{"id":789,"date":"2021-11-14T10:34:41","date_gmt":"2021-11-14T09:34:41","guid":{"rendered":"https:\/\/macchina.io\/blog\/?p=789"},"modified":"2024-04-26T07:43:59","modified_gmt":"2024-04-26T05:43:59","slug":"communication-with-low-energy-bluetooth-devices-on-linux","status":"publish","type":"post","link":"https:\/\/macchina.io\/blog\/internet-of-things\/communication-with-low-energy-bluetooth-devices-on-linux\/","title":{"rendered":"Communication with Bluetooth Low-Energy Devices on Linux"},"content":{"rendered":"
\"macchina.io<\/a><\/figure>\n

What is Bluetooth and Bluetooth Low Energy?<\/h2>\n

Bluetooth\u2122\ufe0f is a wireless technology used to build Personal Area Networks (PAN) or piconets. Since it\u2019s original development by Ericsson in 1989, it has grown in popularity to the point where today it has become a standard feature in many segments of the consumer electronic market.<\/p>\n

The use of Bluetooth in industrial IoT is also growing, mostly due to Bluetooth LE, a newer variant of Bluetooth optimized for minimum power usage, as is required for wireless, battery-powered sensor devices. <\/p>\n

This blog post takes you through the important details of the Bluetooth LE technology from the perspective of an IoT developer. It is based on the presentation at the Internet of Things conference \u201cFrom the sensor to the cloud\u201d 2021, by our Founder & Chief Technologist G\u00fcnter Obiltschnig.<\/p>\n

A few facts about Bluetooth<\/h2>\n

Development of Bluetooth technology was originally initiated by Nils Rydbeck (Ericsson) in 1989. The first use case was not until ten years later, and was released at Comdex in 1999 as the first hands-free mobile headset. It won the “Best of show Technology Award”. This first product had a range of 10 meters but nowadays, that range can go up to 100m with Bluetooth 5.0.<\/p>\n

Bluetooth uses the globally unlicensed ISM (industrial, scientific, medical) radio bands from 2402 to 2480 GHz. One of the major advantages of Bluetooth is that it does not rely on a wireless network infrastructure.<\/p>\n

The Bluetooth standards are developed and maintained by the Bluetooth Special Interest Group.<\/a><\/p>\n

\n
\"Harald<\/a><\/figure>\n<\/div>\n

Why \u201cBluetooth\u201d?<\/h2>\n

The name Bluetooth is an anglicized version of the Scandinavian Bl\u00e5tand\/Bl\u00e5tann, the epithet of the tenth-century king Harald Bluetooth who united dissonant Danish tribes into a single kingdom. The implication is that Bluetooth unites communication protocols in the same way king Bluetooth united tribes.<\/p>\n

Bluetooth Low Energy (LE)<\/h2>\n

Bluetooth LE (formerly also known as Bluetooth Smart) was introduced with the Bluetooth 4.0 specification in 2010. It is intended to reduce power consumption and cost while maintaining a similar communication range. The actual connection times are reduced to a few milliseconds; significantly less than Bluetooth, which has connection times ranging from a few seconds up to a few hours.<\/p>\n

Bluetooth LE can co-exist with Bluetooth on the same controller, however, the Bluetooth LE protocol stack is different from classic Bluetooth. It uses the same 2.4 GHz radio bands as Bluetooth, but a different communication protocol and different channels with 2 MHz bandwidth. <\/p>\n

Bluetooth LE is targeted at devices with very low-power requirements, such as fitness and health sensors (heart rate monitors, thermometers, blood pressure, etc) as well as fitness trackers, battery-powered environmental and industrial sensors, beacons, etc.<\/p>\n

Bluetooth LE uses a unique 48-bit address per device (MAC address). Similar to Ethernet MAC addresses, the first part of the address is the “vendor prefix”, which allows to deduct the vendor of a Bluetooth device (or at least its chipset) from its address.<\/p>\n

Bluetooth LE Radio<\/h2>\n

Bluetooth LE uses 40 channels with 2 MHz bandwidth. Within each channel, Gaussian Frequency Shift Keying (GFSK) is used, similar to classic Bluetooth 1.0. The bitrate is 1 Mbit\/sec, with an option for 2 Mbit\/sec in Bluetooth 5.0.<\/p>\n

Bluetooth LE uses frequency hopping like \u201cclassic\u201d Bluetooth, but in a different variant (direct sequence spread spectrum).<\/p>\n

Bluetooth LE Protocol Stack<\/h2>\n
\"Bluetooth<\/a><\/figure>\n

GAP – Generic Access Profile<\/h3>\n

Bluetooth LE devices use the Generic Access Profile for device discovery and advertisement.<\/p>\n

GAP distinguishes between devices based on their roles. Central devices are typically a computer or smartphone. Peripheral devices are often small, low-power and resource-constrained devices like sensors.<\/p>\n

In order to discover peripheral devices, a central device sends out a broadcast message (scan response request). Upon receiving the scan response request, the peripheral device will respond with advertising data. This includes device name and address, and other data. Advertising data can also include small amounts of custom data. This is used by Bluetooth LE beacons (e.g., iBeacon).<\/p>\n

Both peripheral and central devices can assume one or both of the other GAP roles, which are Broadcaster and Observer. A very typical example would be a sensor in broadcast mode sending data to a central device in observer mode.<\/p>\n

GATT – Generic Attribute Profile<\/h3>\n

GATT defines the following concepts, which are often reflected in Bluetooth LE APIs.<\/p>\n

Client:<\/b> typically a computer or smartphone that sends GATT commands and requests and receives responses from servers. Also referred to as central device.<\/p>\n

Server: <\/b>a device (e.g., a sensor) that receives commands and requests and returns responses. Also referred to as peripheral device.<\/p>\n

\"Bluetooth<\/a><\/figure>\n

Characteristic:<\/strong> a data value transferred between client and server. Consists of multiple attributes<\/strong> containing the actual value, as well as configuration options and meta data.<\/p>\n

Different data types are supported, but on protocol level an attribute value is always a sequence of bytes. Characteristics and their attributes are used for reporting sensor values (e.g., temperature) and also for configuring devices (e.g., setting sample rate on an accelerometer). The maximum length is 512 bytes. Numeric values are usually stored in little-endian format.<\/p>\n

Service:<\/strong> a collection of related characteristics, which operate together, e.g. the sensor value and configuration parameters.<\/p>\n

Descriptor:<\/strong> provides additional information about a characteristic’s attribute, e.g. physical unit or minimum and maximum values.<\/p>\n

Identifier:<\/strong> services, characteristics and descriptors are attributes identified by UUIDs. The 128-bit UUIDs are mapped to device-specific 16-bit values (handles) for use in the protocol. Bluetooth reserves UUIDs in range xxxxxxxx-0000-1000-8000-00805F9B34FB for standard attributes, which are transmitted as 16-bit or 32-bit values in the protocol.<\/p>\n

GATT Operations<\/h3>\n

GATT comes into play once a connection is made between two devices. For data to be delivered and received, some or all of the following operations can be executed.<\/p>\n