examples/BLE_server_multiconnect/BLE_server_multiconnect.ino


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/*
    Video: https://www.youtube.com/watch?v=oCMOYS71NIU
    Based on Neil Kolban example for IDF: https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/tests/BLE%20Tests/SampleNotify.cpp
    Ported to Arduino ESP32 by Evandro Copercini
    updated by chegewara
 
   Create a BLE server that, once we receive a connection, will send periodic notifications.
   The service advertises itself as: 4fafc201-1fb5-459e-8fcc-c5c9c331914b
   And has a characteristic of: beb5483e-36e1-4688-b7f5-ea07361b26a8
 
   The design of creating the BLE server is:
   1. Create a BLE Server
   2. Create a BLE Service
   3. Create a BLE Characteristic on the Service
   4. Create a BLE Descriptor on the characteristic
   5. Start the service.
   6. Start advertising.
 
   A connect hander associated with the server starts a background task that performs notification
   every couple of seconds.
*/
#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h>
 
BLEServer* pServer = NULL;
BLECharacteristic* pCharacteristic = NULL;
bool deviceConnected = false;
bool oldDeviceConnected = false;
uint32_t value = 0;
 
// See the following for generating UUIDs: 
// https://www.uuidgenerator.net/ 
 
#define SERVICE_UUID        "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"
 
 
class MyServerCallbacks: public BLEServerCallbacks {
    void onConnect(BLEServer* pServer) {
      deviceConnected = true;
      BLEDevice::startAdvertising();
    };
 
    void onDisconnect(BLEServer* pServer) {
      deviceConnected = false;
    }
};
 
 
 
void setup() {
  Serial.begin(115200);
 
  // Create the BLE Device 
  BLEDevice::init("ESP32");
 
  // Create the BLE Server 
  pServer = BLEDevice::createServer();
  pServer->setCallbacks(new MyServerCallbacks());
 
  // Create the BLE Service 
  BLEService *pService = pServer->createService(SERVICE_UUID);
 
  // Create a BLE Characteristic 
  pCharacteristic = pService->createCharacteristic(
                      CHARACTERISTIC_UUID,
                      BLECharacteristic::PROPERTY_READ   |
                      BLECharacteristic::PROPERTY_WRITE  |
                      BLECharacteristic::PROPERTY_NOTIFY |
                      BLECharacteristic::PROPERTY_INDICATE
                    );
 
  // https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.descriptor.gatt.client_characteristic_configuration.xml 
  // Create a BLE Descriptor 
  pCharacteristic->addDescriptor(new BLE2902());
 
  // Start the service 
  pService->start();
 
  // Start advertising 
  BLEAdvertising *pAdvertising = BLEDevice::getAdvertising();
  pAdvertising->addServiceUUID(SERVICE_UUID);
  pAdvertising->setScanResponse(false);
  pAdvertising->setMinPreferred(0x0);  // set value to 0x00 to not advertise this parameter 
  BLEDevice::startAdvertising();
  Serial.println("Waiting a client connection to notify...");
}
 
void loop() {
    // notify changed value 
    if (deviceConnected) {
        pCharacteristic->setValue((uint8_t*)&value, 4);
        pCharacteristic->notify();
        value++;
        delay(10); // bluetooth stack will go into congestion, if too many packets are sent, in 6 hours test i was able to go as low as 3ms 
    }
    // disconnecting 
    if (!deviceConnected && oldDeviceConnected) {
        delay(500); // give the bluetooth stack the chance to get things ready 
        pServer->startAdvertising(); // restart advertising 
        Serial.println("start advertising");
        oldDeviceConnected = deviceConnected;
    }
    // connecting 
    if (deviceConnected && !oldDeviceConnected) {
        // do stuff here on connecting 
        oldDeviceConnected = deviceConnected;
    }
}