Logic Gates

• Computing
• Lower Secondary (Key Stage 3)

Logic Gates

Year 8 

KO: Demonstrate an understanding of logic gates and Boolean logic

All

• To be-able to recognise the different logic gates.
• To be-able to understand the different logic gates.

Most 

• To be-able to recognise the different logic gates and complete truth tables for them.
• To be-able to solve several gate problems. 

Some 

• To be-able to create a circuit using the different logic gates.
• To demonstrate a clear understanding of Boolean logic and Algebra.

Starter

What have you just seen?

Main Activity

Reminder - What is a Logic Gate?

A logic gate is a device that acts as a building block for digital circuits. They perform basic logical functions that are fundamental to digital circuit.

Reminder - What is a 'Truth Table'?

This is a way of representing the inputs of the gates in a table using Boolean representation – 1’s & 0’s, or true & false. Each logic diagram has its own unique truth table.

Reminder - What are the different Logic Gates?

AND, OR, XOR, NOT, NAND, NOR and XNOR.

What we are going to look at

AND Gate

NOT Gate 

OR Gate

Video 

Click here to watch 

AND Gate - Diagram and Truth Table

Output is true if: All inputs are true

NOT Gate - Diagram and Truth Table

Output is true if:​ Input is false​

Output is false if:​ Input is true

OR Gate-Diagram and Truth Table

Output is true if:​  At least one Inputs is true

Main Task

Logic.ly

Click on this link 

Worksheet 

Click on the link below and save it to your area.

Click here

More than one input...

AND Gate 

Answers

More than one input

OR Gate

Answers

Multiple Gates

Gates can be connected to other gates for more complex circuits​

Below we can see an AND gate along with a NOT gate. 

Answers

Multiple Gates

Below we can see an AND gate along with a OR gate.

Answers

What we have learnt so far...

• Truth tables represent what a binary output will be based on binary inputs and the currently used logic gate​.

• AND gates will produce a binary value of 1 when all inputs are a binary value of 1​.

• OR gates will produce a binary value of 1 when at least 1 input is a binary value of 1​.

• NOT gates will produce the opposite value of the input.

Boolean Algebra

What is 'Boolean Algebra'?

The text that describes the way the gates are connected.

How do we write this as an equation?

How we need to write the equation...

How do we write this as an equation?

Correct Answer is 

Y = NOT(A AND B)

How do we write this as an equation?

Correct Answer is 

Y = (A AND B) OR C

What would be the expression for this?

Research Task - Extension

In your small groups you must research and create the remainder of the gates. I want an example and the truth table.

XOR, NOR, XNOR, NAND

Plenary

OR

NOT

AND

What is the correct expression for the OR Gate?

1. Y = A OR B
2. Y = A OR C
3. A OR B = Y
4. Y = A - B

What is the correct expression for this?

1. Y = NOT (A AND B) OR C
2. Y = NOT A AND B OR C
3. Y = NOT A AND (B OR C)
4. Y = (NOT A) AND B OR C