USB to COM Port Assignment

I’m using the Arduino Duemilanove in a project where I’ve built several instances of the project. When I plug in any given board to my PC for uploading a revised sketch each board chooses a different COM port on the PC. I’m running Windows XP Pro.

This may not really be an Arduino question but is there any way to make all of my Arduino boards show up on the same COM port? Assuming of course there is only one of them plugged in at any given time.

Thanks,

Tim

You can assign each board to a specific serial port. It’s a several step process. Would that help?

I know how to change the COM port a USB connection maps to in Windows. Is there a way to specify to the Arduino board that I always want it to end up on a specific COM port?

I don’t have them plugged in at the same time. I just need to update the sketch in each of them and it would be handier if I could force them to always be COM3 (or whatever.)

Tim

Is there a way to specify to the Arduino board that I always want it to end up on a specific COM port?

The Arduino board doesn’t have any say in the matter and indeed doesn’t even know what COM port it is talking to. It is purely a matter of what COM port is allocated by your PC.

The Arduino board doesn’t have any say in the matter and indeed doesn’t even know what COM port it is talking to. It is purely a matter of what COM port is allocated by your PC.

I wonder why with only one plugged in Windows chooses a different port number for different boards? It almost seems like there must be something unique in the FDTI chip that Windows keys in on to identify it. That sort of makes sense since you can have multiple USB devices but I’m speculating. I have no knowledge of the inner workings of USB.

Thanks for the help everyone. This isn’t a serious issue and I think I will not worry over it much.

Tim

It almost seems like there must be something unique in the FDTI chip that Windows keys in on to identify it.

Yes there is!
The FTDI-chip provides a unique serial-number. (Many USB devices do this, but not all of them)

Eberhard

The FTDI-chip provides a unique serial-number.

There is a manufacturers name and number and it is possible to change this. So you might want to try changing all the names of your board to be the same.
You have to do this when making a monome with an arduino. There is a description of how to do this on my page:-
http://www.thebox.myzen.co.uk/Hardware/Mini_Monome.html
That might be enough into fooling the PC it has seen the board before. However if two were ever plugged in at the same time it could jam things up.

The FTDI-chip provides a unique serial-number.

There is a manufacturers name and number and it is possible to change this.

Just for clarification:
Every USB-device has a vendor-ID (something like the “manufacturers name”) and a product-ID. The product-ID stays the same for each “type” of chip.
For instance every FTDI USB2Serial-converter on the Arduino has a vendor-ID of 0x0403 and a product-ID of 0x6001.
It is not a good idea to change any of these numbers because the standard drivers for the device will stop working and have to be patched to recognize the arduino-board again.

Then there is the serial-number. This is a unique number (or better a combination of numbers and characters “FB675TZ6”) burned into each chip, so there should be no reason to change it.

On Linux you can do some very cool stuff with these numbers. My Arduino that drives a LedMatrix for instance appears at a port named /dev/LedControl another one that runs the bitlash-shell at
/dev/bitlash. I don’t if Windows provides similar functions.

Eberhard