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AN983
User Manual
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Silicon Labs AN983 User Manual

AN983: BLUETOOTH® 4.0 HEART RATE SENSOR
APPLICATION NOTE
Wednesday, 02 December 2020 Version 1.5
VERSION HISTORY
Version
Comment
1.0
First version
1.1
Services added
1.2
Updated BGscript code examples
1.3
Changed broadcast=”true” to advertise=”true”
1.4
Updated compile and installation instructions
1.5
Renamed "Bluetooth Smart" to "Bluetooth Low Energy" according to the official Bluetooth SIG nomenclature
TABLE OF CONTENTS
1 Introduction ..................................................................................................................................................4
2 What is Bluetooth Low Energy Technology? ...........................................................................................5
3 Typical Bluetooth 4.0 Application Architecture .......................................................................................6
3.1 Overview ...............................................................................................................................................6
3.2 What is a Profile? ..................................................................................................................................7
3.3 What Is a Service? ................................................................................................................................8
3.4 What is a Characteristic? ......................................................................................................................9
3.5 Relationship Between Profiles, Services and Characteristics ........................................................... 10
4 Introduction to the Bluegiga Bluetooth Low Energy Software ............................................................ 11
4.1 The Bluetooth Low Energy Stack ...................................................................................................... 11
4.2 The Bluetooth Low Energy SDK ........................................................................................................ 11
4.3 The BGAPI Protocol .......................................................................................................................... 13
4.4 The BGLib Host Library ..................................................................................................................... 14
4.5 BGScriptTM Scripting Language ......................................................................................................... 15
4.6 The Profile Toolkit .............................................................................................................................. 16
5 Heart Rate Profile v1.0 ............................................................................................................................. 17
5.1 Description ......................................................................................................................................... 17
5.2 Service requirements ......................................................................................................................... 17
5.3 Heart Rate Service requirements ...................................................................................................... 18
5.4 Device Information Service requirements .......................................................................................... 18
5.5 Other requirements ............................................................................................................................ 18
5.6 Connection establishment requirement ............................................................................................. 19
5.7 Security requirements ........................................................................................................................ 20
6 Implementing a Heart Rate Sensor ......................................................................................................... 21
6.1 Creating a project .............................................................................................................................. 22
6.2 Hardware configuration ...................................................................................................................... 23
6.3 Heart Rate Profile GATT database .................................................................................................... 24
6.4 Writing BGScript application .............................................................................................................. 29
6.5 Compiling and Installing the Firmware .............................................................................................. 33
6.6 Testing the Heart Rate Sensor .......................................................................................................... 37
6.7 Testing with BLEGUI ......................................................................................................................... 37
7 Debugging Heart Rate sensor code ....................................................................................................... 44
8 External resources ................................................................................................................................... 47
Page 4 of 49
1 Introduction
This application note discusses how to build Bluetooth 4.0 Heart Rate Profile (HRP) sensor using Bluegiga’s Bluetooth 4.0 software and DKBLE112 hardware development kits. The application note contains a practical
example of how to build GATT based Heart Rate Profile and how to make a standalone sensor device using BGScript scripting language.
Notice that this application note only focuses on the Heart Rate Profile sensor implementation, not the Heart Rate Profile Collector implementation.
Page 5 of 49
2 What is Bluetooth Low Energy Technology?
Bluetooth Low Energy (Bluetooth 4.0) is a new, open standard developed by the Bluetooth SIG. It’s targeted
to address the needs of new modern wireless applications such as ultra-low power consumption, fast connection times, reliability and security. Bluetooth Low Energy consumes 10-20 times less power and is able to transmit data 50 times quicker than classical Bluetooth solutions.
Link: How Bluetooth low energy technology works? Bluetooth Low Energy is designed for new emerging applications and markets, but it still embraces the very
same benefits we already know from the classical, well established Bluetooth technology:
• Robustness and reliability - The adaptive frequency hopping technology used by Bluetooth Low Energy allows the device to quickly hop within a wide frequency band, not just to reduce interference but also to identify crowded frequencies and avoid them. On addition to broadcasting Bluetooth Low Energy also provides a reliable, connection oriented way of transmitting data.
• Security - Data privacy and integrity is always a concern is wireless, mission critical applications. Therefore Bluetooth Low Energy technology is designed to incorporate high level of security including authentication, authorization, encryption and man-in-the-middle protection.
• Interoperability - Bluetooth Low Energy technology is an open standard maintained and developed by the Bluetooth SIG. Strong qualification and interoperability testing processes are included in the development of technology so that wireless device manufacturers can enjoy the benefit of many solution providers and consumers can feel confident that equipment will communicate with other devices regardless of manufacturer.
• Global availability - Based on the open, license free 2.4GHz frequency band, Bluetooth Low Energy technology can be used in world wide applications.
There are two types of Bluetooth 4.0 devices:
• Bluetooth 4.0 single-mode devices that only support Bluetooth Low Energy and are optimized for low-power, low-cost and small size solutions.
• Bluetooth 4.0 dual-mode devices that support Bluetooth Low Energy and classical Bluetooth technologies and are interoperable with all the previously Bluetooth specification versions.
Key features of Bluetooth Low Energy wireless technology include:
• Ultra-low peak, average and idle mode power consumption
• Ability to run for years on standard, coin-cell batteries
• Low cost
• Multi-vendor interoperability
• Enhanced range
Bluetooth Low Energy is also meant for markets and applications, such as:
• Automotive
• Consumer electronics
• Smart energy
• Entertainment
• Home automation
• Security & proximity
• Sports & fitness
Page 6 of 49
3 Typical Bluetooth 4.0 Application Architecture
3.1 Overview
Bluetooth Low Energy applications typically have the following architecture:
• Server Service is the device that provides the information, so these are typically the sensor devices, like
thermometers or heart rate sensors. The server exposes implements services and the services expose the data in characteristics.
• Client Client is the device that collects the information for one or more sensors and typically either displays it
to the user or passes it forward. The client devices typically do not implement any service, but just collect the information from the service provided by the server devices. Clients are typically devices like mobile phones, tablets and PCs.
The figure below shows the relationship of these two roles.
Client Server
Service 1
Servic e 2
Service n
Figure 1: Bluetooth Low Energy device roles
Page 7 of 49
3.2 What is a Profile?
Profiles are used to describe devices and the data they expose and also how these devices behave. The data is described by using services, which are explained later and a profile may implement single or multiple services depending on the profile specification. For example a Heart Rate Service specification mandates that the following services need to be implemented:
• Heart Rate Service
• Device Information Service
Profile specifications might also define other requirements such as security, advertisement intervals and connection parameters.
The purpose of profile specifications is to allow device and software vendors to build standardized interoperable devices and software. Standardized profiles have globally unique 16-bit UUID, so they can easily identify.
Profiles are defined in profiles specifications, which are available at:
https://developer.bluetooth.org/gatt/profiles/Pages/ProfilesHome.aspx
Page 8 of 49
3.3 What Is a Service?
Services such as a Heart Rate service describes what kind of data a device exposes, how the data can be accessed and what the security requirements for that data are. The data is described using characteristics and a service may contain single or multiple characteristics and some characteristics might be optional where as some are mandatory.
Two types of services exist:
• Primary Service
A primary service is a service that exposes primary usable functionality of this device. A primary service can be included by another service.
• Secondary Service
A secondary service is a service that is subservient to another secondary service or primary service. A secondary service is only relevant in the context of another service.
Just like the profiles also the services are defined in service specifications and the Bluetooth SIG standardized services are available at:
https://developer.bluetooth.org/gatt/services/Pages/ServicesHome.aspx
Every service standardized by the Bluetooth SIG has a globally unique 16-bit UUID so just like the profiles also the services can be easily identified.
However not every use case can be fulfilled by the standardized service and therefore the Bluetooth Low Energy specification enables device vendors to make proprietary service. The proprietary services are described just as the standardized services, but 128-bit UUIDs need to be used instead of use 16-bit UUIDs reserved for the standard services.
Page 9 of 49
3.4 What is a Characteristic?
Characteristics are used to expose the actual data. Characteristic is a value, with a known type (UINT8, UINT16, UTF-8 etc.), a known presentation format. Just like profiles and services also characteristics have unique UUID so they can be easily identified and the standardized characteristics use 16-bit UUIDs and vendor specific characteristics use 128-bit UUIDs.
Characteristics consist of:
• Characteristic Declaration describing the properties of characteristic value such as:
• characteristic (UUID)
• Access control (read, write, indicate etc.)
• Characteristic value handle (unique handle within a single device)
• Characteristic Value containing the value of a characteristic (for example temperature reading).
• Characteristic Descriptor(s) which provide additional information about the characteristic (characteristic
user description, characteristic client configuration, vendor specific information etc.).
Figure 2: Characteristic structure
Standardized characteristics are defined in Characteristic Specification and the standardized characteristics are available at:
https://developer.bluetooth.org/gatt/characteristics/Pages/CharacteristicsHome.aspx
Page 10 of 49
3.5 Relationship Between Profiles, Services and Characteristics
The illustration below shows the relationship between profiles, services and characteristics.
Health thermometer profile
GAP service
(UUID: 1800)
Health thermometer
service
(UUID: 1809)
Device information
service
(UUID:180A)
Health thermometer service
(UUID: 1809)
Temperature measurement
(UUID: 2A1C)
Mandatory
Temperature type
(UUID: 2A1D)
Optional
Intermediate temperature
(UUID: 2A1E)
Optional
Measurement interval
(UUID: 2A21)
Optional
Temperature measurement
Handle : 1
UUID: 2803 (declaration)
Data:
Data UUID: 2A1D
Data Handle: 2
Data Properties: Indicate
Handle : 2
UUID: 2A1C (attribute value)
Data: Flags: <uint8> Measurement value:<float>
Time stamp: <date_time>
Temperature type: <temperature_type>
Handle: 3
UUID: 2903
Client characteristics configuration
Properties: Read, write
Figure 3: Health thermometer profile
Page 11 of 49
4 Introduction to the Bluegiga Bluetooth Low Energy Software
The Bluegiga Bluetooth Low Energy Software enables developers to quickly and easily develop Bluetooth Low Energy applications without in-depth knowledge of the Bluetooth Low Energy technology. The Bluetooth Low Energy Software consist of two parts:
• The Bluetooth Low Energy Stack
• The Bluetooth Low Energy Software Development Kit (SDK)
4.1 The Bluetooth Low Energy Stack
The Bluetooth Low Energy stack is a fully Bluetooth 4.0 single mode compatible software stack implementing slave and master modes, all the protocol layers such as L2CAP, Attribute Protocol (ATT), Generic Attribute Profile (GATT), Generic Access Profile (GAP) and security and connection management.
The Bluetooth Low Energy is meant for the Bluegiga Bluetooth Low Energy products such as BLE112, BLE113 and BLED112 and it runs on the embedded MCU used in these products, so no host is needed.
4.2 The Bluetooth Low Energy SDK
The Bluetooth Low Energy SDK is a software development kit, which enables the device and software vendors to develop products on top of the Bluegiga’s Bluetooth Low Energy hardware and software.
The Bluetooth Low Energy SDK supports multiple development models and the software developers can decide whether the application software runs on a separate host (a low power MCU) or whether they want to make fully standalone devices and execute their code on the MCU embedded in the Bluegiga Bluetooth Low Energy modules. The SDK also contains documentation, tools for compiling the firmware, installing it into the hardware and lot of example application speeding up the development process.
fully standalone applications using a simple scripting language called BGScriptTM. Several profiles and examples are also offered as a part of the Bluetooth Low Energy Software in order to easily develop the Bluetooth Low Energy compatible end products.
Bluegiga’s Bluetooth Low Energy Software provides a complete development framework for Bluetooth Low Energy application implementers.
Page 12 of 49
Figure 4: Bluetooth Low Energy Software
The Bluetooth Low Energy Software architecture is illustrated and it consists of the following components
• The Bluetooth Low Energy stack implementing the Bluetooth Low Energy protocol
• BGAPI
TM
APIs that enable the software developers to interface to the Bluetooth Low Energy Stack
• BGScriptTM Virtual Machine (VM) and scripting language which enable application code to be developed and executed directly on the Bluetooth Low Energy hardware
• BGLibTM lightweight host library which implements the BGAPI binary protocol and parser and is target for applications where separate host processor is used to interface to the Bluetooth Low Energy modules over UART or USB.
• Profile ToolkitTM is a GATT based profile development tool that enables software developers quickly and easily to describe the Bluetooth Low Energy profiles, services and characteristics using simple XML templates
Each of these components are described in more detail in the following chapters.
Page 13 of 49
4.3 The BGAPI Protocol
For applications where a separate host is used to implement the end user application, a transport protocol is needed between the host and the Bluetooth stack. The transport protocol is used to communicate with the Bluetooth stack as well to transmit and receive data packets. This protocol is called BGAPI and it's a lightweight binary based communication protocol designed specifically for ease of implementation within host devices with limited resources.
The BGAPI protocol is a simple command, response and event based protocol and it can be used over UART SPI (at the moment not supported by the Bluetooth Low Energy hardware) or USB interfaces.
Figure 5: BGAPI protocol
The BGAPI provides access for example to the following layers in the Bluetooth Low Energy Stack:
• Generic Access Profile - GAP allows the management of discoverability and connetability modes and open connections
• Security manager - Provides access the Bluetooth Low Energy security functions
• Attribute database - An class to access the local attribute database
• Attribute client - Provides an interface to discover, read and write remote attributes
• Connection - Provides an interface to manage Bluetooth Low Energy connections
• Hardware - An interface to access the various hardware layers such as timers, ADC and other
hardware interfaces
• Persistent Store - User to access the parameters of the radio hardware and read/write data to non- volatile memory
• System - Various system functions, such as querying the hardware status or reset it
Page 14 of 49
4.4 The BGLib Host Library
For easy implementation of BGAPI protocol an ANSI C host library is available. The library is easily portable ANSI C code delivered within the Bluetooth Low Energy SDK. The purpose is to simplify the application development to various host environments.
Figure 6: BGLib host library
Page 15 of 49
4.5 BGScriptTM Scripting Language
The Bluetooth Low Energy SDK Also allows the application developers to create fully standalone devices without a separate host MCU and run all the application code on the Bluegiga Bluetooth Low Energy Hardware. The Bluetooth Low Energy modules can run simple applications along the Bluetooth Low Energy stack and this provides a benefit when one needs to minimize the end product’s size, cost and current consumption. For developing standalone Bluetooth Low Energy applications the SDK includes the Script VM, compiler and other BGScript development tools. BGScript provides access to the same software and hardware interfaces as the BGAPI protocol and the BGScript code can be developed and compiled with free­of-charge tools provided by Bluegiga.
Typical BGScript applications are only few tens to hundreds lines of code, so they are really quick and easy to develop and lots of readymade examples are provides with the SDK.
Figure 7: BGScript application model
BGScript code example:
# System Started
event system_boot(major, minor, patch, build, ll_version, protocol_version,hw)
#Enable advertising mode
call gap_set_mode(gap_general_discoverable,gap_undirected_connectable)
#Enable bondable mode
call sm_set_bondable_mode(1)
#Start timer at 1 second interval (32768 = crystal frequency)
call hardware_set_soft_timer(32768)
end
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