private byte[] ConvertStringtoByte(String str)
{
        if (!String.IsNullOrEmpty(str))
            return System.Text.Encoding.ASCII.GetBytes(str);
        return null;
}
If you have any questions let me know :)
                    Code Snippet - To convert String to Byte Array in C#
                        It's easy to convert a string to a byte array. For an ASCII string, use the System.Text.Encoding.ASCII.GetBytes static method.
Code Snippet example below :
                