Implement ESP32 BLE GATT Server for Real-Time Temperature and Humidity Data

Introduction

This tutorial will guide you through implementing a BLE (Bluetooth Low Energy) GATT (Generic Attribute Profile) server on an ESP32 to transmit real-time temperature and humidity data from a sensor. By the end of this tutorial, you will have a working ESP32 setup that can send sensor data to a BLE client, such as a smartphone or tablet.

Prerequisites

• Basic understanding of Arduino programming and the ESP32 platform.
• ESP32 development board.
• Temperature and humidity sensor (e.g., DHT11 or DHT22).
• Arduino IDE installed with ESP32 board support.
• Bluetooth-enabled device (smartphone/tablet) for testing.

Parts/Tools

• ESP32 Development Board
• DHT11 or DHT22 Sensor
• Jumper wires
• USB cable for programming the ESP32
• Arduino IDE with ESP32 libraries

Steps

1. Set up the hardware:
   • Connect the DHT sensor to the ESP32.
   • For DHT11 or DHT22, typically, connect:
   • VCC to 3.3V
   • GND to GND
   • Data pin to a digital pin (e.g., GPIO 4)
2. Install necessary libraries:
   • Open Arduino IDE.
   • Go to Sketch > Include Library > Manage Libraries…
   • Search for and install DHT sensor library and ESP32 BLE library.
3. Write the code:
   • Create a new sketch in Arduino IDE and include the necessary libraries:

   #include <DHT.h>
   #include <BLEDevice.h>
   #include <BLEUtils.h>
   #include <BLEServer.h>

   • Define the DHT sensor and BLE server parameters:

   #define DHTPIN 4 // Data pin for the sensor
   #define DHTTYPE DHT22 // DHT 22 (AM2302)
   
   DHT dht(DHTPIN, DHTTYPE);
   BLEServer *pServer = NULL;

   • Initialize BLE server and characteristics:

   void setup() {
       Serial.begin(115200);
       dht.begin();
   
       BLEDevice::init("ESP32_Temp_Hum");
       pServer = BLEDevice::createServer();
       BLECharacteristic *pCharacteristic = pServer->createCharacteristic(
           BLEUUID((uint16_t)0xFF01),
           BLECharacteristic::PROPERTY_READ |
           BLECharacteristic::PROPERTY_NOTIFY
       );
       pCharacteristic->addDescriptor(new BLE2902());
   }

   • Set up a loop to read sensor data and notify clients:

   void loop() {
       float h = dht.readHumidity();
       float t = dht.readTemperature();
       
       if (isnan(h) || isnan(t)) {
           Serial.println("Failed to read from DHT sensor!");
           return;
       }
   
       String data = "Temp: " + String(t) + " °C, Hum: " + String(h) + " %";
       pCharacteristic->setValue(data.c_str());
       pCharacteristic->notify();
       Serial.println(data);
       delay(2000); // Send data every 2 seconds
   }

4. Upload the code:
   • Select the correct board and port in Arduino IDE.
   • Click on the upload button to compile and upload the code to your ESP32.
5. Test the BLE server:
   • Use a BLE scanner app (like nRF Connect) on your smartphone or tablet.
   • Scan for devices and connect to "ESP32_Temp_Hum".
   • Read the notifications to see real-time temperature and humidity data.

Troubleshooting

• ESP32 not showing up: Ensure the ESP32 is powered and properly connected to your computer. Verify the correct COM port is selected in Arduino IDE.
• Sensor not reading: Check the wiring of the sensor. Ensure the data pin is connected to the correct GPIO.
• No notifications on the app: Ensure you have the correct UUID and that you are subscribed to notifications in your BLE client app.

Conclusion

Congratulations! You have successfully implemented a BLE GATT server on an ESP32 to transmit real-time temperature and humidity data. You can now explore further by adding additional sensors or functionalities to your project. Happy coding!