With a RasPi and a common 8-channel relay block, show how to create a smart sprinkler system that can be scheduled/controlled via a phone or browser (home network is fine... bonus points for Internet accessible), allow individual ad hoc zone control if you're testing/repairing/adjusting sprinkler heads, read local precipitation trends to turn off when rain is anticipated, optional alert when sprinklers are starting or advance notice in case you need a dry lawn for something, automatically adjust start time(s) to occur based on sunrise or sunset (or avoid peak times), maybe an easy-to-program remote touchscreen interface for somewhere in the house, and bonus points for Amazon Echo integration.