Welcome to the forum
Which board do you have selected in the IDE ?
Hi @znemesis. Try this:
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Use a jumper wire (or whatever else you have on hand that can make a temporary electrical connection) to connect these two pins on the board:
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Remove the connection between the pins.
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Check Windows Device Manager.
After doing that, do you still see the "Unknown USB Device" in Device Manager?
The ATmega16U2 USB chip on the UNO board should come with a "DFU" bootloader installed. When you momentarily short those two pins, that bootloader is activated, which will cause the UNO board to act as a different type of USB device.
This experiment is intended to determine whether the DFU bootloader is present on the ATmega16U2, and whether the ATmega16U2 is in a functional enough state to run the bootloader. If so, it might be possible for you to flash the ATmega16U2 with the normal Arduino "usbserial" firmware (as described in this tutorial). If the problem with the board is caused by a glitch in the ATmega16U2 firmware, that might fix the board.
i have 2 brand new boards same problem,
OK, this tells us that either the firmware is missing/corrupted on the ATmega16U2, or else that there is some physical problem with the board's USB system.
You could try using an ISP programmer to flash the firmware to the board, but that is a fairly complex procedure that would only be possible if you have access to a dedicated ISP programmer, or to a working Arduino board (which can be used as a DIY "Arduino as ISP" programmer).
I suggest you contact the seller of the boards about the problem. They may be willing to give you a refund or replacement.
I've had a similar problem.
I got two clone boards about a month apart, same supplier. The first board seems fine and will enter DFU mode with no problems.
The second one gives the device descriptor error but only on some USB ports. If I try it on a laptop or a hub it works fine and I can send sketeches across. It wont enter DFU mode and connecting usbasp to the 16U2 ICSP doesn't work either (works fine on the other ICSP connector). The board layout around the 16U2 is noticably different between the two. I'm contacting the seller about the second board.
This is the working R3:
This is the one with the misbehaving "16U2" (assuming it isn't a counterfeit chip). Note that the IC number is horizontal on this one and the large track to the lower left is a connected to a different pin and is a different shape on the good board. If anyone has a board that looks like this second one and it can enter DFU mode I'd be interested to know.
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