BLE 蓝牙客户端和服务器连接

🕗 发布于 2024-11-20 04:58 ardunio BLE

蓝牙通信在设计小型智能设备时非常普遍，之前一直没有使用过，最近使用ardunio ESP32 做了一些实验，做了一个收听播客的智能旋钮（Smart Knob），它带有一个旋转编码器和两个按键。

本文介绍BLE 服务器Server和Web BLE API 作为Client。的程序

BLE 服务器和客户端

使用蓝牙低功耗，有两种类型的设备：服务器和客户端。

服务器 宣传它的存在，因此它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。

2. GATT 协议

GATT （Generic Attribute Profile）代表通用属性，它定义了向连接的 BLE 设备公开的分层数据结构。这意味着 GATT 定义了两个 BLE 设备发送和接收标准消息的方式。

服务集合 Profile: 针对特定用例的标准服务集合；
服务 Service: 收集相关信息，如传感器读数、电池电量、心率等；
特征 Characteristic: 它是实际数据保存在层次结构（值）上的位置；
描述 Descriptor: 关于数据的元数据；
属性 Properties: 描述如何与特征值交互。例如：读、写、通知、广播、指示等。

UUID

每个服务 、特征和描述符都有一个 UUID（通用唯一标识符。UUID 是唯一的 128 位（16 字节）数字。

ardunio 代码(1）

使用两个charactic

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

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

#define SERVICE_UUID        "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID_1 "beb5483e-36e1-4688-b7f5-ea07361b26a8"
#define CHARACTERISTIC_UUID_2  "cba1d466-344c-4be3-ab3f-189f80dd7518"
bool deviceConnected = false;
  //创建一个旋钮属性 
  BLECharacteristic KnobCharacteristic(
                                         CHARACTERISTIC_UUID_1,
                                         BLECharacteristic::PROPERTY_READ   |
                                         BLECharacteristic::PROPERTY_WRITE  |
                                         BLECharacteristic::PROPERTY_NOTIFY |
                                         BLECharacteristic::PROPERTY_INDICATE
                                       );
BLEDescriptor KnobDescriptor(BLEUUID((uint16_t)0x2902));
         //创建一个开关（Button）
   BLECharacteristic ButtonCharacteristic(
                                         CHARACTERISTIC_UUID_2,
                                         BLECharacteristic::PROPERTY_READ   |
                                         BLECharacteristic::PROPERTY_WRITE  |
                                         BLECharacteristic::PROPERTY_NOTIFY |
                                         BLECharacteristic::PROPERTY_INDICATE
                                       );    
BLEDescriptor ButtonDescriptor(BLEUUID((uint16_t)0x2903)); 
int KnobValue  =100;
int ButtonValue=1;   

class MyServerCallbacks: public BLEServerCallbacks {
  void onConnect(BLEServer* pServer) {
    deviceConnected = true;// 客户端连接到服务器，状态为true
  };
  void onDisconnect(BLEServer* pServer) {
    deviceConnected = false;
  }
};

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

  BLEDevice::init("ESP32_KNOB");
  BLEServer *pServer = BLEDevice::createServer();
  // 将 BLE 设备设置为服务器并分配回调函数
   pServer->setCallbacks(new MyServerCallbacks());


  BLEService *pService = pServer->createService(SERVICE_UUID);
  //Knob
   pService->addCharacteristic(&KnobCharacteristic);
   KnobDescriptor.setValue("Knob");
  KnobCharacteristic.addDescriptor(&KnobDescriptor);

  pService->addCharacteristic(&ButtonCharacteristic);
  ButtonDescriptor.setValue("Button");
  ButtonCharacteristic.addDescriptor(&ButtonDescriptor);


  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() {
  KnobValue++;
  ButtonValue++;

  if (deviceConnected) {
   String KnobStr=String(KnobValue);
    String ButtonStr=String(ButtonValue);

 KnobCharacteristic.setValue(KnobStr.c_str());
 KnobCharacteristic.notify();
 ButtonCharacteristic.setValue(ButtonStr.c_str());
 ButtonCharacteristic.notify();
  }
  delay(50);
}

adunio代码（2）

在测试的时候发现，Notify 两个Caractic时候，Web Bluetooth ，只能接收到第一个notify，第二个value 始终为空，于是我使用一个charactic 传送两个参数。

另外，在loop 中增加 startAdvertising 的程序，保证在断开时不断地startAdvertising.web 能够扫描到BLE Server。

 if (!deviceConnected && oldDeviceConnected) {
    Serial.println("Device disconnected.");
    delay(500); 
    pServer->startAdvertising(); // restart advertising
    Serial.println("Start advertising");
    oldDeviceConnected = deviceConnected;
  }
  // connecting
  if (deviceConnected && !oldDeviceConnected) {
    // do stuff here on connecting
    oldDeviceConnected = deviceConnected;
    Serial.println("Device Connected");
  }

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

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

#define SERVICE_UUID        "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID_1 "beb5483e-36e1-4688-b7f5-ea07361b26a8"
BLEServer* pServer = NULL;
bool deviceConnected = false;
bool oldDeviceConnected = false;
  //创建一个旋钮属性 
  BLECharacteristic KnobCharacteristic(
                                         CHARACTERISTIC_UUID_1,
                                         BLECharacteristic::PROPERTY_READ   |
                                         BLECharacteristic::PROPERTY_WRITE  |
                                         BLECharacteristic::PROPERTY_NOTIFY |
                                         BLECharacteristic::PROPERTY_INDICATE
                                       );
BLEDescriptor KnobDescriptor(BLEUUID((uint16_t)0x2902));

int KnobValue  =100;
int ButtonValue=1;   

class MyServerCallbacks: public BLEServerCallbacks {
  void onConnect(BLEServer* pServer) {
    deviceConnected = true;// 客户端连接到服务器，状态为true
  };
  void onDisconnect(BLEServer* pServer) {
    deviceConnected = false;
  }
};

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

  BLEDevice::init("ESP32_KNOB");
 pServer = BLEDevice::createServer();
  // 将 BLE 设备设置为服务器并分配回调函数
   pServer->setCallbacks(new MyServerCallbacks());


  BLEService *pService = pServer->createService(SERVICE_UUID);
  //Knob
   pService->addCharacteristic(&KnobCharacteristic);
   KnobDescriptor.setValue("Knob");
  KnobCharacteristic.addDescriptor(&KnobDescriptor);


  pService->start();

  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();
  pServer->getAdvertising()->start();
  Serial.println("Characteristic defined! Now you can read it in your phone!");
}

void loop() {
  if (deviceConnected) {
    KnobValue++;
  ButtonValue++;
  byte buffer[8];
  memcpy(&buffer[0],&KnobValue,4);
  memcpy(&buffer[4],&ButtonValue,4);
  // String KnobStr=String(KnobValue);
  //  String ButtonStr=String(ButtonValue);

 KnobCharacteristic.setValue((uint8_t*)&buffer, 8);
 KnobCharacteristic.notify();
  delay(500);
  }
   // disconnecting
  if (!deviceConnected && oldDeviceConnected) {
    Serial.println("Device disconnected.");
    delay(500); 
    pServer->startAdvertising(); // restart advertising
    Serial.println("Start advertising");
    oldDeviceConnected = deviceConnected;
  }
  // connecting
  if (deviceConnected && !oldDeviceConnected) {
    // do stuff here on connecting
    oldDeviceConnected = deviceConnected;
    Serial.println("Device Connected");
  }
  delay(200);
}

通过web 访问蓝牙

为了简单地做测试，我使用Web BlueTooth 的API 。

连接到设备

从浏览器连接到设备。可以调用函数 navigator.bluetooth.requestDevice() 并为函数提供配置对象，该对象含有关我们要使用哪个设备，以及都有哪些服务可用的信息。

let device = await navigator.bluetooth.requestDevice({
    filters: [ 
        { namePrefix: 'PLAYBULB' } 
    ],
    optionalServices: [ 0xff0f ]
});

当我们调用此函数时，会弹出一个窗口，显示符合过滤规则的设备列表。现在必须手动选择我们想要连接的设备。这是出于安全和隐私的需要，并为用户提供控制的权利。用户决定是否允许 Web 应用连接到设备，当然还有已经被允许连接的设备。如果没有用户手动选择设备，Web 应用则无法获取设备列表或连接。

在我们访问设备之后，可以通过调用设备 gatt 属性上的 connect() 函数连接到 GATT 服务器并等待返回结果。

let server = await device.gatt.connect();

一旦我们连上服务器，就可以调用 getPrimaryService() 并传递服务的UUID，然后等待结果返回。

let service = await server.getPrimaryService(0xff0f);

然后使用特性的UUID作为参数调用服务上的 getCharacteristic() 并再次等待结果返回。

现在就得到了可用于读写数据的特性：

let characteristic = await service.getCharacteristic(0xfffc);

写数据

要写入数据，我们可以在特性上调用函数 writeValue() ，以 ArrayBuffer 的形式传递想要写入的值，这是二进制数据的存储方法。

characteristic.writeValue(
    new Uint8Array([ 0, r, g, b  ])
);

读数据

要读取灯泡的当前颜色，可以使用 readValue() 函数并等待结果返回。

let value = await characteristic.readValue();
    
let r = value.getUint8(1); 
let g = value.getUint8(2);
let b = value.getUint8(3);

获得通知变更

最后，还有一种方法可以在设备值发生变化时收到通知。

characteristic.addEventListener(
    'characteristicvaluechanged', e => {
        let r = e.target.value.getUint8(1); 
        let g = e.target.value.getUint8(2);
        let b = e.target.value.getUint8(3);
    }
);

characteristic.startNotifications();

简单的方式

    async function onButtonClick() {
        let device = await navigator.bluetooth.requestDevice({
            acceptAllDevices: true,
        });
        let server = await device.gatt.connect();
        console.log(server);
        let services = await server.getPrimaryServices();
        console.log(services);
        let characteristics = await services[0].getCharacteristics();
        let value = await characteristics[0].readValue();
        console.log(value);
    }

代码（读取方式）

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>BLE Server </title>


</head>

<body>
    <h1>  Ble Server Connection</h1>
    <button onclick="Connection()">连接</button>
    <button onclick="ReadOut()">读操作</button>
    <p id="Knob">Knob:null</p>
    <p id="button">button:null</p>
    <script>
        var server
        var services
        async function ReadOut() {
            let characteristics = await services[0].getCharacteristics();
            let value = await characteristics[0].readValue();
            let textDecoder = new TextDecoder('ascii');
            let Val = textDecoder.decode(value.buffer);
            console.log("Knob:" + Val);
            document.getElementById("Knob").textContent="knob:"+Val
            value = await characteristics[1].readValue();
            textDecoder = new TextDecoder('ascii');
            Val = textDecoder.decode(value.buffer);
            console.log("button:" + Val);
            document.getElementById("button").textContent="button:"+Val
        }
        async function Connection() {
            let device = await navigator.bluetooth.requestDevice({
                filters: [
                    { name: 'ESP32_KNOB' }
                ]
            });
            server = await device.gatt.connect();
            services = await server.getPrimaryServices();
        }

    </script>
</body>

</html>

代码（使用Notify）

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>BLE Server </title>


</head>

<body>
    <h1> Ble Server Connection</h1>
    <button onclick="Connection()">连接</button>
    <h4>Parameters</h4>
    <p id="Knob">Knob:null</p>
    <p id="button">button:null</p>
    <script>
        var server
        var services
        async function startNotification() {
            let textDecoder = new TextDecoder('ascii');
            let characteristics= await services[0].getCharacteristics()       
           let characteristic = await services[0].getCharacteristic("beb5483e-36e1-4688-b7f5-ea07361b26a8");
            characteristic.addEventListener(
                'characteristicvaluechanged', e => {
                 v1=e.target.value.getUint8(0); 
                 v2=e.target.value.getUint8(1); 
                 v3=e.target.value.getUint8(2); 
                 v4=e.target.value.getUint8(3); 
                 Val=(v4<<24)|(v3<<16)|(v2<<8)|v1
                    console.log("Knob:" + Val);
                    document.getElementById("Knob").textContent = "knob:" + Val
                    //
                    v1=e.target.value.getUint8(4); 
                 v2=e.target.value.getUint8(5); 
                 v3=e.target.value.getUint8(6); 
                 v4=e.target.value.getUint8(7); 
                 Val=(v4<<24)|(v3<<16)|(v2<<8)|v1
                    console.log("button:" + Val);
                    document.getElementById("button").textContent = "button:" + Val
                }
            );
            characteristic.startNotifications(); 
        }
        async function Connection() {
            let device = await navigator.bluetooth.requestDevice({
                filters: [
                    { name: 'ESP32_KNOB' }
                ],
                optionalServices: [  "4fafc201-1fb5-459e-8fcc-c5c9c331914b"]
            });
            server = await device.gatt.connect();
           services = await server.getPrimaryServices();
           startNotification()
        }

    </script>
</body>

</html>

结论

本文已经覆盖了 WebBluetooth API 的90％。只需调用几个函数并发送 4 个字节，你就可以创建一个控制灯泡颜色的 Web 应用。如果再添加几行，你甚至可以控制玩具车或驾驶无人机。随着越来越多的蓝牙设备进入市场，将产生无穷的可能性。