Beginner 05 — Start/Stop (no latch)
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Briefing
Combine an NO START with an NC STOP. Hold START to turn the LIGHT on, release it and the LIGHT drops out. STOP also turns it off. This is the obvious-but-wrong design. Try it. Notice what you have to do to keep the LIGHT on. The next lesson fixes the problem with a latch.
Objectives
- Holding START with STOP released turns LIGHT on
- Releasing START turns LIGHT off (you will discover this)
- Pressing STOP turns LIGHT off
Hints
- One rung: an NO contact for START in series with an NC contact for STOP, driving the LIGHT coil.
- In IEC, AND between contacts gives you a series circuit.
I/O Table
Inputs
STARTMomentary start push-button (NO)
BOOL · %I0.0
STOPStop push-button (read as NC)
BOOL · %I0.1
Outputs
LIGHTIndicator lamp
BOOL · %Q0.0
Your program will be tested against:
All test cases run automatically when you submit. Assertions are hidden until you pass.
- #1Press STOP → LIGHT off
STOP breaks the rung even while START is held
- #2Hold START → LIGHT on
While START is true and STOP is false, LIGHT is on
- #3Release START → LIGHT off
No latch — releasing START drops the LIGHT
Related scenarios
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