Teaching Computer Science: Day 14 - 007-bit (License to encode)

In this week’s lesson, I continued the theme of how data is stored in computers, this week focusing on how characters are represented in a computer system.



Learning Objectives:

• Explain the use of binary codes to represent characters
  
• Explain the term character set
  
• Describe with examples (for example ASCII and Unicode) the relationship between the number of bits per character in a character set and the number of characters which can be represented
  

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Lesson 1: Theory (Characters)

Suggested time: 50 mins

Starter:

Students were given the following worksheet and asked to complete the tasks:

starter.pdf
File Size:	57 kb
File Type:	pdf

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Main:

I explained that, in the previous lesson, we have looked at how numbers are represented in a computer using binary. I then explained that characters are converted in the same way using something called a character set.

Next, I explained that one of the most commonly used character sets is ascii (American Standard Code for Information Interchange). I then showed students the full 7-bit ascii table (See below).

7-bit_ascii_table.pdf
File Size:	84 kb
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I then explained that the ascii character set uses 7 bits which allows the computer to encode up to 128 characters.

Finally, I gave students each a worksheet containing part of the ascii table (containing the letters A to Z in uppercase and lowercase) and asked the students to fill in the gaps in the table. Once complete, I asked the students to attempt the challenges on the worksheet (see below)

ascii_secret_agent_challenge.pdf
File Size:	119 kb
File Type:	pdf

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ascii_secret_agent_challenge_answers.pdf
File Size:	121 kb
File Type:	pdf

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Resources:

Representation of text - http://web.eecs.utk.edu/research/cs100modules/module3/index.html

Ascii text to Binary converter - http://www.binaryhexconverter.com/ascii-text-to-binary-converter

Ascii Binary conversion chart - http://www.nthelp.com/ascii.htm

Text to Ascii and Binary converter - http://www.computingacademy.org.uk/text-ascii-and-binary-converter    

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Lesson 2: Programming (Python)

Suggested time: 50 mins

Main:

Students were instructed to setup their Raspberry Pis and to launch IDLE 3.

Students were then asked to continue to work through Mark Clarckson’s Introduction to Python booklet: (http://community.computingatschool.org.uk/resources/14)

Alternative:

Alternatively, if you do not have access to a set of Raspberry Pis, students can still complete the Python challenges:

To install Python for FREE, go to the python.org website and download a standard installation of the latest version of Python. This will provide you with everything you need.