I am new to Arduino and am reading Learn Electronics with Arduino: An Illustrated Beginner's Guide to Physical Computing. On page 118, it says:

Remember, whenever you make adjustments to a circuit, your Arduino should not be attached to your computer.

To give more context, it means when you make adjustment to the circuit on the breadboard, you should detach the USB cable from the computer.

I am wondering why?

Is it because a short circuit can crash my computer similar to how the USBKill works? Are there other reasons?

  • 1
    Arduino should not be attached to your computer. that is misleading ... it should say Arduino should not be powered.
    – jsotola
    Commented Nov 2, 2021 at 22:23

3 Answers 3


Is it because a short circuit can crash my computer ...

It is more that you don't want an inadvertent mis-routing of cables to burn out your chips while they are powered.

I wouldn't personally be making changes to a breadboard circuit while it is powered. It is better to do it un-powered, and then check it over, than wonder why there is smoke coming from it.


"Adjustments to a circuit" can mean removing, adding or repositioning components on the breadboard. One can accidentally position a component lead in an incorrect location on the board, creating a circuit that is undesirable and possibly damaging to the assembled project.

If the misplaced lead or leads are in a particularly unsuited location, the circuit can include the USB portion of the system. The probabilities are low that one would accidentally damage that specific set of traces, or send voltage where it should not be, but they are non-zero. Even if one damages the Arduino, the cost is low compared to a damaged USB port or computer.

If you've been creating simple Arduino circuits and have misplaced or mis-routed a lead or component, you've learned how easily that can happen. Disconnecting the USB is comparably a minor inconvenience.


Is it because a short circuit can crash my computer

More than crashing it, there is some risk that a short-circuit on your board could cause damage to the computer's USB port that is powering it. Most computers have overload protection on their USB ports but you don't want to test it unnecessarily, risking permanent damage to the port.

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