Arduino Uno Performs Differently when Powered by Wall Adapter


So I have my desired program running fine on my Uno when it is plugged in via USB to my computer, however, when I unplug the USB cord and plug in my 9V DC line from my wall adapter to the power plug on the Uno, my LCD screen and servos do not perform correctly at all. Also, the performance is never consistent with the wall adapter. I also tried just using a 5V USB wall adapter to power the Uno through its USB port, but the components still did not operate how they did when the Uno was plugged into my computer.

Any thoughts on how to get my Uno to work properly when not plugged into my PC?


Is your PC a laptop or desktop? Basically is the computer connected to a power cable that is plugged into the wall.

What is your power supply’s current rating? LCD screens and servos can draw a decent amount of current and your power supply may not be able to keep up.

I'm on a desktop.

And I am using 2 of these servos:

and my LCD screen is:

My power supply's current rating is 1A.

Sounds like you might be overloading the UNO on board voltage regulator when you use the external power jack.

Power the servo with your external 5V power supply (its gnd goes to the Arduino gnd). Then try the 9V supply with the UNO.

I know when you use the vin pin you have to be well higher than 5v. I had to use 12v on the Vin pin. Before the sketch wasn’t working right at all. I think the barrel jack uses the same regulator

The barrel jack does use the same regulator, except there's an extra polarity-protection diode. So for completeness, the barrel jack does need 0.7v higher than Vin.

But 12V on the inputs (either of them) will overload the regulator in this case because the LCD and the servos are drawing so much from the 5V line that the small onboard regulator cannot supply enough current.


Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png or pdf?

Tom.... :)