When setting up a CNC using Arduino UNO do I need to connect one of the grounds on the Arduino board to the chassis ground? The same one that comes from the wall?
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When setting up a CNC using Arduino UNO do I need to connect one of the grounds on the Arduino board to the chassis ground? The same one that comes from the wall?
yes
There is no need to connect the arduino GND pin to the Earth ground or any chassis ground. If you do, ground loops can destroy the Arduino or generate hard to find errors. This is also the reason you should not use the chassis ground as signal transmitter. The chassis ground should be connected to the earth pin on the wall outlet. Because it is probably made of aluminum you should use a toothed washer between the chassis and the screw to make a good connection (Aluminum is always covered with an thin oxidized layer).
ok now who is right??
Both?
Use a multimeter to ensure that arduino's power supply's input ground is connected to its negative output. If it doesn't, ie it's floating, I'd consider replacing it because you have no idea what potential it's floating around at.
Bond the supply input ground to a star point on the chassis which leads off to the earth pin, with the star washer etc.
Don't use the chassis as an earth wire for the arduino inputs or outputs, though - run a separate lead to wherever you're going. Eg running a single wire to an endstop and using the chassis as a ground might work when you try it but guaranteed it's going to cause freakiness when you need it to be stable.
My arduino is getting it's power from the USB cable. No separate power supply.
Is that a problem?
The USB breakout I had before I replaced it with an ethernet one was like that - completely floating, no grounding, nothing.
I used to get a 2mm spark when I plugged it into the computer, across the shield line. You can't tell me that's good. I also got a bunch of interference issues - until I grounded the frame of the machine to the same earth that the computer was grounded to (on the power board). If the arduino is talking to stepper drivers or a VSD then it's going to ground through them anyway, so I wouldn't get too worried about it.
There should be a common ground point on the chassis and all components should ground to this point including the negative terminal of any power supplies, the Arduino ground, the 120VAC ground wire, and other individually-powered components. This is referred to as "star" grounding and If they are all going to the same ground point then there should not be a ground loop issue.
why the toothed washer? Aluminum and aluminum oxide are both conductors.Quote:
Originally Posted by hfjbuis
The power common terminal of a USB socket in a Tower or Desk Top PC is connected to earth ground via the Mobo power supply common and the board ground plane, which is connected to the chassis and hence sourced from the earth pin on your power socket.Quote:
Originally Posted by tkms002
There is no problem in taking any processor to ground as long as it is done correctly.
The Galil Motion boards I use also do this automatically via the PC P.S. earth ground.
It occurs exactly the same with the printer port common.
Al.
Whenever you make a electrical (screw) connection to an protected conductive (painted steel,stainless steel, aluminum, titanium, etc) you need a toothed washer. When tightened, the tooth "make sure" there is a good electrical connection even is the surface is painted or oxidized. Whenever you loosen the srew connection, you have to change the toothed washer.Quote:
Originally Posted by tkms002
Most (dry) oxides are not conductive,
Here a WIKI quote:
Quote:
Al2O3 is an electrical insulator but has a relatively high thermal conductivity (30 Wm?1K?1) for a ceramic material. Aluminium oxide is insoluble in water. ... Aluminium oxide is responsible for the resistance of metallic aluminium to weathering.
Hmm.Quote:
Originally Posted by hfjbuis
If I put a continuity tester on the surface it makes a connection.
I am using a laptop that is not always plugged in.Quote:
Originally Posted by Al_The_Man
You mean, the probe is able to break through this oxidized layer. Probes should have a very sharp point. Enen if you use a (soft) copper wire, you will probably measure conductivity, the question is if this conductivity will last during the lifetime of the machine.
In Europe this toothed washer is a safety requirement.
Which changes things because most laptops don't even have a third pin for ground (at least in Oz). So you need a way of locally grounding your arduino and, indeed, the laptop via the USB connection so everyone's talking the same reference zero voltage. Star point ground, even consider soldering a nice fat wire to the board next to the USB connector's shield to that star point as a low impedance path for normalising voltages from the laptop.Quote:
Originally Posted by tkms002
Most places it is. Don't forget that brushing a probe on continuity sense has a very low current and thus minimal voltage drop across the connection. Crank up the current and you may find that the connection to an oxidised ali surface creates such a high voltage drop it becomes next to useless.Quote:
Originally Posted by hfjbuis
thanks I will add themQuote:
Originally Posted by hfjbuis
my laptop does have a third wire on the charging cord. When I created my electronics box I added a grounded 120v power outlet that I plug the laptop into.Quote:
Originally Posted by dharmic
So, I will run a wire from the Arduino GRD to my common ground(a bus bar). I will add star washers in between the ground bus and the chassis.
Thanks