Looks great! Out of curiosity, why go with the hub/node approach using ZigBee for sending such a small amount of data? There are WiFi modules like TI's CC3000 (http://www.ti.com/product/cc3000) available for very low cost that would make separate hub hardware unnecessary. This is the product used in Spark Core (https://www.spark.io/), for example. I imagine there are a few different reasons why you might spring for a hub-based solution despite the higher cost, but just wondering what your thinking is.