I'm trying to make a DIY cessna simulator, and for that I'm using servos and steppers for the gauges and different instruments. I use a 300 W pc power supply for the servos and steppers, the arduino is connected with USB to my pc. I use +5v and the ground out of a molex of the psu for all the servos and the ground of the arduino is connected to psu ground. A CD rom drive is connected to the psu for allowing it to work with a minimal load. My problem is that despite the connected ground I still have ground issues. When I use even a single servo with the psu, the servo behave strangely. When a send it to a position it's working perfectly without any vibrations or unwanted mouvement but when I move of I touch something big and metallic (like my chair) around me the servos make some big movements and goes back to position right after. So I tried to power a servo from the arduino and it's working perfectly even if I move or touch anything.... Tous i'm suspecting that's related to the power supply but I'm note sure .... If someone had the same trouble or have any suggestions about it, I will highly appreciate it.
Tanks for the reply Morgan
the 5v and the ground are from the same connector but i made a mistake in the previous post by saying that i used molex. What im using is a sata connector; I dont think it change anything but who know....
I have new things to report after some testing. After thinking about my ground issue i plug the servo PSU with an extansion plug to the same wall plug of my pc, this way i'm sure that the 2 psu are on the same ground and it's not a issue from my house electrical ground. But as expected the problem is the same. Afte that i try to power the servo with my pc Power supply, and before that i was sure that if i try this the servo and the arduino will be on the same ground. But it doesn't change anything....... So now i realy dont now what else to try ..... If i still have this problems it means that the usb of the arduino and the servo are on differnet grounds or i'm totaly wrong from the begining and the solution has noting to do with the ground.
But still i'm full of question now and i hope that someone have the ansers for these questions :
Are any reason for the Usb and the molex to be on different grounds ? is it even possible ?
If a use a capasitor between the +5V and the GND of the servo for "smoothing" the signal will the issue be fixed ? and does this solution means that i will lose some reactivity from the servo as the signal is passing through a filter ?
I now there are a lots of questions but it start to drive me crazy...... I dont see why it works preferctly when i power up the servo from the arduino and then it become sensible to electomagnetic nose ( i assume that's what hapens when i start moving or touching metalic things) when i use and external PSU even if all the psu are to the same ground...
Do you mean that my psu and pc have a floating ground ? In that case I assume that the each psu have internaly a metal plate for a ground reference. (but I'm not sure). If that's true I don't understand why I have a ground loop in my system as the signal grounds and the power ground are note the same
I'm back with some news. After trying almost anything I found a 9g servo from a different brand, it's the velleman vr006, and I give it a try because you never now..... Surprisingly It works ! The arduino connected to the pc and the +5 and Gnd of the servo to the psu, without any unwanted mouvement when I move something metallic near it. So now I want to now why this happen to me, why the behaviour of the servo are different and why all my previous servos, btw the are kuman sg90, are so sensible to noise. I understand that quality is involved but at these states the kuman servo are not suitable for any project if you need to use a psu. One last thing I will try with the kuman servo is to use a capacitor between the signal and Gnd and between the +5 and Gnd just to see if it help.
A mains ground loop won't normally affect logic signals, which have several volts of noise rejection,
so usually just connect all the grounds. If you have several volts of IR loss across your wiring it will
be getting very hot!
Low voltage analog signals like audio signals are a completely different matter, its very easy to get
mains hum from any ground loop as signals of a few mV are very audible.
It is more likely in your situation that there's a source of high frequency noise involved, which sees
the inductance of the wiring, not just its resistance, and hence can easily generate many volts of difference,
and the normal strategy is to prevent the noise coupling into circuitry, usually meaning shielding, and to
filter it out where possible.
Putting a capacitor more than a few hundred pF between your servo signal and ground will overload the Arduino pin - don't do this, use an RC filter instead, the R protects the pin, the C prevents noise entering the servo.
Try 1k / 1nF perhaps, a timeconstant of 1us.
The other way noise can get in is by induction (ie magnetic interference), which couples to any loop.
