อยากทราบวิธีทำปุ่มโทรศัพท์สมัยก่อน ที่กดซ้ำแล้วจะเปลี่ยนตัว หากไม่กดภายในกี่วินาทีจะนำตัวนั้นไปใช้ C# WindownForm Visual Studio

if (textBox1.Text == string.Empty)
            {
                first = true;
                push = 1;
                textBox1.Text = "1";
                value = "1";
                timer1.Interval = 500;
                timer1.Start();
            }
            else
            {
                //  if(sec !=0)
                if (sec < 3)
                {
                    if (first == true)
                    {
                        timer1.Stop();

                        if (push == 0)
                        {
                            textBox1.Text = "1";
                            value = "1";
                            push = 1;
                            timer1.Start();
                            return;
                        }
                        if (push == 1)
                        {
                            textBox1.Text = "A";
                            value = "A";
                            push = 2;
                            timer1.Start();
                            return;
                        }
                        if (push == 2)
                        {
                            textBox1.Text = "B";
                            value = "B";
                            push = 3;
                            timer1.Start();
                            return;
                        }
                        if (push == 3)
                        {
                            textBox1.Text = "C";
                            value = "C";
                            push = 0;
                            timer1.Start();
                            return;
                        }
                    }
                    else
                    {
                        timer1.Stop();

                        if (push == 0)
                        {
                            if (sec < 3)
                            {


                                value = "1";
                                push = 1;
                                timer1.Start();
                                return;
                            }
                        }
                        if (push == 1)
                        {
                            if (sec < 3)
                            {
                                value = "A";
                                push = 2;
                                timer1.Start();
                                return;
                            }
                        }
                        if (push == 2)
                        {
                            if (sec < 3)
                            {
                                value = "B";
                                push = 3;
                                timer1.Start();
                                return;
                            }
                        }
                        if (push == 3)
                        {
                            if (sec < 3)
                            {
                                value = "C";
                                push = 0;
                                timer1.Start();
                                return;
                            }
                        }
                    }
                }
            }

namespace TestPhone
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        string str = "";
        string chr = "";
        int i = 0;
        private void button1_Click(object sender, EventArgs e)
        {
            textBox1.Text += "1";
        }

        private void button2_Click(object sender, EventArgs e)
        {
            if (str == "")
            {
                str = textBox1.Text;
                chr= "2";
            }
            else if  (chr== "2"){chr = "A";}
            else if (chr == "A") { chr = "B"; }
            else if (chr == "B") { chr = "C"; }
            else if (chr == "C") { chr = "2"; }
            textBox1.Text = str + chr;
            i = 0;
            timer1.Enabled = true;
        }
        private void button3_Click(object sender, EventArgs e)
        {
            if (str == "")
            {
                str = textBox1.Text;
                chr = "3";
            }
            else if (chr == "3") { chr = "D"; }
            else if (chr == "D") { chr = "E"; }
            else if (chr == "E") { chr = "F"; }
            else if (chr == "F") { chr = "3"; }
            textBox1.Text = str + chr;
            i = 0;
            timer1.Enabled = true;
        }
        private void timer1_Tick(object sender, EventArgs e)
        {
            i++;
            if (i >= 3)
            {
                str = "";
                timer1.Enabled = false;
                return;
            }
        }
    }
}