wx.openBluetoothAdapter({
 success (res) {
 console.log(res)//res:{errMsg: "openBluetoothAdapter:ok"}
 }
})

wx.startBluetoothDevicesDiscovery({
 //services: ['FEE7'],只搜索主服务 UUID 为 FEE7 的设备，如果明确知道主服务UUID可以用此项做筛选
 success (res) {
 console.log(res)//res:{errCode: 0, errMsg: "startBluetoothDevicesDiscovery:ok", isDiscovering: true}
 }
})

wx.getBluetoothDevices({
 success: function (res) {
 console.log(res)//res:{errMsg: "getBluetoothDevices:ok", devices: Array(3)}
 }
})

wx.onBluetoothDeviceFound(function(res) {
 console.log(res)//res:{devices: Array(1)}
})

wx.createBLEConnection({
 deviceId,//上面选择蓝牙设备的deviceId,例：连接第一个设备devices[0].deviceId
 success (res) {
 console.log(res)//{errCode: 0, errMsg: "createBLEConnection:ok"}
 }
})

onUnload（）函数里）
wx.stopBluetoothDevicesDiscovery({
 success (res) {
 console.log(res)
 }
})

wx.getBLEDeviceServices({
 deviceId,//已连接的蓝牙设备ID
 success (res) {
 console.log(res)//{errMsg: "getBLEDeviceServices:ok", services: Array(5), errCode: 0}
 }
})
//这边获取到了5个服务

var characteristics="";
wx.getBLEDeviceCharacteristics({
 deviceId,
 serviceId,//第七步的服务ID，
 success (res) {
 //res:{errMsg: "getBLEDeviceCharacteristics:ok", characteristics: Array(4), errCode: 0}
 //characteristics[0].properties: {read: true, write: false, notify: false, indicate: false}
 //特征值有好几种类型，我们这边打印需要的是item.properties.write为true的特征值
 for (var i = 0; i < res.characteristics.length; i++) {
 var item = res.characteristics[i];
 if (item.properties.write) {
 characteristics = item.uuid;
 }
 }
 //保存特征值
 }
})

wx.writeBLECharacteristicValue({
 deviceId,
 serviceId,
 characteristicId,//上面保存的特征值
 value: buffer, // 这里的value是ArrayBuffer类型，中间层传过来的打印数据前端自己做转换，转换过程我这边就不描述了；
 success (res) {
 console.log('writeBLECharacteristicValue success', res.errMsg)
 }
})
//特别提醒建议每次写入的buffer不超过20字节，超过会有写入错误的风险，所以一个打印的内容可能要拆成N个20字节的buffer去循环writeBLECharacteristicValue，这样就能打印成功啦。