user37187: I'm trying to control this servo, and whenever I leave the Uno connected, via USB, to the PC, most of the time the servo barely moves, and sometimes jitters.

simulate this circuit – Schematic created using CircuitLab
I connected the oscilloscope to try to understand / solve my problem, and I see that the signal I send is the same whether or not the USB is connected. I measured the voltage over the 5V/GND and it's constant at 5V and doesn't dip/spikes. I tried with a pull-down resistor on the signal pin (don't know if it's a good idea) and it doesn't change anything.
If I unplug the battery, but keep the USB connected, the servo stays immobile, but I figure that's because the Arduino can't feed a servo, hence why I wanted to use an external power for it. The second power source is a PowerBoost 1000C with a LiPo battery.
As soon as I unplug the USB port, the servo just starts moving properly, so I figured it must be interference of some kind. I saw the accepted answer to this question and it has me doubt whether I should use a battery while it's plugged in, but surely there is a way. Would I kind of need to connect the GND of my circuit to the GND wire of the USB before it actually enters the Arduino?
I didn't post the code as it's basically just the swipe demo from the website, and because it works when on battery only.
Regards

user37187: Beginner error: As stated in the diagram, I connected the external source of power to the 5V pin, while it should have been connected to the Vin pin. /ashame

37187: <p>I'm trying to control <a href="https://www.parallax.com/sites/default/files/downloads/900-00005-Standard-Servo-Product-Documentation-v2.2.pdf" rel="nofollow noreferrer">this servo</a>, and whenever I leave the Uno connected, via USB, to the PC, most of the time the servo barely moves, and sometimes jitters.</p>



<p><img src="https://i.stack.imgur.com/6YHV7.png" alt="schematic"></p>



<p><sup><a href="/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f6YHV7.png">simulate this circuit</a> &ndash; Schematic created using <a href="https://www.circuitlab.com/" rel="nofollow">CircuitLab</a></sup></p>

<p>I connected the oscilloscope to try to understand / solve my problem, and I see that the signal I send is the same whether or not the USB is connected. I measured the voltage over the 5V/GND and it's constant at 5V and doesn't dip/spikes. I tried with a pull-down resistor on the signal pin (don't know if it's a good idea) and it doesn't change anything.</p>

<p>If I unplug the battery, but keep the USB connected, the servo stays immobile, but I figure that's because the Arduino can't feed a servo, hence why I wanted to use an external power for it. The second power source is a <a href="https://cdn-learn.adafruit.com/downloads/pdf/adafruit-powerboost-1000c-load-share-usb-charge-boost.pdf" rel="nofollow noreferrer">PowerBoost 1000C</a> with a LiPo battery.</p>

<p>As soon as I unplug the USB port, the servo just starts moving properly, so I figured it must be interference of some kind. I saw the accepted answer to <a href="https://arduino.stackexchange.com/questions/21061/two-arduinos-one-power-source">this question</a> and it has me doubt whether I should use a battery while it's plugged in, but surely there is a way. Would I kind of need to connect the GND of my circuit to the GND wire of the USB before it actually enters the Arduino?</p>

<p>I didn't post the code as it's basically just the swipe demo from the website, and because it works when on battery only.</p>

<p>Regards</p>
 37187: <p>Beginner error: As stated in the diagram, I connected the external source of power to the 5V pin, while it should have been connected to the Vin pin. /ashame</p>
