Help with different types of grounds

Discussion in 'General Electronics Chat' started by ChaosRyder, Mar 13, 2008.

  1. ChaosRyder

    Thread Starter New Member

    Mar 13, 2008
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    0
    This is a quiet simple question but I really don't get it. I've just started with electronics not a while ago and I'm experiencing problems with the different types of ground (signal ground, chassis ground, earth ground) in DC circuits. As to what I knew, the ground was a wire that linked a circuit to the earth to discharge any current if something would got bad. Now, when I started looking at circuit schematics, I noticed the little arrow pointing down meant signal ground, I assumed it was the negative of the DC circuit. Then came time to hook my circuit to a 5V current regulator to provide it with 5V current from a 9V battery. The problem is the regulator (LM7805) has three legs: Input, Ground and Output. :confused: Where am-I supposed to connect those to? Anyways, if anyone could explain to me what all this means, or perhaps refer me to a website with would provide me the information I need. Thanks.

    Also, I came across this example circuit:

    Input + --------------------LM7805-----------------Output +
    |
    |
    Input - -----------------------|--------------------Circuit(Signal) Ground

    Would this perhaps solve the issue? To my knowledge, there is something wrong as there is a direct connection between a 9V negative and 5V negative since we're talking DC. Maybe I'm wrong and everything is right since all grounds are referred as to 0V, but its the DC part that gets me confused.

    Anyways, hope someone will understand and shed light on this for me, because I'm rather lost. Thanks again.
     
  2. ChaosRyder

    Thread Starter New Member

    Mar 13, 2008
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    I'm sorry I just noticed the forum removed my spaces before the " | ". The correct connection would be between the LM7805 and the wire passing bellow it, not a connection between the Input + and Input -. Sorry about that.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Yes, it can be confusing. ;)

    When you're dealing with portable electronics like that, you basically have to declare SOMEthing as "ground" as a point of reference; even though the item may not be physically connected to "earth ground".

    You will find once you start using SPICE software tools to model circuits (like Linear Technology's free LTSpice/SwitcherCad) that the program requires you to define at least one point in your circuit as being "ground"; otherwise it can't proceed.

    "Signal ground" is usually used in linear circuits like audio and RF, and are joined to power/earth ground in only one place. Have you ever heard an annoying buzzing sound in a public address system? Odds are that they either have multiple signal ground paths to earth ground, or a bad signal ground path somewhere.

    Digital grounds and signal grounds will wreak havoc if they are combined in the wrong places. Digital circuits generate a tremendous amount of electrical "noise" due to the rapid "edge" transitions (on/off) and sudden changes in power demands.

    But don't let all of this confuse you - basically, "ground" is simply a reference point in the circuit.

    Even spacecraft have "grounds" - many haven't touched earth in decades. ;) It all comes down to needing to have a logical and understandable point of reference somewhere.
     
  4. ChaosRyder

    Thread Starter New Member

    Mar 13, 2008
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    Alright I see, after reading you post and looking some more over the internet, I think I understand now, thanks for the info.
     
  5. nomurphy

    AAC Fanatic!

    Aug 8, 2005
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