Instruction Guide: EV3 - "Switches"
In this Lesson we have 3 Primary Instruction Resources:
- The EV3 Trainer lesson on Switches,
- The STEMcentric Switch Basics video (under Differentiated Instruction Material; Alternative), Including a Switch Exercise
- And finally, there is an Switches-Advanced video from STEMcentric (under Differentiated Instruction Material; Alternative).
Resource 1:
The EV3 Trainer has a lesson describing Switches
Behaviors > Decisions > 8. Switches
The EV3 Trainer Teacher's Guide references this on pages 70 to 76.
Students should be able to answer all the review questions at the end of each step and end up with a solid command of each parameter in the Switch Block. They should also complete all the Mini Challenges below these review questions, including those under Optional Activites.
The "Try It" section below the review questions in Step 4 has the Maze Runner Challenge.
The EV3 Trainer Teacher’s Guide has additional reproducibles for those who have purchased the product. The reproducibles for Switches can be found on pages 107-108.
As students progress through, have them document their milestones in the Switches Task Assignment Sheet.
For this Task Assignment, final teacher sign-off is the Strawberry Plant Challenge. Although, at first blush, this sounds like a simple extension of the Loops Container Handling Challenge, in reality this challenge involves integrating and extending a great deal of the skills learned to date. Many students will find this the most difficult challenge in the entire EV3 Trainer series. If students get bogged down at this point, it may be useful to introduce the Advanced Flow Charts Lesson, to help students organize their approach to this challenge.
There are four key stumbling blocks for students with this challenge:
- Software Design: Students need to break the challenge into separate behaviors and then assemble them into a Flow Chart (as covered in the first Flow Chart Lesson). This involves using Decision blocks to create parallel branches rather than simple wait blocks - an new concept for students. It may be helpful to walk through the first few slides of the Advanced Flow Charts II Lesson as it develops the idea of using sub-processes.
- Incremental Design: Once students have a flow chart to represent their design, they are tempted to jump in and write the whole program at once (especially since they already did the Container Handling Challenge ). They need, instead, to tackle the software development incrementally as shown previously in the EV3 Trainer Basics > Big Ideas > 4-5 - get one small piece working and then incrementally add additional small pieces, checking the program as a whole between each increment.
- Lagging Loops: Students often start with a Ultrasonic Switch Block, and place a Stop block on one branch and a Move block on the other. While this is the correct structure to start with, students are sometimes tempted set the Move block for the duration required to cover the length of the challenge arena. However, this is exactly the problem they had with the Container Handling Challenge of the Loops lesson - if they build a delay (wait-for x seconds, or y rotations) at the core of their Switch Block loop, then the robot will only check for obstacles once, rather than continuously. The Switch Block at the heart of a loop must execute without delay, and therefore any Move blocks should be set to "On" (i.e. turn the motors on and then immediately run the next step in the program).
- Nested Loops: To be its most efficient (i.e. smallest number of blocks), this program will have a switch block nested inside a loop (for obstacle detection over 4 plants) and inside this another loop (to control sorting of the strawberries). This can be a very confusing EV3-G program and highlights the need to start with a flow chart to keep organized and use comments in EV3-G to keep track of what's what.
When signing off the Strawberry Plant Challenge:
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Start with their flow chart to get an overall view of the program
- Ask how they developed this flow chart
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Use the EV3-G program to show how each block in the flow chart was implemented (including comments that identify the flow chart blocks)
- Ensure they have no lag in their core Switch block
- Have them describe the nested loops
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Ask about the program development process - did they use the incremental approach.
- What other "Best Practices" would they recommend for program development
- What obstacles (no pun intended) did they encounter and how did they overcome them.
Resource 2:
The STEMcentric Switch Basics video (under Differentiated Instruction Material; Alternative), covers the introductory Switch concepts. There is also an additonal Switch Exercise here.
Resource 3:
The STEMcentric Switches-Advanced video (under Differentiated Instruction Material; Alternative) get into advanced Switch Block concepts, including the case-based approach required for the Color Name Reader Challenge.
