Technology - : Electronics

Technology | Topic Notes
Electronics
Electrical conductors allow an electric current to flow through them - they have low resistance
• E.g. most metals
Electrical insulators do not allow an electric current to easily flow through them - they have a
high resistance
• E.g. plastic, wood, rubber
Semiconductors are a hybrid between insulators and conductors. The resistance they have lie
between that of insulators and conductors. Semiconductors allow for electrical current to be
routed in one direction or another and can be used to switch a current on or off. Semiconductors
are vital components in many electrical appliances.
• E.g. silicon
Electronic Components
Electronic components are devices that are arranged into a circuit to control the flow of an
electric current around that circuit. There are 3 classifications of components:
• Inputs
• Processes
• Outputs
Technology | Topic Note 1

Inputs Processes Outputs
Variable Resistor LEDs LEDs
Switches Integrated Circuits Buzzers
Sensors Relays Motors
Fuses Resistors Speakers
Motors (when used as Solenoids Light Bulbs

generator)
Resistors
Resistors control the direction of a current, divide voltages, adjust signal levels and reduce
current flow.
2 common resistor types:
• Fixed
• Variable
Fixed Resistor
Resistance is set and cannot be changed
Variable Resistor
Can have it’s resistance set to any value between 0Ω and whatever value is stated
on the packaging. Resistance is usually changed by twisting a dial on the resistor.

Reading Resistor Values
When reading the value of a fixed resistor it is indicated on the

body of the resistor. Each coloured band corresponds to a set
number. Reading from left to right so that the 3 bands closest
together are on the left hand side.
1. The first band tells us the value of the first number

2. The second band tells us the value of the second number
3. The third band tells us the number of zeros on the end of
the number
4. The fourth band tells us the accuracy of the resistance
within the stated value i.e. the tolerance - red means 2%,
gold means 5%, silver means 10%, no band means
within 20%
Value = 82000Ω/82kΩ +/- 5%
Diodes
Diodes are polarised devices. This means that they only allow current to flow through them in one
direction. They are semiconductors.
Polarisation
When a component is polarised it matters what direction they are inserted into a circuit. They
have a positive leg (anode) at one end and a negative leg (cathode) at the other end. In order to
conduct electricity the anode must be connected to the positive end of the battery and the
cathode must be connected to the negative end. This configuration is called forward biased.

If the diode is connected the other way around it will not conduct electricity. This is called reverse
bias.
LEDs (Light Emitting Diodes)
LEDs are diodes that emit light when supplied with a current. The long leg of the LED is the
anode while the short leg next to the flat side of the LED is the cathode. LEDs require significantly
less power than bulbs.
Sensors
• Thermistors - sense heat change

• LDRs (Light Dependent Resistors)/Photo-resistors - sense light change
• Resistance high in the dark and low in the light
• Moisture Sensors - detect moisture or water levels
• Pressure Sensors - sense pressure
• IR sensors - can be used to detect proximity
Capacitors
Capacitors are essentially two pieces of metal separated by an insulator. Capacitors are used for
storing electric charge. Capacitors are used in timing circuits.
Capacitance is a measure of how much charge the capacitor can hold. The unit of capacitance is
the farad.
Types of capacitors:
• Fixed capacitor
• Electrolytic/Polarised capacitor
• Variable capacitor

Switches
Switches allow for an electric circuit to be turned on and off. They are used in nearly all electrical
appliances. Switches are binary devices meaning that they are either on or off.
Types of switches:
• PTM - Push-to-make (red)

• PTB - Push-to-break (black)
• DPDT - Double pole double throw
• DPST - Double pole single throw
• SPST - Single pole single throw
• SPDT - Single pole double throw
• Reed switch
• Tilt switch
Transistors
Transistors are very sensitive electronic switches. They have three legs:
emitter, base & collector. They mainly function as a high speed,
automatic switch in a circuit or as an amplifier of current.
Solenoids
Solenoids convert electric current into linear movement. Inside the solenoid is a small wire coil.
As a current is passed through it it becomes magnetised and pulls a metal var into the centre of
the coil. When the current is then switched off the spring pushes the bar back to its original
position. Solenoids are often used to operate switches or to electronically lock doors.
Relays
A relay is an electronic switch which contains a solenoid which is used to safely turn on and off
circuits that require very high electrical currents. Relays are used in the opening and closing of
security gates, raising and lowering high window blinds etc.

Integrated Circuits (IC)
Integrated circuits combine many components into one body allowing them to carry out a variety
of tasks. They are vital in nearly every electrical appliance. Most ICs have 8+ legs which allow
them to slot into a larger circuit. To find out which number corresponds to which leg you start
counting from the top left (indicated by a semi-circular notch) in an anticlockwise direction.
Series vs Parallel
The components of an electrical circuit can be connected in different configurations to

accomplish different tasks.
Series
Resistors connected in series are connected one after another and the total resistance is
calculated by simply adding up all the individual resistances.
Parallel
When connected in parallel each resistor is connected parallel to the other one from a central
wire that splits to each resistor.
Total Resistance in Parallel = 1/Rtotal = 1/R1 + 1/R2...
Signals
Analogue Signals
Analogue signals can have any value within a certain range. The value of the signal continuously
rises and falls.
• E.g. petrol gauge, household clock
Digital Signals
Digital signals can only have one or two possible values: on or off. On is referred to as 1 which off
is referred to as 0.
• Most modern electronic appliances work in digital signalling.

Logic Gates
NOT Gate
Input Output
1 0
0 1
AND Gate
Input X Input Y Output W
0 0 0
0 1 0
1 0 0
1 1 1
OR Gate
Input X Input Y Output W
0 0 0
0 1 1
1 0 1
1 1 1

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Technology | Topic Notes

• E.g. most metals

• E.g. plastic, wood, rubber

Technology | Topic Note 1

Variable Resistor LEDs LEDs

Switches Integrated Circuits Buzzers

Sensors Relays Motors

Fuses Resistors Speakers

Motors (when used as Solenoids Light Bulbs

2 common resistor types:

Resistance is set and cannot be changed

Technology | Topic Note 2

When reading the value of a fixed resistor it is indicated on the

1. The first band tells us the value of the first number

Value = 82000Ω/82kΩ +/- 5%

Technology | Topic Note 3

LEDs (Light Emitting Diodes)

• Thermistors - sense heat change

Technology | Topic Note 4

• PTM - Push-to-make (red)

Technology | Topic Note 5

The components of an electrical circuit can be connected in different configurations to

Total Resistance in Parallel = 1/Rtotal = 1/R1 + 1/R2...

• E.g. petrol gauge, household clock

• Most modern electronic appliances work in digital signalling.

Input X Input Y Output W

Input X Input Y Output W

Technology | Topic Note 7

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