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Topic: [SOLVED] Instability on ATX suply for Servos (Read 143 times) previous topic - next topic


May 19, 2019, 05:56 pm Last Edit: Jun 01, 2019, 08:45 pm by maccraft
[Solution at the end of post]

Hi everyone! This is my first post in this forum.
I've searched for this answer in many places and I can't seem to find it, so I hope I'm not double posting or something like that.

I'm starting working with Arduino projects, and in my actual project, I need to run a few servo motors.

I, like many others, turned an old ATX1 PSU into a "bench" power supply (since Arduino can't provide enough current to power all the servos).
I connected an 8.2-ohm 10-watt resistor in the 5v rail of the PSU (which is the one with the most current available) and then tested it. I did this because of the many recommendations I saw online. In theory, this would make the tension more stable when drawing small currents.
I noticed that in the 3 rails I connected (3.3v, 5.v and 12v) I read a slight but continuous voltage fluctuation, around +/- 0.02 volts.
I thought that this would be insignificant, but when I connect my servos to the 5v rail, they jitter a lot, they work in a very unstable fashion.

If I connect them to the Arduino's 5v instead, they work like a charm.

So... is there any way to make this ATX's Outputs more stable?

Or is it that the problem is another one that I'm not seeing?

I connected both, Arduino's and ATX's, Grounds together.
The Arduino Uno is powered by the USB port.
Every Servo (SG90) is connected to the positive of the 5v ATX Rail, and to its Ground.
The signal pins of each servo are connected to a PWM output pin in Arduino.

If I unplug the +5v and GND of the ATX from the breadboard and connect the 5v from Arduinos 5v pin instead, it works fine.

For these tests, I'm only using 1 servo to avoid overloading the Arduino.

Thank you all in advance for your attention, and excuse my poor English T_T


First of all, thank you to the ones that took the time to reply to this. I know it is a very noob question so, again, thanks!

I solved the issue simply by connecting a 7805 voltage regulator to the output of the power supply, and then connected my project to the regulator's output and bam! No fluctuations at all and my servos work great now.

I've read that putting a 470uF (or above) capacitor in parallel with each of the servos would smooth their movement, so I will try it.

Thanks again!


You can also add some big caps. Or check the +5V with an oscilloscope, maybe the supply is bad.


Don't forget you can use the +5 volt and +12 volt pins to get 7 volts out of a atx powersupply

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