servo jitter with DC

I have a servo that is set as a knob with 10k potentiometer. When I connect the servo to arduino usb, it works just fine. If i connect the servo to a DC breadboard jack seperate from arduino, it jitters badly. Now, when i have this servo hooked up as a sweep (preprogrammed motion), it works just fine, no issues. It seems that only when i am using a pot that it jitters when hooked up to a seperate DC source. Ideas?

My answer is going to be bad and likely wrong, but I’ll provide it anyways. If you have the Arduino on a separate power source as the servo, make sure you connect the Arduino’s ground to the separate power source’s ground. The Arduino then would have two grounds (one via USB or other source, one for signaling the servo).

My guess is this is not the problem as I would expect this to cause the servo to just not work, rather than jitter. But lacking another response, I thought I’d provide you with something.

Thanks noble, I do have the ground routed from the breadboard to the arduino ground. If I didn't, than the servo just doesn't work. What puzzles me, is that the sweep program works fine, is I assume there is something wrong with either the pot or the analog pin, highly unlikely though.

Show us a picture of the setup the has the problem.

Hi, what is the power supply you are using to power the servo?

Tom........ :)

Tom, I am using a 4.5v @ 500 MA. After testing it, it actually reads at 6v. The servos take up to 7v at max. I thought it was a power issue until I saw the sweep program run nicely.

Hi, okay but servos can draw more than that 500mA on peak loads. I'd put a 1000uF cap across the supply wires at the servo to see if it makes any difference, a servo in motion and a servo keeping position are two different dynamics. Also try 10uF from the pot wiper to gnd.

Tom..... :)

Tom, I am using a 4.5v @ 500 MA

No, you're using (I imagine) a "4.5V @ 500mA".

Tom, thanks, I happen to have those caps lying around.

Be aware that most hobby servos are rated for 4.8v to 6v, and may pull more than 500mA when operating. Attach your multimeter to the power supply and see what the actual voltage is when the servo is attempting to move.

You have a decoupling capacitor on the analog input pin? 100nF or so would remove most noise from the pot or wiring.

You must run a separate ground wire from the Arduino to the 0V side of the pot, you should not share this with the servo ground, nor run the pot wires alongside the servo power wiring.

Mark, you are saying that I need to keep the negatives of the servo and pot grounded seperately? So would I be able to do that on the secondary ground on the uno?