These are the brain of an IoT system. Controllers perform most of the action in the IoT space. In industry, controllers may be referred as IoT gateways. From data acquisition to processing this data to uploading it to the cloud and control actuators, are all performed by the controller. Usually, controllers have the capabilities of networking and wireless communication. If some controllers don't have that capability, then usually they are stacked up with external networking devices. Arduino, Raspberry Pi, Intel Galileo, and Intel Edison are some of the most commonly used controllers. Controllers normally come with GPIO pins that interface with other devices. Most of the details of Intel Edison, the controller that we are using, were discussed in Chapter 1, Setting up Intel Edison.