How should I conceptualize circuits?

I apologize in advance if this isn't the right place for this or if my question is too general.

I've been trying to understand circuits for a while now. Not the simple three light bulbs in series/parallel kind of thing, or Ohm's law or anything like that. My problem is with more complicated circuits, the kind you'd find in an actual device. I don't understand how to follow the circuit because everything is interconnected.

I come from a programming background and I'm used to thinking of things functionally. Given a certain input I can watch the data be processed step by step until the final output. But trying to apply this model to electronic circuits hasn't helped me. I'll call this the marble model.

I've attached an image of a circuit. It's just a random one I found on google images. I'm not interested in what this one does, I just want to use it for illustrative purposes.

If I had a piece of data, represented by a marble, and I'm rolling it along the circuit path, where does it go? Does it roll out to one of the resistors/capacitors connected to ground? If it gets to IC2a, does it exit via the red path or the green path? And so on, at each juncture, where does it go? Perhaps this is a bad model.

One way I've been told to think of it is like water through a pipe. In some ways this makes more sense. The system is already full of water (electrons) and things are happening everywhere all at once. Adding power just gets the electrons moving. But this falls apart for me when I start to think about digital circuits and data processing since there isn't a clear defined path that the data flows through, there's all kinds of parallel branches that aren't "switched" the way there are branches in programming where only one path is chosen via some kind of condition (if/else, etc).

The other problem that confuses me with the water model is area of effect. I circled some capacitors hooked to ground in blue and a resistor hooked to ground in red. Do they affect and/or "see" each other? Do they affect some kind of global state/properties of the circuit, or just specific areas of it?

Thanks for taking the time to read this long winded question. I'd really like to have some kind of visual/intuitive understanding of electronics that extends beyond memorized formulas and simple circuits like flashlights.

You have to have an idea what the components do. Some have juice going in specific ways and others have not. If you look at the big square that says PIC....., that's a programmable device. You know that by googling the partnumber. How the signals go depends on the software inside it. That beings said, the schematic gives clues, like the 3 legged parts with a circle around are transistors, the leg labeled B is always in input. That means there are signals going from the PIC part's pins labeled RA0..RA4 to the transistors.
If you looks at the big triangle, thats an operational amplifyer, it amplifies the difference between the + and - inputs and outputs it at the point of the triangle. That means there's a signal going from that thing to PIC input RB0. RA1 is an output because it connects to the + input of that same operational amplifyer on the left.
On the topright of the schematic it says +12V. That must be the supply voltage, and GND, the negative pole of the supply voltage. The text also says: to ignition, so it's most likely a car circuit.
That 12V goes to a little blob called 7805 (note the words IN, OUT and GND here). In goes 12V, out comes +5V as you can see by the markings, so the line to the left of it carries 5V. You don't even have to google that one.

So in short: figure out what the parts are, google if necessary, how they work, and the rest is deduction and reading the descriptions. You can draw little arrows on the lines to make it clearer.

Hope it helps

Thanks for the reply. Unfortunately it's not what I was looking for. In a very simple sense, my problem is understanding the order in which things happen. Since there are so many ways to traverse a given circuit I can't tell how it works.

It'd be like if someone gave you a list of 100 instructions, but they were presented in random order. How would you know which instructions affect which? A circuit isn't quite as confusing because there are paths (wires), but since there are so many routes, I find it confusing.

That's why it is extremely inefficient to use a microcontroller to emulate another microprocessor. The microcontroller has to carry out all the various functions, usually using many sequencial instructions per function, but can only do one thing at a time, whereas the huge circuit of the original processor has gobs and gobs of things that happen concurrently (not one after another), all in the same clock cycle. The microcontroller requires many consecutive instructions in order to emulate everything that happens in a single clock cycle of the processor it is trying to emulate.

The same can be said for analog circuits of course. When you mentally process what is going on, you can often handle it one part at a time too; but when it operates, it may have many parts doing things at the same time, often affecting, and being affected by, each other, yet not really caring. They just do their jobs. If you're that far along in EE [[b]Edit: [/b]I thought you said you were in your 3rd year in school, but since I can't find it again, maybe I'm confusing you with someone else], you definitely know what I mean when you think of Kirchhoff's laws. If you have a complex linear network, you might set up a system of simultaneous equations and solve it with matrices. You definitely can't think of it as a path that a marble takes to get from beginning to end (using your analogy), because not only with the marble get split up, but each part's behavior will also be affected by neighboring marble traffic. Or think of something like a 2nd-order VCVS active filter, or any of many kinds of other feedback systems.

You asked:
[quote]The other problem that confuses me with the water model is area of effect. I circled some capacitors hooked to ground in blue and a resistor hooked to ground in red. Do they affect and/or “see” each other? Do they affect some kind of global state/properties of the circuit, or just specific areas of it?[/quote]
Basically, everything affects everything; but with a good circuit board layout, the effect of the ones you circled on each other will be pretty insignificant.

With all the technicians and a the few engineers I've hired, it's amazing how few really have a good handle on basic things like Ohm's law, Thevenin, complex-number arithmetic, how to bias up a transistor, and how few could do even really basic circuit design. I've had some who could throw the equations and Greek letters around far better than I, but still didn't have an understanding of what was going on in their circuit on the workbench when it was really not that complicated. Engineering is not about memorizing formulas. Schools tend to teach students to blindly throw the numbers in the chute and turn the crank, ie, plug numbers into a pre-written equation, which doesn't help the student understand, and it does not produce real engineers. What happens when they lose or forget the equation, or have an application for which there is no pre-written solution? They're lost. Somewhere--I wish I could find it now--I have an editorial I cut out from one of the industry magazines about this, saying that the industry is telling academia, "You are not turning out the kind of engineers we need. We need them to be able to do this, this, and this..." and academia responds, "Look, you know your field, and we know education. Leave the education to us, 'kay?", so the problem persists. I would say don't be happy to just fulfill the requirements. Seek to really understand what's behind the methods and equations, and to be resourceful.

Thanks for the reply. I have no background in electronics, my background is programming web applications.

I thought it'd be cool to build a small 8-bit computer around a Z80. However, I'm finding it more difficult to understand than I anticipated.

I'm new at this forum, and it looks like the limit of indented replies to replies has already been reached, so we'll see if this reply goes in the right place.

I need to find some good web pages to help people in your situation get going in electronics in general, and link to them on my website. You mention wanting to build an 8-bit computer around a Z80. I can't help you directly there, but if you had said 6502 instead, you'd be exactly the kind of person I wrote my extensive 6502 primer for. However, there are many areas that carry over, like talking about logic families and gate delays, construction methods, displays, steps to a successful project, interfacing to loads of different things, etc.. The table of contents is at http://wilsonminesco.com/6502primer/index.html and the intro page is at http://wilsonminesco.com/6502primer/65tutor_intro.html

I'm not attached to the Z80 in particular, it just seems be a popular 8-bit CPU. The 6502 has quite the legacy as well though, being the CPU of the Apple I/II and NES among other things.

I've been reading your site and it's really getting me excited to build a 6502 computer. However I have to admit some of it still feels over my head.

Ideally, I'd like to build something around the 6502 with an RS-232 for input and another for output that could be hooked up to my PC so I can program it. Something kind of like this: http://www.youtube.com/watch?v=cKoRRA4MyM4 although this particular one was built with an eZ80. Ultimately this could be a great tool for me to learn the basics of microprocessors.

I'm glad you're finding it helpful. There's quite a bit there, and twice that much additional material coming as time permits.

Note that RS-232 is bidirectional, so you probably only need one UART and one connector for what you're talking about. I have an RS-232 primer at http://wilsonminesco.com/RS-232/RS-232primer.html . (My apologies-- there are almost no pictures for the first half of it! )

You mention programming web applications. Our tiny daughter-in-law is a senior software engineer doing that, and our other son works in computer networking and IT consulting. Interestingly, there's not a whole lot of overlap between the fields of expertise of the three of us.

To learn programming, you had to read up on the basics, and progressively put those principles into practice. You learned by doing (and by making mistakes !)

To learn electronics, once again you need to start from the basics. The water pipe model is an excellent mental tool for understanding circuits.
There are a number of circuit simulation programs like Spice that may be useful to you, but practical hands-on circuit building and testing will also help to get a grip on the subject.
Electronic components are now very cheap from the Far east, and a basic multimeter costs only a few dollars.
There is a "Toolbox" page on this site which may come in handy:
http://www.eeweb.com/toolbox/

May I suggest a few sites offering free courses of instruction and advice for beginners. Have look at a few, and discover which one(s) suit your approach. Start with simple projects and work your way up.

We will always be here to offer the best advice and wisdom we can.
Old (allegedly Chinese) proverb: “A journey of a thousand miles begins with but a single step.”

Many sites have a user forum for asking questions.

http://www.allaboutcircuits.com
series of online textbooks covering electricity and electronics

www.learnabout-electronics.org/index.php
Descriptions of components and principles, good diagrams, animations, & fault-finding techniques

http://www.satcure-focus.com/hobby/index.htm
Useful range of ideas tutorials circuits links etc

http://electronics-for-beginners.com/links.php

http://www.hobby-hour.com/electronics/
Teaching from basic principles, resistor code calculators, projects

http://www.radio-electronics.com
Useful information and tutorials

http://www.electronics-tutorials.ws/index.html
Plus calculators & tools

http://talkingelectronics.com/

http://electronics-diy.com
Many projects - 0.3-1.5V LED Flashlight - LED Torch Using MAX660 - Stepper Motor Controller - Strobe

http://www.kpsec.freeuk.com/index.htm
Electronics Club - 555 and 556 Circuits - Logic Symbols - WMF circuit symbols - Logic IC details - Projects

http://www.circuitstoday.com

http://www.eleinmec.com/index.asp
Electronics in Meccano
- Controlling Motors - PWM &c - sound generator ICs

http://www.ecelab.com/circuit-astable-555.htm
Electronics & Communications Engineering - from basic concepts

The circuit "ground" is like the sea into which all rivers run. Of course, some rivers divide before they get there, and what goes down one branch won't go down the other. (Sum of the currents at any point equals zero.)

Thanks for the links. I've been working my way through allaboutcircuits.com