Today I'd like to talk about the Bluetooth Low Energy (or LE) APIs now available in the Android framework, and show you how easy it is to add some really interesting capabilities to mobile applications using this technology. Bluetooth LE was introduced to the core Android framework in 4.3, or API Level 18. Prior to this, there were several OEM-specific SDKs providing this behavior, but we will not be going into detail on those here.

Bluetooth GATT Basics

There are four primary roles that a device can fulfill in the Bluetooth LE paradigm:

• Broadcaster
• Observer
• Central
• Peripheral

We are going to look at two examples today; first with the Android application acting in the Central role to communicate with a Peripheral device, and second with the Android device acting in an Observer role monitoring data advertisements from several Broadcaster devices.

Bluetooth LE is primarily built around the Generic Attribute profile, or GATT, as it is often called. This profile defines a structured approach to how peripherals expose data to other devices. Peripheral information is organized as a collection of Services that describe logical functions of the device. A specific sensor or feature (such as thermometer or heart rate monitor) would have its own service. Each Service includes a collection of Characteristics to transfer discrete data values between devices. A Characteristic can represent service data (such as the current value of the heart rate) or configuration data (such as whether this peripheral should notify anyone when its value changes).

Characteristics are minimally made up of property flags and a value. The flags describe information about a characteristic's capabilities; such as whether it is readable, writeable, or supports notification. Additionally, they may contain one or more descriptor elements to indicate the value's type and perhaps provide additional configuration that is specific to the given characteristics. If this sounds like a lot of layers to try and follow, fear not. When you see them all put together in a real-world example each of their roles should become clear.

Source: newcircle.com