Lesson video

Hello, my name is Mrs. Holborow and welcome to Computing.

I'm so pleased that you've been able to join me for the lesson today.

We are going to be looking at how we can use logic gate simulator software to create and test logic circuits.

Welcome to today's lesson from the unit, Boolean Logic.

This lesson is called Logic Gate Simulator Software.

And by the end of today's lesson, you'll be able to use logic gate simulator software to model logic circuits.

Shall we make a start? We will be exploring these key words throughout today's lesson.

Logic gate simulator.

Logic gate simulator, a piece of software that allows you to build a logic circuit and test it with different input values.

Circuit diagram.

Circuit diagram, a picture used to represent a more complex logical statement.

There are two parts to today's lesson.

We'll start by using logic gate simulator software, then we'll move on to model and test a more complex circuit.

Let's make a start by using logic gate simulator software.

A logic gate simulator is a piece of software that allows you to build an interactive circuit diagram.

You can use the software to test a circuit with different input values and see the output.

Throughout this lesson, we are going to be using the free logic gate simulator at oak.

link/logicly-demo.

Aisha says, "I can turn the inputs on and off in my circuit and see what happens." Should we go and see how this works? You are going to use logic gate simulator software to help you test your circuits.

People who design computers use a logic gate simulator to check the design of complex circuits before they are built out of expensive materials.

This prevents mistakes and wastage.

Here's a screen grab from the logic gate simulator software.

I've identified some of the key tools that you may need to use.

So on the left hand side we've got the menu bar, which is split into sections.

The top sections is the inputs.

So for example, a toggle switch, or a high or low constant, 1 or 0.

Next are the outputs.

So we have a light bulb and a 4-Bit Digit.

And then underneath that we've got the logic gates, which hopefully you should be familiar with by now.

In the main panel is the space where you are going to create the circuit.

Let's start by simulating an AND gate.

Drag an AND gate into the circuit creation area.

Next, you are going to drag in a toggle switch from the input controls.

Click on the white dot and drag to one of the AND gate inputs to connect it to the AND gate.

This picture shows you how it should be connected.

Repeat that step to create another toggle switch and connect it to the other AND gate input.

Your diagram should look like the one below.

Now drag a light bulb output and connect it to the output of the AND gate.

We can now test if this works.

When both inputs are off, the output is off.

But if you turn both inputs on, the light bulb should turn on to.

Test your circuit now and see if it works.

You can also add a label to your inputs to help you understand more complex circuits.

So in this example, I've labelled my two toggle switches as A and B.

This isn't a very complex circuit, but you can imagine when we've got multiple gates and multiple inputs, it's really useful to label them.

Time to check your understanding.

Which diagram shows a correctly wired OR gate? Is it a, b, or c? Pause the video whilst you have a think.

Did you select a, well done.

a is the correct answer because it uses the OR gate and all of the connections are connected up correctly.

Each input can only be wired to one logic gate.

Is this true or false? Pause the video whilst you have a think.

Did you say false? That's correct.

You can wire an input to as many gates as you want.

The expression A OR A AND B would require A to be both wired to the OR and the AND gates.

We are now moving on to the first set of activities for today's lesson.

You're doing a fantastic job so far, so well done.

For each of the expressions below, I'd like you to create the circuit using the logic gate simulator software.

Then, use the circuit to construct the truth table for the expression.

So the three expressions are a, which is A AND B, B, A AND NOT B, and then c, A AND B in brackets OR A AND NOT B in brackets.

Pause the video here whilst you complete the activity.

How did you get on using the simulator? Did you come across any problems? Let's have a look at some sample answers together.

The first one, part a was A AND B.

On the right hand side, I've got a screenshot of my logic gate simulator and you can see I've got an AND gate and I've got the two inputs, A and B.

On the left hand side, I've completed the truth table for this circuit.

So if A AND B are zero, A AND B results in zero.

If A is zero and B is one, A AND B is zero.

If A is one and B is zero, A AND B are zero.

And then lastly, if A is one and B is one, A AND B is one.

So to test this in the logic gate simulator software, the light bulb or output should only light up if A and B are on.

Let's have a look at part b.

So the logic statement for this one was A AND NOT B.

So on the right hand side I've got my screenshot from the logic gate simulator and you can see that I have got two inputs, A and B, and then I have an AND gate.

But before B goes into the AND gate, it goes through a NOT gate because we've got A AND NOT B.

I've then completed the truth table on the left hand side for this circuit.

So the column A AND NOT B, reading from top to bottom is 0, 0, 1, 0.

And then part c, the logic statement was A AND B in bracket OR A AND NOT B in bracket.

So you can see this one is a little bit more complicated because it includes four logic gates.

I have two AND gates, an OR gate and a NOT gate.

And you can see some of my inputs are connected to more than one logic gate.

So A is connected to the first AND gate and the second AND gate and B is connected to the first AND gate and then the NOT gate before then being connected to the second AND gate.

If you need to make any corrections to your logic gate in your simulator software, you can always pause your video now and make any corrections.

For part two, I'd like you to explain why logic gate simulator software is useful when building a circuit.

Pause the video whilst you have a think and answer the question.

Let's have a look at a sample answer for this one together.

So you were asked to explain why logic gate simulator software is useful when building a circuit.

When we are learning about logic gates, we can use a simulator to test our circuit and check whether it represents the logic we intended.

Computer designers use logic gate simulator software to test their complex designs before they're manufactured onto circuit boards.

We are now moving on to the second part of today's lesson where we are going to model and test a more complex circuit.

This circuit shows A AND B in brackets OR A AND NOT B in brackets.

What do you notice about its truth table? Maybe pause the video whilst you have a quick think.

Hopefully you noticed that when A is false, the expression is false, and when A is true, the expression is true.

Jun's got a really good point.

"The two highlighted columns have exactly the same values." But what does this mean? Jun says, "I think you could replace this whole circuit with just an input A.

Is this right? Let's check your understanding.

Jun thinks you can replace the circuit with just an input A and get the same output.

He is a, correct, b, wrong because you need a minimum of one gate, or c, wrong because that would give a different output.

Pause the video whilst you have a think.

That's right, Jun was correct.

This is possible because the columns in the truth table were identical.

All circuits with more than one gate can be simplified.

Is this true or false? Pause the video and have a think.

This is false.

Just because a circuit uses more than one gate does not mean that it could be constructed in a simpler way.

An OR gate is true if one or both outputs are true.

AND, OR and NOT are the fundamental logic gates.

So here I've got the symbol for the OR gate and I've got the truth table.

Familiarise yourself with the OR gate for a few seconds.

We are now moving on to the second set of tasks for today's lesson, and you're doing a fantastic job so far, so well done.

Using and or are not, write down a logical statement to describe a circuit that is true only if the inputs are different to each other.

Pause the video whilst you complete the activity.

How did you get on? <v ->There was actually more than one way to do this.

</v> So let's have a look at the possible solutions.

Solution 1, was A OR B in brackets AND NOT A AND B in bracket.

So that would've resulted in the final column being 0, 1, 1, 0.

So, only true if the inputs are different to each other.

The second solution is A AND NOT B in brackets OR B AND NOT A in brackets.

Again, the truth table remains the same.

Now, I'd like you to use the logic gate simulator software to create this statement as a circuit.

Remember, there's more than one solution, so you can create either of those circuits.

Then I want you to use that circuit to fill in the truth table to test whether your answer was correct or not.

Pause the video here whilst you complete the activity.

How did you get on? Did you manage to build the circuit in the simulator software? Great work.

Let's have a look at the sample answer together.

So here I've got a screenshot from my simulator software and this was for solution one.

So I have A and B labelled as my inputs with the toggle switches.

I then have four gates in total, so I have two AND gates and OR gate and a NOT gate.

So A goes into an input for the first OR gate and the first AND gate, and then B goes in as an input to the first OR gate and the first AND gate.

The output of the OR gate goes into an input for the second AND gate, the output of the first AND gate goes into an input of a NOT gate, which then goes into the second AND gate as an input.

Remember, we can check the circuit works correctly by using the toggle switches.

And in this example, we wanted the light bulb only to come on if the toggle switches were different.

So if A was on and B was off, or if A was off and B was on.

Okay, let's now have a look at the second solution.

So this solution still uses four logic gates, but it's slightly different.

So I've got my two toggle switches with my inputs A and B.

A goes into the input for the first AND gate and then a NOT gate which goes into the input of the second AND gate.

And then B does exactly the same but for the other way round.

So it's an input for the second AND gate, and then also an input for the NOT gate going into the first AND gate, and then the output of the two AND gates goes into an OR gate before finally being connected to the output or the light bulb.

Again, remember we can test the circuit using the toggle switches to make sure it produces the expected output.

If you need to, remember you can pause the video here and go back and make any adjustments to your circuits that you need to.

We've come to the end of today's lesson and you've done a fantastic job, so well done.

Let's summarise what we have learned during this lesson.

Logic gate simulator software allows you to create an interactive circuit diagram.

You can use this to test whether the circuit you have created is correct by changing the inputs and observing the output.

A logic gate simulator can help you quickly generate a truth table for a logic circuit.

I hope you've enjoyed today's lesson and I'll see you again soon.

Bye.