1. Logic
What is logic?
Logic is the name given to an electronic component which will monitor a number of inputs and give an output depending on them
Input – something which activates a circuit
Output – the result of a circuit working

2. Example – burglar alarm
If you had a burglar alarm which only monitored the front door, it would be pretty useless as the burglar could get in through the back door
If you had a burglar alarm which monitored the front and back door, the burglar could still get in through the kitchen window

3. If you had a burglar alarm which monitored the front and back door and the kitchen window the burglar could still get in through the living room window
If you had a burglar alarm which monitored the front and back door, the kitchen and living rooms windows, the burglar could still get in through the upstairs window
Understand?

4. The easiest way of monitoring all of these different inputs and allowing the alarm to sound if any of them are activated is using logic gates
Logic is an example of digital electronics – it is described by ‘0’ or ‘1’
0 means off, 1 means on

5. For KS4 electronics it is usual to consider a logic gate with 2 inputs
If the logic gate has 2 inputs where 0 means off and 1 means on, how many different input arrangements could a logic gate have?

6. Logic gates There are a number of different logic gates.
Each logic gate works in a different way – it looks at the input stages and does something depending on them.
Each logic gate has its own circuit symbol
Each logic gate has its own truth table

7. AND gate
If A and B are on, the output will be on

8. OR gate
If A or B or both are on, the output will be on

9. NAND gate If A and B are on, the output will be off.
This is the opposite of the AND gate…

10. NOR gate If A or B or both are on, the output will be off.
This is the opposite of the NAND gate…

11. XOR gate
If A or B but not both are on, the output will be on

12. NOT gate
Only 1 input – A. The output inverts the input.

13. Exercise
Using the panels and your knowledge of truth tables, can you identify which gate is which?

14. Crocodile Clips Now called Yenka
Software to model and simulate electronic circuits and components