I had been happily using my first UNO board, and then added a 2nd board (Win7, 32-bit, Arduino-0022 IDE).
The 1st UNO always showed up as COM3 and worked fine.
Plugging in the 2nd UNO brought it on as COM4 when both are plugged in. No device found dialogs, no driver installs (all on board already).
Plugging in each alone to the same USB cable, I am able to talks to each, upload and use a sketch.
Plugging in both, one connecting as COM3, the other as COM4, always generates the message that COM4 is busy when I try to upload to COM4 (COM3 does okay).
I thought I saw this discussion several months ago but could not find the relevant entry (if it exists). Any suggestions on being able to use both UNO boards concurrently connected to separate USB cables?
I think there was a posting sometime this week asking a related question, can you run two instances of the Arduino IDE, attached to two different boards/com ports? I think the answer given was no, something about some resource used that can't be shared? Perhaps someone more knowledgeable then I will opine.
With regard to "can't talk to both", that was only partially correct. I actually hit two different problems. One was a message indicating COM4 was busy. The other was that a sketch load would compile but then hang and not finish the uploading. Firmata would also hang.
However, I have achieved some success.
Using the Sysinternals Process Explorer for Win7, I found a hung process, called AVR or AVRdude, that was terminated when the sketch upload was hung (even though the IDE was stopped successfully). I believe this orphaned process was holding COM4 and later produced the subsequent message about COM4 being busy.
Next, I installed a program called USBDview. This lists all the USB device connections. I found a ghost device for the new UNO board (I will take steps to eliminate this ghost device). Noting that the ghost device and the real device were on the SAME USB port and hub, I then plugged the new UNO board into a different physical USB port on the computer.
That worked. In USBDview, it now shows up at a different port/hub. I could talk to the device using Firmata_test. In fact, I brought up 2 copies of Firmata_test, one to COM3 and one to COM4, and both function as expected. I was able to load a sketch to the new UNO and the sketch ran properly.
My first UNO board is an R2 version with the removable CPU chip. This new UNO board is an SMD R2 version but it has updated firmware (0.01 versus 0.00, numbers reported by USBDview). Who has information on that firmware update? It might be hard to find since we have seen little about the R2 revision itself.
Lastly, I need to get rid of that ghost device. I will try rebooting Win7, and failing that, USBDview has an option to remove entries.
A reboot of Win7 did not eliminate the ghost device.
I have the expected devices, COM3 and COM4, with COM5 as a ghost device (have the same port/hub location as COM4).
I used USBDview in administrative mode, to uninstall COM5. Unfortunately for me (or not), selecting uninstall for the ghost device uninstalled all Arduino devices, COM3 through COM5.
I rebooted, Win7 detected the Arduino connections, and now have only two devices, but called COM6 and COM7. I don't understand that! I read somewhere that there is a limit when you hit COM10, that the Arduino IDE can't handle it (feedback please).
But, no more ghost device and for some time now, that should be okay. However, I worry about moving the new UNO back to its former USB port location. What will that bring?
One observation worthy of note: if you add an additional UNO to your USB ports (with one or more already connected), make sure all are connected, including the new one, and then do a power up boot. That seems to be the cleanest way to have a new Arduino recognized. However, the dynamic nature of USB connections and Arduino devices is such that I expect the COM numbers to routinely change over time.
In attempting to use the new Arduino UNO SMD R2 device today, it once again FAILED to load a new sketch. Ouch! Reboot with the device plugged in also failed.
On a whim, I connected it with the USB cable that I normally use for my older UNO. It worked.
Then, I swapped out the USB cable that came with the SparkFun kit, and used one from my inventory. It worked. It appears that I got a bad USB cable with the SparkFun kit.
So, for now, I am up to Circuit 5, and progressing.