Three or More State Programs

In more advanced robotics programming, your robot may need to respond in three or more different ways depending on sensor input. Up to this point, we've created programs with only two possible outcomes using a switch block: a condition is checked, and the robot performs one action or the other based on the result.

But what if the robot needs more than just two responses? To handle this, we can use multiple conditions—often implemented with nested switch blocks or structured decision chains. In this section, we’ll explore how to build programs that go beyond binary choices and enable your robot to react intelligently to more complex environments.

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30 Mar 2018
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Let’s revisit the 3-state line-following example using the following setup:

Threshold Diagram

Suppose we use a single switch block that checks whether the value read by the color sensor is less than 27:

Initial Switch Block

In this case, the robot knows to turn right when the value is less than 27. However, it has no instructions for what to do when the value is greater than or equal to 27. At that point, the robot needs to choose between going straight or turning left. If the value is less than 37, it should go straight. If it's greater, it should turn left. So how can we add this decision-making?

The same way we handled the first condition—by using another switch block. If we place a second switch inside the "false" branch of the first one, comparing the value to 37, we can handle all three cases. Since the second switch is only evaluated if the first condition is false, we already know the value is at least 27 when it runs.

Nested Switch Diagram

This approach—placing a switch block inside another—is known as a nested switch.

Courses and lessons with this Tutorial

This Tutorial is used in the following courses and lessons

Instructors Remote Training

If you are working with students and you want to introduce Robotics to your class or you want to mentor a FLL team, but you are insecure about your technical knowledge in the Robotics field, then this is the right place for you. Having in mind teachers' busy schedule, we have design two different schedules and added an option to design one just for you. FLLCasts's Mindstorms EV3 Robotics Online Training is the perfect match for any teacher.

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For the first time robots with steering wheels are built in this level. Those robots use one or two drive motors. The work of the differential and its usage in vehicles is explored. Students learn in-depth the working of the light sensor to create better line-following programs. The first two-wheeled motorcycle-robot is built.

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It appears we have more time to work on improvements

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Lesson 5 - Personal Yacht

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Build, Code, Play: Your First Adventures with SPIKE Prime

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And if you're ready for a challenge, we’ve also prepared some advanced tasks! These will encourage you to research and experiment with both the programs and the robot itself. Of course, you're always welcome to add your own creative touches and enjoy the process along the way.