How to Set Up ESP32 BLE GATT Server for DHT22 Data Transmission Every 5 Seconds

Implementing ESP32 BLE GATT Server to Transmit DHT22 Temperature and Humidity Data Every 5 Seconds

This tutorial will guide you through the process of implementing a Bluetooth Low Energy (BLE) GATT server on an ESP32 device to transmit temperature and humidity data from a DHT22 sensor every 5 seconds. By the end of this tutorial, you will have a working BLE server that can be accessed by BLE clients, such as smartphones or computers.

Prerequisites

• Basic understanding of Arduino programming
• ESP32 development board
• DHT22 temperature and humidity sensor
• Arduino IDE installed on your computer
• ESP32 board library installed in Arduino IDE
• BLE scanner app on your smartphone (optional, for testing)

Parts/Tools

• ESP32 Development Board
• DHT22 Sensor
• Breadboard and jumper wires
• Arduino IDE

Steps

1. Wiring the DHT22 Sensor
   • 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 pin 23 on the ESP32.
2. Setting Up Arduino IDE
   • Open Arduino IDE.
   • Go to File > Preferences and add the following URL to Additional Board Manager URLs: https://dl.espressif.com/dl/package_esp32_index.json.
   • Go to Tools > Board > Board Manager, search for “ESP32”, and install it.
3. Install Required Libraries
   • Go to Sketch > Include Library > Manage Libraries.
   • Search for “DHT sensor library” by Adafruit and install it.
   • Search for “Adafruit Unified Sensor” and install it as well.
4. Create the Arduino Sketch

   
   #include <BLEDevice.h>
   #include <BLEServer.h>
   #include <DHT.h>
   
   #define DHTPIN 23
   #define DHTTYPE DHT22
   #define SERVICE_UUID "12345678-1234-5678-1234-56789abcdef0"
   #define CHARACTERISTIC_UUID "12345678-1234-5678-1234-56789abcdef1"
   
   DHT dht(DHTPIN, DHTTYPE);
   BLEServer* pServer = NULL;
   BLECharacteristic* pCharacteristic = NULL;
   
   void setup() {
       Serial.begin(115200);
       dht.begin();
   
       BLEDevice::init("ESP32_DHT22");
       pServer = BLEDevice::createServer();
       pCharacteristic = pServer->createCharacteristic(
           CHARACTERISTIC_UUID,
           BLECharacteristic::PROPERTY_NOTIFY
       );
       pServer->getAdvertising()->start();
   }
   
   void loop() {
       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(5000);
   }
           

5. Upload the Sketch
   • Select your ESP32 board from Tools > Board.
   • Select the correct COM port from Tools > Port.
   • Click the upload button in the Arduino IDE.
6. Testing the BLE GATT Server
   • Open a BLE scanner app on your smartphone.
   • Scan for devices and look for “ESP32_DHT22”.
   • Connect to the device and subscribe to notifications for the characteristic.
   • You should start receiving temperature and humidity data every 5 seconds.

Troubleshooting

• Device Not Found: Ensure that your ESP32 is powered and running the correct code. Check the wiring connections of the DHT22 sensor.
• No Data Received: Check if the BLE characteristic UUIDs are correctly specified. Make sure you are subscribed to notifications in your BLE app.
• Inaccurate Readings: Verify that the DHT22 sensor is functioning properly and is not exposed to direct sunlight or drafts.

Conclusion

In this tutorial, you successfully implemented a BLE GATT server on an ESP32 to transmit temperature and humidity data from a DHT22 sensor. You can now access this data from any BLE-capable device, allowing for easy monitoring of environmental conditions. Feel free to expand on this project by adding more sensors or implementing a data logging feature.