I have one of the original microcontroller-based systems. My irrigation system is actually in a pretty ‘hostile’ environment. We have some wires running several hundred feet to valves. There are also many noisy power tools and engines scattered about near wire access points. Plus we have coyotes, ground squirrels, feral cats and other unknown critters chewing off sprinkler heads, pulling up wires and stripping the insulation – sometimes shorting them. They are attracted to the water and the drought makes them aggressive.
I think that I was getting some significant electrical noise coming back on the wires that even the MOV’s couldn’t stop. since I installed the relays, the OS has been running continuously without any issues, so I think it’s solid. The relays seem to be holding up ok even though we have had a couple of shorted wires.
I am currently designing a wireless sprinkler network that will be ‘zero’ power and full monitoring (stuck valves, broken valves, soil moisture, temperature and humidity) and use a WPAN to manage all the sprinkler nodes. These will be used for the ‘far field’ irrigation. It will probably take me 6 more months to get it running.