• Translate decimal to binary representation.
• Translate binary to decimal representation.
• Understand the difference between digital and analog designs.
• Understand how digital systems such as binary code relate to real world applications, for example in CD-ROMs, video games, digital cameras, and cellular phones.
• Understand that working with binary is cumbersome, error prone and difficult for humans to read.

• At the beginning of class, explain to students that they will be decoding messages using special boards. Each board has its own code for different letters. There are four different switches; therefore we can have only 16 combinations (24). Each switch will be in one of two different positions: on or off. On = 1 and off = 0. Each letter has its own code, for example, on this box (hold up a box), "off, off, off, off" or "0000" lights up a light beneath the letter "A," while "1111" represents "S."
• Have each student take out a piece of paper and write down "0000" on the first line and "1111" on the 16th line. Since there are 16 possible combinations of zeros and ones, have students come up with the remaining 14 combinations of zeros and ones.
• Explanation of boards: Once most students are finished with the patterns, explain how to use the boards. Explain that up = 1 and down = 0. After you set the switches in an on/off pattern, press "reset" and the light will appear. Write down which letter corresponds to the pattern.
• Creating a "key": Divide the class into groups. Ideally, there should be two students per box, but there can be up to four students. Have one student be a "scribe" and the other a "switcher." The scribe should work from the list of combinations and tell the other student which pattern to set. The switcher then reports which light appears. Test all 16 combinations and create a "key" for that box. (Remember, each box is different).
• Decoding: Once the group has all of the letters, then pass out the code that goes with the box. (Since each box has only 16 letters, be sure to give the right code for the right box). Instruct the students to switch roles, so the scribe can get a turn switching. (Often, girls are relegated to the "note taker" role, so switching roles is important!) Students use the key they just decoded to interpret the message. The group with the code that says they are the winners gets a prize.
• Switch Boards: Switch boards and codes and have students decode other codes.
• Group Discussion: At the end of the class, collect the boards and have a full group discussion using the discussion questions below. Be sure to stress how binary is used in many everyday forms of technology, such as computers, CD players, cellular phones, and video games.
• Create new codes: Explain that the wires can be rearranged so that the combinations now correspond to different letters. Students rearrange the wires and then try the different combinations of 0's and 1's to come with a new key. Students come up with a new message using their 16 letters. They write the code for that message and give it to another group to interpret. Groups should follow the steps listed in the "Binary Encoding Activity" worksheet.

If binary boxes are not available to your class, you can simulate the activity above on the Tufts Binary Box website (http://www.engineering.tufts.edu/stemteams/binarybox/STEMSrb.html).

• Have all students visit the website above. The first page will look like the figure below

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• Have the students click on the introduction, read it, and then proceed to the main activity by clicking on the black arrows.
• The Binary Box page will look like the figure below. It may be helpful to have the students copy the binary code onto a sheet of paper and write the letters below the numbers as they go. If not, they can use the worksheet provided in the attachments.

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