1. Thursday, 22 November 2018 Logic Gates
Learning Objective: To be able to demonstrate an understanding of logic gates and the notation/diagrams used.
Success Criteria:
I can complete a logic gate diagram.
I can write a logic statement.
I can create truth tables for AND, OR and NOT gates.
I can use correct logic notation.

2. What is binary?
Binary is the representation of the ‘presence’ of electricity
If present or ‘on’ we use a: 1
If absent or ‘off’ we use a: 0
We can use this idea to change 1 and 0 states through the use of logic gates
Logic Gates take inputs and covert them to an output
You can see why we need binary, logic and transistors in this video here:

3. Key Words Logic Gate Transistor Bit (Binary Digit) Logic Circuit AND
NOT (Inverter)
A ⋀ B
A ⋁ B
¬ A

4. Logic Gates
Used to change bits and perform calculations within a computer
Created by using transistors
There are 3 basic logic gates:
AND OR NOT
Every logic circuit can be made up from these 3 logic gates

5. Truth Tables
The output of Logic Gates can be shown through a Truth Table
The Truth Table shows what an output will be, based on the inputs
You will need to know the basic truth tables
You will need to be able to construct a truth table from a logic statement

6. ON/OFF ON/OFF ON /OFF Input AND Output Input AND BURGLAR ALARM GATE
An AND gate can have two or more inputs.
The output will be positive (true) when both inputs (the input one AND the input two) are positive (true).
Y = A AND B
Input
AND
GATE
Output
Input
ON/OFF c
ON/OFF
PERSON SENSOR
AND
GATE
BURGLAR ALARM
ON SWITCH
FOR ALARM
The output is "true" when both inputs are "true.” Otherwise, the output is "false."
If one input will be off – the output will be off as well.
ON /OFF

7. The AND Gate Only has an output of 1 if both A AND B are 1
We write this as: A ⋀ B

8. ON/OFF ON/OFF ON /OFF Input Y = A OR B OR Output Input OR
An OR gate can have two or more inputs.
The output will be positive (True) if at least one input is true.
Y = A OR B OR
GATE
Output
Input
ON/OFF
ON/OFF
FRONT DOORBELL
SWITCH OR
GATE
DOORBELL
BACK DOORBELL
SWITCH
ON /OFF
The output is "true" if either or both of the inputs are "true." If both inputs are "false," then the output is "false.”
It is doesn’t matter if one input will be off- the output will be on

9. The OR Gate Has an output of 1 if either of A OR B are 1
We write this as: A ⋁ B

10. ON OFF NOT Output Input CENTRAL NOT HEATING
A NOT gate (inverter) has only one input.
It reverses the logic state.
Y = NOT A
NOT
GATE
Input
Output
NOT
GATE
HEAT DETECTOR
(ABOVE 20 C)
CENTRAL
HEATING ON
OFF
NOT gate has only one input. It reverses the logic state.
If the input will be on – the output will be off
If the input will be off –the output will be on.

11. To add more sensors to alarm
GATE
AND
BEDROOM
SENSOR
FRONT ROOM
BURGLAR
ALARM
ON SWITCH
FOR ALARM
ON or OFF ?

12. The NOT Gate Has an 1 input only It INVERTS or swaps the input
We write this as: ¬ A

13. ON OFF Is the Final Output ON (True) or OFF (false) ? OR AND
GATE
AND
NOT ON
OFF
FINAL
OUTPUT
ON ? OFF ?

14. Activity 1: ? ? ? ? ? ? The output is ON or OFF ? 1. 4. ON OFF ON OFF5. 2. ? ON ? ON
OFF 6. ? ON
OFF
1- off, 2- on, 3-off, 4- on, 5-off, 6-on 3. ? ON
OFF
The output is ON or OFF ?

15. Activity 1: ? ? ? ? The output is ON or OFF ? 7. 10. OFF ON ON OFF OFF8. ON ON ? ON
OFF 9. ON ?
7- on, 8-off, 9-off, 10- on ON ON ON ON ON
The output is ON or OFF ?

16. Activity 3: Truth Tables
Complete the Table

17. Activity 3 – Answers Complete the Table
Well done spotting it was an OR gate!

18. Activity 4: Truth Tables
Create the Truth Table for the following:
A ⋀ ( B V C )
Have a go yourself and then check your steps with the PowerPoint

19. Activity 4
A ⋀ ( B V C )
Here is the diagram

20. Activity 4 – Answer A ⋀ ( B V C ) Here is the empty truth table A B C

21. Activity 4 – Answer
A ⋀ ( B V C )
Here is the empty truth table