| Electronics > Beginners |
| Talk me through this simple circuit? |
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| DimitriP:
--- Quote ---And if we were only talking about circuits in intergalactic space, the term "ground" would be a meaningless and confusing obfuscation. --- End quote --- Not for earth people. (pardon the pun :) ) All those terms, no matter what they are called mean what they mean in the context they are being used. A flashlight uses a ground connection. It won't make sense until it makes sense. Analyzing your post makes obvious two issues. The first issue is your use of the circuit simulator. Ditch it. The second issue is not understanding the concept of single vs dual rail power supplies. --- Quote ---So could someone look at the circuit in the first post and choose one of those connections to ground (apart from the rail splitter connection) and explain why, at that point, the designer said to himself "right, here we need to connect to the return path"? (he probably thought of it as "ground" --- End quote --- As for that first circuit.....I'm not sure what you mean by "apart from the rail splitter connection". There are three connections available +4.5V , ground, -4.5V |
| LateLesley:
Well, another name that gets used for ground is "common". It is the common point that all the other rails are "referenced" to. So all those ground symbols in the circuit are wired, or commoned, together. If you start disconnecting them all, the circuit won't work, as there is then no path for the electrons to flow. Remember circuits need to complete the loop to work. In most cases, the ground, or common is connected to the chassis (well at least in metal boxed equipment) and that got used as the reference point to measure the other voltages in the circuit. Some of them may have been positive in respect to the chassis ground, others may be negative. Anyway, the upshot is, yes those grounds all need connecting together, and if you just start disconnecting components of the circuit from it, then it won't work as designed, as you'll have taken that component out of circuit. |
| virtualparticles:
Yet another way of thinking about a "ground" is to simply consider it to be a "net". It is common on a schematic to label a node with a "net" name, like "Vout-1". On the schematic it might be shown as a line that ends in a flag shape with the net name inside it. It might also be just be a small circle on the end of a line with the net name written next to it. Somewhere else on the page another circuit might use that output as an input and the "net" name will be repeated and a wire will be shown going from the net to the second circuit. This is done to reduce clutter on the schematic. Functional blocks are fully represented with labeled ins and outs, nets. "Ground" can be considered to be just another net. Some circuits on here show a direct connection to the battery. One could easily have the battery symbol sitting off by itself with a ground symbol on the negative and a "+V" net name attached to the positive side perhaps with an arrow symbol. Then whenever the positive voltage is needed in the schematic one simply draws a little arrow and labels it "V+" and you have an implied connection. The same is true of the ground but the net name isn't required because the symbol itself is unique. |
| Mr D:
Hi folks, I feel like i'm still banging my head against a wall, i just don't think anyone is understanding what i mean! Let me try, at the risk of boring you all to tears, one more time, after which i'll shut up about it and move on. What i'm not getting is whether there is anything SPECIAL about ground in a battery powered circuit where there is no physical earth to contend with, and no observer to worry about a reference. Under these limited conditions, i can see no reason not to substitute the word "ground" with "piece of wire". So if you agree with that (i'm sure you won't), surely a circuit could have multiple "pieces of wire"? In the attached pix i have drawn the same (useless, do-nothing) circuit in two different ways. In the second pic i have used two (yes, count them, 2!) grounds, on the basis that "ground" can be substituted with "piece of wire". So to be clear, in the second pic i'm assuming that ground 1 & 2 are not attached to each other. (EDIT: i'm also not expecting the two versions of the circuit to perform the same way in EveryCircuit, i was just using it to create the images) So is it correct that if we were only dealing with this limited case, you could create as many seperate (unconnected to each other) "grounds" as you might like? Before you answer please remember i'm talking about a circuit in intergalactic space where no-one will ever observe or measure anything! |
| hamster_nz:
Completely unscientific here... by convention, for battery powered devices, even when a design doesn't have an external Ground/Earth connection, GND is now usually the negative terminal of the main battery. One of the first things I do when looking at a schematic is "how is the power supply connected to the GND symbol". It wasn't always the way, if you look at old schematics from the days before EDA & CAD tools if they do have a GND it is the physical external connection, and is conceptually different from the negative power rail, even if it is connected directly to it. Most schematics for battery-powered pocket radios usually doesn't have a GND at all. It is now not uncommon to have multiple GNDs in a design - for example, an analog GND and a digital GND, but you pretty much be sure that they are solidly connected together at some point, unlike your schematic where the two GNDs will be at different potentials. |
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