Bredhurst Receiving and Transmitting Society

Technical Basics Part 1

The ELECTRON

Welcome to the electronics parts of the course. The word electronics comes from the word electron and an electron is defined in the "Oxford" dictionary as :-

An electron is a stable elementary particle with indivisible charge of negative electricity, found in all atoms and acting as carrier of electricity in solids.

What that means to you and I is that the electron forms the basis of all electrical theory and has a negative charge and therefore is attracted to anything with a positive charge.

Electrons can flow easily in some materials that are called conductors and not flow easily in others which are called insulators. An example of a conductor is a piece of copper wire and an insulator is plastic such as you often find around the out side of a wire so that your fingers are "insulated" from the wire carrying electrons.

This following could be a big learning jump for you - so take it slowly and anything you do not understand let your course tutor know - they should be able to explain it further - so that you have it clear in your mind from the start.

We are now going to look at the parts of the syllabus but are changing the order to help introduce you to the subject of electronics.

Cells and batteries

Up to this moment you probably thought that the picture above shows a battery. In terms of going into a shop and asking for a battery you would still be right, but for the course you have to know that the picture above shows a single cell and that a battery is a number of cell either linked in series or parallel.

What does series and parallel mean ? Ok I will come back to that in a minute.

First let me tell you about a cell. One end is marked + and is the "positive" end and the other is often but not always marked - and is the "negative" end. The positive end is often the one with a protruding pip.

It is from the negative end that electrons are in abundance and they are all trying to reach the positive end. If you were to link a wire from the negative end to the positive end then electrons would flow. What you would have created is what is called a "CIRCUIT" between the positive and the negative terminals.

It would not do any good purpose except what we call flatten the battery, when all the spare electrons have flowed down the wire to the positive end. Even with a battery shown above if the wire is not thick enough it could get hot and thus burn your fingers.

NEVER connect a wire from the positive terminal to the negative terminal of any cell or battery else a fire could result. Such connection is called a "short circuit".

VOLTS

In the battery we have said that there is an abundance of electrons trying to leave the negative terminal and reach the positive terminal. We could also say that there is an opportunity for a current to flow if a wire was connected (or the "potential" for a current to flow if a wire was connected). The word potential is taken further in electronics and added to the word "difference" and we say that there is a POTENTIAL DIFFERENCE between the negative and positive terminals and the greater the number of electrons trying to make the journey the larger the potential.

The potential difference is measured in volts. Thus it is also said that a battery supplies a voltage.

Series and parallel

Linked in Parallel

What does series and parallel mean? It is the way batteries can be connected together. Let us explain further below.

You are now aware that a cell has two terminals one + and one -.

If we had three cells and joined all the + together and then joined all the - together we would have the cells in parallel. See diagram below.

Remember that a combination of 2 or more cells forms a battery.

Linked in Series

If we had three cells and joined the - of one cell to the + of the next and the - of that cell to the + of the third cell the cells would be arranged in series.

You might like to remember that linked in SERIES is just like a STRING of SAUSAGES you can buy at the supermarket  - each join only to the next one.

Remember that a combination of 2 or more cells forms a battery.

CIRCUIT DIAGRAM SYMBOLS

These circuit diagram symbols will be introduced to you bit by bit (as necessary).

The two drawings above are representations of parallel and series batteries but they took a great number of lines to draw and there is an easier way by the use of what are called "circuit diagrams symbols" to represent the batteries.

Above is the circuit symbol of a cell and the second one is annotated to show the positive and negative terminals. In circuit diagrams the annotation is not used but is given here for you to learn. The positive side is the longer of the two lines.

The batteries shown above could therefore have been drawn as follows:-

A circuit is needed to allow current to flow.

To make a circuit we need several items :-

1. A battery as a source of electrons

2. a resistance for the current to flow thorough

3. some wire to make make all the connections

4. and a switch but this could just be releasing a wire connection.

	What does this circuit have ? Battery Yes Resistance Yes Wire links  Yes Links from one side of battery to another No - thus not a complete circuit in which electron (current) can flow.
	Battery Yes Resistance Yes Wire links  Yes Links from one side of battery to another No - thus not a complete circuit in which electron (current) can flow.
	Battery No Resistance Yes Wire links  Yes No battery thus no source of electrons thus not a complete circuit in which electron (current) can flow.
	Battery Yes Resistance Yes Wire links  Yes Links from one side of battery to another Yes - thus a complete circuit in which electron (current) can flow.
The resistance could just have easily have been a lamp when this circuit symbol would have been used in place of the resistor .

3b.5 Recall that the polarity of a battery is not relevant if a filament bulb is used but that electronic circuits can be damaged by the wrong polarity.

Polarity of a battery  + and - 

A battery has two terminals to which you could connect wires. One is marked + and one marked - . The + indicated the positive terminal and the - the negative terminal.

Polarity sensitive

There are very few electronic components that are NOT said to be "polarity sensitive".

What does polarity sensitive mean ? This means that if a positive terminal of a battery ( the one marked with a + ) is connected to where the negative terminal ( the one marked with a - ) should be connected and the negative connected to the positive terminal DISASTER will occur in most circumstances and the components ruined or a fire could occur !! So if you connected a battery the wrong way round in a portable battery radio not only would it not work when the battery is connected the wrong way round it will almost certainly not work when then connected the right way round.

HOWEVER --- A filament lamp such as a torch bulb - relies upon the battery pushing an electric current through the filament in the bulb to shine BUT the bulb do not mind which way round the terminals of the bulbs are connected to a battery. It is therefore safe to connect either terminal of the battery to either of the wire leads from the bulb.

A lamp (bulb) does not mind which way round the electron are pushed by the battery

Why does it not matter which way round they are connected ? It is because the filament bulb is just a special piece of wire inside a glass holder and like any other piece or wire it can be connected which ever way round happens first!

Electronic circuits

When connecting a battery to an electronic circuit whether it is a simple circuit on the bench or a complex one such as a battery radio the polarity of the battery connection of the piece of equipment must be carefully observed.

Failure to observe the polarity and to connect the battery with the wrong, or what is sometimes called "reverse" polarity the piece of equipment will :-

a. not work and

b. may have been damaged to such an extent that it might never again even with the battery connected the right way round.

This use of correct polarity will be particularly important to you when connecting your first transceiver to a power supply. You will be shown how to connect up in the practicals but when doing it your self should you get it wrong because the currents that could flow from the power supply will far exceed those from a "dry cell" battery not only could damage to the equipment result but this could could a fire.

OBSERVE CORRECT POLARITY when connecting electronic equipment.

3b.6 Recall what is meant by the abbreviations D.C and A.C

DIRECT CURRENT

The flow of electrons from the battery is called a current and because it flows only in one direction it is called DIRECT CURRENT and often written as DC.

Right back at the start it was mentioned that the electrons flow from the Negative to the Positive terminal through a circuit. That is correct information and you could say that it is "actual current flow" because that is what is actually happening.

BUT (and there is a big BUT) in the old days, at the start of science, it was thought that the current flowed from the positive to the negative and this is called "conventional current flow" and even today we often think in terms of this current flow when discussing electronics. Often "conventional current flow" is shortened to just "current flow" or just "current".

ALTERNATING CURRENT

A moment ago we were discussing that it did not matter which way round the wires from a bulb were connected to a battery and that once connected a current would flow and that would be a DIRECT CURRENT.

Well what would happen if we were able to very quickly change the connection around and then back again and do that over and over again, in fact never stop doing it.

Other than being very tired we would actually be supplying ALTERNATING CURRENT to the bulb because alternating current is a flow of electrons first one way and then the other at a regular rate several time a second. So whilst the battery is still producing DIRECT CURRENT, as it cannot produce anything else, the effect on the bulb is an ALTERNATING CURRENT ,often written as AC.

This flow of AC in the bulb, lights the bulb just as well as DC and in fact if we had a small mains transformer which supplied the right voltage it could take the place of you in switching round the wire and stop you getting tired. The transformer (without any other electronics) supplies AC.

What's a transformer ? This is an item of electronics which can change the mains AC voltage to a different voltage of AC usual much lower than that going in. You may be familiar with the little plug in transformer used to charge mobile phones but these also have a little more electronics in side them.

Why bother to have AC ? Because it is easier to generate at the power stations and even in a bicycle dynamo!

Confusing Eh!

Well not if you take if slowly, so here is a re-cap and if there is anything here you do not understand stop and re-read as to progress from here will not make much sense until you have a good grasp of what is written above.

RE-CAP

• it is the little electron which is negatively charged that is the basis of all electronics

• what you used to think of as a battery is now called a CELL and that several cells joined in series or parallel make up what is called a BATTERY.

• a battery is a source of electrons at its negative terminal and these electrons are wanting to reach the positive terminal through a circuit.

• that a battery provides a voltage to push the electrons around the circuit.

• that the flow of electrons from a battery is called a current flow and because it is only in one direction is called a Direct Current flow or DC.

• the electric lamp bulb is one of very few electronic components which do not mind which terminal of a battery is connected to which wire connecting to the lamp.

• the electric lamp (bulb) can work just as well from AC and DC including AC from a mains transformer so long as it is at the correct voltage for the bulb.

• you know the circuit symbol for a battery

• a circuit has to have a complete linkage through other components from the positive terminal of a battery to the negative terminal of a battery to complete a circuit and allow the circuit to operate.