Logic Gates | IGCSE Computer Science

Video

Introductory Video

https://www.youtube.com/watch?v=gI-qXk7XojA

Boolean Logic & Logic Gates: Crash Course Computer Science #3 (https://www.youtube.com/watch?v=gI-qXk7XojA)

NOT

NOT Gates

A NOT Gate is the simplest form of logic gate. It merely takes the single input and reverses the signal.

NOT Gate Truth Table
Input A	Output
0	1
1	0

AND

AND Gates

An AND Gate is gate that only produces an output if both inputs are turned on.

AND Gate Truth Table
Input A	Input B	Output
0	0	0
0	1	0
1	0	0
1	1	1

OR

OR Gates

An OR gate is a type of gate that will produce an output if either(or both) the inputs are on.

OR Gate Truth Table
Input A	Input B	Output
0	0	0
0	1	1
1	0	1
1	1	1

NAND

NAND Gates

A NAND gate is a gate that only turns off both if both inputs are on, otherwise it stay on. It is made up of an AND gate feeding into a NOT gate.

NAND Gate Truth Table
Input A	Input B	Output
0	0	1
0	1	1
1	0	1
1	1	0

NOR

NOR Gates

An NOR gate only turns on if both inputs are off. It is made up of an OR gate feeding into a NOT gate.

NOR Gate Truth Table
Input A	Input B	Output
0	0	1
0	1	0
1	0	0
1	1	0

XOR

XOR Gates

AN XOR Gate will only turn on if either (but not both) inputs are on.

NOR Gate Truth Table
Input A	Input B	Output
0	0	0
0	1	1
1	0	1
1	1	0

Practice

Activity 1

Have a go at connecting up multiple logic gates to see what happens, using the simulator below. Can you work out the inputs and outputs for the following examples.

https://academo.org/demos/logic-gate-simulator/

Example 1

Example 2

Example 3

Example 4

Activity 2

Activity 2 – Applying Logic Gates

Using the link below, see if you can make the following systems:

Logic Gates Application Simulator

System 1 – Fan cooling system.

If the main system switch is turned on, then the fan will operate when:

Every 5 seconds
When The manual override button is pressed.

System 2 – Basic Alarm System

Make a system where if any of the 3 sensors (use 3 switches to represent sensors) are triggered, the alarm light will flash RED.

System 3 – Advanced Alarm System

Adapt the system so that:

The alarm will not be triggered if the system has not been armed first (use another switch for this)
The alarm should alternate between flashing red and sound a siren every 1 second.

System 4 – Button operated traffic light.

Make a traffic light that starts on green, then goes to amber – red – amber – green again.

Hint – You’ll need to flip flop!