What students build
- Three visible light states
- A timed sequence
- Safe transition rules
- Optional pedestrian request
- Repeat behaviour
- Reset state
Guided Project
Guided ProjectLED Traffic Light
Keep a tiny intersection orderly with outputs, timing, and a sequence that does not show red and green together.
Project brief
What students learn
- Digital output
- Sequence timing
- State transitions
- Loops
- Safety constraints
- Testing impossible combinations
What students need
- Browser circuit simulator or paper state diagram
- Optional LEDs and suitable supervised components
The state diagram and simulator version need no hardware. A physical build uses teacher-arranged components under supervision; availability is confirmed separately.
Suggested build order
- 01
Name the states
Task: Define STOP, READY, and GO before wiring or coding.
- Checkpoint
- Each state has one light pattern.
- Likely mistake
- Starting with timing before defining states.
- 02
Test one output
Task: Make one simulated or physical LED turn on and off.
- Checkpoint
- The output responds reliably.
- Likely mistake
- Using the wrong output or connection.
- 03
Create the sequence
Task: Move through states in a safe order.
- Checkpoint
- Red and green are never active together.
- Likely mistake
- Several scripts control the same lights.
- 04
Add timing
Task: Choose readable delays and repeat the cycle.
- Checkpoint
- A full cycle is easy to observe.
- Likely mistake
- Delays are too short to inspect.
- 05
Test a request
Task: Optionally add a button-request state without interrupting unsafely.
- Checkpoint
- The request is handled at a defined point.
- Likely mistake
- Button input jumps directly to an unsafe state.
Test questions
- Can red and green appear together?
- Does restart begin from STOP?
- Can a request interrupt any state?
- Does the loop preserve sequence order?
- Can every output be tested alone?
Common mistakes
- Outputs are controlled from competing scripts.
- Timing hides a wrong state order.
- Reset begins at an unsafe state.
- A button press is read but not acknowledged.
Extension ideas
- Add a pedestrian signal.
- Display the current state.
- Add a night flashing mode.
- Draw a complete state transition map.
Challenge levels
Builder
Create a reliable three-state loop.
Inventor
Add a queued pedestrian request.
Boss Level
Design and test normal and night operating modes.
What to demonstrate
- State diagram
- Three outputs
- Safe sequence
- Readable timing
- Complete reset
- One impossible-state test