Jerky servo motion using 9vdc wall-wart.

My program(servo control using sonar ranging) works great as long as the usb is connected however, when a 9vdc 500ma wall-wart is used without usb, my servo movement is extremely jerky(continuous rotation servos ). There are no Serial statements used at all so the PC is needed only to program. The range is read using the pwm on pin 10 of the Uno. Any ideas would be appreciated.

9V is too high for most servos, 0.5A is too low for almost all servos…

Typical servos pull an amp or two from 6V or 7.2V supply, many run down to 4.8V

I was using the 5v from the Uno to power the servos and after a lot of reading it seems that could be my problem. From all I have read the way to power servos is with a dedicated battery source making sure the ground is connected to the Uno. I will try this with hopes it solves my problem. Thank you for the reply :slight_smile:

slvrhawk2134:
I was using the 5v from the Uno to power the servos

That's even worse, you even risk damaging sensitive ICs by sharing power with motors like
that.

Power servos if possible from 6V 1A (or more) separate supply. The onboard regulator
cannot handle large currents, and may just shutdown if you try to pull too much
current through it. It can also overheat.

In general for high power / high current devices using a linear regulator is a poor
choice - make the supply be the correct voltage in the first place. Then you don't have
to worry about thermal management (cooling regulators)

It worked great after I used separate battery power for the servos and Uno. It really does feel good when a plan comes together :slight_smile: Thanks for all the wisdom passed on to me. :slight_smile:

Excellent! For future reference, you were probably seeing the effects of the over-current protection/shutdown kicking in on your power supply.

MarkT:
In general for high power / high current devices using a linear regulator is a poor
choice - make the supply be the correct voltage in the first place.

Also for future reference, here is a 5v 2a switching wall wart that will drive the crud out of servos.

(no affiliation, I just own one)