some electronic components are very sensitive to voltage, once the amount of voltage getting to them is below or above the normal, they damage. Especially the group of integrated circuits called CMOS. So, before you use any electronic component in your design, you must know the amount of voltage the component can take and work efficiently.

RESISTANCE

Resistance is the opposition to the flow of electricity or current in an electronic circuit. Resistance can be seen as bumps that inhibit the smooth flow of current. The greater the bumps, the slower the rate of current flow, and the lesser the bumps the faster the rate of current flow. This means that in a circuit that has two or more paths of current flow, more current will tend to flow through the least resistive path. And this is a concept that enables us to analyze electronic circuits.

Current, voltage and resistance are related by the formula, the ohm’s law.

OHM’S LAW

Ohm’s law is one of the indispensable mathematical formulae that cannot be overemphasized in electronic circuit design. Every electronic circuit designer must have the formula handy and utilize it as and when necessary. The formula shows the relationship between current; voltage and resistance as can be shown in the equation below:

Voltage = Current x Resistance, V= IR.

If we have any two of the circuit parameters, we can find the third one. The formula can be shown with this triangle

With Ohm’s law, you can determine the right value of resistor you need in your circuit. Let’s use our project 1 as an example. We have a simple circuit that contains a battery, an LED and a resistor. The voltage of the battery is written on its body. To determine the value of resistor we need to connect to the LED as a current limiting resistor, we use ohm’s law formula.

From the image above, we have that the resistor and LED are connected in series, this means that the same amount of current will flow through them.

Note that electronic components connected in series have the same amount of current flowing through them, but if they are connected in parallel, same voltage is dropped across them. So, since we aware that same amount of current flows across the resistor and LED in the circuit, we can easily determine the amount of resistance that is appropriate for the circuit. A typical LED will take about 20mA of current. So, using Ohm’s law we have: V = IR, where V=Voltage, I= Current and R= Resistance.

V= 9volt

I= 20 mA = 0.02A

R=?

 if we make R the subject of the formula, we have R =

hence, R = 9/0.02 = 450Ω.

The omega symbol we used here is the symbol for Ohm as a unit of resistance. What this answer means is that the minimum resistance value we can use in the design is 450Ω, hence using 1k as we used in the design is not a problem.

As long as we have two of the parameters in the formula, we can calculate the other parameter. E.g. if we have current and voltage, we can calculate resistance, if we have resistance and voltage, we can calculate current, and if we have resistance and current, we can calculate voltage.

POWER

Power is the time rate of doing work. Power in electronics tells us the rate at which electrical energy is transferred in a circuit. It helps us to determine how much energy the components in a circuit can handle of the current and voltage of the electrical charges entering the circuit. You need to know the power rating of the electrical components you work with. Power can be calculated thus:

Power= IV

Since voltage is also V=IR, we have that I = V/R and R =V/I  then we can make some substitutions to obtain new formulae for power.

For the first case, we substitute the equation for current in the equation of power we have:

Power = IV= V/R x V = V x V/R  = V2/R also, we substitute the equation of voltage in the equation of power we have:

Power = IV = I x IV = I2R.

Therefore, the formulae we can use to calculate power are:

Power = IV or V2/R or I2R. so, once you are meant to calculate power, and you have any two parameters, you can use them to calculate power. For example, in project one above, we have calculated the resistance value we can use in the circuit, however, we should also calculate the power rating of this resistor. If we use a resistor that does not have the capacity to handle the electrical energy that comes to it, then it will burn out. So, since we have the current and voltage values of the system, we can calculate power thus:

Power= IV = 0.02 x 9 = 0.18 Watts.

The power rating of the resistor we need is anything equal to or above 0.18 watts, but must not be less than 0.18W. The unit of power is Watts, abbreviated as W.

Now that you have designed your first circuit and have understood few basic electronic circuit design rules, formulae and calculations, use your understanding to tackle the design challenges below. as you are practicing the designs, be focused and observant, if things didn’t work out as expected in your design, start afresh until you solve the problem, never feel frustrated, remember that you learn more by practicing more.

Challenges

  1. If your project 1 circuit worked perfectly, then try reverse connecting the legs of the light emitting diode. What did you observe when you did that? Did the LED come on? If it did not come on, what do you think could be the cause?
  2. Experiment with various values of resistors and different colors of LEDs. what did you observe in your experiment?

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