Two grounds - same symbol

Thread Starter

El Zu

Joined Jan 13, 2016
22
Hi!

Can anybody explain the meaning of the GNDs on the schematic? The same symbol for the two GNDs?
By the way, this is the power supply part of the audio device.
 

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dl324

Joined Mar 30, 2015
10,538
Welcome to AAC!

Nets with the same name are assumed to be connected; it's a convenience that tends to make schematics easier to read, if not abused.
 

AnalogKid

Joined Aug 1, 2013
8,385
Don't know. The 7812 is a non-isolated voltage regulator, so the input circuit and output circuit references voltages (grounds) should be the same for proper operation. Another question is why are there two rail-splitters, especially when one of them is so lightly loaded.

ak
 

GopherT

Joined Nov 23, 2012
8,012
Hi!

Can anybody explain the meaning of the GNDs on the schematic? The same symbol for the two GNDs?
By the way, this is the power supply part of the audio device.
Are there other pages for the schematic of your project? This first one doesn't make much sense my itself.
 

Papabravo

Joined Feb 24, 2006
13,560
Normally GND nets with different net names are used to separate the routing of digital ground from analog ground. In layout they are generally connected at one point only, where power comes into the board. This means noise on a digital GND has to travel all the way to the single common point and then all the way out to the analog chip.
 

Thread Starter

El Zu

Joined Jan 13, 2016
22
Welcome to AAC!

Nets with the same name are assumed to be connected; it's a convenience that tends to make schematics easier to read, if not abused.
Thanks. I get it, they are all the same, but what about that two notes GND and GND1. I can't the reason to
Don't know. The 7812 is a non-isolated voltage regulator, so the input circuit and output circuit references voltages (grounds) should be the same for proper operation. Another question is why are there two rail-splitters, especially when one of them is so lightly loaded.

ak
Both are go to opamps. Maybe it refers to pcb layout, separate chassises to avoid the hum? It makes no sense, anyway :)
 

Thread Starter

El Zu

Joined Jan 13, 2016
22
Normally GND nets with different net names are used to separate the routing of digital ground from analog ground. In layout they are generally connected at one point only, where power comes into the board. This means noise on a digital GND has to travel all the way to the single common point and then all the way out to the analog chip.
It sounds reasonable! So, i should connect GND and GND1 to one point only on the pcb layout, and GND1 goes to all the points?
 

dl324

Joined Mar 30, 2015
10,538
So, i should connect GND and GND1 to one point only on the pcb layout, and GND1 goes to all the points?
Eventually, all grounds will be connected together; it's how you do it that matters.

What are you trying to do? Understand the design, replicate, or repair?

There is an art to laying out circuits that can't be captured in a schematic. You need to use your knowledge of the circuit and components being used to lay them out properly to avoid certain problems. Proper component placement can mean the difference between a circuit that works and one that doesn't.
 

MaxHeadRoom

Joined Jul 18, 2013
20,465
The common chassis ground symbol can be used for different/separate commons in a circuit, to keep them electrically separate they are labelled with different notation.
Max.
 

SLK001

Joined Nov 29, 2011
1,543
Are the GND and GND1 just labels, or are they the name of the NETS? If they are just labels added by the drawer of the schematic, then the drawer made a mistake. If they are the names of the NETS, then you will have trouble routing the board, since net GND and net GND1 are NOT the same, so they cannot be connected. As AnalogKid said in post #5, your regulator has common grounds - both input and output grounds are the same. In you schematic, they are DIFFERENT (in error), so your circuit doesn't work. Since it obviously does work, the two grounds are just mislabeled, so just ignore the two labels.

Conventional design standards state that different GROUNDS should have different symbols. If they are eventually connected, you will have a net that connects the two symbols somewhere on the schematic.
 

MikeML

Joined Oct 2, 2009
5,444
Back in my day I designed circuits with as many as five grounds, each with a unique Net Name (Gnd, AGnd, DGnd, Vss, MotGnd) for PCB layout. In the final application, all of these externally connected to the 0V terminal of some external power supply, but they were never bridged on the PCB. This is done to prevent common-mode currents from large motors/relays/valves from flowing along analog sensor grounds, for-example. Single Point grounding to avoid ground-loops is the secret from allowing low-level analog sensor circuits to work properly alongside MCUs, and high-power switching. Same principles apply to audio...

There have been dozens of posts on these forums asking for help because "my MCU resets when I switch off a motor/solenoid". I always give them the same advice, but it universally gets misunderstood or ignored, and the threads go on for pages without a resolution... I know what I am talking about here. School of hard knocks, and it made a lot of consulting money for me...
 

Thread Starter

El Zu

Joined Jan 13, 2016
22
Eventually, all grounds will be connected together; it's how you do it that matters.

What are you trying to do? Understand the design, replicate, or repair?

There is an art to laying out circuits that can't be captured in a schematic. You need to use your knowledge of the circuit and components being used to lay them out properly to avoid certain problems. Proper component placement can mean the difference between a circuit that works and one that doesn't.
I just try to understand the design to use it somewhere. And i try to get the reason why this notes was labeled, because it has no sense for this schematic. But maybe can be important for the layout.
 

MaxHeadRoom

Joined Jul 18, 2013
20,465
And i try to get the reason why this notes was labeled, because it has no sense for this schematic. But maybe can be important for the layout.
Whether the circuit is correct is one thing, but if using the same symbol for a different common then it requires independent labeling to distinguish each, if this is not what the circuit projects, then the original composer of the schematic is wrong, and does not conform to current practice.
Max.
 

Thread Starter

El Zu

Joined Jan 13, 2016
22
Are the GND and GND1 just labels, or are they the name of the NETS? If they are just labels added by the drawer of the schematic, then the drawer made a mistake. If they are the names of the NETS, then you will have trouble routing the board, since net GND and net GND1 are NOT the same, so they cannot be connected. As AnalogKid said in post #5, your regulator has common grounds - both input and output grounds are the same. In you schematic, they are DIFFERENT (in error), so your circuit doesn't work. Since it obviously does work, the two grounds are just mislabeled, so just ignore the two labels.

Conventional design standards state that different GROUNDS should have different symbols. If they are eventually connected, you will have a net that connects the two symbols somewhere on the schematic.
Both are just labels, and have no another connections (except the GND).
 

Papabravo

Joined Feb 24, 2006
13,560
Back in my day I designed circuits with as many as five grounds, each with a unique Net Name (Gnd, AGnd, DGnd, Vss, MotGnd) for PCB layout. In the final application, all of these externally connected to the 0V terminal of some external power supply, but they were never bridged on the PCB. This is done to prevent common-mode currents from large motors/relays/valves from flowing along analog sensor grounds, for-example. Single Point grounding to avoid ground-loops is the secret from allowing low-level analog sensor circuits to work properly alongside MCUs, and high-power switching. Same principles apply to audio...

There have been dozens of posts on these forums asking for help because "my MCU resets when I switch off a motor/solenoid". I always give them the same advice, but it universally gets misunderstood or ignored, and the threads go on for pages without a resolution... I know what I am talking about here. School of hard knocks, and it made a lot of consulting money for me...
Me too. That and EMC compatibility and fast transient response.
 
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