What is electrical ground?

Discussion in 'Wireless & RF Design' started by Swampgoat, Jan 19, 2012.

  1. Swampgoat

    Thread Starter New Member

    Jan 19, 2012
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    Hello, this is my first post of possibly many future fundamental questions.

    My crystal radio requires a cold water pipe or rod in the earth ground. My transistor radio (or iPod or any other handheld electronic device) has a circuit board with many points labeled "ground", but no wire into the earth.

    Is there a simple way (or link) to explain what a circuit board ground is? I guess I'm asking how something can be grounded if it isn't connected to... the ground.

    Thanks for any insight.
     
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  2. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Everybody encounters this misunderstanding along the road of learning electronics, because the terms are frequently misused and almost always used interchangeably. On you circuit board, there will be a common point; this is the point from which voltage measurements will be taken from. So instead of saying "i read 3.3V between point A and point C, and 5V between point A & point D" - you can say "I read 3.3V on C and 5V on D", and it is understood that point A is the circuit common and all voltage readings are referenced to it. The symbol for circuit common is an upside down triangle. Some people will call it "ground" even if it isn't physically connected to the earth. It can be connected to the earth (ground) but doesn't have to be.
    Ground refers to the earth. A Physical connection with a grounding rod (or metal pipe, although metal pipes are not considered good earth grounds) or preexisting wired-in earth connection. The symbol for ground is a like a upside down christmas tree (long horizontal line on top, then successively smaller horizontal lines going downward)
    There is one more ground, called chassis ground. This ground is used in automobiles and some machines. It's symbol looks like a rake, with slanted teeth pointing downwards. The difference between chassis ground an earth ground in systems, is that chassis ground is actually used as a return path for current through the chassis of the vehicle, and earth ground is usually just used for fault detection and protection.
     
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  3. crutschow

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    Mar 14, 2008
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    As strantor notes, generally circuit ground is the circuit common and common is the proper term if it's not actually connected to earth ground. But the words are often used interchangeably to indicate circuit common. Also the earth ground symbol is often incorrectly used for circuit ground on schematics. If the ground is actually connected to earth, it is usually referred to as "earth ground".
     
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  4. Swampgoat

    Thread Starter New Member

    Jan 19, 2012
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    Holy cow!! This question has nagged at me for years and you two have cleared up my confusion, which apparently many others have experienced, in just one day!

    Thank you very much... you will likely see some more of my fundamental questions soon.

    SG
     
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  5. thatoneguy

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    Feb 19, 2009
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    When looking at schematics, there are two different symbols for "Ground"

    The one with a horizontal line that has 3 or 4 diagonal lines connected to that line means "Earth Ground", which your crystal radio uses, as well as Earth Ground in home wiring, and power supplies. The Second Earth Ground symbol looks sort of like a capacitor, with the gap in between filled with cross hatching, and an arrow from the bottom (Visual analogy of dirt, I guess).

    The other ground is "Common" as explained above. There are two schematic symbols for it.

    The first/most common is a horizontal line, with a narrower horizontal line below it, followed by a point. All of them are cenered, so it looks like a triangle pointing down.

    The second/less common "ground" that is actually "common" in schematics is simply a triangle with the point at the bottom. Be sure it is pointing down. The same triangle pointing upwards can indicate "connect to +V" and sideways triangles can mean "connect to a different point in schematic". The latter three are used to simplify the number of lines in schematics.

    Stolen from wikipedia:

    [​IMG] Signal Ground / Common

    [​IMG] Wiki calls this "Earth Ground", while most schematics use this symbol for "supply common" (vs. signal common, above)

    [​IMG] Chassis Ground / Earth Ground



    The most important for crystal radio is the "Earth Ground", which in most schematics is the Chassis Ground above.
     
    Last edited: Jan 19, 2012
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  6. Adjuster

    Well-Known Member

    Dec 26, 2010
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    From the point of view of signal reception, portable radios often use loop aerials, or variations thereof such as the ferrite rod antenna: these essentially respond to the magnetic components of radio waves, and are independent of any earth connection. Alternatively, a short telescopic aerial may operate with the common wiring of the radio acting as an adequate reference or "counterpoise".

    A crystal radio is a different proposition. In order to collect enough energy to make these work, a long aerial is needed. In theory, a dipole could be used, but generally this would be impracticable at the longer wavelengths. More usually, as long as possible a wire is used, returning a signal referenced to Earth. In this case, if only a little bit of wiring in the radio formed the reference, it would be analogous to coupling in the antenna via a very small capacitor - the signal would be far too weak.
     
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  7. Swampgoat

    Thread Starter New Member

    Jan 19, 2012
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    Thank you thatoneguy and Adjuster. I have seen the various schematic symbols but never really understood them until now. Of course, these answers have led to other questions in my mind which I need to better formulate for next time. One thing I will experiment with is crystal radio antennas: I wonder if multiple antenna wires will improve reception. Maybe thicker wire is better. I'll play around a bit and report back. Again, thanks to all.
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    The important thing is the length of the wire. The one consideration on the thickness of the wire is the strength and how prone it will be to breakage. Consider that you will need a very long wire, 50 feet or longer. Consider the wind, birds etc and hence you do not want a flimsy wire. Solid or stranded plain 16 or 18 AWG wire will do, insulated or non-insulated. You have to figure out how to secure the wire, whether to a tree, pole, house or garage frame. The proper solution is to find a pair of egg insulators and guy wires. A bit of length of rope will do when you are just experimenting. Keep the wire away from physical objects and AWAY FROM ANY OVERHEAD POWER LINES.

    As a precaution, disconnect your antenna during electrical storms.

    You do need a proper ground for the crystal radio to work. You can clamp a wire on to a cold water tap after you check that your water plumbing is all metal. You can also hammer a long metal pipe or stake into the ground and connect a wire to that.
     
    Last edited: Jan 21, 2012
  9. crutschow

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    Mar 14, 2008
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    When I was a kid on my home farm we had an AM antenna wire going from the house to a tree perhaps 75' away. The wire was attached, with an insulator, to the tree with a long screen door spring so that any movement of the tree in the wind would not break the wire.
     
  10. Electro-learner

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    Mar 18, 2015
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    After reading so much about it and practically building a circuit with ground, I have understood that ground is just where all the connections go to.It is a junction point to all the wires.All the current in an electrical circuit flows to the ground, but never does it happen that the current flows from ground to other components.As all the wires going to the ground join there, a ground appears to have zero potential.That's the reason why current cannot flow from ground, but it always flows to the ground.

    For your purpose, you can connect all the wires going to the ground together, and connect them all to the negative terminal of your power supply.Or if you are using a dual power supply, connect it to the junction formed by positive terminal of one supply and negative of the other.
     
  11. Electro-learner

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    Mar 18, 2015
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    A "ground"
    A "ground" in an electronic circuit does not necessarily refer to Earth ground
     
  12. strantor

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    Oct 3, 2010
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    This thread is 3.5yr old
     
  13. MaxHeadRoom

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    Unfortunately
    Unfortunately the term ground is used in N.A. to describe power common And Earth ground, the symbols in post #5 have the wrong description, the centre one is the Internationally universal symbol for Earth ground, the bottom one should be used for chassis only, not earth.
    Many use the earth ground symbol incorrectly to indicate power common, earth grounded or not.
    Max.
     
    Last edited: Jul 15, 2015
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  14. Electro-learner

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    Mar 18, 2015
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    ...But still active because of common confusion.
     
  15. MaxHeadRoom

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    Also unfortunately publication such as 'The Art Of Electronics' add to the confusion by using the Earth Ground symbol throughout the book, and incidentally do not even detail a list or chart of officially recognized symbols, at least in the copy I have.
    Max.
     
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