So Confused About Basic Ground

[funguy]

circuit basics ground

Hello all. I've posted this question on one other board, but no-one answered. I hope someone here will please.

I've queried this question on Google, and I've read many articles on it, but I still don't understand what it is. I've taken basic electrical courses. I know about RC, RL, RCL circuits, and I know about Ohm's Law, Kirchoff's Law, and I've studied various other things. With this though, I've never truly understood one thing: Ground. I simply truly do not understand what it means when people say, "it's a zero reference voltage", or "this is your ground", or in a schematic for some digital part, the GRN pin. Suppose I have a wire, a battery, and some IC. Do I take that wire, attach it to the negative side of the battery, then take the other end of that wire, and connect it to the GRN pin? When I think of ground in a schematic, does this mean that this is the return path to the negative side of a battery in a DC circuit? What then for an AC circuit?

Sorry for sounding really, really stupid, but In Figure 1, that's easy to understand because the "picture" translates directly to how one may wire it in real life, but when ever someone draws something like Figure 2, with ground symbols, I get lost. Why and what does it mean when someone draws ground symbols? Am I to interpret Figure 2 to mean something like Figure 3, where the ground symbols used in Figure 2 really mean that the connections/wires go to some common "ground", or conducting material? If true then, looking at Figure 4, where the heck is my ground if I wire it up? Or put another way in reverse, if I have the circuit in Figure 4 to start, then if I draw a schematic for it, how am I supposed to know where to draw little ground symbols? Ground is always the negative terminal end of the battery for DC circuits?

 

[A.Anand Srinivasan]

it is nothing big... whenever something is expressed as ground then what is being meant is that it is assumed to be zero voltage and is considered as a reference voltage.... so all the other voltages in the circuit are expressed in terms of the difference between that point and the point which is expressed as ground....

in circuit when multiple points are expressed it means that they are of same voltage and so it is immaterial whether they are connected or not but the point is they are in same potential... that is all..

 

[halls]

Ground is just a common point to all points in the circuit. You know that a voltage is a difference in the potential, this means you need two points to measure voltage. Ground is that point taken as the common one.

In the first picture you showed, you could say for example that ground is the negative of the battery, so when you measure voltage in the battery, you measure in the positive, assuming the other terminal is attached to the negative (ground).

All points in the ground have the same potential value, so in practice, in a circuit you can join all ground points together, because they are the same point.

I think I haven't made myself clear, so be free to ask

 

[davidgrm]

With regards to AC - the ground connection will depend on the circuit. Amplifiers for example will often have Gnd or 0 volts and the signal going positive and negative when referenced to ground. In digital circuits most IC's will have a ground. These pins will normally all be connected together. Many PCB,s will have an entire layer that is ground and then all the component pins that need to be connected to ground will connect to that layer. Note however that when dealing with mixed signal boards such as a board with both digital and analog signals the grounds for the analog section will usually only join the digital ground at a single point. Most mixed boards will give the grounds different names on the schematics such as AGND and DGND. The same applies to mixed signal IC's

 

[Kral]

funguy,
In your diagrams, Figures 1, 2, 3, 4 are all correct. Whenever the same symbol is used for a ground, it is implied that they are electrically connected together. This is for convenience in drawing a schematic, since showing all the connections to ground clutters up the schematic without adding any useful information. In practical systems, there are 4 types of grounds; analog, digital, power and chassis. They must all be connected together at one point. Chassis ground is not always a separate ground, but if it exists, it must be connected to the other grounds at some point. The best place to connect the grounds together is usually at the power supply, which may or may not be a battery. The idea behind providing separate analog, digital and power grounds is to keep currents from one subsystem (e.g. analog) from flowing in the ground path of another subsystem (e.g. analog). and creating volttge drops which appear as signals to to the inputs. The scheme of connecting the grounds together at one and only one point is know as the "star" grounding system. In an ideal world where the ground connections have no resistance or inductance, it would not matter how the various grounds were interconnected. However, in the real world currents in the ground connections produce voltage drops.
regards,
Kral

 

[funguy]

Hey all, thank you very much! I think I understand what was said by all now, so I am hopeful I will get to study more electronics. It's just that when it comes to going from what's on paper to actually wiring it, I tend to get lost (especially when looking at a schematic with tons of parts), so attached is Figure 5. Is my interpretation correct of this "real" schematic diagram?

 

[A.Anand Srinivasan]

yeah it is right... i believe you've understood what we meant clearly....

 

[funguy]

Hi, and thank you again. I am so relieved. I will diligently study all that I can, and I aim to learn as much as I can.

 

[halls]

Just in case, there is a detail you have to remember. Whenever you see a voltage reading in an schematic, which involves just one point (for example the +10V or -10V seen in the circuit you posted) they are always referred to the ground. This means that between those two points you will actually have 20V, but any point measured against ground, will be 10V...

Maybe you had it already clear, but just in case... Hope this doesn't mess you up with what you already had clear :-D

 

[wizard of oz]

ANY point in the circuit can be asigned as "ground". Ground node is just a schematic convention so you draw less. Is just for the drawing, has no other special physical meaning.
When you have a circuit, you can take the node with the most conections and asign is as ground. After this you can deleate the wire from circuit and put the ground symbol instead. Cleaner schematic.

 

[si14]

Bear in mind, ground is a conventional term (because of the reality of the ground). It uses to refer to some source with infinite electrons. That is no matter how powerful your positive source would be, the ground will supply the negatives for you. So we use it as a reference in our analysis.
Hope that helped.

 

[davidgrm]

ANY point in the circuit can be asigned as "ground".
When you have a circuit, you can take the node with the most conections and asign is as ground.

This is not a good idea if you are using a schematic cad package. Most of the CAD libraries have components with ground pins that assume the ground is the 0V. If you call some other pin ground the cad will automatically connect the 0V of the IC's to this point