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.

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: https://www.youtube.com/watch?v=GdqbLmdKgw4

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

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

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

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. http://whatis.techtarget.com/definition/0,,sid9_gci213512,00.html ON /OFF

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

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 http://www.kpsec.freeuk.com/gates.htm

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

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.

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

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

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

Activity 1: ? ? ? ? ? ? The output is ON or OFF ? 1. 4. ON OFF ON OFF 5. 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 ?

Activity 1: ? ? ? ? The output is ON or OFF ? 7. 10. OFF ON ON OFF OFF 8. 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 ?

Activity 3: Truth Tables Complete the Table

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

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

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

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

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