1、效果描述：

通過簡單的 Android APP 實現與 ESP32 的雙向藍芽通訊。

2、實現步驟

Step 1：ESP32 硬體支援

1、支援藍芽 4.0 以上協議的安卓手機；

2、支援 Micro USB 的 ESP32 dev board;

Step 2：配置 Arduino IDE 環境

1、下載 Arduino IDE：https://www.arduino.cc/en/Main/Software；

2、安裝 ESP32 支援包：https://github.com/espressif/arduino-esp32/blob/master/docs/arduino-ide/windows.md

根據網站步驟安裝 GIT 工具，並根據提示下載 BLE 支援開發包

在 Arduino 編寫例項：

/*
    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

   Create a BLE server that, once we receive a connection, will send periodic notifications.
   The service advertises itself as: 6E400001-B5A3-F393-E0A9-E50E24DCCA9E
   Has a characteristic of: 6E400002-B5A3-F393-E0A9-E50E24DCCA9E - used for receiving data with "WRITE" 
   Has a characteristic of: 6E400003-B5A3-F393-E0A9-E50E24DCCA9E - used to send data with  "NOTIFY"

   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.

   In this example rxValue is the data received (only accessible inside that function).
   And txValue is the data to be sent, in this example just a byte incremented every second. 
*/
#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h>

BLECharacteristic *pCharacteristic;
bool deviceConnected = false;
float txValue = 0;
const int readPin = 32; // Use GPIO number. See ESP32 board pinouts
const int LED = 2; // Could be different depending on the dev board. I used the DOIT ESP32 dev board.

//std::string rxValue; // Could also make this a global var to access it in loop()

// See the following for generating UUIDs:
// https://www.uuidgenerator.net/

#define SERVICE_UUID           "6E400001-B5A3-F393-E0A9-E50E24DCCA9E" // UART service UUID
#define CHARACTERISTIC_UUID_RX "6E400002-B5A3-F393-E0A9-E50E24DCCA9E"
#define CHARACTERISTIC_UUID_TX "6E400003-B5A3-F393-E0A9-E50E24DCCA9E"

class MyServerCallbacks: public BLEServerCallbacks {
    void onConnect(BLEServer* pServer) {
      deviceConnected = true;
    };

    void onDisconnect(BLEServer* pServer) {
      deviceConnected = false;
    }
};

class MyCallbacks: public BLECharacteristicCallbacks {
    void onWrite(BLECharacteristic *pCharacteristic) {
      std::string rxValue = pCharacteristic->getValue();

      if (rxValue.length() > 0) {
        Serial.println("*********");
        Serial.print("Received Value: ");

        for (int i = 0; i < rxValue.length(); i++) {
          Serial.print(rxValue[i]);
        }

        Serial.println();

        // Do stuff based on the command received from the app
        if (rxValue.find("A") != -1) { 
          Serial.print("Turning ON!");
          digitalWrite(LED, HIGH);
        }
        else if (rxValue.find("B") != -1) {
          Serial.print("Turning OFF!");
          digitalWrite(LED, LOW);
        }

        Serial.println();
        Serial.println("*********");
      }
    }
};

void setup() {
  Serial.begin(115200);

  pinMode(LED, OUTPUT);

  // Create the BLE Device
  BLEDevice::init("ESP32 UART Test"); // Give it a name

  // Create the BLE Server
  BLEServer *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_TX,
                      BLECharacteristic::PROPERTY_NOTIFY
                    );
                      
  pCharacteristic->addDescriptor(new BLE2902());

  BLECharacteristic *pCharacteristic = pService->createCharacteristic(
                                         CHARACTERISTIC_UUID_RX,
                                         BLECharacteristic::PROPERTY_WRITE
                                       );

  pCharacteristic->setCallbacks(new MyCallbacks());

  // Start the service
  pService->start();

  // Start advertising
  pServer->getAdvertising()->start();
  Serial.println("Waiting a client connection to notify...");
}

void loop() {
  if (deviceConnected) {
    // Fabricate some arbitrary junk for now...
    txValue = analogRead(readPin) / 3.456; // This could be an actual sensor reading!

    // Let's convert the value to a char array:
    char txString[8]; // make sure this is big enuffz
    dtostrf(txValue, 1, 2, txString); // float_val, min_width, digits_after_decimal, char_buffer
    
//    pCharacteristic->setValue(&txValue, 1); // To send the integer value
//    pCharacteristic->setValue("Hello!"); // Sending a test message
    pCharacteristic->setValue(txString);
    
    pCharacteristic->notify(); // Send the value to the app!
    Serial.print("*** Sent Value: ");
    Serial.print(txString);
    Serial.println(" ***");

    // You can add the rxValue checks down here instead
    // if you set "rxValue" as a global var at the top!
    // Note you will have to delete "std::string" declaration
    // of "rxValue" in the callback function.
//    if (rxValue.find("A") != -1) { 
//      Serial.println("Turning ON!");
//      digitalWrite(LED, HIGH);
//    }
//    else if (rxValue.find("B") != -1) {
//      Serial.println("Turning OFF!");
//      digitalWrite(LED, LOW);
//    }
  }
  delay(1000);
}
 

Step 3：下載安裝 APP 測試工具

可以在資源欄下載：https://download.csdn.net/download/liwei16611/10526621

3、程式碼解釋

3.1、庫檔案：

#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h>

建立 BLE 裝置：

BLEDevice::init("ESP32 UART Test"); // Give it a name

建立 BLE server：

BLEServer *pServer = BLEDevice::createServer();
pServer->setCallbacks(new MyServerCallbacks());
 

建立 BLE service：

BLEService *pService = pServer->createService(SERVICE_UUID);

新增 characteristics：

pCharacteristic = pService->createCharacteristic(
                    CHARACTERISTIC_UUID_TX,
                    BLECharacteristic::PROPERTY_NOTIFY
                  );
pCharacteristic->addDescriptor(new BLE2902());
BLECharacteristic *pCharacteristic = pService->createCharacteristic(
                                       CHARACTERISTIC_UUID_RX,
                                       BLECharacteristic::PROPERTY_WRITE
                                     );
pCharacteristic->setCallbacks(new MyCallbacks());

啟動廣播：

pServer->getAdvertising()->start();
Serial.println("Waiting a client connection to notify...");

3.2、定義 service 和 characteristic UUID：TX | RX

#define SERVICE_UUID           "6E400001-B5A3-F393-E0A9-E50E24DCCA9E" // UART service UUID

#define CHARACTERISTIC_UUID_RX "6E400002-B5A3-F393-E0A9-E50E24DCCA9E"
#define CHARACTERISTIC_UUID_TX "6E400003-B5A3-F393-E0A9-E50E24DCCA9E"

3.3、藍芽連接回調函式

class MyServerCallbacks: public BLEServerCallbacks {<br>    void onConnect(BLEServer* pServer) {
      deviceConnected = true;
    };
    void onDisconnect(BLEServer* pServer) {
      deviceConnected = false;
    }
};

3.4、資料接收回調函式

class MyCallbacks: public BLECharacteristicCallbacks {<br>    void onWrite(BLECharacteristic *pCharacteristic) {
      std::string rxValue = pCharacteristic->getValue();</p><p>      if (rxValue.length() > 0) {
        Serial.println("*********");
        Serial.print("Received Value: ");</p><p>        for (int i = 0; i < rxValue.length(); i++) {
          Serial.print(rxValue[i]);
        }</p><p>        Serial.println();</p><p>        // Do stuff based on the command received from the app
        if (rxValue.find("A") != -1) { 
          Serial.print("Turning ON!");
          digitalWrite(LED, HIGH);
        }
        else if (rxValue.find("B") != -1) {
          Serial.print("Turning OFF!");
          digitalWrite(LED, LOW);
        }</p><p>        Serial.println();
        Serial.println("*********");
      }
    }
};

refer：

http://www.instructables.com/id/ESP32-BLE-Android-App-Arduino-IDE-AWESOME/