A Flashing Warning

Courses

• Grades 3-12

Materials

• Cellphone, tablet, or computer
• Internet connection

Educational Objectives

• Understand the concept of “loop,” both general and nested.
• Develop a technological object (prototype) using a device.
• Identify relationships between technology and the surrounding environment.
• Evaluate one’s own work and that of others, both individually and in teams.
• Participate in dialogues and reflections to propose improvements.

Start (10 minutes) - The Flashing Challenge

1. Welcome students and introduce the day’s activity: “Today, we are going to learn how to create a more advanced and realistic traffic light.”
2. Ask the class to think about real-world traffic lights: “What does the yellow light often do right before it turns red to get your attention?” Guide them to the idea of a flashing warning.
3. Pose the programming challenge: “How would we code that? We could copy-paste the ON/OFF blocks for the yellow light, but our code would get long and messy very fast!” This introduces the problem of repetition.
4. Explain that to solve this efficiently, we need a new kind of loop—one that can run a specific number of times inside our main “forever” loop. This is the perfect introduction to the concept of nested loops.

How can we program a flashing light?

Imagine we’ve built an automated traffic light that cycles through its colors inside a “repeat forever” loop. It’s a great start, but we can make it more realistic. What if we wanted the yellow light to flash a few times before turning red? This would be a much better and safer warning for drivers.

So, do we just add more blocks?

To make the light flash, we’d need to add a sequence like this to our main loop: Green → Yellow ON → OFF → Yellow ON → OFF → Yellow ON → OFF → Red This works, but it’s just repeating the “Yellow ON → OFF” sequence. Once again, our code would become very long and repetitive! There must be a smarter way.

Why Not Another ‘Forever’ Loop?

You can’t have two captains on one ship, and you can’t have more than one “repeat forever” (Main Loop) in a program! If you did, the computer wouldn’t know which one is the main program or what to run. It would get confused!

The Solution: A Loop Inside a Loop!

This is where a different kind of loop comes in handy! We can use a loop that repeats a specific number of times (in the image, 3 times). This is perfect for the flashing part. Even better, we can nest loops. This means putting one loop inside another. Repetitions within repetitions!

Flashing Yellow: A Nested Loop

By using a numbered loop, we can repeat the “Yellow ON → OFF” blocks as many times as we need. By putting this smaller loop inside our main “forever” loop, we create a powerful and efficient program: Main Loop ( Green → Inner Loop ( Yellow ON → OFF [x4] ) → Red )

Development (20-30 minutes) - Building with Nested Loops

1. Now that they’ve grasped the concept of nesting one loop inside another, it’s time to build the advanced traffic light.
2. Lead them through the instructions for modifying the traffic light sequence, showing them exactly where to add the new numbered loop to create the flashing yellow effect. This will be their first time creating a loop within a loop.

Closure (5-10 minutes) - Seeing Loops Everywhere

1. Once everyone has a working, flashing traffic light, broaden the discussion to think about where else this powerful concept applies.
2. Use the final section to spark a creative discussion about loops in everyday life and challenge them with an even more complex traffic simulation.

Reflect

You’ve now mastered nested loops! Ask yourself:

• Loops aren’t just for code; they’re everywhere. Where can you see repeating patterns or cycles in everyday life (think music, daily routines, nature)?
• What other cool prototype could you build using a loop inside a loop?