Keep running after the button is released

A branch with the output's own coil in parallel with Start holds the rung true after Start drops; a normally closed Stop breaks it.

Hone is a place to practise programming. This is one of its lessons, written out in full and free to read without an account.

What it is for

The most common rung in industry: press start once, machine runs, press stop.

What keeps it on after the button is released? Start OR (own coil), then AND NOT Stop, then the coil. The coil feeding back is the memory.

{ [Go] | [Conveyor] } [/Halt] (Conveyor)

Go starts it; Conveyor keeps itself on; Halt breaks it.

Seal in the pump.

{ [Start] | [] } [/Stop] (Pump)

Putting Stop inside the branch instead of after it. Then Stop only blocks the Start path and the seal keeps running.

Practise seal-in circuits on HoneA question on it now, a coding challenge where there is one, and it is remembered for review. Free, no email needed.