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Projects General Guidance
1

Arduino: 1.8.9 (Windows 7), Board: "Arduino/Genuino Uno"

Sketch uses 3420 bytes (10%) of program storage space. Maximum is 32256 bytes.
Global variables use 216 bytes (10%) of dynamic memory, leaving 1832 bytes for local variables. Maximum is 2048 bytes.
Sketch uses 3420 bytes (10%) of program storage space. Maximum is 32256 bytes.
Global variables use 216 bytes (10%) of dynamic memory, leaving 1832 bytes for local variables. Maximum is 2048 bytes.
avrdude: ser_open(): can't open device "\.\COM3": The semaphore timeout period has expired.

Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

2

You've either chosen the wrong serial port or your user doesn't have permissions to use it.

3

sometimes you have to completely shut down the IDE program and the arduino and restart them both for them to recognize each other. The COM usually shows up automatically when it's recognized by the IDE program, but sometimes you have to select it in the tools. also if your using an older or longer USB cable, it could have an issue with it as well. But i'd restart everything, and close any unnecessary windows and try it again. I've had other programs effect an upload before.