Bluetooth Low Energy

BME554L -Fall 2025 - Palmeri

Author
Affiliation

Dr. Mark Palmeri, M.D., Ph.D.

Duke University

Published

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What is Bluetooth?

  • Bluetooth Low Energy (BLE) is a wireless serial communication protocol.
  • Part of BT 4.0 core; very distinct from previous version of BT.
  • Standardized via the BT Special Interest Group (SIG)
  • “Only” ubiquitous communication protocol between device:OS (iOS, Android, OS X, Windows, Linux)
  • Designed for technology in smart homes, health, sport and fitness.
  • “Low energy” - months/years of power on single battery (e.g., CR2032)
  • Small size & low cost

Generic Access Profile (GAP)

  • Peripheral Device: more resource-constrained (power, size, horsepower) device
  • Central Device: more resource-equipped device that will do most processing and data storage

Device Advertising

  • 31 bytes of data
  • Can configure advertising interval (frequency proportional to energy consumption)
  • Optional: Scan Response Request

  • Once a connection is established, advertising ceases and GATT operations take over.

Broadcast Topology

Mesh Profiles

  • BLE peripherals can communicate with one another to pass information to other devices (that might otherwise be out of range).
  • Common example: lights in a building
  • Zephyr has its own standard protocol: https://launchstudio.bluetooth.com/ListingDetails/95153

Generic Attribute (GATT) Profiles

  • API used by all BLE devices.
  • Client: initiates GATT commands/requests & accepts responses (e.g., smartphone)
  • Server: receives GATT commands/requests & returns responses (e.g., wearable sensor)
  • Characteristic: Data value communicated between client/server
  • Service: Collection of related characteristics (similar to a structure or class/object)
  • Descriptor: optional characteristic metadata (e.g., value units)

GATT Profiles

Universally Unique Identifier (UUID)

  • Identifiers are used to identify all attributes.
    • Services
    • Characteristics
    • Descriptors
  • UUIDs are specified by the BT SIG. They are 128-bits, but 16- or 32- bits represent the unique information.
  • Can be used to encode information, such as manufacturer, project ID, firmware revision, etc.

Generating UUIDs

Online generators exist to create valid UUIDs: https://www.uuidgenerator.net/

  • Example: b562bf0c-0039-418e-9756-8b271b33d5be
  • The “base” UUID can be set for a device and then incremented for custom services not in the standard GATT.

GATT Workflow

  • UUIDs can be discovered or explicitly found.
  • Service characteristics can be discovered.
  • Data can be read (server -> client) using either a UUID or handle (similar to an “alias”).
  • Data can be written to the server using the handle (with or without response).
  • Data streams are limited / dictated by the Maximum Transfer Unit (MTU), which can be extended, but with tradeoffs.

Notifications

  • A notification can be sent by the server when a characteristic is available for the client (e.g., data stored in the characteristic has been updated). The client is responsible for then reading the characteristic.
  • Notifications avoid the client having to periodically read a characteristic to determine if a value has been updated or is available.
  • Notifications are similar to an ISR for the client to know to send a read request to the server.
  • An indication is a notification that requires a response from the client.

Firmware Implementation

The following library is used as a skeleton for BLE communication in your final project:

Resources