STM32WB Bluetooth® LE – Heart Rate Sensor Project

1. Heart Rate Profile Presentation

Heart Rate Profile (HRP) is a Generic Attribute Profile (GATT) based low energy profile defined by the Bluetooth^® Special Interest Group
The HRP, widely used in fitness applications, defines the communication between a GATT-server of a Heart Rate Sensor device, such as a wrist band, and a GATT-client Collector device, such as a smartphone or tablet.
Heart Rate Sensor is the device that measures heart rate data and other information, it can be defined as a GAP peripheral and GATT server implemented with the Heart Rate Service

This wiki page is the description of the Heart Rate Sensor project provided within the STM32CubeWB MCU Package

Bluetooth® LE Heart Rate profile overview

The table below describes the structure of Heart Rate Sensor services :

Heart Rate Sensor services
File:Connectivity HR Services UUID.png

2. Heart Rate Profile Interaction

Heart Rate Profile is a combination of a Heart Rate Collector and a Heart Rate Sensor to connect and exchange data in differents applications.

• The Heart Rate Sensor:
  • Measures the heart rate and exposes it via the Heart Rate Service.
  • Contains the Device Information Service, which contains information for example about the manufacturer of the device.
  • Is the GATT server.
• The Heart Rate Collector:
  • Accesses the information exposed by the Heart Rate Sensor and can for example display it to the end user or store it on non-volatile memory for later analysis.
  • Is the GATT client.

The GAP - Generic Access Profile defines and manages advertising and connection.

Collector Central device and Sensor Peripheral device

The GATT - Generic Attribute Profile defines and manages in/out data exchanges.

Collector GATT Client device and Sensor GATT Service device

Once Bluetooth^® LE connection established & notification enabled :

• Heart Rate measurement provided to remote every 1s.
• Connection interval may be change by application.

3. Requirements

3.1. Software and System requirements

Software required are the following (minimum IDEs version) :

• IAR Embedded Workbench for ARM (EWARM) toolchain V8.20.2
• RealView Microcontroller Development Kit (MDK-ARM) toolchain V5.31
• STM32CubeIDE toolchain V1.7.0 .

Programmer:

• STM32CubeProgrammer : To flash the board with an already generated binary

3.2. Hardware requirements

P-NUCLEO-WB55 or STM32WB5MM-DK Discovery Kit is necessary to install the application.

Hardware platforms illustration

3.3. Smartphone Application

ST BLE Sensor application (for Android, or iOS) or ST BLE ToolBox application (for Android, or IOS).

4. STM32WB Heart Rate Sensor Example Description

4.1. Project Directory

The "BLE_HeartRate" application is available by downloading STM32CubeWB MCU Package.

Heart Rate project directory

4.2. Project Description

4.2.1. Structure

Software project structure with the most important parts :

Main applicative part files

Bluetooth® LE Stack API Interface

Services management

System commands

Transport Layer Interface

WARNING: Do not modify the files in Middlewares folder

4.2.2. Application Initialization

The different steps of application initialization are described bellow :

Initialize the system (HAL, Clock, Power Mode, RTC IP, Timer Server) Infinite loop for run mode

Initialize the BSP (LEDs, buttons…), Transport Layer Interface, Debugger Wait for initialization done

Initialize the Bluetooth® LE App – GAP level Manage GAP events (advertising,scanning)

Initialize the Bluetooth® LE App – GATT level Initialize the Bluetooth® LE Stack Manage GATT events

Initialize services Manage services

4.2.3. GAP & GATT Initialization & Interaction

The GAP level of Heart Rate Sensor is managed by the file app_ble.c - APP_BLE_init()

• initialization of the device as Peripheral - Configure & Start Advertising : ADV Parameters, Local Name, UUID
• call the services controller initialization SVCCTL_Init() - svc_ctl.c
• management of the GAP event:
  • EVT_LE_CONN_COMPLETE - Provides information of the connection interval, slave latency, Supervision timeout
  • EVT_LE_CONN_UPDATE_COMPLETE - Provides the new information of the connection
  • EVT_DISCONN_COMPLETE - Informs the application about the link disconnection and the reason
  • EVT_ENCRYPT_CHANGE - Informs the application weather the link is encrypted

The Services management is done by the service controller - svc_ctl.c

• Calls the Initialization function of all the developed services
  • Heart Rate service - HRS_Init() hrs.c
  • Device Information service - DIS_Init() dis.c
• Registers Services Event Handler
  • SVCCTL_RegisterSvcHandler() - function receiving the GATT events from the BLE Host Stack and redirect them to the services registered - Heart Rate Event Handle (hrs.c)

The Heart Rate Service hrs.c manages the specification of the service:

• Service Init - HRS_Init()
  • Register Heart Rate Event Handle to Service Controller
  • Initialize Service UUID
    • aci_gatt_add_serv – add Heart Rate service as Primary services
  • Initialize Heart rate Measurement Characteristic
    • aci_gatt_add_char – add Heart Rate Characteristic
  • Initialize Body Sensor Location Characteristic
    • aci_gatt_add_char – add Body Sensor Location Characteristic
• Update Heart Rate Measurement Characteristic
  • aci_gatt_update_char_value – update the wished characteristics with a value aligned with the specification
• Update Body Sensor Location Characteristic Value
  • aci_gatt_update_char_value - update the wished characteristics with a value aligned with the specification
• HeartRate_Event_Handler(void *Event) – manage HCI Vendor Type Event:
  • EVT_BLUE_GATT_WRITE_PERMIT_REQ
    • Server receives a Write Command
    • HR Control Point Char. Value
    • Reset Energy Expended command then:
      • Send an aci_gatt_write_response() with an OK status.
      • Notify HRS application to Reset Energy Expended
      • Or Send an aci_gatt_write_response() with an Error.

• • EVT_BLUE_GATT_ATTRIBUTE_MODIFIED
    • HR Measurement Char. Description Value
      • ENABLE Or DISABLE Notification
    • Notify HRS application of the Measurement Notification

Heart Rate sensor software module interaction

4.3. Build and Install

Follow steps described in Bluetooth^® LE Build and Install Application page, applying it for BLE_HeartRate project.

5. Heart Rate Collector - Smartphone Application

Once the BLE Heart Rate application installed on the STM32WB platform, launch the ST BLE Sensor smartphone application.

Click on Connect one Device interface:

Heart Rate application interface 1

Your device should be visible from this interface, connect to it:

Heart Rate application interface 2

Now bpm measurement is displayed in real time.

Heart Rate application interface 3

With Discovery Kit Platform, the Heart Rate is also visible from the board LCD screen, and Heart pulse is illustrated:

Heart Rate on DK illustration