PLC-Course

Lab 01 — Traffic Light Controller

Sprint: 1 — Architecture & I/O (with timer concepts previewed) Languages allowed: ST or LD (this auto-grader checks ST) Time: ~90 minutes

🎯 Brief

Implement a basic traffic light controller for a single intersection (north-south and east-west). When the START button is pressed, the system runs through the standard sequence. STOP returns it to all-red.

For Sprint 1 we keep this simple — full timer-driven sequencing comes back in Sprint 5. Here you’ll handle the state transitions only, given pre-computed timer outputs.

📋 I/O List

Inputs

Tag	Type	Description
`Start`	BOOL	Start button (pulse)
`Stop`	BOOL	Stop button (pulse)
`T_Green_Done`	BOOL	True when the green-phase timer has elapsed
`T_Yellow_Done`	BOOL	True when the yellow-phase timer has elapsed

Outputs

Tag	Type	Description
`Sequence_Active`	BOOL	True between Start and Stop
`RedNS`	BOOL	North-south red lamp
`YellowNS`	BOOL	North-south yellow lamp
`GreenNS`	BOOL	North-south green lamp
`RedEW`	BOOL	East-west red lamp
`YellowEW`	BOOL	East-west yellow lamp
`GreenEW`	BOOL	East-west green lamp
`Phase`	INT	Current phase (0–4)

State variables (you’ll need these)

Tag	Type	Description
`Phase`	INT	0=Stopped, 1=NS_Green, 2=NS_Yellow, 3=EW_Green, 4=EW_Yellow

📐 Sequence

Phase 0: STOPPED      All red, sequence inactive
Phase 1: NS_GREEN     NS green, EW red             (until T_Green_Done)
Phase 2: NS_YELLOW    NS yellow, EW red            (until T_Yellow_Done)
Phase 3: EW_GREEN     NS red, EW green             (until T_Green_Done)
Phase 4: EW_YELLOW    NS red, EW yellow            (until T_Yellow_Done)
        → back to Phase 1

Transitions

Phase 0 → 1: Start pressed
Phase 1 → 2: T_Green_Done
Phase 2 → 3: T_Yellow_Done
Phase 3 → 4: T_Green_Done
Phase 4 → 1: T_Yellow_Done
Any phase → 0: Stop pressed

✅ Your Task

Open solution-template.st, implement the logic, save as solution.st, and submit a PR.

The auto-grader will run your solution against tests/cases.json and post a Markdown report on your PR.

💡 Hints

The grader runs your code once per test scan. You don’t need to write a real-time loop — just respond to the inputs as they’re presented.
Phase is an INT. Use IF...ELSIF or CASE to set the lamp outputs from it.
Don’t double-coil the lamps — set them once per scan based on Phase.

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