1. Computers
Logic Gates

2. Logic Gates
Logic gates are the fundamental building blocks of digital circuits.
There are three main logic gates.
NOT
AND OR

3. NOT Gate
The NOT gate reverses the input, so if a 1 is inputted into a NOT gate it will output a 0.
NOT 1

4. AND Gate
The AND gate will only output a 1 if both inputs are 1, otherwise the output will be 0.
AND 1 1 1

5. OR Gate
The OR gate will output 1 if either or both of the inputs are set to 1. OR 1 1

6. Learn about truth tables by watching this video.

7. Example
Truth tables are used to show all the possible outcomes for a logic problem. Here is the truth table for an AND gate:

8. Go to the Logic Lab and recreate this simple logic diagram.
Activity 1
Go to the Logic Lab and recreate this simple logic diagram.
Use your completed diagram to help you complete this truth table for a NOT gate: A Q

9. Now recreate this logic diagram:
Activity 2
Now recreate this logic diagram:
Use your completed diagram to help you complete this truth table for an OR gate: A B
Q=(A OR B)

10. Alarm = Heart Rate AND Oxygen
Logic Statements (1)
Logic statements can be used to represent logic diagrams using text.
Example
Brunel University use a system to monitor their athletes when they are training. They monitor heat rate and oxygen levels. These are Boolean variables that are set to 0 when the values are within safe limits and 1 when they are outside safe limits.
The microcontroller monitors the readings and sounds an alarm if both of the readings are outside safe limits.
Logic Statement
Alarm = Heart Rate AND Oxygen

11. Alarm = Heart Rate AND Oxygen
Logic Statements (2)
Logic Statement
Alarm = Heart Rate AND Oxygen
INPUTS
OUTPUT
Heart Rate
Oxygen
Alarm 1

12. Activity 3a
A greenhouse climate control system monitors the temperature and humidity. These are Boolean variables that are set to 0 when the values are within the set limits and 1 when they are outside these limits.
The microcontroller monitors the readings and opens a vent if any of the readings are outside the set limits.
Give the logic statement the microcontroller uses to determine if the vent should be open.
Logic Statement

13. Complete the truth table for the logic statement you wrote in Task 3a.
Activity 3b
Complete the truth table for the logic statement you wrote in Task 3a.
INPUTS
OUTPUT
Temperature
Humidity
Vent

14. Activity 4a
A baby alarm system monitors heart rate, temperature and movement. These are Boolean variables that are set to 0 when the values are within safe limits and 1 when they are outside safe limits.
The microcontroller monitors the readings and sounds an alarm if any two of the readings are outside safe limits.
Give the logic statement the microcontroller uses to determine if the alarm should be sounded.
Logic Statement

15. Complete the truth table for the logic statement you wrote in Task 4a.
Activity 4b
Complete the truth table for the logic statement you wrote in Task 4a.
INPUTS
OUTPUT
Heart Rate
Temperature
Movement
Alarm

16. Activity 5a
A car alarm is set off if a window is broken or if it senses something moving inside car, and if the engine is not on.
Give the logic statement the microcontroller uses to determine if the car alarm should be sounded.
Logic Statement

17. Complete the truth table for the logic statement you wrote in Task 5a.
Activity 5b
Complete the truth table for the logic statement you wrote in Task 5a.
INPUTS
OUTPUT
Engine
Window
Movement
Alarm