![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2021\/11\/ESP32-BLE-Client-Server.jpg?resize=1200%2C675&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\nRecommended Reading:<\/strong> Getting Started with ESP32 Bluetooth Low Energy (BLE)<\/a><\/p>\n\n\n\n Before going straight to the project, it is important to take a quick look at some essential BLE concepts so that you’re able to better understand the project later on. If you’re already familiar with BLE, you can skip to the Project Overview<\/a> section.<\/p>\n\n\n\n Bluetooth Low Energy, BLE for short, is a power-conserving variant of Bluetooth. BLE\u2019s primary application is short-distance transmission of small amounts of data (low bandwidth). Unlike Bluetooth that is always on, BLE remains in sleep mode constantly except for when a connection is initiated.<\/p>\n\n\n\n This makes it consume very low power. BLE consumes approximately 100x less power than Bluetooth (depending on the use case). You can check the main differences between Bluetooth and Bluetooth Low Energy here<\/a>.<\/p>\n\n\n\n With Bluetooth Low Energy, there are two types of devices: the server and the client. The ESP32 can act either as a client or as a server.<\/p>\n\n\n\n The server advertises its existence, so it can be found by other devices and contains data that the client can read. The client scans the nearby devices, and when it finds the server it is looking for, it establishes a connection and listens for incoming data. This is called point-to-point communication.<\/p>\n\n\n\n There are other possible communication modes like broadcast mode and mesh network (not covered in this tutorial).<\/p>\n\n\n\n GATT stands for Generic Attributes and it defines a hierarchical data structure that is exposed to connected BLE devices. This means that GATT defines the way that two BLE devices send and receive standard messages.\u00a0Understanding this hierarchy is important because it will make it easier to understand how to use BLE with the ESP32.<\/p>\n\n\n\n In our example, we’ll create a service with two characteristics<\/em>. One for the temperature and another for the humidity. The actual temperature and humidity readings are saved on the value <\/em>under their characteristics<\/em>. Each characteristic has the notify <\/em>property, so that it notifies the client whenever the values change.<\/p>\n\n\n\n Each service, characteristic, and descriptor have a UUID (Universally Unique Identifier). A UUID is a unique 128-bit (16 bytes) number. For example:<\/p>\n\n\n\n There are shortened UUIDs for all types, services, and profiles specified in the SIG (Bluetooth Special Interest Group)<\/a>.<\/p>\n\n\n\n But if your application needs its own UUID, you can generate it using this UUID generator website<\/a>.<\/p>\n\n\n\n In summary, the UUID is used for uniquely identifying information. For example, it can identify a particular service provided by a Bluetooth device.<\/p>\n\n\n\n For a more detailed introduction about BLE, read our getting started guide:<\/p>\n\n\n\n In this tutorial, you\u2019re going to learn how to make a BLE connection between two ESP32 boards. One ESP32 is going to be the BLE server, and the other ESP32 will be the BLE client. <\/p>\n\n\n\n The ESP32 BLE server is connected to a BME280 sensor<\/a> and it updates its temperature and humidity characteristic values every 30 seconds. <\/p>\n\n\n\n The ESP32 client connects to the BLE server and it is notified of its temperature and humidity characteristic values. This ESP32 is connected to an OLED display and it prints the latest readings. <\/p>\n\n\n\n This project is divided into two parts:<\/p>\n\n\n\n Here’s a list of the parts required to follow this project:<\/p>\n\n\n\n ESP32 BLE Server:<\/strong><\/p>\n\n\n\n ESP32 BLE Client:<\/strong> <\/p>\n\n\n\n You can use the preceding links or go directly to MakerAdvisor.com\/tools<\/a> to find all the parts for your projects at the best price!<\/p> In this part, we’ll set up the BLE Server that advertises a service that contains two characteristics: one for temperature and another for humidity. Those characteristics have the Notify<\/em> property to notify new values to the client.<\/p>\n\n\n\n The ESP32 BLE server will advertise characteristics with temperature and humidity from a BME280 sensor. You can use any other sensor as long as you add the required lines in the code.<\/p>\n\n\n\n We\u2019re going to use I2C communication with the BME280 sensor module. For that, wire the sensor to the default ESP32 SCL (GPIO 22<\/span>) and SDA (GPIO 21<\/span>) pins, as shown in the following schematic diagram.<\/p>\n\n\n\n Recommended reading: ESP32 Pinout Reference: Which GPIO pins should you use?<\/a><\/p>\n\n\n\n As mentioned previously, we’ll advertise sensor readings from a BME280 sensor. So, you need to install the libraries to interface with the BME280 sensor.<\/p>\n\n\n\n You can install the libraries using the Arduino Library Manager. Go to Sketch <\/strong>> Include Library<\/strong> > Manage Libraries<\/strong> and search for the library name.<\/p>\n\n\n\n If you’re using VS Code with the PlatformIO extension, copy the following to the platformio.ini<\/span> file to include the libraries.<\/p>\n\n\n\n With the circuit ready and the required libraries installed, copy the following code to the Arduino IDE, or to the main.cpp<\/span> file if you’re using VS Code.<\/p>\n\n\n View raw code<\/a><\/p>\n\n\n\n You can upload the code, and it will work straight away advertising its service with the temperature and humidity characteristics. Continue reading to learn how the code works, or skip to the Client section<\/a>.<\/p>\n\n\n\n There are several examples showing how to use BLE with the ESP32 in the Examples<\/em> section. In your Arduino IDE, go to File <\/strong>> Examples<\/strong> > ESP32 BLE Arduino<\/strong>. This server sketch is based on the Notify <\/em>example.<\/p>\n\n\n\n The code starts by importing the required libraries.<\/p>\n\n\n\n By default, the ESP sends the temperature in Celsius degrees. You can comment the following line or delete it to send the temperature in Fahrenheit degrees.<\/p>\n\n\n\n The following line defines a name for our BLE server. Leave the default BLE server name. Otherwise, the server name in the client code also needs to be changed (because they have to match).<\/p>\n\n\n\n Create an Adafruit_BME280<\/span> object called bme<\/span> on the default ESP32 I2C pins.<\/p>\n\n\n\n The temp<\/span>, tempF<\/span> and hum<\/span> variables will hold the temperature in Celsius degrees, the temperature in Fahrenheit degrees, and the humidity read from the BME280 sensor.<\/p>\n\n\n\n The following timer variables define how frequently we want to write to the temperature and humidity characteristic. We set the timerDelay<\/span> variable to 30000 milliseconds (30 seconds), but you can change it.<\/p>\n\n\n\n The deviceConnected<\/span> boolean variable allows us to keep track if a client is connected to the server.<\/p>\n\n\n\n In the next lines, we define UUIDs for the service, for the temperature characteristic in celsius, for the temperature characteristic in Fahrenheit, and for the humidity.<\/p>\n\n\n\n I recommend leaving all the default UUIDs. Otherwise, you also need to change the code on the client side\u2014so the client can find the service and retrieve the characteristic values.<\/p>\n\n\n\n In the setup()<\/span>, initialize the Serial Monitor and the BME280 sensor.<\/p>\n\n\n\n Create a new BLE device with the BLE server name you\u2019ve defined earlier:<\/p>\n\n\n\n Set the BLE device as a server and assign a callback function.<\/p>\n\n\n\n The callback function MyServerCallbacks()<\/span> changes the boolean variable deviceConnected<\/span> to true<\/span> or false<\/span> according to the current state of the BLE device. This means that if a client is connected to the server, the state is true<\/span>. If the client disconnects, the boolean variable changes to false<\/span>. Here\u2019s the part of the code that defines the MyServerCallbacks()<\/span> function.<\/p>\n\n\n\n Start a BLE service with the service UUID defined earlier.<\/p>\n\n\n\n Then, create the temperature BLE characteristic. If you\u2019re using Celsius degrees it sets the following characteristic and descriptor:<\/p>\n\n\n\n Otherwise, it sets the Fahrenheit characteristic:<\/p>\n\n\n\n After that, it sets the humidity characteristic:<\/p>\n\n\n\n Finally, you start the service, and the server starts the advertising so other devices can find it.<\/p>\n\n\n\n The loop()<\/span> function is fairly straightforward. You constantly check if the device is connected to a client or not. If it\u2019s connected, and the timerDelay<\/span> has passed, it reads the current temperature and humidity.<\/p>\n\n\n\n If you\u2019re using temperature in Celsius it runs the following code section. First, it converts the temperature to a char variable (temperatureCTemp<\/span> variable). We must convert the temperature to a char variable type to use it in the setValue()<\/span> function.<\/p>\n\n\n\n Then, it sets the bmeTemperatureCelsiusCharacteristic<\/span> value to the new temperature value (temperatureCTemp<\/span>) using the setValue()<\/span> function. After settings the new value, we can notify the connected client using the notify()<\/span> function.<\/p>\n\n\n\n We follow a similar procedure for the Temperature in Fahrenheit.<\/p>\n\n\n\n Sending the humidity also uses the same process.<\/p>\n\n\n\n Upload the code to your board and then, open the Serial Monitor. It will display a message as shown below.<\/p>\n\n\n\n Then, you can test if the BLE server is working as expected by using a BLE scan application on your smartphone like nRF Connect<\/strong>. This application is available for Android <\/a>and iOS<\/a>.<\/p>\n\n\n\n After installing the application, enable Bluetooth on your smartphone. Open the nRF Connect app and click on the Scan button. It will find all Bluetooth nearby devices, including your BME280_ESP32<\/strong> device (it is the BLE server name you defined on the code).<\/p>\n\n\n\n Connect to your BME280_ESP32 device and then, select the client tab (the interface might be slightly different). You can check that it advertises the service with the UUID we defined in the code, as well as the temperature and humidity characteristics. Notice that those characteristics have the Notify<\/em> property.<\/p>\n\n\n\n Your ESP32 BLE Server is ready!<\/p>\n\n\n\n Go to the next section to create an ESP32 client that connects to the server to get access to the temperature and humidity characteristics and get the readings to display them on an OLED display.<\/p>\n\n\n\n In this section, we’ll create the ESP32 BLE client that will establish a connection with the ESP32 BLE server, and display the readings on an OLED display.<\/p>\n\n\n\n The ESP32 BLE client is connected to an OLED display. The display shows the readings received via Bluetooth.<\/p>\n\n\n\n Wire your OLED display to the ESP32 by following the next schematic diagram. The SCL pin connects to GPIO 22<\/span> and the SDA pin to GPIO 21<\/span>.<\/p>\n\n\n\n You need to install the following libraries to interface with the OLED display:<\/p>\n\n\n\n To install the libraries, go Sketch<\/strong>> Include Library<\/strong> > Manage Libraries<\/strong>, and search for the libraries\u2019 names.<\/p>\n\n\n\n If you’re using VS Code with the PlatformIO extension, copy the following to the platformio.ini<\/span> file to include the libraries.<\/p>\n\n\n\n Copy the BLE client Sketch to your Arduino IDE or to the main.cpp<\/span> file if you’re using VS Code with PlatformIO.<\/p>\n\n\nWhat is Bluetooth Low Energy?<\/h2>\n\n\n\n
BLE Server and Client<\/h3>\n\n\n\n
![\"BLE](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2021\/11\/BLE-Server-Client-Server-Advertising-03.png?resize=750%2C308&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\nGATT<\/h3>\n\n\n\n
![\"GATT](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2021\/11\/GATT-ESP32-BLE-Server-Client-Example.png?resize=750%2C423&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\nUUID<\/h3>\n\n\n\n
55072829-bc9e-4c53-938a-74a6d4c78776<\/strong><\/pre>\n\n\n\n
Project Overview<\/h2>\n\n\n\n
![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2021\/11\/ESP32-BLE-Server-nRF-Connect-App-f.jpg?resize=750%2C422&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\nParts Required<\/h3>\n\n\n\n
![](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2017\/10\/header-200.png?w=1200&quality=100&strip=all&ssl=1\")
<\/a><\/p>\n\n\n\n1) ESP32 BLE Server<\/h2>\n\n\n\n
![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2021\/11\/ESP32-BLE-Server-nRF-Connect-App.jpg?resize=750%2C422&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\nSchematic Diagram<\/h3>\n\n\n\n
![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2020\/10\/ESP32-BME280-Sensor-Temperature-Humidity-Pressure-Wiring-Diagram-Circuit_f.png?resize=675%2C670&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\nInstalling BME280 Libraries<\/h3>\n\n\n\n
Installing Libraries (VS Code + PlatformIO)<\/h4>\n\n\n\n
lib_deps = adafruit\/Adafruit Unified Sensor @ ^1.1.4\n adafruit\/Adafruit BME280 Library @ ^2.1.2 <\/code><\/pre>\n\n\n\nESP32 BLE Server – Code<\/h3>\n\n\n\n
\/*********\r\n Rui Santos\r\n Complete instructions at https:\/\/RandomNerdTutorials.com\/esp32-ble-server-client\/\r\n Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files.\r\n The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.\r\n*********\/\r\n\r\n#include <BLEDevice.h>\r\n#include <BLEServer.h>\r\n#include <BLEUtils.h>\r\n#include <BLE2902.h>\r\n#include <Wire.h>\r\n#include <Adafruit_Sensor.h>\r\n#include <Adafruit_BME280.h>\r\n\r\n\/\/Default Temperature is in Celsius\r\n\/\/Comment the next line for Temperature in Fahrenheit\r\n#define temperatureCelsius\r\n\r\n\/\/BLE server name\r\n#define bleServerName "BME280_ESP32"\r\n\r\nAdafruit_BME280 bme; \/\/ I2C\r\n\r\nfloat temp;\r\nfloat tempF;\r\nfloat hum;\r\n\r\n\/\/ Timer variables\r\nunsigned long lastTime = 0;\r\nunsigned long timerDelay = 30000;\r\n\r\nbool deviceConnected = false;\r\n\r\n\/\/ See the following for generating UUIDs:\r\n\/\/ https:\/\/www.uuidgenerator.net\/\r\n#define SERVICE_UUID "91bad492-b950-4226-aa2b-4ede9fa42f59"\r\n\r\n\/\/ Temperature Characteristic and Descriptor\r\n#ifdef temperatureCelsius\r\n BLECharacteristic bmeTemperatureCelsiusCharacteristics("cba1d466-344c-4be3-ab3f-189f80dd7518", BLECharacteristic::PROPERTY_NOTIFY);\r\n BLEDescriptor bmeTemperatureCelsiusDescriptor(BLEUUID((uint16_t)0x2902));\r\n#else\r\n BLECharacteristic bmeTemperatureFahrenheitCharacteristics("f78ebbff-c8b7-4107-93de-889a6a06d408", BLECharacteristic::PROPERTY_NOTIFY);\r\n BLEDescriptor bmeTemperatureFahrenheitDescriptor(BLEUUID((uint16_t)0x2902));\r\n#endif\r\n\r\n\/\/ Humidity Characteristic and Descriptor\r\nBLECharacteristic bmeHumidityCharacteristics("ca73b3ba-39f6-4ab3-91ae-186dc9577d99", BLECharacteristic::PROPERTY_NOTIFY);\r\nBLEDescriptor bmeHumidityDescriptor(BLEUUID((uint16_t)0x2903));\r\n\r\n\/\/Setup callbacks onConnect and onDisconnect\r\nclass MyServerCallbacks: public BLEServerCallbacks {\r\n void onConnect(BLEServer* pServer) {\r\n deviceConnected = true;\r\n };\r\n void onDisconnect(BLEServer* pServer) {\r\n deviceConnected = false;\r\n }\r\n};\r\n\r\nvoid initBME(){\r\n if (!bme.begin(0x76)) {\r\n Serial.println("Could not find a valid BME280 sensor, check wiring!");\r\n while (1);\r\n }\r\n}\r\n\r\nvoid setup() {\r\n \/\/ Start serial communication \r\n Serial.begin(115200);\r\n\r\n \/\/ Init BME Sensor\r\n initBME();\r\n\r\n \/\/ Create the BLE Device\r\n BLEDevice::init(bleServerName);\r\n\r\n \/\/ Create the BLE Server\r\n BLEServer *pServer = BLEDevice::createServer();\r\n pServer->setCallbacks(new MyServerCallbacks());\r\n\r\n \/\/ Create the BLE Service\r\n BLEService *bmeService = pServer->createService(SERVICE_UUID);\r\n\r\n \/\/ Create BLE Characteristics and Create a BLE Descriptor\r\n \/\/ Temperature\r\n #ifdef temperatureCelsius\r\n bmeService->addCharacteristic(&bmeTemperatureCelsiusCharacteristics);\r\n bmeTemperatureCelsiusDescriptor.setValue("BME temperature Celsius");\r\n bmeTemperatureCelsiusCharacteristics.addDescriptor(&bmeTemperatureCelsiusDescriptor);\r\n #else\r\n bmeService->addCharacteristic(&bmeTemperatureFahrenheitCharacteristics);\r\n bmeTemperatureFahrenheitDescriptor.setValue("BME temperature Fahrenheit");\r\n bmeTemperatureFahrenheitCharacteristics.addDescriptor(&bmeTemperatureFahrenheitDescriptor);\r\n #endif \r\n\r\n \/\/ Humidity\r\n bmeService->addCharacteristic(&bmeHumidityCharacteristics);\r\n bmeHumidityDescriptor.setValue("BME humidity");\r\n bmeHumidityCharacteristics.addDescriptor(new BLE2902());\r\n \r\n \/\/ Start the service\r\n bmeService->start();\r\n\r\n \/\/ Start advertising\r\n BLEAdvertising *pAdvertising = BLEDevice::getAdvertising();\r\n pAdvertising->addServiceUUID(SERVICE_UUID);\r\n pServer->getAdvertising()->start();\r\n Serial.println("Waiting a client connection to notify...");\r\n}\r\n\r\nvoid loop() {\r\n if (deviceConnected) {\r\n if ((millis() - lastTime) > timerDelay) {\r\n \/\/ Read temperature as Celsius (the default)\r\n temp = bme.readTemperature();\r\n \/\/ Fahrenheit\r\n tempF = 1.8*temp +32;\r\n \/\/ Read humidity\r\n hum = bme.readHumidity();\r\n \r\n \/\/Notify temperature reading from BME sensor\r\n #ifdef temperatureCelsius\r\n static char temperatureCTemp[6];\r\n dtostrf(temp, 6, 2, temperatureCTemp);\r\n \/\/Set temperature Characteristic value and notify connected client\r\n bmeTemperatureCelsiusCharacteristics.setValue(temperatureCTemp);\r\n bmeTemperatureCelsiusCharacteristics.notify();\r\n Serial.print("Temperature Celsius: ");\r\n Serial.print(temp);\r\n Serial.print(" \u00baC");\r\n #else\r\n static char temperatureFTemp[6];\r\n dtostrf(tempF, 6, 2, temperatureFTemp);\r\n \/\/Set temperature Characteristic value and notify connected client\r\n bmeTemperatureFahrenheitCharacteristics.setValue(temperatureFTemp);\r\n bmeTemperatureFahrenheitCharacteristics.notify();\r\n Serial.print("Temperature Fahrenheit: ");\r\n Serial.print(tempF);\r\n Serial.print(" \u00baF");\r\n #endif\r\n \r\n \/\/Notify humidity reading from BME\r\n static char humidityTemp[6];\r\n dtostrf(hum, 6, 2, humidityTemp);\r\n \/\/Set humidity Characteristic value and notify connected client\r\n bmeHumidityCharacteristics.setValue(humidityTemp);\r\n bmeHumidityCharacteristics.notify(); \r\n Serial.print(" - Humidity: ");\r\n Serial.print(hum);\r\n Serial.println(" %");\r\n \r\n lastTime = millis();\r\n }\r\n }\r\n}\r\n<\/code><\/pre>\n\tImporting Libraries<\/h4>\n\n\n\n
#include <BLEDevice.h>\n#include <BLEServer.h>\n#include <BLEUtils.h>\n#include <BLE2902.h>\n#include <Wire.h>\n#include <Adafruit_Sensor.h>\n#include <Adafruit_BME280.h><\/code><\/pre>\n\n\n\nChoosing Temperature Unit<\/h4>\n\n\n\n
\/\/Comment the next line for Temperature in Fahrenheit\n#define temperatureCelsius<\/code><\/pre>\n\n\n\nBLE Server Name<\/h4>\n\n\n\n
\/\/BLE server name\n#define bleServerName \"BME280_ESP32\"<\/code><\/pre>\n\n\n\nBME280 Sensor<\/h4>\n\n\n\n
Adafruit_BME280 bme; \/\/ I2C<\/code><\/pre>\n\n\n\nfloat temp;\nfloat tempF;\nfloat hum;<\/code><\/pre>\n\n\n\nOther Variables<\/h4>\n\n\n\n
\/\/ Timer variables\nunsigned long lastTime = 0;\nunsigned long timerDelay = 30000;<\/code><\/pre>\n\n\n\nbool deviceConnected = false;<\/code><\/pre>\n\n\n\nBLE UUIDs<\/h4>\n\n\n\n
\/\/ https:\/\/www.uuidgenerator.net\/\n#define SERVICE_UUID \"91bad492-b950-4226-aa2b-4ede9fa42f59\"\n\n\/\/ Temperature Characteristic and Descriptor\n#ifdef temperatureCelsius\n BLECharacteristic bmeTemperatureCelsiusCharacteristics(\"cba1d466-344c-4be3-ab3f-189f80dd7518\", BLECharacteristic::PROPERTY_NOTIFY);\n BLEDescriptor bmeTemperatureCelsiusDescriptor(BLEUUID((uint16_t)0x2902));\n#else\n BLECharacteristic bmeTemperatureFahrenheitCharacteristics(\"f78ebbff-c8b7-4107-93de-889a6a06d408\", BLECharacteristic::PROPERTY_NOTIFY);\n BLEDescriptor bmeTemperatureFahrenheitDescriptor(BLEUUID((uint16_t)0x2901));\n#endif\n\n\/\/ Humidity Characteristic and Descriptor\nBLECharacteristic bmeHumidityCharacteristics(\"ca73b3ba-39f6-4ab3-91ae-186dc9577d99\", BLECharacteristic::PROPERTY_NOTIFY);\nBLEDescriptor bmeHumidityDescriptor(BLEUUID((uint16_t)0x2903));<\/code><\/pre>\n\n\n\nsetup()<\/h4>\n\n\n\n
\/\/ Start serial communication \nSerial.begin(115200);\n\n\/\/ Init BME Sensor\ninitBME();<\/code><\/pre>\n\n\n\n\/\/ Create the BLE Device\nBLEDevice::init(bleServerName);<\/code><\/pre>\n\n\n\n\/\/ Create the BLE Server\nBLEServer *pServer = BLEDevice::createServer();\npServer->setCallbacks(new MyServerCallbacks());<\/code><\/pre>\n\n\n\n\/\/Setup callbacks onConnect and onDisconnect\nclass MyServerCallbacks: public BLEServerCallbacks {\n void onConnect(BLEServer* pServer) {\n deviceConnected = true;\n };\n void onDisconnect(BLEServer* pServer) {\n deviceConnected = false;\n }\n};<\/code><\/pre>\n\n\n\nBLEService *bmeService = pServer->createService(SERVICE_UUID);<\/code><\/pre>\n\n\n\n#ifdef temperatureCelsius\n bmeService->addCharacteristic(&bmeTemperatureCelsiusCharacteristics);\n bmeTemperatureCelsiusDescriptor.setValue(\"BME temperature Celsius\");\n bmeTemperatureCelsiusCharacteristics.addDescriptor(new BLE2902());<\/code><\/pre>\n\n\n\n#else\n bmeService->addCharacteristic(&dhtTemperatureFahrenheitCharacteristics);\n bmeTemperatureFahrenheitDescriptor.setValue(\"BME temperature Fahrenheit\");\n bmeTemperatureFahrenheitCharacteristics.addDescriptor(new BLE2902());\n#endif <\/code><\/pre>\n\n\n\n\/\/ Humidity\nbmeService->addCharacteristic(&bmeHumidityCharacteristics);\nbmeHumidityDescriptor.setValue(\"BME humidity\");\nbmeHumidityCharacteristics.addDescriptor(new BLE2902());<\/code><\/pre>\n\n\n\n\/\/ Start the service\nbmeService->start();\n\n\/\/ Start advertising\nBLEAdvertising *pAdvertising = BLEDevice::getAdvertising();\npAdvertising->addServiceUUID(SERVICE_UUID);\npServer->getAdvertising()->start();\nSerial.println(\"Waiting a client connection to notify...\");<\/code><\/pre>\n\n\n\nloop()<\/h4>\n\n\n\n
if (deviceConnected) {\n if ((millis() - lastTime) > timerDelay) {\n \/\/ Read temperature as Celsius (the default)\n temp = bme.readTemperature();\n \/\/ Fahrenheit\n tempF = temp*1.8 +32;\n \/\/ Read humidity\n hum = bme.readHumidity();<\/code><\/pre>\n\n\n\nstatic char temperatureCTemp[6];\ndtostrf(temp, 6, 2, temperatureCTemp);<\/code><\/pre>\n\n\n\n\/\/Set temperature Characteristic value and notify connected client\nbmeTemperatureCelsiusCharacteristics.setValue(temperatureCTemp);\nbmeTemperatureCelsiusCharacteristics.notify();<\/code><\/pre>\n\n\n\n#else\n static char temperatureFTemp[6];\n dtostrf(f, 6, 2, temperatureFTemp);\n \/\/Set temperature Characteristic value and notify connected client\n bmeTemperatureFahrenheitCharacteristics.setValue(tempF);\n bmeTemperatureFahrenheitCharacteristics.notify();\n Serial.print(\"Temperature Fahrenheit: \");\n Serial.print(tempF);\n Serial.print(\" *F\");\n#endif<\/code><\/pre>\n\n\n\n\/\/Notify humidity reading from DHT\nstatic char humidityTemp[6];\ndtostrf(hum, 6, 2, humidityTemp);\n\/\/Set humidity Characteristic value and notify connected client\nbmeHumidityCharacteristics.setValue(humidityTemp);\nbmeHumidityCharacteristics.notify(); \nSerial.print(\" - Humidity: \");\nSerial.print(hum);\nSerial.println(\" %\");<\/code><\/pre>\n\n\n\nTesting the ESP32 BLE Server<\/h3>\n\n\n\n
![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2021\/11\/ESP32-BLE-Server-Started-Serial-Monitor.png?resize=632%2C411&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\n![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2021\/11\/Scan-ESP32-BLE-Device-nRF-Connect-App.png?resize=450%2C390&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\n![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2021\/11\/ESP32-BLE-Server-Characteristics-nRF-Connect.png?resize=450%2C974&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\n
\n\n\n\n2) ESP32 BLE Client<\/h2>\n\n\n\n
Schematic<\/h3>\n\n\n\n
![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2019\/05\/ESP32_OLED.png?resize=873%2C685&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n\nInstalling the SSD1306, GFX and BusIO Libraries<\/h3>\n\n\n\n
Installing Libraries (VS Code + PlatformIO)<\/h4>\n\n\n\n
lib_deps = \n\tadafruit\/Adafruit GFX Library@^1.10.12\n\tadafruit\/Adafruit SSD1306@^2.4.6\n<\/code><\/pre>\n\n\n\nESP32 BLE Client – Code<\/h3>\n\n\n\n
\/*********\r\n Rui Santos\r\n Complete instructions at https:\/\/RandomNerdTutorials.com\/esp32-ble-server-client\/\r\n Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files.\r\n The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.\r\n*********\/\r\n\r\n#include "BLEDevice.h"\r\n#include <Wire.h>\r\n#include <Adafruit_SSD1306.h>\r\n#include <Adafruit_GFX.h>\r\n\r\n\/\/Default Temperature is in Celsius\r\n\/\/Comment the next line for Temperature in Fahrenheit\r\n#define temperatureCelsius\r\n\r\n\/\/BLE Server name (the other ESP32 name running the server sketch)\r\n#define bleServerName "BME280_ESP32"\r\n\r\n\/* UUID's of the service, characteristic that we want to read*\/\r\n\/\/ BLE Service\r\nstatic BLEUUID bmeServiceUUID("91bad492-b950-4226-aa2b-4ede9fa42f59");\r\n\r\n\/\/ BLE Characteristics\r\n#ifdef temperatureCelsius\r\n \/\/Temperature Celsius Characteristic\r\n static BLEUUID temperatureCharacteristicUUID("cba1d466-344c-4be3-ab3f-189f80dd7518");\r\n#else\r\n \/\/Temperature Fahrenheit Characteristic\r\n static BLEUUID temperatureCharacteristicUUID("f78ebbff-c8b7-4107-93de-889a6a06d408");\r\n#endif\r\n\r\n\/\/ Humidity Characteristic\r\nstatic BLEUUID humidityCharacteristicUUID("ca73b3ba-39f6-4ab3-91ae-186dc9577d99");\r\n\r\n\/\/Flags stating if should begin connecting and if the connection is up\r\nstatic boolean doConnect = false;\r\nstatic boolean connected = false;\r\n\r\n\/\/Address of the peripheral device. Address will be found during scanning...\r\nstatic BLEAddress *pServerAddress;\r\n \r\n\/\/Characteristicd that we want to read\r\nstatic BLERemoteCharacteristic* temperatureCharacteristic;\r\nstatic BLERemoteCharacteristic* humidityCharacteristic;\r\n\r\n\/\/Activate notify\r\nconst uint8_t notificationOn[] = {0x1, 0x0};\r\nconst uint8_t notificationOff[] = {0x0, 0x0};\r\n\r\n#define SCREEN_WIDTH 128 \/\/ OLED display width, in pixels\r\n#define SCREEN_HEIGHT 64 \/\/ OLED display height, in pixels\r\n\r\n\/\/Declaration for an SSD1306 display connected to I2C (SDA, SCL pins)\r\nAdafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);\r\n\r\n\/\/Variables to store temperature and humidity\r\nchar* temperatureChar;\r\nchar* humidityChar;\r\n\r\n\/\/Flags to check whether new temperature and humidity readings are available\r\nboolean newTemperature = false;\r\nboolean newHumidity = false;\r\n\r\n\/\/Connect to the BLE Server that has the name, Service, and Characteristics\r\nbool connectToServer(BLEAddress pAddress) {\r\n BLEClient* pClient = BLEDevice::createClient();\r\n \r\n \/\/ Connect to the remove BLE Server.\r\n pClient->connect(pAddress);\r\n Serial.println(" - Connected to server");\r\n \r\n \/\/ Obtain a reference to the service we are after in the remote BLE server.\r\n BLERemoteService* pRemoteService = pClient->getService(bmeServiceUUID);\r\n if (pRemoteService == nullptr) {\r\n Serial.print("Failed to find our service UUID: ");\r\n Serial.println(bmeServiceUUID.toString().c_str());\r\n return (false);\r\n }\r\n \r\n \/\/ Obtain a reference to the characteristics in the service of the remote BLE server.\r\n temperatureCharacteristic = pRemoteService->getCharacteristic(temperatureCharacteristicUUID);\r\n humidityCharacteristic = pRemoteService->getCharacteristic(humidityCharacteristicUUID);\r\n\r\n if (temperatureCharacteristic == nullptr || humidityCharacteristic == nullptr) {\r\n Serial.print("Failed to find our characteristic UUID");\r\n return false;\r\n }\r\n Serial.println(" - Found our characteristics");\r\n \r\n \/\/Assign callback functions for the Characteristics\r\n temperatureCharacteristic->registerForNotify(temperatureNotifyCallback);\r\n humidityCharacteristic->registerForNotify(humidityNotifyCallback);\r\n return true;\r\n}\r\n\r\n\/\/Callback function that gets called, when another device's advertisement has been received\r\nclass MyAdvertisedDeviceCallbacks: public BLEAdvertisedDeviceCallbacks {\r\n void onResult(BLEAdvertisedDevice advertisedDevice) {\r\n if (advertisedDevice.getName() == bleServerName) { \/\/Check if the name of the advertiser matches\r\n advertisedDevice.getScan()->stop(); \/\/Scan can be stopped, we found what we are looking for\r\n pServerAddress = new BLEAddress(advertisedDevice.getAddress()); \/\/Address of advertiser is the one we need\r\n doConnect = true; \/\/Set indicator, stating that we are ready to connect\r\n Serial.println("Device found. Connecting!");\r\n }\r\n }\r\n};\r\n \r\n\/\/When the BLE Server sends a new temperature reading with the notify property\r\nstatic void temperatureNotifyCallback(BLERemoteCharacteristic* pBLERemoteCharacteristic, \r\n uint8_t* pData, size_t length, bool isNotify) {\r\n \/\/store temperature value\r\n temperatureChar = (char*)pData;\r\n newTemperature = true;\r\n}\r\n\r\n\/\/When the BLE Server sends a new humidity reading with the notify property\r\nstatic void humidityNotifyCallback(BLERemoteCharacteristic* pBLERemoteCharacteristic, \r\n uint8_t* pData, size_t length, bool isNotify) {\r\n \/\/store humidity value\r\n humidityChar = (char*)pData;\r\n newHumidity = true;\r\n Serial.print(newHumidity);\r\n}\r\n\r\n\/\/function that prints the latest sensor readings in the OLED display\r\nvoid printReadings(){\r\n \r\n display.clearDisplay(); \r\n \/\/ display temperature\r\n display.setTextSize(1);\r\n display.setCursor(0,0);\r\n display.print("Temperature: ");\r\n display.setTextSize(2);\r\n display.setCursor(0,10);\r\n display.print(temperatureChar);\r\n display.setTextSize(1);\r\n display.cp437(true);\r\n display.write(167);\r\n display.setTextSize(2);\r\n Serial.print("Temperature:");\r\n Serial.print(temperatureChar);\r\n #ifdef temperatureCelsius\r\n \/\/Temperature Celsius\r\n display.print("C");\r\n Serial.print("C");\r\n #else\r\n \/\/Temperature Fahrenheit\r\n display.print("F");\r\n Serial.print("F");\r\n #endif\r\n\r\n \/\/display humidity \r\n display.setTextSize(1);\r\n display.setCursor(0, 35);\r\n display.print("Humidity: ");\r\n display.setTextSize(2);\r\n display.setCursor(0, 45);\r\n display.print(humidityChar);\r\n display.print("%");\r\n display.display();\r\n Serial.print(" Humidity:");\r\n Serial.print(humidityChar); \r\n Serial.println("%");\r\n}\r\n\r\nvoid setup() {\r\n \/\/OLED display setup\r\n \/\/ SSD1306_SWITCHCAPVCC = generate display voltage from 3.3V internally\r\n if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) { \/\/ Address 0x3C for 128x32\r\n Serial.println(F("SSD1306 allocation failed"));\r\n for(;;); \/\/ Don't proceed, loop forever\r\n }\r\n display.clearDisplay();\r\n display.setTextSize(2);\r\n display.setTextColor(WHITE,0);\r\n display.setCursor(0,25);\r\n display.print("BLE Client");\r\n display.display();\r\n \r\n \/\/Start serial communication\r\n Serial.begin(115200);\r\n Serial.println("Starting Arduino BLE Client application...");\r\n\r\n \/\/Init BLE device\r\n BLEDevice::init("");\r\n \r\n \/\/ Retrieve a Scanner and set the callback we want to use to be informed when we\r\n \/\/ have detected a new device. Specify that we want active scanning and start the\r\n \/\/ scan to run for 30 seconds.\r\n BLEScan* pBLEScan = BLEDevice::getScan();\r\n pBLEScan->setAdvertisedDeviceCallbacks(new MyAdvertisedDeviceCallbacks());\r\n pBLEScan->setActiveScan(true);\r\n pBLEScan->start(30);\r\n}\r\n\r\nvoid loop() {\r\n \/\/ If the flag "doConnect" is true then we have scanned for and found the desired\r\n \/\/ BLE Server with which we wish to connect. Now we connect to it. Once we are\r\n \/\/ connected we set the connected flag to be true.\r\n if (doConnect == true) {\r\n if (connectToServer(*pServerAddress)) {\r\n Serial.println("We are now connected to the BLE Server.");\r\n \/\/Activate the Notify property of each Characteristic\r\n temperatureCharacteristic->getDescriptor(BLEUUID((uint16_t)0x2902))->writeValue((uint8_t*)notificationOn, 2, true);\r\n humidityCharacteristic->getDescriptor(BLEUUID((uint16_t)0x2902))->writeValue((uint8_t*)notificationOn, 2, true);\r\n connected = true;\r\n } else {\r\n Serial.println("We have failed to connect to the server; Restart your device to scan for nearby BLE server again.");\r\n }\r\n doConnect = false;\r\n }\r\n \/\/if new temperature readings are available, print in the OLED\r\n if (newTemperature && newHumidity){\r\n newTemperature = false;\r\n newHumidity = false;\r\n printReadings();\r\n }\r\n delay(1000); \/\/ Delay a second between loops.\r\n}\r\n<\/code><\/pre>\n\t
![<\/a><\/p>\n\n\n\nContinue reading to learn how the code works or skip to the Demonstration <\/a>section.<\/p>\n\n\n\nImporting libraries<\/h4>\n\n\n\nYou start by importing the required libraries:<\/p>\n\n\n\n#include \"BLEDevice.h\"\n#include <Wire.h>\n#include <Adafruit_SSD1306.h>\n#include <Adafruit_GFX.h><\/code><\/pre>\n\n\n\nChoosing temperature unit<\/h4>\n\n\n\nBy default the client will receive the temperature in Celsius degrees, if you comment the following line or delete it, it will start receiving the temperature in Fahrenheit degrees.<\/p>\n\n\n\n\/\/Default Temperature is in Celsius\n\/\/Comment the next line for Temperature in Fahrenheit\n#define temperatureCelsius<\/code><\/pre>\n\n\n\nBLE Server Name and UUIDs<\/h4>\n\n\n\nThen, define the BLE server name that we want to connect to and the service and characteristic UUIDs that we want to read. Leave the default BLE server name and UUIDs to match the ones defined in the server sketch.<\/p>\n\n\n\n\/\/BLE Server name (the other ESP32 name running the server sketch)\n#define bleServerName \"BME280_ESP32\"\n\n\/* UUID's of the service, characteristic that we want to read*\/\n\/\/ BLE Service\nstatic BLEUUID bmeServiceUUID(\"91bad492-b950-4226-aa2b-4ede9fa42f59\");\n\n\/\/ BLE Characteristics\n#ifdef temperatureCelsius\n \/\/Temperature Celsius Characteristic\n static BLEUUID temperatureCharacteristicUUID(\"cba1d466-344c-4be3-ab3f-189f80dd7518\");\n#else\n \/\/Temperature Fahrenheit Characteristic\n static BLEUUID temperatureCharacteristicUUID(\"f78ebbff-c8b7-4107-93de-889a6a06d408\");\n#endif\n\n\/\/ Humidity Characteristic\nstatic BLEUUID humidityCharacteristicUUID(\"ca73b3ba-39f6-4ab3-91ae-186dc9577d99\");\n<\/code><\/pre>\n\n\n\nDeclaring variables<\/h4>\n\n\n\nThen, you need to declare some variables that will be used later with Bluetooth to check whether we’re connected to the server or not.<\/p>\n\n\n\n\/\/Flags stating if should begin connecting and if the connection is up\nstatic boolean doConnect = false;\nstatic boolean connected = false;<\/code><\/pre>\n\n\n\nCreate a variable of type BLEAddress<\/span> that refers to the address of the server we want to connect. This address will be found during scanning.<\/p>\n\n\n\n\/\/Address of the peripheral device. Address will be found during scanning...\nstatic BLEAddress *pServerAddress;<\/code><\/pre>\n\n\n\nSet the characteristics we want to read (temperature and humidity).<\/p>\n\n\n\n\/\/Characteristicd that we want to read\nstatic BLERemoteCharacteristic* temperatureCharacteristic;\nstatic BLERemoteCharacteristic* humidityCharacteristic;<\/code><\/pre>\n\n\n\nOLED Display<\/h4>\n\n\n\nYou also need to declare some variables to work with the OLED. Define the OLED width and height:<\/p>\n\n\n\n#define SCREEN_WIDTH 128 \/\/ OLED display width, in pixels\n#define SCREEN_HEIGHT 64 \/\/ OLED display height, in pixels<\/code><\/pre>\n\n\n\nInstantiate the OLED display with the width and height defined earlier.<\/p>\n\n\n\nAdafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire);<\/code><\/pre>\n\n\n\nTemperature and Humidity Variables<\/h4>\n\n\n\nDefine char variables to hold the temperature and humidity values received by the server.<\/p>\n\n\n\n\/\/Variables to store temperature and humidity\nchar* temperatureChar;\nchar* humidityChar;<\/code><\/pre>\n\n\n\n](\"https:\/\/rntlab.com\/wp-content\/uploads\/2018\/03\/activate_notify.jpg\"){kind=link}