public List<int> Temperatura()
        {
            List<int> Datos = null;
            string connStr = "server=localhost;user=root;database=sensores;port=3306;password=123456;";
            MySqlConnection conn = new MySqlConnection(connStr);
            try
            {
                Console.WriteLine("Connecting to MySQL...");
                conn.Open();

                string sql = "Select temperatura From datos where fecha  between '" + Label3.Text + "' and '" + Label4.Text + "';";
                MySqlCommand cmd = new MySqlCommand(sql, conn);
                MySqlDataReader rdr = cmd.ExecuteReader();

                while (rdr.Read())
                {

                    Datos.Add(Convert.ToInt32(rdr[0]));
                }
                rdr.Close();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }

            conn.Close();
            Console.WriteLine("Done.");
            return Datos;