There are WiFi controlled sprinklers out there, doubtful any open sourced for control. According to Google it is a popular DIY project, so why should they get all the fun.
Most people seem to be using 8 relay boards available on Amazon for under $10. That really is quite deal, but relays are overkill for a sprinkler system running at 24 VAC.
Most consumer units use run of the mill triacs. And you can get opto-isolated versions.
So here is the schematic design. I have to go through some of the unsorted boxes (unsorted from the move to FL) to figure out what I have to order, vs what I have on hand.
I will post the KiCAD project when finished (layout to do)



