The WGL Designs 41017 Rain8net Pro Sprinkler Controller Expansion Module with RS232 is used to expand an existing Rain8 Pro System. The Rain8 PRO is a modular 8-zone sprinkler controller. The UPB version is driven by a UPB power line interface (PIM). The RS232 version can be controlled over the Internet by any computer or other control device. It is capable of driving standard 24VAC irrigation valves directly. The master module is the first 8-zone module in an installation. Additional modules may be daisy chained for those large installations.