Wilteq WILTEQArduino Uno Course
Week 4 · Timing & Evidence

Session 17: State machines

Teach & build120 minLesson 11: Non-Blocking Timing & State Machines

Learning outcomes

  • Describe a behaviour as a state table
  • Implement a timed state machine with a state variable and stateStart
  • Explain why every state change must record stateStart
  • Plan a state machine with a button event

Kit and components

  • Uno, red, amber and green LEDs with 330 Ω resistors, push button, breadboard

Pre-reading about 20 min

Students read these on their phones before class. They are listed on the student Before class page.

  1. Lesson 11: State machines: one variable, many steps
  2. Theory Reference: State machines
  3. Lesson 11: Example 2: traffic light state machine

Session plan

  1. 0:0010 min
    Recap

    Quiz: millis()

  2. 0:1020 min
    Demo

    From table to code

    Draw the traffic light state table and turn each row into one branch. Remove stateStart = millis() and show the lights racing through the states.

  3. 0:3015 min
    Code Along

    Two states first

  4. 0:4530 min
    Build

    Traffic light: Code Along at the bench

    One activity, not two: students write the traffic light in Code Along until it passes, then upload the same sketch to red, amber and green LEDs on the bench and add a Serial report of each state change. There is no separate build of the lesson's example 2.

  5. 1:1525 min
    Code Along

    Catch-up and check

    Time saved by building the traffic light once. Students finish any S16 timing exercises still open while you check each traffic light against its state table. Students who are up to date start the pedestrian crossing state table early.

  6. 1:4020 min
    Plan

    Design a pedestrian crossing

    In pairs, students write a state table for the lesson challenge's pedestrian button - the planning style Task A needs.

Checkpoint: ready to move on?

Students have a working traffic light driven by a state variable, and a written state table for the pedestrian version.

Extension for fast finishers

Code the pedestrian crossing from the state table.

Catch-up path

Code the two-state flasher first, then add the third state.

Homework and practice

Pre-reading for S18; finish the pedestrian crossing state table if it is not done.

Facilitator notes

  • Students who can write a state table before coding will find Task A much easier.
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