Instructor Notes — Week 5

Theme: Inputs, Patterns, and Timing
Focus Concept: Reading and reasoning about loops, timing, and events (PRIMM)
Mini‑Project: Complex PRIMM demo (sparkle + sweep) and a preview build of Barrel Jumper (On Start only)

Learning Objectives

By the end of this session, participants should be able to:

Read and explain TTC‑style pseudocode for a multi‑step program.
Describe how loops and nested loops create patterns on the LED grid.
Explain how a program can use system time ([milliseconds since start]) to control how long something runs.
Understand the role of a state variable (like btnlock) in enabling or blocking other parts of a program.
Recognise the difference between start‑up code (ON START) and event‑driven code (button presses).

Vocabulary Focus

You do not need to test these formally, but it helps to use them aloud:

event – something the micro:bit reacts to (e.g. WHEN button A is pressed).
loop – a set of instructions that repeat.
nested loop – a loop inside another loop.
variable – a named storage place for a value that can change.
state – what “mode” the program is in (for example, locked or unlocked).
sprite – a movable object on the LED grid (used later in Barrel Jumper).
system time – the internal clock the micro:bit uses to measure milliseconds.

Try to model sentences like:

“This loop repeats 6 times.”
“This variable keeps track of whether the buttons are locked.”
“System time tells us how long the animation has been running.”

Session Flow (≈ 80 minutes)

Starter (5–10 min) – quick recap of loops and button events from previous weeks.
Part A – PRIMM Deep Dive (30–35 min) – complex demo with countdown, random sparkle, nested sweep animation.
Part B – Rebuild PRIMM in blocks (15–20 min) – participants recreate all or part of the program.
Part C – Barrel Jumper Preview (10–15 min) – build only the ON START section of the game and talk through what comes next.
Wrap‑up (5–10 min) – reflection questions and “what we’ll do in Week 6”.

Timing can flex slightly depending on how quickly participants get through the PRIMM Investigate step.

Part A — PRIMM Deep Dive: Sparkle and Sweep Demo

We use a single program that ties together:

a countdown
a button lock (btnlock)
a random sparkle effect on button A with a 10‑second timer
a sweeping fill + clear pattern on button B using nested loops

The aim is to read and reason about the program together.

Blocks version (MakeCode)

A1 — TTC Pseudocode for the Full Demo

ON START

WHEN program starts DO
    SET btnlock TO 1

    SHOW ICON happy_face
    PAUSE 1000 ms
    CLEAR SCREEN

    SET counter TO 5
    REPEAT 6 TIMES
        SHOW NUMBER counter
        SET counter TO counter - 1
        PAUSE 500 ms
    END REPEAT

    SHOW ICON arrow_west
    SET btnlock TO 0
END WHEN

Button A — Random Flicker with Time Limit

WHEN button A is pressed DO
    SET timer TO [milliseconds since start]
    CLEAR SCREEN

    WHILE btnlock = 0 DO
        TOGGLE LED AT
            [random number from 0 to 4],
            [random number from 0 to 4]

        PAUSE 50 ms

        SET stoptimer TO [milliseconds since start]

        IF stoptimer > timer + 10000 THEN
            BREAK LOOP
        END IF
    END WHILE

    SHOW ICON arrow_east
END WHEN

Button B — Sweep Fill and Sweep Clear

WHEN button B is pressed DO
    CLEAR SCREEN

    WHILE btnlock = 0 DO

        FOR x FROM 0 TO 4 DO
            FOR y FROM 0 TO 4 DO
                PLOT LED AT (x, y)
                PAUSE 50 ms
            END FOR
        END FOR

        FOR y FROM 0 TO 4 DO
            FOR x FROM 0 TO 4 DO
                UNPLOT LED AT (x, y)
                PAUSE 50 ms
            END FOR
        END FOR

        BREAK LOOP
    END WHILE
END WHEN

A2 — PRIMM Structure

You can explicitly label each stage to participants: Predict → Run → Investigate → Modify → Make.

1) Predict

Show only the pseudocode, not the micro:bit yet.

Guiding questions:

“What do you think happens when the program starts?”
“What do you think btnlock is for?”
“What do you think button A will do?”
“What about button B?”

Encourage rough guesses — the goal is to get them thinking about structure.

2) Run

Now run the finished program on the micro:bit:

Show the happy face and the countdown 5 → 0.
Watch the arrow pointing west.
Press button A and observe the random sparkle.
Press button B and watch the fill + clear pattern.
Notice that both effects stop after a while (about 10 seconds).

Ask:

“What did you notice?”
“Did anything surprise you?”
“Did your prediction match what happened?”

3) Investigate — Detailed Walkthrough

This is where you slow down and work through line by line.

ON START — Countdown and Button Lock

Key points to highlight:

SET btnlock TO 1 means buttons are locked at first.
The happy face + pause is just a friendly intro.
counter starts at 5 and the REPEAT 6 TIMES loop shows:
- 5, then 4, then 3, then 2, then 1, then 0
After the loop ends, btnlock is set to 0 → buttons now work.

Good questions:

“Why do we need 6 loops if we start at 5?”
“What would happen if we only repeated 5 times?”

You can sketch a small table on the board:

loop number	shown	new counter
1	5	4
2	4	3
3	3	2
4	2	1
5	1	0
6	0	-1

Explain that the program doesn’t “know” about 0 — it just repeats 6 times.

Button A — Random Flicker with Timer

Focus on the concept of system time:

[milliseconds since start] is the micro:bit’s internal clock.
timer remembers the time when the button was pressed.
stoptimer is updated each loop.

We compare:

stoptimer with timer + 10000
If more than 10 000 ms (10 seconds) have passed → BREAK LOOP.

Ask participants:

“What would happen if the IF condition was removed?”
“What if we changed 10 000 to 5 000?”
“What if we removed the PAUSE 50 ms?”

Emphasise:

“The WHILE loop itself doesn’t know when to stop. The IF + BREAK give it a way out.”

Button B — Sweep Pattern with Nested Loops

Explain visually using the board:

First FOR x 0 → 4, inside that FOR y 0 → 4.
This visits every (x, y) pair in order.
The first pair of nested loops plots LEDs → fills the screen.
The second pair unplots LEDs → clears the screen.

Good questions:

“Which loop controls columns, and which controls rows?”
“How many LEDs will be turned on in total before we start clearing?”
“What is the purpose of BREAK LOOP at the end?”

Reinforce that nested loops are powerful: a short bit of code can affect many LEDs in a structured way.

4) Modify

Offer small, safe modifications that participants can make:

Change the speed of the sparkle (PAUSE 50 ms → PAUSE 100 ms).
Change the total time (10000 → 5000).
Change the order of the sweep loops (swap x and y) and see how the pattern feels different.
Change the countdown start (e.g. start at 3 instead of 5).

Encourage them to predict the effect before testing.

5) Make

Finally, invite participants to design their own variation:

A custom countdown image sequence instead of numbers.
A sparkle that stops when both buttons are pressed together.
A fill pattern that draws a diagonal instead of column/row sweeps.

These “make” ideas can be simple; the important thing is that participants feel they can change the code on purpose.

Part B — Barrel Jumper (Week 5 Preview Only)

In Week 5, we only build the starting setup:

Intro picture (a simple frame / character).
Creating the jumper and barrel sprites.
Initial speed and score.

The jump mechanic and the full forever loop (movement, scoring, game over) are built in Week 6.

Blocks version (MakeCode)

B1 — TTC Pseudocode (Week 5 Version)

ON START (Game Setup Only)

WHEN program starts DO
    SHOW PICTURE:
        . # # # .
        # . # . #
        # . # . #
        # . # . #
        . # # # .

    PAUSE 200 ms

    SET jumper TO NEW SPRITE AT (0, 4)
    SET barrel TO NEW SPRITE AT (4, 4)

    SET speed TO 200
    SET score TO 0
END WHEN

You can either draw the picture on the board or refer to it as “a frame / little character”.

At this stage, do not build:

the jump,
barrel movement,
collision detection,
score changes,
speed changes.

Those belong to Week 6’s extended build.

B2 — Instructor Notes for Barrel Jumper Intro

Key ideas to highlight:

Sprites and coordinates –
- (0, 4) is bottom‑left.
- (4, 4) is bottom‑right.
Variables for behaviour –
- speed controls how fast things will move later.
- score will track progress in the future game.

You can tell participants:

“This week, we are just setting the stage.
Next week, we will make the barrel move and try to dodge it.”

Make sure they see the link:

Today: reading and understanding a complex, pre‑written program (PRIMM).
Next week: applying those ideas to build and improve their own game.

Differentiation

Support:

Provide a printed or on‑screen version of the pseudocode with key lines highlighted.
Let some participants focus only on ON START + Button A, if the full program feels overwhelming.
Use physical grids (5×5 drawn on paper) so participants can trace LED patterns without staring at the screen.

Extend:

Let confident participants design their own sweep patterns (different loop orders).
Invite them to change the sparkle so that it slows down or speeds up over time.
Ask them to design an alternative Barrel Jumper intro screen (different picture, same logic).

Assessment & Evidence of Learning

Look for:

Participants explaining what a loop does in their own words.
Participants describing the difference between WHILE and REPEAT n TIMES.
Participants correctly reasoning about the 10‑second timer (they may say “it keeps checking the time until 10 seconds have passed”).
Participants placing sprites correctly based on (x, y).

Quick checks you can use:

“Show me on the grid: where is (0, 4)? Where is (4, 4)?”
“What does this condition mean: stoptimer > timer + 10000?”

Troubleshooting & Common Issues

Buttons do nothing:
- Often btnlock never gets set to 0. Check ON START is running and the countdown finishes.
Sparkle never stops:
- The BREAK might be missing, or the comparison uses the wrong sign or number.
Sweep pattern looks wrong:
- Loops might be nested in the wrong order or the wrong variable used for x / y.

Encourage participants to read the pseudocode out loud when debugging.

Reflection & Wrap‑Up

End with a short discussion:

“Which part of today’s program felt most confusing at first?”
“How did the pseudocode help you understand what was going on?”
“Where did we use loops inside loops?”
“What are you most excited to add to Barrel Jumper next week?”

You can also invite a few participants to show their favourite modification or pattern.

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