BeginnerStart/Stop Circuit~10 min

Start / Stop Circuit

The first circuit every controls engineer learns: a motor that starts on a button press, keeps running when the button is released, and stops on a stop button with stop always winning.

Your goal

  • Pressing Start turns the Motor ON.
  • Releasing Start keeps the Motor ON (it must seal itself in).
  • Pressing Stop turns the Motor OFF even if Start is held at the same time.
Stuck? Show hints (3)
  1. One rung is enough. Put a NO contact of Start in series with a NC contact of Stop, driving the Motor coil.
  2. The seal-in: add a branch row with a NO contact of Motor in parallel with the Start contact, joined by a vertical link on the right side of that column.
  3. Because Stop is a NC contact placed AFTER the parallel group, opening it breaks both paths that's why stop wins.

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

I/O for this exercise

Inputs
StartStart push button (TRUE while pressed)
StopStop push button (TRUE while pressed)
Outputs
MotorMotor contactor
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