private void button_card_Click(object sender, EventArgs e)
        {
            com.writePrice(a, '0');
            final_page frm = new final_page();

            frm.Show();
            Close();
        }
        private void paymentSuccsess()
        {
            ComPort com = new ComPort();

            if (com.waitForPayment())
            {
                Thread.Sleep(3000);

                final_page frm = new final_page();
                frm.Show();
                Close();
            }
        }