Connect Arduino Safely


This is my first message here ...

I have this a Uno R3 that I had it connected to a 12V 1500 mA source. And I decided to created a small test so see how easy is to program it.

The moment I plug in the USB cable into the laptops port the laptop when dark and will not start!

I will try later today to take the battery out and see if that helps but I am afraid I fried it...

What is the best way to connect an arduino safely and if there is a risk to the computers why is this not clearly stated ?!

Can anyone chime in a bit about this topic ? Thank you!

The only real risk involved is when you have made a wiring mistake or are sitting a working project on a conductive surface etc.

USB ports are or should be designed to shut down if a fault occurs.
That fault should clear when the offending item is removed and a computer is re-booted.

If all you had connected was additional power and it was connected properly then there should not be any issue.


Just to be clear there was no shield connected on top of the arduino and no other circuitry.

The power supply was connected and the board was mounted on a plastic case so it was 100% electrically insulated.

The laptop went black the moment the usb cable was connected to it.

I really hope I haven't fried my laptop. Will know more in the evening after I pull the battery out.

The one thing I do recommend is to keep the voltage lower than 12 volts as it means the regulators have less work to do and will ultimately last longer.

Let us know how it goes.


I removed the battery and the laptop doesn't want to go.

When I get the power supply plugged only the power led turns on. Now I can't trust that board to plug it in any other pc without inline hub or inline measurement tool.

Sorry about your computer. Hopefully it will be ok. Can you post a picture of the way you have the external power supply attached to the UNO?

Agree with Olaf.

Also double check the output of the power supply you used for the Arduino with a multimeter / dvm.
Something seems to have been horribly wrong with some wiring for it to take out a laptop.

For additional reading this may be of use.
Notice the killing of USB is almost always misuse of external power rails.


Hello there,

Please note that by connecting the USB between your PC and Arduino your board is already receiving 5V required to operate. There is no need to power the board externally when connecting via USB.

Other good practices to consider to connect Arduino safely below:

  • Make sure the board is resting in a secure place with no conductive materials close to it. Also make sure it is not laying down on metallic surfaces.

  • Check the connections are secure and not touching/interfering to each other.

  • Remove the protective foam that comes with the board package box before connecting the board

  • When powering the board from external sources such as batteries and voltage suppliers make sure the voltage applied is within the recommended range of that specific board. This information is usually found on the back of the box and on the product page tech specs. The voltage must be applied between VIN pin and ground.

  • Never attempt to power the board through other I/O pins (unless it is the VIN designed to power the board). Please refer to specific board type to find out maximum voltage input for I/O Pins. Some boards operate at 5V but other do at 3.3V so ensure what is the right voltage before making connections.

I hope this was useful.

Well yes. Having electrodes close to vital organs, operated by insufficiently skilled people does require a certain degree of bravery...or carelessness.

However people work constantly within these levels and rarely there are lethal accidents. Also, considering the electrodes are attached to the skin surface...the safety margin widens.

Speaking strictly personally...if it was my project, tested on myself...i'd probably go forward without that much hesitation. Especially if it's more of a one time only kind of thing. If it would be tested on others in variable circumstance...then it would be very wise to give it a second thought.

If you're really paranoid then i guess running the system on low voltage batteries and saving the data on an SD module for later analysis is a...doable way.

Hopefully you connected the battery between “Vin” and “0v” , with battery “+” to Vin .

Finally got some time for an update.

The Laptop is Dead, Long live the Laptop(waiting for Black Friday)

Secondly, the Arduino, which is an Elegoo Uno R3 clone seems dead too. I connected it, not powered externally, using an older another laptop and shows as Unknown device. Has the TX LED on regardless if is connected or not. Also using same machine I managed to program successfully a brand new Arduino Genuino.

Ps. for the record this Elegoo was connected on the barrel roll connector and never via the Vin.

Is the lesson learn here not to connected an externally powered Arduino to any machine? I am surprised my PI never had that issue. As a matter a fact I did have that connected with an external powered arduino for years... Weird!