WeChat applet automatically connects to a bluetooth electronic scale

 For different brands, you only need to print the return value of the function below and process it according to your own needs.

wx.onBLECharacteristicValueChange(function (res) {
          let receiverText = that.buf2string(res.value);
}

---

 The first connection needs to be manually configured, and then the required parameters (deviceId) are saved in the storage to facilitate the next automatic connection.

App({

  globalData: {
    serviceId: '',
    characteristicId: '',
    deviceId: '',  // 已连接蓝牙的设备ID
    BluetoothState: false, // 蓝牙适配器状态
    connectState: false, // 蓝牙连接状态,
    weight: 0,  // 重量
  },

  onLaunch: function () {
    // 设置初始重量为0
    wx.setStorageSync('weight', 0)
  },

  onShow() {
    // 读取本地数据，实现蓝牙自动连接
    let deviceId = wx.getStorageSync('deviceId') || []
    if(deviceId){
      this.globalData.deviceId = deviceId
      this.initBlue()
    } else {
      wx.showToast({
        title: '蓝牙未连接',
        icon: 'error',
        duration: 3000,
      })
    }
  },

  // 初始化蓝牙
  initBlue(){
    var that = this;
    wx.openBluetoothAdapter({//调用微信小程序api 打开蓝牙适配器接口
      success: function (res) {
        console.log('app初始化蓝牙成功')
        that.getTheBlueDisConnectWithAccident();//监听蓝牙是否会异常断开
        that.globalData.BluetoothState = true
        that.monitorTheBlue();  // 监听手机蓝牙的开关
        that.startConnect(that.globalData.deviceId)  // 连接蓝牙
      },

      fail: function (err) {//如果手机上的蓝牙没有打开，可以提醒用户
        if (err.errCode === 10001) { // 手机蓝牙未开启
          that.globalData.BluetoothState = false
          wx.showToast({
            title: '手机蓝牙未开启',
            icon: 'error',
            duration: 3000,
          })
        } 
      }
    })
  },

  // 监听手机蓝牙的开关
  monitorTheBlue:function(){
    var that =this;
    wx.onBluetoothAdapterStateChange(function(res){
      if (res.available){
        that.globalData.BluetoothState = true
        if(!that.globalData.connectState){
          let deviceId = wx.getStorageSync('deviceId') || []
          if(deviceId){
            that.globalData.deviceId = deviceId
            that.initBlue()
          }
        }
      }else{
        wx.showToast({
          title: '蓝牙已关闭',
          icon: 'error',
          duration: 3000,
        })
      }
    })
  },

  // 监听蓝牙设备是否会异常断开
  getTheBlueDisConnectWithAccident:function(e){
    var that = this;
    wx.onBLEConnectionStateChange(function (res) {
      if (!res.connected){
        that.globalData.connectState = false
        wx.showToast({
          title: '蓝牙已断开连接',
          icon: 'error',
          duration: 3000,
        })
        that.monitorTheBlue()
      } 
    })
  },
  // 停止搜索附近蓝牙
  stopSearchDevs: function () {
    wx.stopBluetoothDevicesDiscovery({
      success: function (res) { },
    })
  },
  // 开始连接
  startConnect(deviceId, isFirst = false){
    const that =this
    wx.createBLEConnection({
      deviceId: deviceId,
      timeout: 10000, // 10s连接超时
      success: function (res) {
        that.globalData.connectState = true
        wx.showToast({
          title: '蓝牙连接成功',
          icon: 'success',
          duration: 3000,
          success: res=>{
            that.getServiceId()
            if(isFirst){
              wx.navigateTo({
                url: `/pages/bluetooth/com/com`,
              })
            }
            
          }
        })     
      },
    })
  },

  // 获取蓝牙设备服务ID
  getServiceId(){
    const that = this
    wx.getBLEDeviceServices({
      deviceId: wx.getStorageSync('deviceId'),
      success: function(res) {
        const services = res.services.filter((item, i) => {
          return !/^000018/.test(item.uuid)
        })
        that.globalData.serviceId = services[0].uuid
        that.getCharacteristicId()
      },
      fail: function(res) {
        wx.showToast({
          title: '设备服务获取失败',
          icon: 'none'
        })
      }
    })
  },

  // 获取特征ID
  getCharacteristicId(){
    const that = this
    wx.getBLEDeviceCharacteristics({
      deviceId: wx.getStorageSync('deviceId'),
      serviceId: that.globalData.serviceId,
      success: function(res) {
        for (var i = 0; i < res.characteristics.length; i++) {//2个值
          var model = res.characteristics[i]
          if (model.properties.notify == true) {
            that.startNotice(model.uuid)//7.0
          }
        }
      }
    })
  },

  // 接收值处理
  buf2string(buffer) {
    var arr = Array.prototype.map.call(new Uint8Array(buffer), x => x)
    return arr.map((char, i) => {
      return String.fromCharCode(char);
    }).join('');
  },

  // 开启通知，通知特征值变化
  startNotice(uuid) {
    var that = this;
    wx.notifyBLECharacteristicValueChange({
      state: true, // 启用 notify 功能
      deviceId: wx.getStorageSync('deviceId'),
      serviceId: that.globalData.serviceId,
      characteristicId: uuid,  //第一步 开启监听 notityid 
      success: function (res) {
        // 设备返回的方法
        wx.onBLECharacteristicValueChange(function (res) {
          let receiverText = that.buf2string(res.value);
          receiverText = receiverText.split('').reverse().join('').slice(1)
          receiverText = Number(receiverText)
          if(that.globalData.weigh == receiverText) {
            return;
          } else {
            // that.globalData.weight = receiverText 
            wx.setStorageSync('weight', receiverText)
          }    
        })
      },
      fail: function (res) {
        console.log(res);
      }
    })
  },

  // 断开连接
  endConnect(deviceId) {
    if (this.globalData.BluetoothState) {
      wx.closeBLEConnection({
        deviceId: deviceId,
        success: function (res) {},
      })
    }
  },

  onHide () {
    // Do something when hide.
    let deviceId = wx.getStorageSync('deviceId') || []
    this.endConnect(deviceId)
    this.globalData.connectState = false
 
    wx.closeBluetoothAdapter({
      success: res=>{
        this.globalData.BluetoothState = false
      }
    })
  },
})

Manual connection

const app = getApp()

Page({
  // 页面的初始数据
  data: {
    devs: []
  },
  // 自定义数据
  customData: {
    _devs: []
  },
  // 监听页面加载
  onLoad: function () {
    // 微信蓝牙模块初始化
    const self = this
    wx.openBluetoothAdapter({
      success: function (res) {
        app.globalData.BluetoothState = true
        self.startSearchDevs() // 搜索附近蓝牙
      },
      fail: function (err) {
        if (err.errCode === 10001) { // 手机蓝牙未开启
          app.globalData.BluetoothState = false
          wx.showLoading({
            title: '请开启手机蓝牙',
          })
        } else {
          // console.log(err.errMsg)
        }
      }
    })
    // 监听蓝牙适配器状态变化
    wx.onBluetoothAdapterStateChange(function(res) {
      if (res.available) {
        app.globalData.BluetoothState = true
        wx.openBluetoothAdapter({
          success: function(res) {
            app.globalData.BluetoothState = true
            wx.hideLoading()
          },
        })
      } else {
        app.globalData.BluetoothState = false
        app.globalData.connectState = false
        wx.showLoading({
          title: '请开启手机蓝牙',
        })
      }
    })
    // 监听BLE蓝牙连接状态变化
    wx.onBLEConnectionStateChange(function(res) {
      if (res.connected) {
        wx.hideLoading()
        wx.showToast({
          title: '连接成功',
          icon: 'success',
          success: function(res) {
            app.globalData.connectState = true
          }
        })
      } else {
        wx.hideLoading()
        wx.showToast({
          title: '已断开连接',
          icon: 'none',
          success: function(res) {
            app.globalData.connectState = false
          }
        })
      }
    })
  },
  
  // 监听页面卸载
  onUnload: function () {
    app.stopSearchDevs()
  },
  // 监听用户下拉动作
  onPullDownRefresh: function () {
    if (app.globalData.BluetoothState) {
      const self = this
      this.customData._devs = []
      wx.closeBluetoothAdapter({
        success: function (res) {
          wx.openBluetoothAdapter({
            success: function (res) {
              self.startSearchDevs()
            }
          })
        }
      })
    }
    setTimeout(() => {
      wx.stopPullDownRefresh()
    }, 2000)
  },
  // 开始搜索附近蓝牙
  startSearchDevs: function () {
    const self = this
    wx.startBluetoothDevicesDiscovery({ // 开启搜索
      allowDuplicatesKey: false,
      success: function (res) {
        wx.onBluetoothDeviceFound(function (devices) {
          var isExist = false
          if (devices.deviceId) {
            for (let item of self.customData._devs) {
              if (item.deviceId === devices.deviceId) {
                isExist = true
                break;
              }
            }
            !isExist && self.customData._devs.push(devices)
            self.setData({
              devs: self.customData._devs
            })
          }
          else if (devices.devices) {
            for (let item of self.customData._devs) {
              if (item.deviceId === devices.devices[0].deviceId) {
                isExist = true
                break;
              }
            }
            !isExist && self.customData._devs.push(devices.devices[0])
            self.setData({
              devs: self.customData._devs
            })
          }
          else if (devices[0]) {
            for (let item of self.customData._devs) {
              if (item.deviceId === devices[0].deviceId) {
                isExist = true
                break;
              }
            }
            !isExist && self.customData._devs.push(devices[0])
            self.setData({
              devs: self.customData._devs
            })
          }
        })
      }
    })
  },
  // 选择设备连接
  connect (event) {
    app.stopSearchDevs()
    if (app.globalData.BluetoothState) {
      const deviceId = event.currentTarget.dataset.dev.deviceId
      app.globalData.deviceId = deviceId
      
      wx.setStorageSync('deviceId', deviceId)
      wx.showLoading({
        title: '正在连接...',
      })
      app.startConnect(deviceId, true)
    }
  },
})