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

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

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?

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

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?

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

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

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

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

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

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

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

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

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