@Stephen: TP-Link has retired TL-WR702N and it’s replaced by TL-WR802N. We haven’t got a batch of the new model so it’s temporarily out of stock on our store. The factory default SSID and password are both printed at the back of the adapter — once reset, it will go back to the factory default setting.
For people who don’t want to mess up with the WiFi adapter, I would recommend the powerline Ethernet adapter — it’s like a wired connection except it uses the powerline wires as the signal wire. So you just plug it into the router and there is no need to reset the adapter etc. Of course if it’s convenient to just run an Ethernet cable from the router to OpenSprinkler, that’s the easiest option 🙂