低功耗蓝牙简介

Bluetooth Low Energy，简称BLE，是蓝牙的一种节能变体。BLE 的主要应用是少量数据的短距离传输（低带宽）。与始终开启的蓝牙不同，BLE 会一直保持睡眠模式，除非发起连接。这使得它消耗非常低的功率。BLE 的功耗比蓝牙低大约 100 倍（取决于使用情况）。

此外，BLE 不仅支持点对点通信，还支持广播模式和网状网络。由于其特性，BLE 适用于需要在纽扣电池上定期交换少量数据的应用程序。例如，BLE 在医疗保健、健身、跟踪、信标、安全和家庭自动化行业中有很大的用途。

BLE 服务器和客户端

对于低功耗蓝牙，有两种类型的设备：服务器和客户端。ESP32 既可以作为客户端也可以作为服务器。

服务器广播它的存在，因此可以被其他设备发现，并包含客户端可以读取的数据。客户端扫描附近的设备，当它找到它正在寻找的服务器时，它会建立连接并监听传入的数据。这称为点对点通信。

BLE 还支持广播模式和网状网络：

• 广播模式：服务器向多个连接的客户端发送数据；
• 网状网络：所有设备都连接在一起，这是多对多连接。

ESP32中 的蓝牙

ESP32 可以充当 BLE 服务器或 BLE 客户端。Arduino IDE 的 ESP32 BLE 库中有几个 ESP32 的 BLE 示例 。当您在 Arduino IDE 上安装 ESP32 时，该库默认安装。

在您的 Arduino IDE 中，您可以转到 文件>示例> ESP32 BLE Arduino并浏览 BLE 库附带的示例。

注意：要查看 ESP32 示例，您必须在Tools > Board上选择 ESP32 board 。

为了简要介绍在 Arduino IDE 上使用 BLE 的 ESP32，我们将创建一个 ESP32 BLE 服务器，然后创建一个 ESP32 BLE 扫描器来查找该服务器。我们将使用和解释 BLE 库附带的示例。

要完成此示例，您需要两块 ESP32 开发板。我们将使用 ESP32 DOIT DEVKIT V1 开发板。

ESP32 蓝牙服务器

要创建 ESP32 BLE 服务器，请打开您的 Arduino IDE 并转到 文件>示例> ESP32 BLE Arduino并选择BLE_server示例。应加载以下代码：

/*
    Based on Neil Kolban example for IDF: https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/tests/BLE%20Tests/SampleServer.cpp
    Ported to Arduino ESP32 by Evandro Copercini
    updates by chegewara
*/

#include 
#include 
#include 

// 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"

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

  BLEDevice::init("Long name works now");
  BLEServer *pServer = BLEDevice::createServer();
  BLEService *pService = pServer->createService(SERVICE_UUID);
  BLECharacteristic *pCharacteristic = pService->createCharacteristic(
                                         CHARACTERISTIC_UUID,
                                         BLECharacteristic::PROPERTY_READ |
                                         BLECharacteristic::PROPERTY_WRITE
                                       );

  pCharacteristic->setValue("Hello World says Neil");
  pService->start();
  // BLEAdvertising *pAdvertising = pServer->getAdvertising();  // this still is working for backward compatibility
  BLEAdvertising *pAdvertising = BLEDevice::getAdvertising();
  pAdvertising->addServiceUUID(SERVICE_UUID);
  pAdvertising->setScanResponse(true);
  pAdvertising->setMinPreferred(0x06);  // functions that help with iPhone connections issue
  pAdvertising->setMinPreferred(0x12);
  BLEDevice::startAdvertising();
  Serial.println("Characteristic defined! Now you can read it in your phone!");
}

void loop() {
  // put your main code here, to run repeatedly:
  delay(2000);
}

查看原始代码

要创建 BLE 服务器，代码应遵循以下步骤：

1. 创建 BLE 服务器。在这种情况下，ESP32 充当 BLE 服务器。
2. 创建 BLE 服务。
3. 在服务上创建 BLE 特性。
4. 在特性上创建 BLE 描述符。
5. 启动服务。
6. 开始广播，以便其他设备可以找到它。

BLE 服务器示例代码的工作原理

首先导入 BLE 功能所需的库。

#include 
#include 
#include 

然后，需要为 Service 和 Characteristic 定义一个 UUID。

#define SERVICE_UUID "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"

可以保留默认 UUID，也可以转到 uuidgenerator.net 创建随机 UUID。

在里面设置（）, 它以 115200 的波特率开始串行通信。

Serial.begin(115200);

然后，创建一个名为“ MyESP32 ”的 BLE 设备。

// Create the BLE Device
BLEDevice::init("MyESP32");

在下一行中，将 BLE 设备设置为服务器。

BLEServer *pServer = BLEDevice::createServer();

之后，使用之前定义的 UUID 为 BLE 服务器创建服务。

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

然后，设置该服务的特征。还使用了之前定义的 UUID，并且需要将特性的属性作为参数传递。在这种情况下，它是：READ 和 WRITE。

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

创建特征后，可以使用设定值（）方法。

pCharacteristic->setValue("Hello World says Neil");

在这种情况下，将值设置为文本“Hello World says Neil”。

最后，可以启动服务和广告，以便其他 BLE 设备可以扫描并找到此 BLE 设备。

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

这只是一个关于如何创建 BLE 服务器的简单示例。。

ESP32 蓝牙扫描器

创建 ESP32 BLE 扫描器很简单。用另一个ESP32，在 Arduino IDE 中，转到 文件 > 示例> ESP32 BLE Arduino并选择BLE_scan示例。加载以下代码。

/*
   Based on Neil Kolban example for IDF: https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/tests/BLE%20Tests/SampleScan.cpp
   Ported to Arduino ESP32 by Evandro Copercini
*/

#include 
#include 
#include 
#include 

int scanTime = 5; //In seconds
BLEScan* pBLEScan;

class MyAdvertisedDeviceCallbacks: public BLEAdvertisedDeviceCallbacks {
    void onResult(BLEAdvertisedDevice advertisedDevice) {
      Serial.printf("Advertised Device: %s 
", advertisedDevice.toString().c_str());
    }
};

void setup() {
  Serial.begin(115200);
  Serial.println("Scanning...");

  BLEDevice::init("");
  pBLEScan = BLEDevice::getScan(); //create new scan
  pBLEScan->setAdvertisedDeviceCallbacks(new MyAdvertisedDeviceCallbacks());
  pBLEScan->setActiveScan(true); //active scan uses more power, but get results faster
  pBLEScan->setInterval(100);
  pBLEScan->setWindow(99);  // less or equal setInterval value
}

void loop() {
  // put your main code here, to run repeatedly:
  BLEScanResults foundDevices = pBLEScan->start(scanTime, false);
  Serial.print("Devices found: ");
  Serial.println(foundDevices.getCount());
  Serial.println("Scan done!");
  pBLEScan->clearResults();   // delete results fromBLEScan buffer to release memory
  delay(2000);
}

此代码将 ESP32 初始化为 BLE 设备并扫描附近的设备。将此代码上传到 ESP32。。

上传代码后，打开两个 ESP32 开发板：

• 一个装载“BLE_server”的 ESP32；
• 另一装载 ESP32“BLE_scan”。

转到运行“BLE_scan”示例的 ESP32 的串行监视器，按下 ESP32）启用按钮以重新启动并在扫描时等待几秒钟。

扫描器发现了设备： MyESP32