RFM12B is not included in the package and you have to purchase it separately. We used to carry them in store but they are now replaced by the simpler, cheaper and more common 433MHz and 315MHz RF transmitter / receiver. You can purchase RFM12B from a variety of places such as SparkFun, Modern Device etc. Note that only OpenSprinkler DIY 1.42u has PCB pads designed to fit RFM12B — the newer version of OpenSprinkler 2.0 does not have PCB pads for it (although it’s still possible to connect it manually to the SPI bus).