Engage (15 minutes):
- Ask what they already know about codes. Have volunteers explain how codes work (symbols, sounds, or patterns stand for letters or words to create a message that can only be understood by someone who knows the code). Have students brainstorm a list of codes used in the past and currently.
Examples:
- Writing is a form of code that uses written symbols to change spoken language and thoughts into graphic form.
- Sign language is a code that uses hand signals for letters and words.
- Drum codes and smoke signals were used by ancient people to communicate across distances.
- A referee’s hand signals at a football game communicate calls.
- Semaphore (flag signals) are used to communicate between boats.
- Telegraph companies and the military used Morse code to communicate before phone communication was possible.
2. Access the Morse Code Translator on the teacher's computer. Type in a message and click translate to show it in symbolic Morse Code. Click play to hear the audio translation of the code. Ask how Morse Code could be used, both when it was first invented in 1836 and today to send SOS signals using lights or electronic pulses when other forms of communication are limited.
3. Watch 5-minute “History of Morse Code” video on YouTube. Discuss that while Morse code can be expressed as dashes and dots, it is more commonly an audible code as they heard in the video.
Explore (25 minutes):
- Codes like Morse code were first used to transmit messages across large distances. Now that communication technology has advanced with the advent of cell phones and the Internet, different types of codes are more common. Introduce the term “binary” and explain that it is the code used by computers to understand letters and numbers.
- Show code.org video for the “Binary Bracelets” lesson (1.5 minutes). Ask students why computers use binary code. (Since robots and computers are composed of thousands of electrical switches that are either “on” or “off,” this code can be used to represent letters and numbers with sequences of only two options.)
- Give students binary code handouts, strips of construction paper, markers, and tape. Using a binary code poster or a projected image of this handout, discuss the 8-symbol code for each letter, which could be thought of as “on” and “off,” “0’s” and “1’s,” “black and white,” or any set of opposites, much the same way as Morse Code is dashes and dots. Have each student circle his or her first initial on the handout and create a “binary bracelet” by drawing the binary code for that letter on the strip of paper. Tape on wrists.
- Have students continue to use binary code by decoding the secret message at the bottom of the page. Students’ success with decoding the secret message can be a formative assessment of their understanding of binary code.
Explain (30 – 40 minutes):
- Codes can be used to transmit verbal messages, but they can also be used to transmit data such as images. When you see a picture on a computer or television, that picture is made of thousands of tiny dots called pixels. The machines transmit these pictures by communicating the color and arrangement of these pixels to make a picture. (Increase the zoom on your computer to begin to show pixels; talk about how zooming on a low-resolution photo results in a more pixelated image.)
- Watch the 2.5-minute video about image compression and transmission of pictures.
- Provide background information to students about image compression (see p.2 of "Unplugged Computer Science: Image Representation"). Project p. 3 from the packet so students can see it and walk students through the compression code for the letter “a.” Have a student volunteer create a new image on the grid at the bottom of the page, and then have students work in small groups to write the compression code for the image. After groups have completed the code, have a student from each group fill in a line or two of the code on the board or projected image. This gives students a chance to self-check their thinking and ask questions before creating and decoding more codes independently.
- Distribute image compression handouts (p. 4-5 copied front and back). Students will decode images from a provided code on p. 4. Then they will create their own images and write codes for them on p. 5. Circulate as students work on these tasks to guide understanding as necessary.
Elaborate (30 minutes):
- Tell students that they will create a new code they can use to communicate a message using only sounds they can create without using their voices. Examples are claps, desk taps, foot stomps, etc. Have students work in groups of four. As students work, circulate and ask guiding questions:
- How can they make the code?
- How will the message receiver be able to understand it?
- Do you need a code for each letter of the alphabet?
- Will you have a sound that represents a space between words, or should the receiver be able to detect spaces by the rhythm of the code?
- Are there some letters that are more important or more common than others? How will this affect your decision for sounds for each letter?
- How will you share your key with the whole team?
2. After 20 minutes, split teams into a communication team and a receiver team. Give the communication team a slip of paper with a simple sentence to transmit. One team at a time, communicators send the message to their receiving team. After the code has been transmitted, the receiving team tells the rest of the class what they decoded. Then the communication team reads the slip of paper aloud to check the decoding from the receiving team.
3. Debrief by discussing problems encountered during code creation, transmission, and decoding. Common problems will include difficulties coming up with unique codes for each letter of the alphabet, understanding boundaries between letters and words, and the availability of a key for all team members. Discuss why computers are commonly used today to create, transmit, and decode messages.
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