How can I send a HEX RFID card number from my MS Access Database to Arduino and write it to an RFID card?
Write a Python script that does it
PC to Arduino: the USB/Serial interface comes to mind.
Have your Access database print the number to USB (this part is well beyond the scope of this forum), and the Arduino can read it and do something with it (this part is where we can help with).
write it to an RFID card?
Most RFID cards will not allow you to write an ID number to them.
Are you trying to make a duplicate card?