Logic GatesEngineering Science S4

Previously…

• We have been working on series circuits• Simulated circuits• Practical circuits• Gained an understand of basic

components

Quick Test Before We Move on

What component would we use in a circuit to make an LED come on at a certain temperature?

What does LDR stand for?

What happens if an LED is connected into a circuit the wrong way round?

Take a moment to think…

We use circuits and components all the time in our daily lives.

Our phones, mum/dads car, bus, Card for the canteen in school, calculators in school, Xbox/PS3 etc.

All the circuits that we have made over the past week are active when they are plugged in, and remain active until

we unplug them.

But is that the case for EVERY circuit that we use in our lives?

Take a moment to think…

Think about playing a computer game on your Xbox or PS3 etc

What is actually happening when you are playing?

You are pressing BUTTONS (push buttons) to send signals to the console.

Take a moment to think…

Lets take an example…

Take a moment to think…

So your about to hit a shot in Fifa…What buttons do you press? Just one?

Chances are you will be pressing at least 2 buttons at the same time in order to get your player to hit an accurate shot.

Take a moment to think…

The circuits we make only have ONE output though. The circuit is either complete or its not.

This is where we need to look at

“Logic Gates”

Logic Gates

There are THREE main types of Logic Gate.

• AND gate• OR gate • NOT gate

Logic Gates

AND gateThe AND gate allows us to change two inputs, into one output.

For example, in FIFA we might press “Square”(Input) and “Left”(Input) to hit a shot towards the left hand side of the goals(Output).

However if we press “Square”(Input) and “Right”(Input) it will NOT hit a shot towards the left hand side of the goals(Output).

This is because the game is programmed to only give the Output when Square and Left are pressed together.

Logic Gates

Here is what an AND gate looks like…

A=Input

B=Input

Q=Output

Logic Gates

We can explain what happens with an AND gate by using a “Truth Table”

Truth TableThe numbers on the Truth Table are a way of showing that the input is “On” or “Off”

1= ON

0= OFF