Hi, I finished the installation and OSPI uses a GPIO pin wired to a Songle SRD-05DC-SL-C relay which toggles a 220VAC line wired to a contactor to turn the pump on/off. I would have done this differently if the installation were from scratch but I already had all the components in place, so I just had to add the 5 dollar relay.
My issue now is that the pi’s Edimax EW-7811UN wifi range is horrible and it does not reach my access point. I am going to use a TP-Link AV500 Powerline kit to solve this problem. I can’t recommend these Powerline adapters enough. Three customers and two relatives are using them and they are fantastic. Just plug and play.
I don’t feel comfortable opening my OSPI to the internet without SSL. Sniffing the OSPI admin password without SSL is trivial and it would give an attacker access to your sprinkler system and possibly to the RPI itself. OSPIi runs as root and my guess is that it would not be too difficult to used malformed HTTP requests to gain root access to the PI and then to my home network.