# Trouble reading some circuit diagrams

For anyone curious, this is not coursework I'm trying to offload onto you people. (Anyway, it's August.) This is all for my own purposes. I simply have a hard time with some circuits omitting all connections (which is sort of a big deal after all).

This is not strictly necessary but to see the circuits drawn in full would be very useful.

Huh?

These are NODAL exercises... technically not real world. Nothing is missing.

this is not coursework

pito:

this is not coursework

It could be self-study though.

In any case pwillard is correct, these are theoretical mathmatics exercises to practice the skills used to determine currents and voltages in arbitrary circuits. They are analogous to word problems in algebra, so actually building them is not point and therefore they don't need all the information normally required to do so.

pito:

this is not coursework

No, it isn't. I let my two university patron library accounts expire because these days pretty much all of my learning comes to me through pirated e-books. That's why it's so easy to show you a small excerpt. I just hit "Print Screen" and cropped the .png scrot left in my home directory.

In fact, I have a massive repository of them (well over one thousand) which I'm uploading to a blog, but it'd probably be against forum rules to post that.

But I think it's safe to say that a little Googling will reveal an awful lot.

Far-seeker:
In any case pwillard is correct, these are theoretical mathmatics exercises to practice the skills used to determine currents and voltages in arbitrary circuits. They are analogous to word problems in algebra, so actually building them is not point and therefore they don't need all the information normally required to do so.

Got it. Well the circuits I worked with up until that chapter (including those with ground symbols) made sense, for the most part; they could actually be constructed. I guess I have a hard time with those that can't.

Far-seeker:
Got it. Well the circuits I worked with up until that chapter (including those with ground symbols) made sense, for the most part; they could actually be constructed. I guess I have a hard time with those that can't.

I don't see why these examples should be particularly harder than others.

Although it might help you to recall the fundamentals. Voltage is the difference in electric potential betwen two specific points, so technically all voltage measurements are relative. Furthermore current will flow between any two points with a non-negligable potential difference, provided the potential difference is high enough to overcome the resistance and/or impedance between the two points (since this is an exercise you can assume that the connections are at worst low resistance wires, if not the mythical totally resistance free kind). Therefore you don't need a ground to have the math work.

For example, Figure 7-58 (b) the difference between +3 VDC and +12 VDC is the same as between a ground and +9 VDC. The rest follows from there...

Far-seeker:
I don't see why these examples should be particularly harder than others.

They screw up the concept of circuits I have in my head that seems to apply to all the other ones. I generally have a very idiosyncratic way of going about things (schizotypy will do that to you) so it may not make sense to others.

In any case my first Arduino project works and no components have blown out.

Clearly, those examples were created to drive home the mathematical concepts needed to understand "where the current flows" and "where the voltage changes" in a passive component nodal network.

As for being proud to have so many books gained in a illicit manner... My opinion is that they seem wasted on you so far.

Regardless, basic concepts like these resistor networks need to be understood so you can build upon them. There are no shortcuts.

pwillard:
As for being proud to have so many books gained in a illicit manner... My opinion is that they seem wasted on you so far.

I once sent in a correction to the 1600 page, 2 volume set Mind as Machine (so acquired) regarding a nuance of recursion and received a "thank you" from the author.

Do you know me?

pwillard:
Regardless, basic concepts like these resistor networks need to be understood so you can build upon them. There are no shortcuts.

I do understand nearly all of these problems. I have a notebook full of ? marks over solved problems. These two are the SOLE exceptions, which is why I asked about them here.

Pilfered e-books, DOH!

I'm not gonna insult you like the other guys [!!!], but these 2 problems are really
rather trivial CircuitTheory101 problems. Can be solved either via nodal equations
[as others mentioned] or via Thevenin equivalent reductions, which is what I
would do, and is probably 5X faster than the other.

Offhand, these are so simple to solve that the pilfered e-books must not have presented
the underlying theory very well. Maybe that's karma.

Re-draw them so there's more "flow" (attached).

oric_dan(333):
but these 2 problems are really
rather trivial CircuitTheory101 problems. Can be solved either via nodal equations
[as others mentioned] or via Thevenin equivalent reductions, which is what I
would do, and is probably 5X faster than the other.

I just reached nodal analysis and Thévenin comes after that.

Perhaps I wasn't clairvoyant enough.

oric_dan(333):
Offhand, these are so simple to solve that the pilfered e-books must not have presented
the underlying theory very well. Maybe that's karma.

The text is the following:

It is well-rated; I have understood its contents, again, with few exceptions perfectly:

(Notice those check marks I was talking about.)

Everything I upload goes through a rigorous vetting process which is what kept Jonah Lehrer's tripe out well before his recent public disgrace; you people are strangely confusing me for someone who isn't at all thorough. Additionally, karma is a concept with little empirical support.

That was actually helpful. It makes sense now. Thanks.

I just reached nodal analysis and Thévenin comes after that.

Perhaps I wasn't clairvoyant enough.

Curioser and curioser. So, you asked for the solution before even reading the theory?

oric_dan(333):

I just reached nodal analysis and Thévenin comes after that.

Perhaps I wasn't clairvoyant enough.

Curioser and curioser. So, you asked for the solution before even reading the theory?

No.

These problems were at the tail end of Chapter 7, "Series-Parallel Circuits". Nodal analysis is discussed in Chapter 8, "Methods of Analysis"; Thévenin is discussed in Chapter 9, "Network Theorems".

7 < 8

7 < 9

What did I tell you about trying harder?

7 < 8

7 < 9

What did I tell you about trying harder?

7 < 9? Who knew? Sorry I didn't have the book here to tell what chapter was what.

Obviously, what he expected you to do was to reduce the diagrams by combining
parallel resistors and series resistors. Hint:

In fig a, the 6K and 3K Rs are in parallel.
In fig b, the 4 and 8 ohms are in series.

Start there.

In retrospect, the concepts in chap 7 are probably 10X easier that what you're gonna
find in chap 8 + 9, assuming those chapters actually go into setting up nodal equations.
The author understands the learning curve. Easy stuff first.

As already mentioned, I got it.

In order to motivate you these sunny August days, this is a classwork/selfstudy you may face in the next term, the same questions..

AC, capacitance and inductance are up ahead.

I think I may hold off on some of that because Arduino is DC. Not exactly fixing to take apart / build household appliances at this juncture.