ESP32: How to use Bluetooth Low Energy (BLE) Server Communication

				
					#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h> // For the standard BLE descriptors

// The service UUID is a unique identifier for the type of service your device offers.
// You can use a generic one or generate your own.
#define SERVICE_UUID        "4E22A700-AA7C-4B79-9945-8C7957731778"
// Characteristic UUID (for a specific data point/functionality within the service)
#define CHARACTERISTIC_UUID "A64BBF3B-F4E7-474F-A186-F98CC5A49603"

BLEServer *pServer = NULL;
BLECharacteristic *pCharacteristic = NULL;
bool deviceConnected = false;

// Callback class to monitor connection events
class MyServerCallbacks: public BLEServerCallbacks {
    void onConnect(BLEServer* pServer) {
      deviceConnected = true;
      Serial.println("Client connected!");
    };

    void onDisconnect(BLEServer* pServer) {
      deviceConnected = false;
      Serial.println("Client disconnected! Restarting advertising...");
      // Restart advertising so it can be re-discovered
      pServer->startAdvertising();
    }
};

void setup() {
  Serial.begin(115200);
  Serial.println("Starting BLE Server...");

  // 1. Initialize the BLE Device (Name is what your phone will see!)
  BLEDevice::init("MyCoolESP32_BLE_Device");

  // 2. Create the BLE Server
  pServer = BLEDevice::createServer();
  pServer->setCallbacks(new MyServerCallbacks());

  // 3. Create a BLE Service
  BLEService *pService = pServer->createService(SERVICE_UUID);

  // 4. Create a BLE Characteristic within the Service
  pCharacteristic = pService->createCharacteristic(
                      CHARACTERISTIC_UUID,
                      BLECharacteristic::PROPERTY_READ |
                      BLECharacteristic::PROPERTY_WRITE
                    );

  // Set an initial value for the characteristic (e.g., a simple status)
  pCharacteristic->setValue("Hello World");

  // 5. Start the Service
  pService->start();

  // 6. Start Advertising (This is the key step for visibility!)
  BLEAdvertising *pAdvertising = BLEDevice::getAdvertising();
  pAdvertising->addServiceUUID(SERVICE_UUID);
  pAdvertising->setScanResponse(true);
  pAdvertising->setMinPreferred(0x06);  // Set minimum advertising interval
  pAdvertising->setMinPreferred(0x12);  // Set maximum advertising interval
 
  BLEDevice::startAdvertising();
  Serial.println("Characteristic defined! Now advertising...");
}

void loop() {
  // Put your main loop code here.
  // You might want to update the characteristic value here if needed.
  if (deviceConnected) {
    // Example: send a '1' to the characteristic every second while connected
    // pCharacteristic->setValue("1");
    // pCharacteristic->notify();
  }
  delay(1000);
}