Electronics > Beginners
Talk me through this simple circuit?
SparkyFX:
--- Quote from: Mr D on May 31, 2019, 10:33:40 pm ---Could someone give me an example of a circuit component or element that would need a ground, how it would work, and why it wouldn't work without this ground reference?
--- End quote ---
Well, the concept of ground as a symbol in a wiring diagram has been elaborated a few posts above, you should read it. The soil you are standing on has barely to do with it.
There are some devices that are only supposed to work with respect to a signal called protective earth, namely RCDs. They do not work as intended in isolated circuits, as they are supposed to break the connection of a circuit if too much current does not flow back to the source through the RCD, the only other path being through "protective earth". I suggest reading that wikipedia article about it, but it bears not much relevance for the circuit you initially posted.
Otherwise circuits can perfectly work without contact to "the ground", except protection or EMI requirements call for something to be connected to protective earth.
Imagine flying a helicopter. The lights work without contact to "the ground", but after some hours of flying around the friction of the blades in air might have charged the whole chassis up to several thousand volts - with respect to the earth´s voltage potential. As long as the lights are only connected to "chassis ground" and the voltage source, the lamp will still work. But anything that touches the surface first will need to dissipate the charge of the chassis.
I am sure you have seen planes or helicopters.
timelessbeing:
--- Quote from: Mr D on May 31, 2019, 10:33:40 pm ---if one takes the observer out of the equation, what is intrinsic to an electronic circuit that it would need a ground?
--- End quote ---
It doesn't
Anything that is battery powered isn't Earth grounded.
And your amplifier circuit doesn't need to be grounded.
So back to your original question.
0 - 9V
or
0 +/-4.5V
Doesn't matter, it's the exact same thing.
And this audio circuit only needs access to the signal and the zero AKA the DC reference, the common mode voltage. This "ground" (virtual in this case) is the potential around which the audio signal swings.
Mr D:
Let's take it back to the original circuit in the first post of this thread.
Let's put aside rstofer's comments about the efficacy of this circuit, i presume it at least works to some degree.
Let's place this circuit on it's own in intergalactic deep space and turn it on.
Now, this circuit contains 6 connections to ground.
My question is simply this: if we cut all those connections to ground, will the circuit still work in exactly the same way?
If not, why not? Could someone give me one or two example of why the components in the circuit won't do what they're expected to do without these ground connections?
timelessbeing:
--- Quote from: Mr D on June 01, 2019, 08:05:03 am ---My question is simply this: if we cut all those connections to ground, will the circuit still work in exactly the same way?
--- End quote ---
The nodes symbolized as ground need to be connected to each other for the circuit to work. They do not need to be bonded to Earth ground, though it might help with shielding out interference.
vk6zgo:
--- Quote from: Mr D on May 31, 2019, 07:51:33 am ---Thanks............
Here's what i'm still struggling with in terms of ground:
Attached are two pix. In the first pic, with have a leg of the circuit going nowhere, so no current through the 5k resistor.
In the second pic, i've grounded that leg, so current can flow.
Hence my understanding that ground can be used to make current flow where it otherwise wouldn't want to flow.
But by this logic one could have multiple different "ground" planes, not connected to each other. But this isn't something i've seen, therefore i surmise this isn't actually the purpose of ground.
Ok, so ground is often (also in this thread) described as being used as a "reference". This is the part i don't understand. When i think of "reference" i think of an intelligent agent referencing some information from a user manual or wikipedia or something like that. But i have no clue as to the meaning of the word "reference" as it's being used in this context.
Could someone please give me an ultra-simple example (maybe an EveryCircuit circuit) of such "referencing" taking place? (With an explanation)
--- End quote ---
I used to work at a TV Station, & on occasion had to climb the tower at the Transmitting site.
This tower was 145m high, so when I was replacing the topmost clearance light, I was that height above the base of the tower.(or "ground")
OK, I was 145m high----- but wait! the site was about 300m above sea level, so was I (145+300) metres high?
So the question is which?
Well, if we are referring to the ground at the base of the tower, it is 145m , if we are referring to the ground at the very point where the beach meets the sea, then I am 445m above ground.
Of course, the reference for height doesn't have to be the ground, either.
The CH2 tower is a bit further up the hill, & is about the same size as our one was, so I may have been about minus 4m with reference to the top of that tower.
You can see that the same vertical position in space can be different heights, depending upon where you measure them from.
You will probably have seen the initials "w.r.t"----these mean, either "with reference to" or "with respect to" which are just different ways of saying the same thing.
On top of the tower, I was 145m high w.r.t the tower base, but I was 445m high w.r.t. sea level, & around minus 4m "height" w.r.t. the top of CH2's tower.
In all cases, a word which could describe the place my height was measured from is a "reference".
As in height, so with voltage.
In your original schematic, using the point you put a "ground" symbol on as your reference, the positive terminal of the battery is 4.5v w.r.t. your reference point.
The negative terminal of your battery now becomes -4.5v w.r.t. your reference point.
Nothing has happened to your battery, if you ignore the point with the ground symbol, & hang your meter across it, you will still read 9v.
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