Difference between these types of ground? (symbols)

Thread Starter

pplg

Joined Nov 19, 2019
14
Hi everyone,

Could anyone tell me what's the difference between these types of GND? What would happen if I connect them? I am trying to connect an external board to this circuit and I am confused. Thank you in advance!

1591653393160.png
 

dl324

Joined Mar 30, 2015
11,000
I think it was just carelessness on the part of whoever created the schematic and I'd connect them together.

As a matter of principle, I wouldn't use any circuits from someone who drew a ground symbol upside down. Ground should always point down.

The generally accepted symbols are:
1591654496822.png
 

nsaspook

Joined Aug 27, 2009
7,356
I think it was just carelessness on the part of whoever created the schematic and I'd connect them together.

As a matter of principle, I wouldn't use any circuits from someone who drew a ground symbol upside down. Ground should always point down.

The generally accepted symbols are:
View attachment 209180
What about when you are in Australia? :eek:
Generator_Safe-768x432.jpg
 
I was chatting with a friend from oz. I said I'd like to be his neighbor so I could play with his toys. Then he said, you could possibly seek asylum from the US. Before that sometime he said, you should live in a civilized country.
 

dl324

Joined Mar 30, 2015
11,000
Then he said, you could possibly seek asylum from the US. Before that sometime he said, you should live in a civilized country.
I meant no disrespect to Australians or their country. I'm not going to take any trips by plane until they can do it safely or there's a vaccine for COVID-19.

For some reason, that's a common perception around the World these days. It has gotten seriously bad recently with talk of using active duty soldiers to quell protests, and having video of police striking foreign reporters and crew, but things are starting to look up because the secretary of defense sent the active duty troops away from DC; or at least that's what they're saying.
 

WBahn

Joined Mar 31, 2012
25,927
Hi everyone,

Could anyone tell me what's the difference between these types of GND? What would happen if I connect them? I am trying to connect an external board to this circuit and I am confused. Thank you in advance!

View attachment 209178
Most schematic capture tools connect global signals by name, so all of those connect to the signal named "GND". Some tools reserve the traditional ground symbol for Node 0 (but some allow you to also associate a named node with it). It's hard to say without digging into either the documentation for your schematic capture tool or examining the netlist.

But which node they are connected to is only the start of the battle -- there are many other issues that might need to be taken into consideration from a layout standpoint. It's possible that the intent of using the different symbols was to at least hint at these, such as a digital ground and an analog ground that, when all is said and done are, to first order, the same node.; but I wouldn't bet on it.
 

Thread Starter

pplg

Joined Nov 19, 2019
14
Most schematic capture tools connect global signals by name, so all of those connect to the signal named "GND". Some tools reserve the traditional ground symbol for Node 0 (but some allow you to also associate a named node with it). It's hard to say without digging into either the documentation for your schematic capture tool or examining the netlist.

But which node they are connected to is only the start of the battle -- there are many other issues that might need to be taken into consideration from a layout standpoint. It's possible that the intent of using the different symbols was to at least hint at these, such as a digital ground and an analog ground that, when all is said and done are, to first order, the same node.; but I wouldn't bet on it.
Thank you all for your replies! The part of the schematic I posted is from a widely used 3D printer main board called "Mini-Rambo". You can see the rest here: Complete schematic.

From a place of ignorance I think that there must be some kind of difference bewtween those two GNDs. It's really strange. The board is a 4-layer type. Could it be to differenciate between ground planes from different layers?

Thank you!
 

Freq

Joined Oct 25, 2019
9
it looks to me like one of the grounds used a traditional gnd symbol while the other used a "power port" (see how the 12V or VCC have the same symbol as one of the GNDs. Like mentioned above, they should be tied together via net name when doing the pcb layout but it wouldn't hurt to verify. If you have this pcba in your possession, I would manually check the resistance between those two nets.
 

Freq

Joined Oct 25, 2019
9
It was not a comment but a question. :confused:
Mostly the wrong symbol is generally used.
Or mis-use of the earth-GND symbol.
Max.
well, an earth-gnd symbol can also be referred to as a power-gnd. I referred to "traditional GND" as a GND symbol that is more commonly used. the power port "bar" symbol is normally used to identify a positive voltage source. Using that power port "bar" symbol for GND isn't the best practice (at least that is what i was tought), but as long as the net names are the same, the software tool should tie them together during layout. There are also other GNDs in the schematic which have different net names (GND1 and FGND).
 

MaxHeadRoom

Joined Jul 18, 2013
20,927
Different names to ID separate ground planes is OK.
It is when the earth GND symbol is used in a general way, whether the plane IS actually at a earth GND reference or not, is where the confusion comes in.
IOW, IS the plane meant to be earthed or not!??
Max.,
 

Thread Starter

pplg

Joined Nov 19, 2019
14
it looks to me like one of the grounds used a traditional gnd symbol while the other used a "power port" (see how the 12V or VCC have the same symbol as one of the GNDs. Like mentioned above, they should be tied together via net name when doing the pcb layout but it wouldn't hurt to verify. If you have this pcba in your possession, I would manually check the resistance between those two nets.
Thank you. I am going to do the test and see then :)
 

schmitt trigger

Joined Jul 12, 2010
284
I have seen several times boards which have "digital grounds" and "analog grounds". Different devices are connected to one or another depending of the type of signal they are manipulating.

Back at the power supply common, they are interconnected with an inductor.

At DC, they are essentially the same ground. But at higher frequencies, or the harmonics of those frequencies, they will be an open circuit. The idea is to prevent digital noise from corrupting sensitive analog circuitry.
 
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