Java: select serial port to read Arduino Uno

Question

I am trying to read from an RFID tag number that is scanned by a parallax RFID reader and sent to the computer using the Arduino device. I am trying to read from the serial port using RXTXCommDrive, but the problem is that when the Arduino is connected to a PC it is connected to COM3 and when connected to a laptop it is connected to COM4. Is there way to loop through the COM ports and find the correct port?

Answer 1

The RXTX wiki lists two examples for listing available ports:

• http://rxtx.qbang.org/wiki/index.php/Discovering_comm_ports
• http://rxtx.qbang.org/wiki/index.php/Discovering_available_comm_ports

But: What do you do if you find two ports? So either you should use some configuration file anyway.

A third possibility would be: Most USB drivers allow assignment of specific chips to a specific COM port id. For Arduinos using the FT232R chip there are two ways: Reassign the port ID via the driver settings OR reassign a bunch of port IDs via registry edits.

The relevant Application Notes can be found here:

http://www.ftdichip.com/Support/Documents/AppNotes.htm

• AN_107 "Advanced Driver Options"
• AN_132 "Re-Assigning COM Port Numbers Using the Windows Registry"

I'm sure the other chips of newer Arduinos have similar capabilities.