Lesson 4 - SDG 15: Life on Land: Design & Build a Composting Prototype
1. Engage: Why is moisture important in compost?
Show students two images:
Key Question
What’s the obvious difference between the two bins?(moisture level)
The right compost bin smells like rotten eggs, and the food scraps inside haven’t broken down at all. What’s gone wrong?
The secret is moisture! Compost relies on tiny helpers—bacteria, fungi, and worms—to break down food scraps. These microbes need water to move around, eat, and multiply. Too little moisture, and they “go to sleep” and stop working. Too much moisture, and air gets squeezed out of the pile; the microbes drown, and stinky anaerobic bacteria take over.
2.Explore: how to adjust moisture levels?
Discuss as a class: How to fix moisture issues?
Key Solutions for Moisture Adjustment:
Too dry: Add small amounts of water while turning the compost (to spread moisture evenly)
Too wet: Turn the compost to let air in, or add dry bulking materials like shredded cardboard, newspaper, or dead leaves.
Key Question
What’s the perfect moisture range for compost?
3. Investigate: What’s the perfect moisture range for compost?
Activity 1
In small groups, use safe, kid-friendly websites to find the ideal moisture percentage for compost.
Groups share their findings: The sweet spot is 45-60% moisture—exactly like a wrung-out kitchen sponge!
Ask: Why do you think this range works best? (Enough water for microbes to thrive, but not so much that air can’t circulate)
4. Design: Complete the Moisture Control Flowchart
Our prototype will use the UNIHIKER K10 and a moisture sensor to check compost levels automatically. We need a flowchart to tell the sensor what actions to take when moisture is too low, too high, or perfect.
Flowchart Prompts
Help students fill in these steps on their activity sheets:
Start: Turn on the UNIHIKER K10 and connect the moisture sensor.
Read the current compost moisture level.
If moisture <45% → Alert: remind the compost user to add water.
If moisture >60% → Alert: Turn compost + remind the compost user to add dry bulking materials.
If moisture is 45-60% → All good! Compost is healthy.
Repeat cycle.
Activity 2
Guide students to complete their flowcharts. Show Flowchart Prompts on the board to help with structure.
Example Flowchart:
5. Build: Assemble Your Composting Prototype
Guide students to read the building block assembly steps on the activity sheet, and assemble the building blocks by following the instructions of the Activity Sheet.
Activity 3
Give students 5-8 minutes to complete the assembly of the building blocks by following the activity sheet.
6.What’s Next?
Preview of Next Class
1.Write code for the UNIHIKER to read the moisture sensor and trigger the stirrer automatically
2.Debug and test your prototype with dry, wet, and just-right compost samples
3.Decorate your compost bin model to look like a real garden bin
4.Present your prototype to the class, explaining how it helps create perfect compost for our school garden!
Lesson4(K10).zip 
