To show how the logic of this program works, print the game's map and black out the red. You will run Ozobot on the map and see how it will continue through the map forever. The shape of the maze is the reason that a program like this works. It is called a binary tree because every branch splits in two. Next, you will play the program on an unedited first map to show how the program helps Ozobot end on red. After students see how Line-End Search is played, the class will compare the actions of the bot to the program itself.

Lesson Outline

Have one map, a device for Ozobot Blockly with the program loaded, and an Ozobot to demonstrate the game. Find the program at https://ozo.bot/line-end-search-game

1. Organize your students into pairs.
2. Explain that you'll be playing a preprogrammed game with Ozobot, then discover how it was programmed. The game makes the bot walk in a maze until it finds the winning color.
3. Hand out one activity sheet to each student.
4. Demonstrate the game on a map with the red line segment covered with black marker. Then demonstrate on a map with one red line end. Explain how the game is played, ie. Start the program and set Ozobot on the start line. Ozobot will follow the line until it lands on a red line segment.
5. Students then complete sections A and B of the activity sheet.
6. Compare what the students wrote on the activity sheet to the Ozobot Blockly program.
7. Discuss how the program works (see below).
8. To get students to make meaningful changes to the program, have students use the second maze map called Challenge. Point out that there is now a blue line end on the second branch from the top.
9. Ask students what changes to the original program are needed to make Ozobot go straight to that line and see blue. Either give the answers or have students discuss and test in groups. ANSWER: Change if there is a way right and pick direction right both to left. Change the line-end color to blue. Change if there is a way left, pick straight to if there is a way right, pick straight. Remember this is a backup code whose importance will be more apparent if and when students make their own binary tree maps.
10. Have students gather materials they need: Computer/tablet, Ozobot, and both maps.
11. Students open the program: https://ozo.bot/line-end-search-game and test it on the original map first. Then make changes to the program for the Challenge Map.
12. Students adjust the program, trying to get Ozobot to the blue line more directly and end the program.
13. Once the Challenge Map program has been completed, students draw their own binary tree maze with different colored line ends and program Ozobot to reach the different colors.
14. Have groups exchange maps and solve a new challenge.

Discuss How the Program Works

1. Open the Ozobot Blockly program found at https://ozo.bot/line-end-search-game on your main classroom display.
2. Point out the Line Navigation blocks.

a. These blocks program Ozobot to follow lines. Be sure to remind students that Ozobot Blockly uses sequential programming. When using the Line Navigation blocks, Ozobot follows a line and looks for an intersection or line-end before it will run the next block of code.

b. Point out that L-shaped turns on the map are not seen as intersections but as the continuation of the line. To be an intersection, there must be a choice of directions to go.

1. Point out the blocks that make Ozobot choose actions. Explain the Program Logic for the instructions if there is a way right, left, or straight.
2. Point out the codes that make Ozobot walk around by itself, the Loops. The program can run forever because it will loop through a line-follow code and a decision at an intersection or line-end over and over. Provide an optional demo of placing Ozobot on a large hand-drawn plus sign. It will walk on the lines counter-clockwise forever.
3. Point out the blocks after the loop: the victory dance.

a. A victory dance can be lights, movements, and sounds. Put lights before movement.

b. Light animations (rainbow, disco, etc) can go anywhere in the victory dance.

1. Optional: Show the alternative program that is hard-coded. https://ozo.bot/line-end-search-hardcoded. This program is what new students might make to solve this maze from scratch. It is correct, but it isn't autonomous and leaves room for error.
2. Lead students in asking questions and discussing how the programs work.
3. Summarize the program to remind students that they can now code autonomous movement, surface color reactions, and the game mechanic of Winning!

Explanation of Loops

Loops allow a section of code to be repeated either a certain number of times or until a 'break' code is called. In this program, use a break to tell Ozobot when to end the loop.

Ozobot will run the 'break' code when it stops at a line-end or intersection and sees that the line color is red. The bot will not stop as soon as it walks on the red, because it only executes code once it knows it is at a line-end or intersection.

Explanation of Conditional Logic

In programming, sometimes we want certain code to run only in a specific situation, or 'condition'. Programming languages make this easy by giving us if statements.

Just like in Part 1 - Color Search, Ozobot can be programmed to check conditions in its sensor after performing a movement. Last time, Ozobot ran the if statement after a forward step. In this lesson, Ozobot runs it at a line-end or intersection. We can also check what type of intersection Ozobot has reached.

In Level 3 of Ozobot Blockly, there are blocks for checking line color and for checking surface color - be sure to notice the difference when building or editing a program!

PROGRAM LOGIC: This program is organized so that taking a right turn when possible is always first and Ozobot will return to the top of the loop to follow the new line. The second priority is when Ozobot needs to walk back on a line. We want it to go straight in those conditions. Last is the end of the line reaction. We prioritize checking if it's red; if it is, end the loop, and if it is not, do nothing. Then choose to go back.

Line Navigation

Line Navigation codes are unique to Ozobot. Use them to tell Ozobot to follow a line and what to do at an intersection or line-end. There are some important things to know about Line Navigation codes:

a. You can only tell Ozobot what to do at an intersection or a line-end, and NOT while it is walking on a line. That means it cannot see the color of a line unless it is an intersection or a line-end. It also cannot make a turn off the line like using a Line Switch Color Code.

b. A right angled turn (or any turn) is not an intersection; Ozobot sees it as the same line continuing.

c. An intersection can be a plus (+) or T shape.

d. You can't mix LIne Navigation movement (orange blocks) with Free Movement (yellow blocks) unless you are transitioning between the two movement types. You can't use steps on a line.

e. If Ozobot doesn't see a line when a Line Navigation code runs, it will stop and end the program. To be most successful, place the bot on the line, then click Run Program.

The game Line-end Search repeats the follow line to next intersection or line end code block and an if statement for what to do at an intersection. Using a follow line code block with an if statement about what to do at an intersection within a loop creates autonomous line-following behavior.