Please help with this error. Arduino: 1.8.10 (Windows 10), Board: "Arduino Uno"

Sketch uses 882 bytes (2%) of program storage space. Maximum is 32256 bytes. Global variables use 9 bytes (0%) of dynamic memory, leaving 2039 bytes for local variables. Maximum is 2048 bytes. avrdude: ser_open(): can't open device "\.\COM4": Access is denied.

Windows 10 Pro Arduino UNO ATmeg 328P-PU Have never been able to Upload a sketch. Pin 13 and Orange LED blink at 1 second


1 Answer 1


Welcome to the Stack Exchange and on the Arduino World.

Just a note: Since yesterday there is a new version of Arduino IDE (the last version is now 1.8.11).

When you buy an Arduino, a default sketch is already present. This will blink your LED (pin13) with a 1 second interval. This just mean that your Arduino is working and has a bootloader.

To program it, you need to know which COM port is created for your Arduino module:

  • Press WIN-'R' (execute application)
  • Write devmgmt.msc

Check the COM port to see wich COM port was used for your Arduino.

This is the only cause, the message could appear if you use a standard USB-cable connected to your standard Arduino UNO board.

  • 1
    did you search for an existing answer?
    – Juraj
    Commented Jan 28, 2020 at 14:36
  • 1
    Checked again and Arduino Uno is connected to Comport 4. And disabled Windows Defender Firewall. No success.
    – Izak Krige
    Commented Jan 28, 2020 at 15:36
  • It seems that the port was already opened (as the question is now marked as duplicate).
    – Adriano
    Commented Jan 28, 2020 at 16:02

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