private void RegisterCharacteristic(Guid service_uuid, Guid characteristicUuid)
{
var accData = DeviceServices.FirstOrDefault(s => s.Uuid == service_uuid).GetCharacteristics(characteristicUuid)[0];
if (!Characteristics.ContainsKey(service_uuid.ToString()))
{
Characteristics.Add(service_uuid.ToString(), new List <GattCharacteristic>());
}
Characteristics[service_uuid.ToString()].Add(accData);
}