Scratch · Grade 3 · Guided practice
How to code this project
What you will make: Make a three-state classroom sound signal on screen.
Scratch loudness is a relative 0–100 input, not decibels or a certified noise measurement. Use a teacher-approved microphone; no recording is needed. Begin with a manual slider if microphone access is unavailable.
Before you start
- Make one sprite with costumes Green, Yellow and Red, each with a matching word or symbol.
- Make variable level with a visible 0–100 slider. First build the manual version below.
Opening and saving: Open the teacher-approved Scratch editor and select your sprite. The recipe is a block-by-block guide, not text to paste into Scratch. Build blocks with matching names and keep indented lines inside their enclosing blocks. Save through File → Save to your computer as an .sb3 file; no public sharing is required.
Build it one step at a time
- Select the signal sprite. Build the green-flag script below using Events, Control, Operators and Looks.
- Test with the level slider before adding a microphone. The two comparisons belong in nested if–else branches.
- For microphone mode only: inside forever, BEFORE the first if, add set level to loudness. Find loudness in Sensing. The teacher approves microphone permission.
- Observe level during ordinary quiet talk. Adjust 20 and 50 to suit this device and room; do not ask children to shout.
- For manual mode, remove set level to loudness so it does not overwrite the slider.
- Use your observations to explain why different microphones may need different thresholds.
Your block recipe
when green flag clicked
set [level] to (0)
forever
if <(level) > (50)> then
switch costume to [Red]
else
if <(level) > (20)> then
switch costume to [Yellow]
else
switch costume to [Green]
wait (0.1) secondsPredict, test and record
Write your name and date on the printed page. Run every test, note the actual result, and retest after one change.
| Try this input | Expected result | Actual result / retest |
|---|---|---|
| Manual level 10, then 20 | Green | ________________ |
| Manual level 35, then 50 | Yellow | ________________ |
| Manual level 70 | Red | ________________ |
If it does not work
- No microphone reading? Check permission with the teacher or use manual mode.
- Slider jumps back? Remove the microphone assignment in manual mode.
- Flickers near a boundary? Record the readings; adjust the classroom signal design rather than treating the number as a safety limit.
Make one change
Choose and justify new thresholds using ordinary classroom observations, then repeat boundary tests.
We changed __________. We predicted __________. Our test showed __________.
Teacher pacing: Use a 45-minute coding session: 5 minutes to predict, 10 to model a first working response, 20 for paired building, 7 for tests and 3 to save and explain. Continue in another meeting if setup or debugging takes longer; do not rush hardware checks.
Grade 3 support: Model one block at a time; partners alternate choosing blocks and explaining the result. Accept spoken or drawn test evidence.
Teacher learning resources
Preview resources before class. Follow this page’s specified reference build; another tutorial may use different hardware.
Print support: The lesson’s Print button includes this guide, recipe and test table.
For teachers
Engineering standards
This shows how the lesson connects to the national NGSS engineering standards and what student work you can collect.
3-5-ETS1-1
Teams define who needs the classroom noise traffic light and set measurable performance, safety, material, and time limits.
What students show: User-centered problem statement with criteria and constraints.3-5-ETS1-2
Teams compare at least two circuit, code, or enclosure ideas against the success criteria.
What students show: Labeled system diagrams and a recorded design choice.3-5-ETS1-3
Teams run a repeatable test—play the same three teacher-approved sound samples at a fixed distance—then change one variable and retest.
What students show: Test table, code or build revision, and evidence-based explanation.Materials
- Cardboard, paper, craft sticks, tape, reusable building pieces, and student-proposed materials
- Project platform: Scratch or simple sound circuit + optional laser cutter
- Breadboard, paper-circuit supplies, or low-voltage power when needed
- sound meter, sensor, or student observer input component or student-designed substitute
- green-yellow-red display output component or student-designed substitute
- LEDs, resistors, jumper wires, copper tape, switches, and clips as needed
- Laser Cutting materials for an optional case, sign, mount, or model
- Computer with approved coding or simulation tools when needed
- Planning sheet, ruler, and test-data table
Teacher preparation
- Build and test one possible reference solution without making it the required design.
- Prepare a basic-materials table plus optional electronics and fabrication stations.
- If coding is used, prepare a starter option for ordered thresholds in Scratch, cards, or an optional controller; students may propose another workable control method.
- Prepare optional fabrication templates and a file rule beginning G3_07.
- Mark adult approval points before power-on and machine fabrication.
Step by step
How to teach it
Meet the user and define success
- Introduce the application: Give a class a visual reminder when group-work sound moves above an agreed level.
- Identify the user, need, criteria, and constraints.
- Draw a system map with input → code → output.
Build a first solution
- Choose basic, electronic, and fabricated materials based on the team's idea.
- Build with power disconnected whenever electronics are used.
- Complete an adult check, then troubleshoot one connection or physical feature at a time.
Create the behavior
- Create the first working control using ordered thresholds in Scratch, cards, or an optional controller.
- Predict what one rule, connection, or code change will do before testing it.
- Make the system understandable with labels, diagrams, comments, or coding blocks.
Test and improve
- Use the same procedure each time: play the same three teacher-approved sound samples at a fixed distance.
- Record at least three results.
- Change one code, circuit, or physical-design variable and retest.
Fabricate and present
- Design a laser cutting part that protects, mounts, or explains the electronics.
- Adult reviews and operates fabrication equipment where required.
- Connect the finished system and demonstrate how the evidence improved it.
Assessment
- Problem statement names a real user and measurable need.
- Circuit matches the team diagram and uses components safely.
- Program connects the intended input to the intended output.
- Test conditions remain consistent and include recorded evidence.
- Revision addresses a documented failure or user need.
Supports & extensions
- Use color-coded wires and a photograph of each breadboard step.
- Provide block coding or partially completed code with one change at a time.
- Assign roles: circuit builder, coder, tester, and recorder.
- Let students explain findings orally or with labeled diagrams.
- Extension: add a second sensor, output, data display, or operating mode.
Safety & responsible use
- Use only teacher-approved low-voltage classroom electronics; never connect projects to wall current.
- Disconnect power before changing wires or components.
- Use the correct resistor with every standard LED and stop immediately if a part becomes hot.
- An adult handles soldering, laser cutting, printer setup, blades, and final power approval.
- Keep liquids away from boards unless a sealed, teacher-approved sensor activity specifically requires them.
No-machine alternative
Build with cardboard, paper mechanisms, paper circuits, or a free on-screen simulator. Students may invent another safe way to model the same function, then compare ideas, test one variable, collect evidence, and revise.
Printable student design brief
The challenge
Create a working classroom noise traffic light for this need: Give a class a visual reminder when group-work sound moves above an agreed level.
Success criteria
- Changes color at useful sound levels
- Responds consistently to repeated samples
- Communicates without recording anyone's speech
Constraints
- Measures level only and stores no voices
- Display may be cardboard, digital, or laser-cut
- Uses the same listening position during testing