https://developers.weixin.qq.com/miniprogram/dev/api/device/bluetooth-ble/wx.writeBLECharacteristicValue.html

官方给的demo有点问题，这是解决方案：

https://blog.csdn.net/zxc147716565/article/details/107973860

    wx.writeBLECharacteristicValue({
      deviceId: this._deviceId,
      serviceId: this._serviceId,
      characteristicId: this._characteristicId,
      value: buffer,
    })