The seal-in: making an output hold

Draft lesson — skeleton content pending the founder’s course outline (issue #32).

A momentary start button can’t hold a motor on by itself — release it and the rung goes false. The seal-in (latch) fixes that by feeding the output back around the start contact.

Build it

|--[ bStart ]--+--[/ bStop ]--( bMotorRun )--|
|              |
|--[ bMotorRun ]--+

• bStart normally-open, in parallel with a bMotorRun contact (the seal),
• bStop normally-closed in series — the stop always wins.

Download, run, and prove it on the watch list: tap start → the motor holds; tap stop → it drops, regardless of start.

Checkpoint

You can now explain why stop is wired normally-closed (fail-safe: a broken wire stops the machine instead of making it unstoppable). Next course puts this on the real machine — with the 3D twin doing the moving.