ShotStopper was created by Tate Mazer retrofit brew-by-weight functionality to handful of popular home espresso machines. I think the source for shotStopper here, but it's part of a repo that is named for just connecting to Acaia scales. This comment on the Full Micra Brew-by-Weight Mod claims that he used to the shotStopper source to make it.

Links

* Someone sharing how great it is on r/LaMarzocco * 1, * 2 * shotStopper Manual - Google Docs