Im about to order the diy kit but I wanted to know if its possible and easy to add a gsm shield to the kit instead of using wifi or ethernet because it will be used in a field far away from any internet. Also would like to know about the flow sensor possibility. Thank you in advance.
Which GSM shield do you plan to use? Basically it boils down to figure out the interface (SPI? I2C? Serial?) and power requirement (5V? 3.3V? how much current)? If you can post a link to the GSM shield I can tell you better how it can interface with OpenSprinkler.
I took a quick look at some Arduino GSM shields, and I think it’s not straightforward to use them directly with OpenSprinkler. These shields pretty much all use the serial interface, which means the commands and data are all sent through serial. This is different from how OpenSprinkler interfaces with its Ethernet controller, so there will be considerable changes in software to make it work.