怎样使用ESP32去连接蓝牙打印机呢

用ESP32连接蓝牙打印机


做项目看用途，用ESP32，打印试验用因为蓝牙连接不能完成的工作。

• 没有说单片机选择与实物实现的例子，快递就是一个难题。
  
• 选择蓝牙打印机，使用机器和实现的介绍的文章很少，我好像找不到片子。
  
• 是打印机用串口但还是其他的通讯方式，打印出看到用的那种方式不是很好用的。
  
• 使用加密货币不支持问，第一次销售，基本没有技术。
  

1.使用硬件
打印机从网上购买，有一个产品，产品介绍中很少涉及单片机的使用。所有硬件硬件都在使用Windows下。 ascii代码的设置打印方式，直接接收字符串的打印。我选择的是58mm的热敏打印机，打印形式小票。
2.单片机

单片机选择了ESP32，因为软件集成了蓝牙，实现方便。
3.

软件选择用了，比较丰富的库的例子可以快速使用。我就是用ESP32中的程序来改变试验实现的。在软件中实现，BLE Utility帮助很大。3.1
BLE

通讯是低速蓝牙通讯，新的蓝牙，比如手环等，支持蓝牙等蓝牙就好像不支持了。

• Central，中心设备，其实是BLE中的客户端。
  
• 外设，外设，BLE中的服务器。
  
  

Central作为主设备一般是需要数据的一方，比如主机需要外部的温度信号等。外围是提供数据的外部设备，比如LED指示灯等。场景一般是设备内容开始做广告，报告的包括：

• 通用访问
  
  
  
  
  • 设备名称
    
  • 外貌
    
  • 外设首选连接
    
    
  
  
• 通用属性
  
  
  
  
  • 服务改变
    
    
  
  
• 设备信息
  
  
  
  
  • 型号字符串
    
  • 软件恢复字符串
    
  • 等等
    
    
  
  
• 未知服务
  -UUID：000018f0-0000-1000-8000-00805f9b34fb
  
  
  
  
  
  • UUID：00002af1-0000-1000-8000-00805f9b34fb
    
    
  • 未知特征
    
    
    
  
  

还有一些是可以读取的UD。不需要的实例程序。或者不用。每个UUID现在还有数字比较大的，在BLE Utility中可以使用，但在中可以使用
。3.2软件编写

ESP32的没有用，例子程序里面有BLE_。打开项目，改成打印机的UUID，将CharacteristicUUID改成写操作的UUID。定时发送客户端的输入信息，然后改成当有输入的命令，就可以完成打印测试工作了。下面是程序。
3.3 例子程序


#include "BLEDevice.h"
//static BLEUUID serviceUUID("4fafc201-1fb5-459e-8fcc-c5c9c331914b");
static BLEUUID serviceUUID("000018f0-0000-1000-8000-00805f9b34fb");
//static BLEUUID    charUUID("beb5483e-36e1-4688-b7f5-ea07361b26a8");
static BLEUUID    charUUID("00002af1-0000-1000-8000-00805f9b34fb");


static boolean doConnect = false;
static boolean connected = false;
static boolean doScan = false;
static BLERemoteCharacteristic* pRemoteCharacteristic;
static BLEAdvertisedDevice* myDevice;


static void notifyCallback(
  BLERemoteCharacteristic* pBLERemoteCharacteristic,
  uint8_t* pData,
  size_t length,
  bool isNotify)
{
    Serial.print("Notify callback for characteristic ");
    Serial.print(pBLERemoteCharacteristic->getUUID().toString().c_str());
    Serial.print(" of data length ");
    Serial.println(length);
    Serial.print("data: ");
    Serial.println((char*)pData);
}


class MyClientCallback : public BLEClientCallbacks
{
        void onConnect(BLEClient* pclient)
            {
            }
    void onDisconnect(BLEClient* pclient)
    {
      connected = false;
      Serial.println("onDisconnect");
    }
  };


bool connectToServer()
{
    Serial.print("Forming a connection to ");
    Serial.println(myDevice->getAddress().toString().c_str());
   
   BLEClient * pClient = BLEDevice::createClient();
   Serial.println(" - Created client");


   pClient->setClientCallbacks(new MyClientCallback());
// Connect to the remove BLE Server
        pClient->connect(myDevice);
// if you pass BLEAdvertisedDevice instead of address,
    //it will be recognized type of peer device address (public or private)
    Serial.println(" - Connected to server");
// Obtain a reference to the service we are after in the remote BLE server.
   
    BLERemoteService* pRemoteService = pClient->>getService(serviceUUID);
    if (pRemoteService == nullptr)
    {
      Serial.print("Failed to find our service UUID: ");
      Serial.println(serviceUUID.toString().c_str());
      pClient->disconnect();
      return false;
    }
    Serial.println(" - Found our service");


// 读取characteristic的值
    if(pRemoteCharacteristic->canRead())
    {
      std::string value = pRemoteCharacteristic->readValue();
      Serial.print("The characteristic value was: ");
      Serial.println(value.c_str());
    }
  if ( pRemoteCharacteristc->canNotify())
          pRemoteCharacteristc->registerForNotify(notifyCallback);
  
  connected = true;
  return true;
}


/**
* Scan for BLE servers and find the first one that advertises
* the service we are looking for.
*/




  class MyAdvertisedDeviceCallbacks : public BLEAdvertisedDeviceCallbacks
  {
          void onResult(BLEAdvertisedDevice advertisedDevice)
          {
                    Serial.print("BLE Advertised Device found: ");
                    Serial.println(advertisedDevice.toString().c_str());         
    // We have found a device, let us now see
    // if it contains the service we are looking for.
       if (advertisedDevice.haveServiceUUID() &&
        advertisedDevice.isAdvertisingService(serviceUUID))
    {
      BLEDevice::getScan()->stop();
      myDevice = new BLEAdvertisedDevice(advertisedDevice);
      doConnect = true;
      doScan = true;
     } // Found our server
    } // onResult
}; // MyAdvertisedDeviceCallbacks


void setup()
{
  Serial.begin(115200);
  Serial.println("Starting Arduino BLE Client application...");
  BLEDevice::init("");
  // Retrieve a Scanner and set the callback we want to use to be informed when we
  // have detected a new device.  Specify that we want active scanning and start the
  // scan to run for 5 seconds. 这里我增加了时间，成功找到了打印机
  BLEScan* pBLEScan = BLEDevice::getScan();
  pBLEScan->setAdvertisedDeviceCallbacks(new MyAdvertisedDeviceCallbacks());
  pBLEScan->setInterval(1349);
  pBLEScan->setWindow(449);
  pBLEScan->setActiveScan(true);
  pBLEScan->start(10, false);
}


// This is the Arduino main loop function.
void loop()
{
  // If the flag "doConnect" is true then we have scanned for and found the desired
  // BLE Server with which we wish to connect.  Now we connect to it.  Once we are
  // connected we set the connected flag to be true.
   if (doConnect == true)
  {
    if (connectToServer()) {
      Serial.println("We are now connected to the BLE Server.");
    } else {
      Serial.println("We have failed to connect to the server; there is nothin more we will do.");
    }
    doConnect = false;
  }
  // If we are connected to a peer BLE Server, update the characteristic each time we are reached
  // with the current time since boot.
  if (connected)
  {
    String newValue = "Time since boot: " + String(millis()/1000);
    Serial.println("Setting new characteristic value to "" + newValue + """);
    // Set the characteristic's value to be the array of bytes that is actually a string.
//   pRemoteCharacteristic->writeValue(newValue.c_str(), newValue.length());
// 在这里进行了更改。当有外部的串口输入时，打印数据到打印机
    if ( Serial.available())
    {
      String xStr = Serial.readString();
      //int x = length(xStr);
      pRemoteCharacteristic->writeValue(xStr.c_str(), xStr.length());     
    }
}else if(doScan)
  {
    BLEDevice::getScan()->start(0);  
    // this is just eample to start scan after disconnect,
    // most likely there is better way to do it in arduino
  }
delay(1000); // delay a second between loop
}
这是整个程序，注意2个地方：

• 更改了serviceUUID和CharacteristicUUID
  
• 更改了每次为有串口输入时才打印。