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I'm using a MacBook Pro Mojave 10.14.6 to code genuine Arduinos. Been working with multiple Uno R3s, no issue. Got a genuine Nano and get the following error: ser_open(): can't open device "/dev/cu.usbmodem14201": No such file or directory

The USB cable I'm using works fine with a cheap Chinese Uno clone, so there are data pins in the cable.

I followed instructions to delete the kext file, rebooted, installed CH341SER_MAC file and rebooted. Still getting the error message. I notice that others have asked this question; where are the answers? Thanks in advance.

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  • What triggered this error message? – JRobert May 16 at 11:42
  • Also, you shouldn't need a CH34x driver. A genuine Arduino would have an FTDI chip, for which MacOS has the driver built-in. – JRobert May 16 at 12:05
  • The error message was triggered when I attempted to upload a simple sketch to make the LED blink on and off, to test the Nano. It is absolutely a genuine Arduino; that's the only thing I buy, in support of the Arduino ecosystem. Got it from Amazon, sealed OE box. I also bought 4 Unos at the same time, all of them work fine with the same sketch. My kid bought a cheap Chinese knock-off for school which doesn't always work perfectly (which is another reason why I buy genuine only), but has the same USB cable connector as the Nano. So the cable isn't the problem. Software is fine, cable is fine. – Hunter Johnson May 17 at 11:53
  • What was the actual action that triggered the message, e.g. connecting the Nano to the Mac? Selecting the port in the IDE's 'Tools' menu? Clicking 'Upload'? You're using the physically same cable for either Nano and one nano works but the other doesn't? Have you tried a cable swap anyway (since your success with the Nano clone was intermittent)? – JRobert May 17 at 14:05
  • What was the actual action that triggered the message, e.g. connecting the Nano to the Mac? "The error message was triggered when I attempted to upload a simple sketch to make the LED blink on and off" You're using the physically same cable for either Nano and one nano works but the other doesn't? "No, the Chinese knock off is a Uno clone that uses an USB-C connector, same as the Nano.", Have you tried a cable swap anyway (since your success with the Nano clone was intermittent)? "Not a nano clone, it's an Uno, and I don't have a second cable that is reliably data and charging capability." – Hunter Johnson May 18 at 0:29
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Timekeeping isn't exact with any of the boards, though .05% - just over 7 minutes/day - doesn't sound like too high an expectation.

Restarting when you connect it to your computer is by design and doesn't indicate a fault. Opening the IDE's terminal or connecting another terminal program to a connected and running Arduino will - and is supposed to - reset it. Here is a forum discussion on how to disable the auto-reset function (Uno-specific) if you want to. Note that it involves modifying the board.

It's quite possible that this one board has a fault, though it still could be the cable. A couple of swaps should confirm it one way or the other.

I'm still not clear on where the error message,

ser_open(): can't open device "/dev/cu.usbmodem14201"

came from, but I'm guess it's from AVRdude, the uploader application on your Mac, and still I'm wondering if the correct port is selected in the IDE's Tools | Port menu? For some reason, a USB device called "cu.usbmodem14201" is expected but not found. Since neither the Mac nor the IDE inherently knows this name - a USB device announces its name when you connect it - could this selection be left over from having previously used the genuine Arduino? Another reason to check the Ports menu. Also note that the Ports menu doesn't update its list spontaneously - only when you open it (and maybe only when you open the top-level, Tools, menu; I don't remember exactly).

Update:

The regular Arduino at 0.5% is pretty crude, I'd pay more for a more accurate crystal, but I was able to develop a sketch that adjusts for the Arduino's inaccuracy.

You could try putting the Arduino in an "oven" - and I emphasize the quotes. This is not a heating chamber per-se but a temperature controlled chamber. If you're getting good results by adjusting the count, adding the oven should get you even better results, especially as the seasons change and if that makes enough difference where you are.

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  • I'll be damned, I went to Tools/Ports and selected "dev/cu.usbserial-AK069QY4 and uploaded a sketch successfully. Regarding the timekeeping, 0.05% doesn't cut it for my application, I'm looking for better than 1 second in 24 hours, which is 1/86,400, or 0.0012%. The regular Arduino at 0.5% is pretty crude, I'd pay more for a more accurate crystal, but I was able to develop a sketch that adjusts for the Arduino's inaccuracy. Anyhow, thanks for pointing me in the right way. :) – Hunter Johnson May 21 at 0:13
  • You're welcome. If the answer solved your problem, please select it so. It will keep it from falling into the barrel of presumed unanswered, but abandoned, questions that like the phoenix, keep rising from their ashes (auto-reposted). – JRobert May 22 at 19:46

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