写一个arduino ESP32 蓝牙从机程序

### 回答1：
非常感谢您的提问，以下是一个简单的 Arduino ESP32 蓝牙从机程序：

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

BLECharacteristic *pCharacteristic;
bool deviceConnected = false;
bool oldDeviceConnected = false;
uint8_t txValue = 0;

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

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

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

BLEDevice::init("MyESP32");
BLEServer *pServer = BLEDevice::createServer();
pServer->setCallbacks(new MyServerCallbacks());

BLEService *pService = pServer->createService(BLEUUID((uint16_t)0x180F));

pCharacteristic = pService->createCharacteristic(
BLEUUID((uint16_t)0x2A19),
BLECharacteristic::PROPERTY_READ |
BLECharacteristic::PROPERTY_NOTIFY |
BLECharacteristic::PROPERTY_INDICATE
);

pCharacteristic->addDescriptor(new BLE2902());

pService->start();

BLEAdvertising *pAdvertising = pServer->getAdvertising();
pAdvertising->addServiceUUID(BLEUUID((uint16_t)0x180F));
pAdvertising->setScanResponse(true);
pAdvertising->setMinPreferred(0x06);
pAdvertising->setMaxPreferred(0x12);
BLEDevice::startAdvertising();
Serial.println("Waiting for a client connection to notify...");
}

void loop() {
if (deviceConnected) {
pCharacteristic->setValue(&txValue, 1);
pCharacteristic->notify();
txValue++;
delay(10);
}

if (!deviceConnected && oldDeviceConnected) {
delay(500);
pServer->startAdvertising();
Serial.println("start advertising");
oldDeviceConnected = deviceConnected;
}

if (deviceConnected && !oldDeviceConnected) {
oldDeviceConnected = deviceConnected;
}
}

希望这个程序能够帮助到您！

### 回答2：
如下是一个简单的Arduino ESP32蓝牙从机程序示例：

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

BLECharacteristic* pCharacteristic;
bool deviceConnected = false;
bool oldDeviceConnected = false;

#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;
    };

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

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

  BLEDevice::init("MyESP32");
  BLEServer *pServer = BLEDevice::createServer();
  pServer->setCallbacks(new MyServerCallbacks());

  BLEService *pService = pServer->createService(SERVICE_UUID);
  pCharacteristic = pService->createCharacteristic(
                      CHARACTERISTIC_UUID,
                      BLECharacteristic::PROPERTY_READ |
                      BLECharacteristic::PROPERTY_WRITE
                    );

  pService->start();
  BLEAdvertising *pAdvertising = pServer->getAdvertising();
  pAdvertising->start();
}

void loop() {
  if (deviceConnected) {
    pCharacteristic->setValue("Hello from ESP32");
    pCharacteristic->notify();
    delay(1000);
  }

  if (!deviceConnected && oldDeviceConnected) {
    delay(500);
    BLEDevice::startAdvertising();
    oldDeviceConnected = deviceConnected;
  }

  if (deviceConnected && !oldDeviceConnected) {
    oldDeviceConnected = deviceConnected;
  }
}

这是一个简单的蓝牙从机程序，在ESP32设备上创建了一个蓝牙广播器和服务。当有一个蓝牙主设备连接时，从机会发送"Hello from ESP32"的消息，并进行周期性通知。在没有连接时，从机会继续以间隔500ms重新开始广播。这段程序使用了ESP32的BLE库，需要事先安装该库。

### 回答3：
Arduino ESP32 是一款功能强大的开发板，它带有蓝牙功能，可以作为蓝牙从机进行通信。下面是一个简单的蓝牙从机程序，使用Arduino IDE编写：

1. 引入必要的库文件

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

2. 定义蓝牙服务和特征

#define SERVICE_UUID        "0000180D-0000-1000-8000-00805F9B34FB" // 通用蓝牙服务UUID
#define CHARACTERISTIC_UUID "00002A37-0000-1000-8000-00805F9B34FB" // 通用特征UUID

BLEServer* pServer = nullptr;
BLECharacteristic* pCharacteristic = nullptr;

3. 初始化蓝牙从机

void setup() {
  // 初始化蓝牙设备
  BLEDevice::init("ESP32");

  // 创建蓝牙服务
  pServer = BLEDevice::createServer();
  pServer->setCallbacks(new MyServerCallbacks());

  // 创建蓝牙特征
  BLEService *pService = pServer->createService(SERVICE_UUID);
  pCharacteristic = pService->createCharacteristic(
                      CHARACTERISTIC_UUID,
                      BLECharacteristic::PROPERTY_READ |
                      BLECharacteristic::PROPERTY_WRITE
                    );

  // 开启蓝牙服务
  pService->start();
  
  // 启动广播
  BLEAdvertising *pAdvertising = pServer->getAdvertising();
  pAdvertising->start();
}

4. 处理蓝牙数据

class MyServerCallbacks: public BLEServerCallbacks {
  void onWrite(BLECharacteristic *pCharacteristic) {
    std::string value = pCharacteristic->getValue();

    if (value.length() > 0) {
      // 接收到蓝牙数据
      Serial.println("Received data: ");
      for (int i = 0; i < value.length(); i++) {
        Serial.print(value[i]);
      }
      Serial.println();
    }
  }
};

5. 主循环

void loop() {}

以上是一个简单的蓝牙从机程序，它创建了一个蓝牙服务和一个可读写的特征，并通过回调函数处理收到的蓝牙数据。你可以根据自己的需求进行修改和扩展。