Unplanned behavior with two power sources 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 &ndash; 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
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