Dot, Dash, Dot, Dot / Dot, Dot, Dot, Dot, Dot

Computational Thinking - Alien Contact! - Lesson 5

Objectives

To understand that encryption is a way to keep data private.
To encode and decode Morse code messages.
To recognise and apply computational thinking concepts and approaches to solve problems.

Lesson Resources

Computational Thinking - Alien Contact!

Lesson 1 - First contact

Lesson 2 - Bits and pieces

Lesson 3 - Sorting out Spacebook

Lesson 4 - Communicate and Collaborate

Lesson 5 - Dot, Dash, Dot, Dot / Dot, Dot, Dot, Dot, Dot

Lesson 6 - All about algorithms

Introduction

Begin the lesson by recapping the classes achievements over the last few weeks, then playing the latest incoming message from the aliens in the teacher presentation:

Play the sound clip (here), it is also available from the teacher presentation slides. The sound file is a more code message of a number. We really don’t expect anyone to be able to listen to and decipher it at first. But you don’t need to tell the students that yet!

Do you have a number for me? Why not?! You could feign disappointment at the lack of a number code from them. Okay, so if we don’t know the number what do we know? How can we use our computational thinking skills to solve this problem? They might recognise it as some kind of code, perhaps an alien language, or even as Morse code. Confirm that the number is hidden in a code. Ask the children how do you think you’ll be able to decipher the message. What else do you need to help you?

Introduce the lesson objectives at this point.

We say that data that has been converted into a code has been encrypted. Unless you have the encryption key the data remains in its code and unreadable. The encryption key is a way to translate the code. Take a look at this excellent video from code.org which explains more about encryption and keys.

So we need a decryption key so we can understand our message! Give out the Morse code decoder sheet and play the sound clip again.

Can you identify any elements now? It’s still likely to be too hard to work out the message as it plays really quickly, but they may now be able to recognise patterns in the sounds, and they may, with the clue of the decoder sheet, identify it as Morse code. Has anybody heard of Morse code before?

Morse code was developed in the 1830s and is named after Samuel F. B. Morse, an inventor of the telegraph. It is a way of converting text characters into a code which can be transmitted using sound or light.

It uses sequences of two different signal durations called dots and dashes. These could be represented by a sound or light flashes. It can be transmitted at different speeds, but a dot is 1 unit and a dash is 3 units long. For example, if a dot (beep or light flash) lasted for 1 second, a dash (beep of light flash) would last for three seconds. Spaces with no signal can be used as follows:

The space between dots and dashes in the same letter sequence is 1 unit
The space between letters in a word is 3 units
The space between words in a sentence is 7 units

Talk through how the Morse code decoder sheet sheet works. If you had a Morse code message to decipher you can follow the branches down to quickly identify the letters or numbers in the message. The slides show the example of the word DOG.

If there is a dash in the code follow the branch to the right, if there is a dot follow the branches to the left.