Hi @elral. There has been a recent spike of reports of strange problems related to the ports of boards using the CH340. The reported symptoms have not included resetting, so I'm not sure your issue is the same, but I'm at least suspicious it might be.
Some users have reported that they determined the cause of their problem was a Windows update that included an update for the CH340 driver:
There are several reports of people solving the problem by installing drivers obtained from various 3rd party sources. Since I think it is risky to install drivers obtained from any source other than the chip manufacturer (WCH in this case), I have been suggesting an alternative possible solution of using Windows Device Manager to do an uninstall/reinstall cycle of the device. The two users who tried that technique reported it fixed the problem they were having with their CH340 boards, so it is worth a try at least. I'll provide instructions you can follow:
- Close any applications that might connect to the port of the Nano (e.g., PuTTY).
- Connect the Arduino board to your computer with a USB cable.
- Open the Windows Device Manager.
- Select View > Devices by type from the Device Manager menus.
- Open the "View" menu.
- If there is a ✓ to the left of the "Show hidden devices" menu item, click on "Show hidden devices" to disable it.
- Open the "Ports (COM & LPT)" section of the Device Manager tree.
- You should see a port identified as "USB-SERIAL CH340 (COM_n_)" under the "Ports (COM & LPT)" section (where "COM_n_" is some serial port e.g., COM4). Right click on that item.
A context menu will open. - Select "Uninstall device" from the context menu.
An "Uninstall Device" dialog will open. - Check the box next to "☐ Attempt to remove the driver for this device" in the "Uninstall Device" dialog.
- Click the "Uninstall" button.
- Wait for the uninstallation process to finish.
- Unplug the USB cable of the Arduino board from your computer.
- Wait for the Device Manager tree to reload.
- Connect the USB cable of the Arduino board to your computer.
- Wait for the "USB-SERIAL CH340 (COM_n_)" port to reappear under the "Ports (COM & LPT)" section of the Device Manager tree.
My experience is that the device will be reinstalled automatically by Windows. However, it is maybe possible that the complete driver removal will actually have been accomplished by the above instructions, in which case it will be necessary to reinstall the driver. If this happens to you, please let me know and I'll provide instructions for installing the driver.
Once the port has reappeared in Device Manager, check to see whether the problem still occurs.