Hands-on Activity Follow the Line:
Programming Robots with Color Sensors

Learning Objectives

After this activity, students should be able to:

• Explain how a color sensor works.
• Develop and explain the logic behind programs that instruct robots to use color sensor readings to make decisions.

Educational Standards

Each Teach Engineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in Teach Engineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

International Technology and Engineering Educators Association - Technology

Materials List

Each group needs:

• 1 micro:bit starter kit
• 1 Elecfreaks Cutebot (https://www.adafruit.com/product/4575)
• 1 Elecfreaks Cutebot Line Follower Track (folded paper comes with the kit)
• 1 laptop or computer to program the micro:bit with (Computer needs a USB-A port. If it has a USB-C port, a USB A-to-C adapter will be needed to connect the micro:bit to the computer.)
• 1 Line Follower Challenge Pre-Quiz per student
• 1 Line Follower Challenge Post-Quiz per student

To share with the entire class:

• Line Follower Challenge Presentation
• 1 laptop or computer with projector to show the presentation

Worksheets and Attachments

Pre-Req Knowledge

Students should be familiar with

• Block-based or text-based programming.
• Logic gates or conditional statements in programming.

Introduction/Motivation

Today’s challenge is to design and program a robot that can follow a black line using its color sensor.

Each group will develop a program that allows its robot to reliably stay on track as it moves along a taped path. At first this may seem simple, but you’ll quickly find that the robot is constantly making small decisions: Am I still on the line? Did I drift left or right? How do I correct my movement?

So how will you make it work?

Think of the built-in color sensors as the robot’s “eyes.” These sensors are constantly reading the surface beneath the robot and sending information back to the micro:bit. This input tells the robot whether it is currently on the black line or off the line on the surrounding surface.

With this real-time feedback, the micro:bit can make decisions about how to adjust the motors. For example, if the sensor detects that the robot has drifted off the line to one side, the program can correct by slowing one motor and speeding up the other, gently steering the robot back toward the line. If it detects the line again, it adjusts accordingly.

This process repeats continuously in a loop: sense → decide → act. That feedback loop is what allows the robot to “track” the line instead of just driving forward blindly.

Your goal is to build a program that uses sensor input to keep the robot’s “eyes” centered on the black tape as it moves. When the robot is correctly tuned, it should be able to navigate the path smoothly and continuously without leaving the line.

Procedure

Before the Activity

• Gather materials for each group.
• Make copies of the Line Follower Challenge Pre-Quiz and Line Follower Challenge Post-Quiz, one each per student. (Note: The quizzes and their answers are also embedded in the presentation, so they can be presented to the class, if desired.)
• Assemble the Elecfreaks Cutebot (with micro:bit inserted) by following the instructions found in the box.
• Find a clear space on a smooth floor for one (or more) of the Elecfreaks Cutebot Line-Tracker Track, which is a folded piece of paper with a dark line for the robot to follow.
• Set up a computer/projector to show the Line Follower Presentation to teach and conduct the activity with the class.
• Review the solution program on Slides 11-17 to fully understand the logic used in this program and to be able to explain it to students after they have had a chance to try developing their own programs.
• Arrange for enough computers so you have one for each student group.
• Mark four paper points on the ground in the classroom (e.g., the corners of a five-foot square.) Note: You can increase the degree of difficulty by spacing the points farther apart.) 

With the Students

Part I – Human Robot

1. Divide the students into pairs.
2. Explain the challenge: One person in each pair will close their eyes while the second team member will direct the first one around the room using verbal commands.
3. The goal is to become the first group to have the member with their eyes closed touch all four points.
4. After all the students have had the opportunity to touch at least a few of the points, bring the class back together to discuss what they discovered.
5. Ask students questions about the exercise they just completed to begin a discussion about what happened. Example questions:

• What did you find easy/difficult?
• What was the hardest part about the exercise?
• Do you think this is a realistic way to think about a robot's computer sending outputs to tell the robot to move? Why or why not?

6.  Ensure students end the activity with the following takeaways:

• The important thing is for the students to discuss how the exercise is similar to or different from an actual robot.
• Expect that they will have discovered that it is difficult to command someone who is unable to sense their environment.
• It is also difficult to give thorough and precise commands without missing steps and details.
• Their experiences model the many challenges and difficulties in programming robots.
• Instructions must be very precise, with EVERY detail included.

Part II: Line Follower Challenge (with the students)

1. Distribute one Line Follower Challenge Pre-Quiz (also Slide 2 with answers on Slide 3) to each student.
2. Give students 5 minutes to answer the pre-quiz questions.
3. Discuss the pre-quiz answers as a class after students have filled out the sheets.
4. Introduce (or review) the engineering design process and walk through the seven steps shown in Image 1.

5. Ask: Use Slide 4 to introduce the line follower design challenge: Program a robot to follow a black line, using color sensors as their "eyes."
6. Research: Before students begin the design challenge, provide a refresher on how the color sensor works using Slides 5-8.

• Explain the reflectivity of light and how the micro:bit represents them.
• Explain that colors close to white reflect more light and colors close to black reflect less light.

7. Show students the provided Elecfreaks line course on the floor as described on Slide 9.
8. Divide the students into groups of three.
9. Imagine and Plan: Give the groups 15-20 minutes to create their line follower programs.

• Direct groups to begin by brainstorming the logic for a program that instructs the robot to successfully follow the line.
• Encourage students to use what they have learned about programming from previous activities.

10. Create:

• Provide each group with a Cutebot with batteries and micro:bit inserted.
• Have each group flash their code that they wrote on MakeCode to their robot.

11. Test:

• Give the groups 20-30 minutes to test their robots on the track and make changes to their program designs.
• To test a line follower program, position the robot's color sensor over the line and start the program.
• Remind students that the testing and redesign steps of the engineering design process are when engineers test their ideas to see if they meet the challenge, and re-design as necessary.

12. Share Out: Gather the class together so each group can demonstrate the performance of its robot and designed program.
13. Optional: Once students have attempted to complete the line follower challenge, walk them through the logic of the complex solution (on Slides 10-17), and explain how to generate the program step by step.
14. Reflect: Discuss the activity as a class, particularly what students learned and any issues or problems. Specifically, ask students:

• How many groups experienced some unsuccessful program design attempts?
• What were some of your programming design ideas that did not work?
• Did the successful program design surprise you?
• Can you understand why engineers say they learn more from failures than successes?

15. Administer the Line Follower Challenge Post-Quiz (also on Slide 19 with answers on Slide 20).
16. Review the answers as a class.
17. Optional: Slide 21 presents vocabulary words and definitions.

Vocabulary/Definitions

design: Loosely defined, the art of creating something that does not exist.

engineering: The use of science and mathematics to solve problems to improve the world around us.

Assessment

Pre-Activity Assessment

Pre-Quiz: Before starting the activity, administer the two-question Line Follower Challenge Pre-Quiz by handing out paper copies (also on Slide 2). Use the pre-quiz to assess students' prior knowledge of how color sensors work and encourage them to brainstorm how a program for this challenge could include the robot turning. The answers are provided on the Line Follower Challenge Pre-Quiz Answer Key (and Slide 3).

Activity Embedded (Formative) Assessment

Line Follower Challenge: Assess each group's performance in the line follower challenge using the following rubric (maximum 20 points).

• The program logic was correct. (10 points maximum) (Note: Refer to solution on Slides 10-17.)
• The group iterated several times and improved its design. (10 points maximum)

Post-Activity (Summative) Assessment

Concluding Discussion: At the end of the activity, lead a class discussion so students can share their observations, difficulties, questions, and conclusions. How many unsuccessful program design attempts did your team go through? What were some of your programming design ideas that did not work? Did the successful program design surprise you? Mention that sometimes engineers say they learn more from failures than successes. Use this opportunity to gauge student comprehension.

Post-Quiz: At the end of the activity, administer the two-question Line Follower Challenge Post-Quiz by handing out paper copies (also Slide 15). Review students' answers to assess their individual understanding of the logic in the program solution for this challenge and ability to relate this logic to real-world engineering problems. Answers are provided on the Line Follower Challenge Post-Quiz Answer Key (and Slide 16).

Troubleshooting Tips

If the robot does not follow a black line, check for these common problems:

• The black line may need to be thicker; if the line is very thin, the color sensor response time might be too slow.
• The light level used in the switch statement (Step 2) might need to be raised or lowered, depending on the surface color/reflectivity of the black line. It is often helpful for debugging to view the output of the color sensor directly from the EV3, via the View menu option.
• Make sure the sensors/motors are connected to the correct ports.
• Read back through the instructions and make sure all of the properties for the commands are set correctly.

Activity Scaling

For lower grades, provide more of the micro:bit code as a starting point. For example, you might give students the basic loop structure and the logic for reading the three possible sensor outputs. Students would then focus on deciding how each sensor reading affects the speed and direction of the Cutebot wheels.

Alternatively, you could provide the motor speed values needed for turning left, turning right, and moving straight, and have students determine the logic that connects each sensor reading to the correct movement.

For older or more advanced students, provide less of the starter code. In an intermediate version of the activity, you might give students only the main loop structure and require them to develop both the decision-making logic for interpreting sensor data and the motor speed values for controlling the robot.

For the most advanced students, provide no starter code at all. Instead, guide them by identifying the key programming components or “tabs” they will need (such as input, logic, and motor control), and have them independently build the full program from scratch.

Copyright

Contributors

Supporting Program

Acknowledgements

This work is based on work supported in part by the National Science Foundation under grant no. EEC-1801666—Research Experiences for Teachers at the University of Missouri. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.