Lesson video

Hi there, I'm Sarah your Computing teacher for this unit representation.

This is lesson 2 of 6, lights and drums, and you will be needing pen and paper to take some notes.

So by all means pause the video to get yourself ready, get pen and paper, remove any distraction such as notifications then you will be good and ready to continue they lesson.

So you can look on what you will be learning in this lesson.

You will learn that characters can be represented as sequences of symbols.

Examine examples of character coding schemes and measure the length of representation as number of symbols it contains.

Take a look at this form.

Here is a nice first task.

Two friends live on huts opposite side of a great lake, a big lake.

They have no wiFi or mobile phones in that part of the world.

But they would like to exchange messages from a distance.

Your job is to try and workout how they can do so.

Pause the video and complete this task and when you have completed press play to continue.

Right from lesson 1, you might remember representations used for communication across distances, such as flag semaphores or sign language, or perhaps you came up with with new examples, such as morse code or using light signals or may be you even devised a new system entirely for communicating across distances.

There are forth amount of coding schemes out there but in this section you will only come across a handful of them.

Coding schemes are ways of representing information that can be communicated across distances.

In this first example, the Morse code, you will see that the coding schemes consists of dits and dahs or what we call dots and dashes.

They can be generated by turning light on and off, tapping on object or by making sounds.

This may be familiar to you actually.

You may have seen this as well.

The next coding scheme you see is called ASCII code.

Which stands for The American Standard Code for Information Interchange.

This is a way of representing texts and numbers in all electronic devices.

It major for 7-bit code which represent characters and numbers on your keyboard.

It uses binary digits 0 and 1 to represent as such as 7 numbers hence 7-bit code.

The next coding scheme you see is International Telegraph Alphabet No.

2 or the ITA2.

It was widely used in telegraphy, and for the first time, telegraphy allowed messages to be sent by electrical signals or by radio waves without the need of physical transportation.

In ITA2 each character consist of a code of 5 bits, and you can use it for long distance communication in what's called telegram.

Coded telegram were printed out on punched paper tapes, in the form you can see on the screen before you.

The next examples of coding scheme you see is the Bacon Cypher or sometimes called the Baconian Cypher, and this was invented by Francis Bacon in 1605.

It's a way of encoding messages also consisting of 5 characters.

Each character could be A or B.

In this section you will learn how to transmit text messages.

This process can be broken down into three steps encoding, transmission and decoding of messages.

In this example we shall demonstrate to you the message or word has been encoded using Morse code which you have seen previously.

I would need you much to watch this.

But before that there is a diagram in front of you of the chart, using that, I'll play you the sounds of Morse code alphabet.

See how many alphabet letters you can spot, perhaps they are 26, let's find out.

I'll be needing this shortly, but let's find out.

Right we are done, so how many did you spot? So onto the demonstrations, I'm going to use a torch.

It's a variable light torch.

So it contains some branson, maybe it's not the best example.

But this will do.

I'm going to demonstrate what the show, that's the light coming on.

I going to demonstrate what dot is.

So that's the dot.

Ignore the clicking sounds, perhaps one doesn't click but torch does.

So ignore the clicking sound.

But just look for the light.

So again, shots, so the long would be.

All right ,okay.

So can we begin.

You can use the chart in front of you to see or to sump to the letters that I'm going to be demonstrating.

So I'll pause for a couple seconds in between and then to let you know, or to kind of demarcate letter from the other.

So I will begin now, so my first letter will be? Next letter.

Next form.

Next form.

And next form.

Right so hopefully, that was very sweet.

They were hopefully, you would have majored on what I have just demonstrated using Morse code how to communicate to you H-E-L-L-O, Which is hello.

In this next example, I will encode using Morse code of four letter word.

So listen carefully, I will demonstrate to you firstly what they should sound like.

So this should be the long words, and the short.

Okay can we begin, so the first word is, Let's start again.

Think like I like that.

So lets start again, so listen out for this one.

Right I hope you got that.

But we got just sent the message.

Using Morse code, I want to use various mediums this time sound to transmit a message to you.

I'll hope you enjoyed actually decoding those messages I've just transmitted to you as much as I have fond of encoding those messages.

So that's task 1, you've got task 2, so your turn, pause the video complete the task and when you are done unpause.

So here is the answer.

Take a moment to pause and check your answer against this.

So what you saw earlier on that activities was me demonstrating to you how to communicate at a distance.

In other words, transmission.

I transmitted to you to encoded words hello and code.

Using two transmission medium, light and sound.

We had agreement also, we agreed on the Morse code, as a coding system and there're rules, in terms for the rules of transmission.

You knew what the sounds were supposed to sound like and you knew what the light was supposed to look like but for the dits and the dahs.

Now that agreement between two parties, for communication is called protocol.

Is like in English language, we have protocols or rules.

For instance, I cannot construct a sentence without using a verb.

Also we have communication equipment, we heard the sound which was like a kind of bell I was striking with the metal and we have the light, the torch.

In our, on your screen you can see two communication medium also.

The first on the top image, is a light, a big torch and the second, a drum.

So drum here is to send messages also.

Right, you might also have noticed during that activity, that there was a time I had to resend another word to you because it wasn't quite distinct.

I might didn't strike the the dits and dots properly.

So in communication protocol there is something called acknowledgement and there's something called retransmission.

In that session I assumed you acknowledged even though I couldn't see you or hear you.

The fact that you received both messages but also I was able to retransmit the message I thought was sent in error.

Right, you have learnt that messages can be transmitted using various mediums. You have seen light being used, we've talked about sounds, we've talked about electricity, we've talked about paper and we've talked about all those such as drums. In my example to you, in the example you saw, 'hello' was transmitted for instance.

The coding scheme used was Morse code, and the transmission medium was the torch, and we have the sound too.

Now it's your turn to encode the message.

So far you have to code the message, that I've encoded to you.

You have seen various transmission medium in action, it's your turn task 3 to encode the the message 'kitty'.

Pause the video and when you have finished, unpause.

Well done, now check your answer.

Well done.

On to task 4, you have received the message and asked to get coding scheme.

Now it's your turn to actually decode that message.

Pause the video and unpause when you complete it.

Well done.

Now check your answer.

You have learnt about coding systems and you have seen quite a few coding system.

In the coding systems that you've seen, sequence series of symbols are used to represent a letter.

Now in the coding system, any sort of information, can be translated into that coding system and stored, transmitted or processed.

Now the physical form, or the choice of symbol that you choose to use, of whatever coding system, does not actually affect the information that is involved or transmitted.

So examples of coding system we've seen, Morse code which uses dots or dashes.

Braille, which uses raised dots or no raised dots at all.

An ASCII that uses not and 1 or 0 and 1 and then you saw the coding system, the Bacon Cypher that uses a set of five letters consisting of As and Bs.

So what is meant by representation length? You will see some examples to find out.

In example 1, you've got kitty, using the encoding system Morse code.

Original word five symbols of five letters, encoded message 11 symbols, four spaces.

Another example, symbol reach the word kitty.

Five symbols, five letters, the encoded message in the Bacon Cypher, 35 symbols.

Another example, again the same original word with the same length, kitty, five letters with 35 symbols, in ASCII code.

In our last example, we've got kitty again, 35 symbols for the same five original symbols.

So this goes to show that different encoding systems, encoding the same original message will result in different length of encoded message, like you've seen.

How the computer represent the information and why it doesn't matter.

What is the link of representation to a computing? You have seen that coding systems uses symbols or sequences of symbols to represent a letter.

You have also seen that the choice of symbol is irrelevant.

As different coding schemes can mean or represent the same original message.

You have also seen that in computing, the symbols used are 0s and 1s.

In other words binary digits.

In computing, every piece of information bit test numbers, images, sounds or representations in a series of 1s and 0s, and physical colour for that is electricity, electric current.

You will examine some important questions to help you reflect on your learning during this lesson.

The first one being, how can 0s and 1s be represented in the real world? Think about what you've seen in different activities.

Pause the video and when you have finished with this thought, you can unpause.

Well done, great answers.

So we know that 1s and 0s can be represented in real world by using different types of medium.

For instance we saw light, the torch for example used in Morse code.

So I had on and off.

We can also use holes on the paper like the punch cards, we can use sounds or electricity as we have in telegraphs or in the computer.

So anything that has two states can be used.

So well done.

Next question, why have people invented so many different coding schemes? You can write down your thoughts down on the paper.

Pause the video and when you have completed this exercise, you can unpause.

Great answers again.

So there are so many ways to communicate, so there is so many coding systems also.

Coding systems have been invented to store information, and there're different schemes convenient for different purposes.

For convenient asking to computer, braille to blind, we've got sign language for hard of hearing and the list continues.

So you've learnt today how to encode, how to transmit and how to decode messages.

You've seen various coding schemes and also you have learnt about transmission medium.

You have also seen how problems can occur during communication.

You have seen it's important to have communication rules called protocol and also it's important to acknowledge when you receive the message and also when there is an error there have to be a way of resending or retransmitting that message.

You have also seen that every piece of information, encoded by in the computer is in 1s and 0s and the physical carrier can be electricity, paper as in hole punch, it can be light, magnetic orientation and the list continues.

So well done, we've reached the end of this lesson and I wish to see you next lesson.

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