Two grounds - same symbol

Discussion in 'General Electronics Chat' started by El Zu, Jan 13, 2016.

  1. El Zu

    Thread Starter New Member

    Jan 13, 2016
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    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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  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    In the schematic there are much more ground symbols.
    All will be connected together.

    Bertus
     
  3. dl324

    Distinguished Member

    Mar 30, 2015
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    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.
     
  4. El Zu

    Thread Starter New Member

    Jan 13, 2016
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    Hi, Bertus! I understand it, but why there are two notes GND and GND1?
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    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
     
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Are there other pages for the schematic of your project? This first one doesn't make much sense my itself.
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    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.
     
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  8. El Zu

    Thread Starter New Member

    Jan 13, 2016
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    Thanks. I get it, they are all the same, but what about that two notes GND and GND1. I can't the reason to
    Both are go to opamps. Maybe it refers to pcb layout, separate chassises to avoid the hum? It makes no sense, anyway :)
     
  9. El Zu

    Thread Starter New Member

    Jan 13, 2016
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    This is whole circuit.
     
  10. El Zu

    Thread Starter New Member

    Jan 13, 2016
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    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?
     
  11. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    It could be as simple as a typo.
     
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  12. dl324

    Distinguished Member

    Mar 30, 2015
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    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.
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    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.
     
  14. SLK001

    Well-Known Member

    Nov 29, 2011
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    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.
     
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  15. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    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...
     
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  16. El Zu

    Thread Starter New Member

    Jan 13, 2016
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    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.
     
  17. MaxHeadRoom

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    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.
     
  18. El Zu

    Thread Starter New Member

    Jan 13, 2016
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    Both are just labels, and have no another connections (except the GND).
     
  19. MaxHeadRoom

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  20. Papabravo

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    Me too. That and EMC compatibility and fast transient response.
     
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