Reaction game

Classroom resources

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Students will be able to

• I can plan a program as an ordered loop.
• I can time an event with millis().
• I can test a design for unfair or unexpected use.

Timing

About 3 lessons (around 150 minutes). Inquire part lesson · Develop 1 · Create 1 · Test and evaluate 1

Before class

random(2000, 5001) and millis() are new: give them as a recipe card. A first version with delay() for the wait cannot catch false starts; that limitation is a good Evaluate point and a reason for the millis() version.

If you assess with MYP Design, the steps line up with the criteria:

• A Inquiring and analysing: the brief, its criteria and constraints, and research into parts (Inquire).
• B Developing ideas: a design specification, the circuit and code plan, and the test table written before building (Develop).
• C Creating the solution: building it (in the simulator, then for real), following the plan and justifying changes (Create).
• D Evaluating: testing against the specification, recording failures, improvements and impact (Test, Evaluate). Otherwise, use the same four headings as a simple rubric: each step's reflect checks are the evidence list.

Running the lesson

1. Develop: ask how the game could know about a press during the wait.
2. Test: the class tries to cheat it.

The hard part (on purpose)

The false start is the hard part: it needs the button checked during the wait, not delay(). Let students meet the problem with delay() first.

When students get stuck

Answers to the checks

1. Inquire: the brief: Sort each line of the brief: a criterion (what it must do, which you can test) or a constraint (a limit you must work within)?
   Waits a random 2 to 5 s before lighting → Criterion; Shows the reaction time in ms → Criterion; Catches a press before the light (false start) → Criterion; Kit parts only → Constraint; USB power → Constraint
   Criteria are what you will test at the end; constraints decide what you are allowed to build with.
2. The loop: Put the game's loop() in order.
   see the program below
   Wait a random time (watching for false starts), light the LED, note millis(), wait for the press, subtract, print.

   waitTime = random(2000, 5001);
   start = millis();
   while (millis() - start < waitTime) { if (digitalRead(2) == HIGH) { falseStart(); return; } }
   digitalWrite(13, HIGH);
   lit = millis();
   while (digitalRead(2) == LOW) { }
   Serial.println(millis() - lit);
   digitalWrite(13, LOW);
   

3. Timing: The LED lit at millis() = 41200 and the button was pressed at 41487. What is the reaction time in ms?
   287
   41487 − 41200 = 287 ms.
4. Which is evidence?: Which is the strongest evidence that the design meets a criterion?
   A test from the table that set the input and recorded the expected result
   A planned test with a recorded result is evidence; everything else is a feeling.

Stretch and support

Stretch: Keep the best time of the session, and show a two-player result.

Support: A recipe card for random and millis, and the loop with the false-start check given.

Exit ticket

Why can't a reaction game use a single delay() for its random wait?

Nothing is read during a delay, so a press before the light (a false start) can't be caught.

What each step is for

• Inquire: the brief: Separating what the design must do (criteria) from the limits it works within (constraints) is the first move of any design brief.
• Develop: plan before you build: Putting the game loop in order and tracing its timing plans the logic; the false-start check is the part most designs forget.
• Create: build it: Building in the simulator first catches wiring and code slips cheaply; the real build then tests the design against the world.
• Test: run your table: Running the test table written in Develop, and recording every result including failures, is the evidence for the evaluation.
• Evaluate: against the brief: Judging the design criterion by criterion, with evidence from the tests, is what separates an evaluation from a description.

Where it leads

Other Years 8–9 projects: Smart plant monitor, Parking assistant.