IntermediateMode~15 min

Mode (Auto / Manual)

Two mutually exclusive mode coils selected by momentary buttons the skeleton behind every Auto/Manual selector. Each mode seals itself in, and pressing the other button switches over cleanly.

Your goal

  • Pressing AutoBtn selects AutoMode; it stays selected after release.
  • Pressing ManBtn switches to ManMode and drops AutoMode in the same scan.
  • The two modes can never be ON together.
Stuck? Show hints (3)
  1. Two mirror-image seal-in rungs. Rung 1: (NO AutoBtn OR NO AutoMode) AND NC ManBtn → OTE AutoMode.
  2. Rung 2: (NO ManBtn OR NO ManMode) AND NC AutoBtn → OTE ManMode.
  3. The NC contact of the OTHER button is what breaks the old mode's seal the instant you ask for the new one.

Pattern from Contact & Coil's classic ladder logic series.

I/O for this exercise

Inputs
AutoBtnAuto mode button
ManBtnManual mode button
Outputs
AutoModeAuto mode active
ManModeManual mode active
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