Arduino Uno recognized as 'Unknown device'(no problems with the driver)

Yesterday, I accidentally had 5V and GND of my board shorted. My computer recognized the board as 'unknown device', but after cooling down the board for a while, it worked normally again.

But when I plugged the board to the computer today, it says 'unknown device' even though I did nothing to the board today. There was no problem to the driver(when I tried to reinstall it, it said that the correct driver was already installed). The board is intact outwardly... what is the problem?

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spycatcher2k: You burned something out!

But then how could my computer recognize my board normally YESTERDAY(after cooling down)? If I really burnt something, then I couldn't have used it yesterday.

  • I managed to make my computer recognize the board normally, but IDE is keep saying "error opening COM8"...

How was the Arduino powered? From USB?

But then how could my computer recognize my board normally YESTERDAY(after cooling down)? If I really burnt something, then I couldn't have used it yesterday.

1) Long ago (when computers still had serial and parallel ports) I had a computer plus device hit by lightning. Fixed the computer up but had issues with the device; although communication with the device initially worked, it started failing at occasion. Eventually I could no longer communicate, whatever I tried.

2) Even longer ago, I worked in the test industry where (amongst others) microcontrollers were tested. We did (independent) QA tests of a certain microcontroller for a certain customer that used those tested micros in their products; average failure rate extremely low. Suddenly the pass rate went down and analysis showed an input leakage that was outside specification on a certain pin of the micro. We rechecked the complete batch again (with full 'debug') against a golden sample and the input leakage of the specific pin was higher than that of the golden sample but still within specification. The test was done again a week later and devices that passed the week before now failed.

Analysis showed a hot spot on the die for the specific pin; the electronics around the pin was damaged resulting in higher currents resulting in more heat resulting in more damage resulting in even higher currents ... Eventually it was found that the micro manufacturer had an ESD problem in the final stage where the microcontrollers were 'packaged' into tubes.

Lesson: lightning and ESD can be slow killers.

The same can apply in your situation.