ESP32 BLE (Bluetooth Low Energy)

Hello readers, I hope you all are having fun in your lives. Welcome to the 2nd Chapter of Section-2 in the ESP32 Programming Series. In today's lesson, we'll go over another built-in feature of the esp32 module that helps it stand out from the competition: BLE or Bluetooth Low Energy.

In the previous tutorial, we discussed the Classic Bluetooth in ESP32, which is considered the predecessor of Bluetooth Low Energy(which we are going to discuss today). We will first look at, what is BLE? and why is it used?, and then will design some examples to utilize the ESP32 BLE in Arduino IDE.

What is BLE?

• There have been numerous adjustments and upgrades to Bluetooth's characteristics since its inception, where Bluetooth 4.0(also called BLE or Bluetooth Smart) is the most influential.
• BLE or Bluetooth Smart is also known as Wibree. The Wibree protocol was designed by Nokia in 2006 and was later included in Bluetooth 4.0 as Bluetooth Low Energy in December 2009.
• Bluetooth Low Energy is a slightly different protocol from Classic Bluetooth, which is used in phones, headphones, TVs etc. Rather than continuously streaming data, BLE "servers" can "notify" clients to send the data chunks on a regular basis(which makes it preferable over traditional Bluetooth). As a result, BLE is better suited to low-power IoT applications that don't require significant volumes of data.
• Both the server and clients now utilize a "service UUID", to determine which server and client needs to be connected. There are various "characteristics" that can be found inside these services.
• Bluetooth Low Energy was developed and promoted by the Bluetooth Special Interest Group (SIG) for use in healthcare, beacons, fitness, home entertainment etc. It does not work with standard Bluetooth and does not have any compatibility, although it can coexist with BR/EDR and LE.
• The Bluetooth Special Interest Group (SIG) recognizes several industries for low-energy technology, including smart homes, health, sport, and fitness.

Difference b/w traditional Bluetooth and BLE

Bluetooth Technology was created with the intention of allowing data to be streamed indefinitely. That implies you can send and receive a large amount of data over a short distance with Bluetooth.

• It's crucial to discuss power usage while discussing the differences between Bluetooth and Bluetooth Low Energy. Bluetooth Low Energy is intended to transfer data only when the client is available to receive the data from the server; otherwise, the BLE device will go into low energy or sleep mode. Thus, use significantly less power as compared to traditional Bluetooth, while retaining a similar communication range.
• Bluetooth Low Energy uses the same 2.4 GHz radio frequencies as traditional Bluetooth, but a different FHSS (Frequency Hopping Spread Spectrum) technique.
• Classic Bluetooth uses Scatter-net topology whereas BLE uses Star topology.

Although Bluetooth Low Energy differs from the previous Bluetooth Basic Rate/Enhanced Data Rate protocol, both can be supported by the same device: the Bluetooth 4.0 specification allows devices to implement any or both of the LE and BR/EDR systems.

Because both, Bluetooth Low Energy and traditional Bluetooth use the same 2.4 GHz radio frequencies, allowing dual-mode devices to use a single radio antenna.

How does BLE work?

BLE Client & Server

• Any BLE device can operate as both a server and a client.
• Server ESP32 will announce its presence to nearby clients so that clients can establish a connection with the BLE server for communication.

• Broadcast mode and mesh networks both are also supported by BLE.
• In broadcast mode, only the BLE server transmits data to all the connected clients.
• In mesh mode, all the devices are connected to each other.  Therefore, all devices can communicate with all other available devices.

GATT

• GATT is an acronym for Generic Attributes.

It defines a data structure that is visible to all BLE devices linked to it. GATT defines how BLE devices can communicate with each other. Understanding this structure is crucial to understand the working of BLE.

• Read through all of the descriptors for a specific characteristic.
• Find out everything there is to know about a specific service.
• Find qualities that match a UUID.
• Find UUIDs for all major services.
• Find a service using a UUID.
• For a particular principal service, locate subsidiary services.

BLE Service

A service is nothing more than a collection of data, such as data from a temperature sensor.

• A profile, which is made up of multiple services, is at the top of the structure. Typically, a BLE-supported device will have multiple services.
• The SIG  has preset services for a variety of data kinds, such as battery level, weight, blood pressure, heart rate, and so on.
• Every service has at least a single feature and can also refer to different services.
  

BLE Characteristics

The characteristic attribute is always held by a particular service, and it is where the hierarchy's real data is stored.

The characteristic has two attributes:

• Characteristic value.
• The characteristic declaration contains the metadata.

It essentially consists of the operations that can be used like Indicate, read, write, notify, broadcast etc.

UUID or Universally Unique Identifier

• In a Generic Attribute (GATT) profile, the UUID is a universally unique 128-bit or 16-byte integer that is used to identify profiles, services, and data kinds.

• In the code description, we will provide a link where you can generate a new UUID.

BLE network topology

BLE uses Star and mesh topology for communication.

A Broadcast Type or a Connection Type communication between two BLE devices is possible. The 'broadcaster' BLE Device sends data to any 'observer' BLE Device in broadcasting. It's a data transfer that only goes one way.

A 'Connection' between the BLE Devices is required for two-way communication. A Central (Master) BLE Device continuously checks for advertising data packets sent by a Peripheral (Slave) BLE Device.

BLE Applications

• BLE is ideal for applications that need to exchange modest amounts of data on a regular basis.
• BLE is used extensively in healthcare, fitness, tracking, beacons, security, and home automation etc.
• Bluetooth Low Energy is natively supported by mobile operating systems such as iOS, Android, and Windows Phone, as well as macOS, Linux, Windows 8 & 10.

ESP32 BLE

• You can use ESP32 BLE either as a BLE server or a client.
• Examples are available in the ESP32 BLE library(Arduino IDE) which you can use to implement BLE services.

Note:

• The Arduino IDE must have the ESP32 board manager file and libraries installed. If you haven't previously prepared your Arduino IDE to operate with the ESP32, then read our previous tutorial, i.e., Introduction to ESP32 Programming Series.

BLE Server Code Description

• For coding, we are using Arduino IDE’s inbuilt example and will make the required changes in that code only.
• I will also explain the code in detail for beginners to understand.

In this code, ESP32, BLE will be used as a server.

• Import the necessary/required libraries for the BLE application.
• Define a UUID for the Service and Characteristic.

• To generate UUIDs, go to the following link:

         https://www.uuidgenerator.net/

• You can either use the default UUIDs if you wish to or go to the above link to generate random UUIDs as per your services and attributes.
• Call back or acknowledge the server whether the client is connected or not

Arduino Setup() Function

• Serial Communication at a baud rate of 115200.
• Create a name for your BLE device for identification, we named it Wibree.
• Set the BLE device as a server.
• Create a service for the BLE server with the UUID defined earlier.
• The characteristic for that service is then set. As you can see, you're still using the UUID you created previously, and you'll need to supply the properties of the characters as arguments. It's read and write in this scenario.
• You can also add other services like battery, indicate, notify etc.
• The setValue() method can be used to set the value of a characteristic.
• The above value can be changed to whatever you like. This could be a sensor reading.
• Finally, activate the service and advertising so that other BLE devices can scan and locate this BLE device.

Arduino Loop() Function

1. Here we can check if the device is connected to the client or not
2. If connected then do some tasks like transmitting data or receiving input from the client.

Data Size Per Packet

20 bytes per packet.

Unfortunately, BLE isn't built to handle large amounts of data. The maximum data size per packet in the BLE specification is 20 bytes, so if you wish to communicate more, you'll have to divide it up into many packets. Fortunately, this isn't a challenging task. Simply put, use a delimiter like "!" or "*" or something unique at the end of your whole message to signal the app that the message is done and to start listening for future communications. If you want to send + > 20 bytes cumulatively, for example, you can send and then proceed with the next message if needed.

Testing ESP32 BLE Server

After creating a BLE server using ESP32, we can use a BLE application available on the Play store for testing purposes.

Demonstration with BLE scanner app:

1. Go to the play store
2. Search for the BLE scanner and download the app
3. After installing the app turn on the Bluetooth.
4. Open the app and search for nearby devices.

• Now connect to ESP32 BLE  by clicking on the ESP32 device.
• In our case, we named the device ‘Wibree’.

• Now you can use the various services provided by BLE like writing and reading data packets, checking battery levels etc. and a lot more.

This concludes the tutorial. I hope you find it helpful.