Teacher Notes — Week 4

Theme: Variables & Thresholds
Focus Concept: Using and comparing variables, applying thresholds to control outputs
Mini-Project: 🌱 Smart Plant Monitor (light + temperature sensors)

Learning Objectives

  • Participants understand what a variable is and how it stores values.
  • Participants use thresholds to decide if a variable is “too high” or “too low.”
  • Participants explore how while true loops work and why break is used.
  • Participants apply variables + thresholds to real-world sensors (light & temperature).
  • Participants link coding to science: plants need the right light and warmth.

Vocabulary Focus

  • Variable
    • A variable is like a labelled box in the computer’s memory.
    • It stores a value that can change (e.g. a sensor reading, a score).
    • In our program, temp and light are variables that hold numbers from sensors.
    • Analogy: like writing a number on a sticky note — you can erase it and write a new one any time.
  • Loop
    • A loop repeats instructions automatically.
    • forever is a type of loop that never ends.
    • while true is also a loop, but we can stop it using break.
    • Analogy: like a song on repeat — it plays again and again until you press stop.

💡 Teaching tip:

  • Show the difference between on start (runs once), forever (runs forever), and while true (runs forever unless broken).
  • Ask participants: “Why would we want the computer to repeat things? What happens if it doesn’t?”

Detailed Lesson Plan (≈90 minutes)

Part 1: PRIMM Starter — Multiplication Quiz with Thresholds (30 min)

Predict (5 min)
Show pupils the code (do not run yet): Simple times tables quiz MakeCode Code

  • Variables: first number, second number, result, threshold.
  • On A → picks 2 random numbers, but only if both are ≤ threshold.
  • On B → shows the multiplication result.

Ask:

  • “What do you think will happen when we press A?”
  • “Why do you think there’s a threshold set at 12?”
  • “When will it show us numbers, and when will it not?”

Run (5 min)
Press A: pupils see pairs of numbers appear.
Press B: shows the result of multiplication.

Investigate (10 min)
Focus on two important pieces of logic:

1. while true

  • A loop that repeats forever.
  • Because “true” is always true, the loop keeps running again and again.
  • Each time round, it picks new random numbers.
  • That’s why it looks like numbers always appear — the loop is running super fast until it finds ones that fit the rule.

2. break

  • break means “stop this loop right now.”
  • Without break, the loop would keep flashing endless random numbers.
  • With break, as soon as good numbers are found (≤ threshold), the program stops looping and shows them.

💡 Analogy to use with children:

  • Imagine you’re picking raffle tickets out of a bag.
  • You only want tickets under 12.
  • If you pick one that’s too big → put it back, try again. (This is the loop.)
  • When you finally pick a good one → shout it out and stop. (This is the break.)

Questions to ask pupils:

  • “What would happen if we removed the break?”
  • “Why is the loop needed if we already pick random numbers?”
  • “Could the program ever run forever without finding a result?” (No, because eventually random numbers will fall under 12.)

Modify (5–7 min)
Challenges:

  • Change the threshold (e.g. 6 for easier, 20 for harder).
  • Switch to addition or subtraction.
  • Remove break deliberately to see what happens.

Make (5 min)
Extensions:

  • Add a score counter.
  • Add an icon or sound if numbers exceed the threshold.
  • Use pick random with a wider range (e.g. 1–200).

Part 2: Main Project — Smart Plant Monitor (55–60 min)

Introduction (5 min)
Ask: “What do plants need to grow well?”

  • Pupils will usually say light and water, sometimes temperature.
  • Explain: “Today we’ll use the micro:bit to check if a plant would be happy here in the classroom!”

Step 1: Read variables (10 min)

  • Create variable light = light level.
  • Create variable temp = temperature.
  • Show them with show number to check real readings.

Discussion:

  • What is a sensor? (a device that measures the world around us).
  • What is a variable doing here? (storing the sensor reading so we can use it).

Step 2: Add thresholds (10 min)
Introduce thresholds:

  • Light < 100 → “too dark” 🌙
  • Temp < 18 → “too cold” ❄️
  • Temp > 28 → “too hot” ☀️🔥

Discuss: “What happens if we cover the micro:bit?” / “What if we warm it with our hands?”

Step 3: Combine with logic (15 min)
If light ≥ 100 AND temp between 18–28 → show 🌱😀 “Happy Plant.”
Else → show warning icon depending on condition.

Step 4: Extension Challenges (10–15 min)

  • Add sound (happy jingle / sad tone).
  • Count how many times the plant was “unhappy” (alert counter).
  • Show both readings (light + temp) before verdict.
  • Design custom LED plant icons.

Wrap-Up (5 min)

  • Quick share: “Show me your Happy Plant!”
  • Reflection: “What variable did we use? What threshold? What happened when…”
  • Science link: real plants need light and warmth — we just simulated checking it.

Differentiation

  • Beginners: scaffold with a starter template (variables created, thresholds suggested).
  • Confident coders: add more conditions (too hot, too bright), or sound.
  • Cross-curricular: maths (inequalities, number comparisons), science (plant growth needs).

Assessment

  • Can participants explain what a variable is?
  • Can they describe what a threshold does?
  • Did they use both light and temperature in their monitor?

Troubleshooting

  • Sensors not changing: remind them values won’t shift quickly; test with torches or hands.
  • Icons not showing: check the order of if/else if/else.
  • Always shows one icon: threshold values may be set too high/low.

Materials & Setup

  • BBC micro:bits (1 per child/pair).
  • USB cables.
  • Chromebooks with MakeCode.
  • Optional: torches, desk lamps, hand warmers, ice packs.

Safety & Safeguarding Notes

  • Handle USB cables safely.
  • No water near electronics.
  • Share devices fairly.

Reflection (for leader)

  • Did participants clearly understand variables vs thresholds?
  • Did the PRIMM starter (maths quiz) help them before moving into sensors?
  • Note pupils who extended with AND/OR logic successfully.