BTC108 1 Introduction To Electronics 1

Lecture 1

Introduction to Electronics 1

James Uren

BTC108
Electronics

Lecture 1

Introduction to Electronics 1

What is Electronics?

Using electricity to move and process information…

Atoms

Atoms are the fundamental building blocks of matter. They consist of a
nucleus containing a number of protons and neutrons, and electrons that orbit
the nucleus. The number of protons, neutrons and electrons defines the
element of the atom and hence the material and its properties.

In some materials the structure of the atoms (the lattice) is such that the
electrons are free to move between atoms. How free the electrons are defines
how well that material will conduct electricity.

The term semi-conductor describes an element whose conductivity changes
under certain conditions. The most commonly used semi-conductor is Silicon,
and forms the foundation of digital electronics and computing.

Lecture 1: Introduction to Electronics 1
BTC108: Electronics – James Uren
2

Charge

Each electron has a charge associated with it, Q, and it is the movement of
this charge that causes the electric current. Charge is measured in
Coulombs (C). The charge of a single electron is tiny – 1 Coulomb is the
charge of 6,250,000,000,000,000,000 (6.25 x 1018) electrons.

What is the charge of 1 electron?

See page 8 of this handout for notes on writing numerical answers in
electronics.

Current

Electric current, I, measured in Amps (A), is the speed of flow of electrons.
The faster the electrons move, the higher the current:

Where I is the current in Amps (A), Q is the charge in Coulombs (C) and t is
the time in seconds (s).

How long does it take for 100 electrons to go past a point
in a circuit with a current of 10mA?

3

Voltage

Voltage, V, also called potential, is the energy difference that causes the
electrons to flow round the circuit. It is measured in Volts (V). A battery, for
example, has a potential difference across it, so if the two ends are connected
via an electronic circuit, a current will flow through the circuit.

A useful analogy is to image that a marble on a flat surface. Lifting
one end will cause the marble to roll down the slope.

This example schematic (circuit diagram) shows a voltage source
connected to a light bulb:

+
12V

4

Practical - Make and test your power cable.

Read the Health and Safety Information on page 10.

Through this electronics course you will be building up a circuit on stripboard
(also called ‘veroboard’). Your circuit will be powered from a bench power
supply, but you will need to connect this to your circuit via a power cable.

The power cable should consist of red (positive) and black (negative) cable to
a two-way Molex KK crimp housing. The mating header should be soldered
to the stripboard.

Test your power cable by taking a voltage measurement (using a Voltmeter)
across the stripboard.

5

Resistance

The freedom of electrons in a material defines the amount of electric current
that will flow through the material. This property is known as Resistance, R,
measured in Ohms (Ω) i.e. the material’s resistance to current flow.

A Resistor is a passive electronic component with a stable and predictable
resistance. It has the following schematic symbols:

OR

Resistors come in a range of values, and multiple resistors can be combined
to create other values. The resistor will have a tolerance associated with it
given as a percentage that describes the range of acceptable resistances, i.e.
how close your resistor could be to the intended value.

The resistor’s value and tolerance can be read from coloured rings on the
resistor itself. See page 9 of this handout for the resistor colour codes.

6

Ohm’s Law

Ohm’s Law relates the voltage, current and resistance in an electronic circuit:

I
+
V R

Ohm’s Law:

Where V is the voltage in Volts (V), I is the current in Amps (A) and R is the
resistance in Ohms (Ω).

What voltage would be required to achieve 3mA through
a 5kΩ resistor?

In a 5V circuit what would be the current through a 1kΩ
resistor?

7

Practical: Measuring Voltage, Current and Resistance

Read the Health and Safety Information on page 10.

This practical shows three methods of finding the resistance of a resistor.
Compare your answers.

• Find the resistance and tolerance from the rings on the resistor body
• Use your digital multi-meter to measure the resistance
• Measure the voltage with a voltmeter and the current with an ammeter
and use Ohm’s law to find the resistance.

Schematic:

+ A

V

R

8

Writing Numerical Answers

Decimal Places

Giving an answer to 3 decimal places means three digits after the decimal
point. If the 4th decimal place is 5 or above, round up the 3rd decimal place.

e.g. 65.342545 given to 3 DPs is 65.343

Significant Figures

Giving an answer to 3 significant figures means showing only the 3 left-most
digits (rounding in the same way.

e.g. 65.342545 given to 3 SFs is 65.3
768593.25 given to 3 SFs is 769000

3 significant figures is normally enough information in electronics. Give all
answers to this accuracy unless directed otherwise.

Units

For large and small numbers it is convenient to use an exponential notation
with 10 - ‘to the power’ - X.

e.g. 768593.25 expressed in this way and to 3 SFs is 7.69 x 105

For the following cases this is simplified:

p pico x10-12
n nano x10-9
μ micro x10-6
m milli x10-3

k kilo x103
M mega x106
G giga x109
T tera x1012

e.g. 768593.25 can be expressed (to 3 SFs) as 769 k or 0.769 M.

9

Black
Brown
Red
Orange
Yellow
Green
Blue
Purple
Grey
White

Sourced from showcase.netins.net

10

Health & Safety Considerations

Soldering and de-soldering:

Solder melts at between 180 and 200°C. Soldering irons will heat up to
between 250 and 400°C. Be extremely careful when soldering and take the
following precautions:

• Switch off the soldering iron at the mains when not in use
• Always keep the iron in its stand
• Make sure your workspace is clear, well lit and well ventilated
• Never solder while your circuit is powered up
• Never solder without tutor supervision
• Only apply the soldering iron for the minimum amount of time
• Keep your soldering tidy and use the minimum amount of solder
• Avoid breathing in solder fumes
• You must only use the lead-free solder provided
• You must use tools e.g. pliers to support components that are
being soldered and ensure the board is secure.

Switching it on:

Powering up a circuit that is incorrectly connected can cause components or
equipment to get extremely hot or even ‘blow’. A short circuit (where
unintended electrical connections are made) for example may damage
equipment or blow components causing them to behave in an unpredictable
way.

• Before powering up your circuit you MUST have it checked by the
tutor
• Have your neighbour physically inspect your work before
powering on
• If your circuit does not behave as you expect, switch it off
immediately
• Use your nose! A faulty circuit with hot components will often
smell or smoke

11

Testing and fault-finding:

If your circuit does not behave as you expect:

• With the power off, confirm by eye that your circuit is connected
correctly and that you are using all the correct components and
mounted with the correct polarities
• Inspect your circuit closely for short circuits, soldering faults and
dry joints:

• Do all the testing on your circuit that you can with it powered off.
• Be extremely careful when probing your circuit live as the probe
itself can cause short circuits
• When probing with an oscilloscope ensure the earth connection is
applied safely

12

BTC108 1 Introduction To Electronics 1

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