How to Set Up a BLE GATT Server on ESP32 for DHT22 Readings

Implementing BLE GATT Server on ESP32 to Transmit DHT22 Temperature and Humidity Readings to a Mobile App

In this tutorial, we will guide you through the process of implementing a BLE GATT server on an ESP32 to transmit temperature and humidity readings from a DHT22 sensor to a mobile app. This is useful for creating a smart home application or monitoring environmental conditions remotely.

Prerequisites

• Basic knowledge of Arduino programming.
• ESP32 development board.
• DHT22 temperature and humidity sensor.
• Arduino IDE installed.
• ESP32 board package installed in Arduino IDE.
• BLE Scanner app installed on your mobile device.

Parts/Tools

• ESP32 Development Board
• DHT22 Sensor
• Jumper wires
• Breadboard (optional)

Steps

1. Wiring the DHT22 Sensor to ESP32
   • Connect the VCC pin of the DHT22 to the 3.3V pin on the ESP32.
   • Connect the GND pin of the DHT22 to a GND pin on the ESP32.
   • Connect the DATA pin of the DHT22 to GPIO 23 on the ESP32.
2. Install Required Libraries

   Open the Arduino IDE and install the following libraries:

   • DHT sensor library by Adafruit
   • ESP32 BLE library
3. Writing the Arduino Code

   Open a new sketch in Arduino IDE and add the following code:

   
   #include <DHT.h>
   #include <BLEDevice.h>
   #include <BLEUtils.h>
   #include <BLEServer.h>
   
   #define DHTPIN 23
   #define DHTTYPE DHT22
   
   DHT dht(DHTPIN, DHTTYPE);
   BLEServer *pServer = NULL;
   BLECharacteristic *pCharacteristic = NULL;
   bool deviceConnected = false;
   
   void setup() {
       Serial.begin(115200);
       dht.begin();
   
       BLEDevice::init("ESP32_DHT22");
       pServer = BLEDevice::createServer();
       pServer->setCallbacks(new MyServerCallbacks());
       pCharacteristic = pServer->createCharacteristic(
           BLEUUID((uint16_t)0xFF01),
           BLECharacteristic::PROPERTY_NOTIFY
       );
       pServer->startAdvertising();
   }
   
   void loop() {
       if (deviceConnected) {
           float h = dht.readHumidity();
           float t = dht.readTemperature();
           String data = "Humidity: " + String(h) + "%, Temperature: " + String(t) + "°C";
           pCharacteristic->setValue(data.c_str());
           pCharacteristic->notify();
           delay(2000);
       }
   }
   
   class MyServerCallbacks : public BLEServerCallbacks {
       void onConnect(BLEServer* pServer) {
           deviceConnected = true;
       }
   
       void onDisconnect(BLEServer* pServer) {
           deviceConnected = false;
       }
   }
           

4. Upload the Code
   • Select the correct board and COM port in the Arduino IDE.
   • Upload the sketch to your ESP32 board.
5. Testing the BLE Connection
   • Open the BLE Scanner app on your mobile device.
   • Search for the device named “ESP32_DHT22”.
   • Connect to the device and subscribe to notifications.
   • You should start receiving temperature and humidity readings every 2 seconds.

Troubleshooting

• ESP32 Not Connecting: Ensure that the ESP32 is powered and properly connected to your computer. Check the selected COM port in the Arduino IDE.
• Incorrect Readings: Verify that the DHT22 sensor is wired correctly and functioning. You can test it with a simple DHT22 reading sketch.
• BLE Notifications Not Working: Ensure that notifications are enabled in your BLE Scanner app. Try disconnecting and reconnecting to the ESP32.

Conclusion

Congratulations! You have successfully implemented a BLE GATT server on the ESP32 that transmits DHT22 temperature and humidity readings to a mobile app. This project can be expanded further by integrating more sensors or creating a more complex user interface on your mobile app. Happy coding!