Circuits don't make sense - Page 1
Forum section: electronics / beginners

author: Legion
author_rank: Frequent Contributor
timestamp: May 01, 2012, 08:12:08 pm
content: I've always been curious about electronics. Since I was a kid I'd look at a circuit board and wonder how a jumble of wires and components could do anything. Every once in a while I'd pick up a book on electronics, but I'd always get stuck at the same point and stop. So about a month ago I signed up for a course. The course is good and being able to do things hands on instead of just reading about them has helped, but I still have a problem. It's the same problem I always run into... circuits.I can understand how an individual component works, and I can handle those simple resistor problems where you take some series/parallel resistors and work backwards to combine them into a single resistor. But I always get lost when I look at a real circuit, even ones designed for a beginner hobbyist. I just can't see how the signal flows, there are too many connections, branches and concurrencies. I come from a computer programming background, and I can draw a direct line from the start of a program to the end. But when it comes to circuits it's all over the place. The electrons will come from some power source and then branch into multiple paths, some of which connect to ground, others merging and splitting off again. It's a mess.At best I can put together a simple circuit from a diagram, but not have any real understanding of how it works as a whole. What do I need to do to figure this out? I've tried websites like electronics-tutorials.ws and books like Forrest Mims "Getting Started In Electronics", but they all just explain a component in isolation and then throw it in some complicated circuit and I can't see how it's interacting with everything else.

author: olsenn
author_rank: Frequent Contributor
timestamp: May 01, 2012, 08:39:49 pm
content: My best advice, and this will seem weird at first, is to not think of current flowing through a circuit. Instead think of it as if the circuit itself is moving... the whole thing. Charge doesn't start at one terminal and move through a wire until it meets two parrallel resistors and then split up into two paths; at the same time charge is moving up the wire, charge is also pushing it's way through those two resistors... it happens simultaneously.Think about sucking soda out of a straw... the soda is charge and the amount of soda you get from the straw per second is current. Adding a resistor would be like narrowing the straw, you will have to suck harder to drink as quickly. Now instead of it being a straw, say it is one of those gatorade bottles that if you tip the bottle upside down none of the liquid will fall out... this is a diode! With enough strength (voltage or suction) it will flow, but up until that point it is sealed. (this was modelled after our heart valves by the way). You can use similar analogies to describe capacitance, inductance, and anything else that may be puzzling you.

author: TerminalJack505
author_rank: Super Contributor
timestamp: May 01, 2012, 09:01:13 pm
content: Stick with it. It takes a lot of time before it clicks.My advice is to study a lot of different circuits. Learn to recognize the different circuit 'patterns.' Learn to recognize a voltage divider or an emitter follower, for example. If you understand the purposes of these little subcircuits or patterns and you can recognize them on sight then you will have a good idea of what is going on at a particular point in a circuit. You can understand the designer's intent much easier. ("Oh, he's just buffering the out voltage between amplifier stages", for example.)I would guess that most people that can read schematics don't "see" individual components. They "see" functional blocks.Build circuits and look at the voltage levels with an oscilloscope. This is hopefully something you will be doing in your class. This helps with understanding circuits a lot. If you read about a circuit but can't quite grasp how it works, build it and watch it with a scope.You will eventually learn that, even though there are hundreds of different factors to consider, there are only a few that really matter. When you learn about transistors, for example, you will likely be overwhelmed by all the different parameters that can affect their behavior. Through experience you will eventually know which parameters you truly need to focus on.

author: T4P
author_rank: Super Contributor
timestamp: May 01, 2012, 09:03:43 pm
content: Just look at it this way : Power can only flow in one direction , so anything that you see as a branch is called a "branch parallel" and take note where power supply flows from and follow down the track to the Ground .

author: Unknown
author_rank: Unknown
timestamp: May 01, 2012, 09:19:21 pm
content: Quote from: Legion on May 01, 2012, 08:12:08 pmI doubt if it makes immediate sense to anybody except some old gray beards. I often find myself looking for hours on a simple circuit until it starts to make sense. With time you learn to recognize some common constructs in a circuit like feedback loops, push-pull stages, filters etc. and it gets easier after that. Long story short, it is not like a photograph where you get everything in a glimpse. Sometimes it is complicated and takes time to digest, that's normal. I'd say you are no worse than most of us around here.

author: Legion
author_rank: Frequent Contributor
timestamp: May 01, 2012, 09:37:29 pm
content: Maybe my expectations are wrong. I figured (at least for digital circuits), since programs run on computers and computers are built on circuits that I'd find analogues to programming paradigms in circuits, but I don't. With a program I can just read through it like it's a book, and when I get to the end, most of the time I get it. But with a circuit I feel more like I'm solving a maze with numerous deadends and paths to the end.

author: IanB
author_rank: Super Contributor
timestamp: May 01, 2012, 09:58:45 pm
content: Quote from: Legion on May 01, 2012, 09:37:29 pmMost real circuits don't work like that. Most real circuits are linear: information starts at the beginning and flows through the circuit to the end.It would help to think of a circuit like a computer program. Consider each wire or connection to be a variable. The voltage on the connection is the value of the variable. Each circuit element is a function that processes the variable in some defined way, converting the input variable to the output variable.With digital circuits this analogy is almost perfect. If you write an "and" function or an "or" function in a computer program, this is just like an AND gate or an OR gate in digital logic. Even the word "gate" describes that. The gate is a functional block that the inputs pass through on the way to the output.With analog circuits it is a bit more complicated since your "variables" can have a range of values. But even so, you can consider a transistor to be a function that transforms its input (the base voltage, or base current) to its output (the collector voltage or emitter current, for example). You must think of each circuit element as a function that does something, and then think of a circuit as a sequence of functions chained together.

author: TerminalJack505
author_rank: Super Contributor
timestamp: May 01, 2012, 10:44:48 pm
content: Quote from: Legion on May 01, 2012, 09:37:29 pmDigital circuits share some things in common with software programs. If you're comfortable with software then digital electronics will probably be much easier to understand than analog.There are similarities between digital electronics and software but there are some big differences to be aware of.First, a digital circuit will operate at lower level, so to speak. It will deal with just a few bits at a time rather than 8-bits, 16-bits, 32-bits, etc. The operations that can be done on these bits are fairly limited as compared to software. You can apply logic operators such as AND, OR, NOT, etc. You can add them and multiply them. You can remember them. You can do things conditionally based on the state of the bits.Something digital circuits do that software can't is do everything concurrently. Unlike software, digital circuits, by nature, operate in parallel. Software, by nature, is sequential. This means flow control in a digital circuit is very different. Doing things sequentially in a digital circuit is a bit of trick. You need to have a clock and do things in a sort of "pipeline."If you truly want to learn digital electronics then I would suggest you get a good book on the subject and watchthesevideo lectures.Since you are familiar with software I would also suggest you get a microcontroller development board. Something like the Arduino Uno, for example. (Radio Shack sells them.) You can program these using, what amounts to, a "user friendlier" version of C++. You can do some interesting things with these without having to know too much about electronics. You can learn the electronics stuff as you go.

author: Legion
author_rank: Frequent Contributor
timestamp: May 01, 2012, 11:23:56 pm
content: I've got a Raspberry Pi on the way. Is that similar to the Arduino?

author: olsenn
author_rank: Frequent Contributor
timestamp: May 01, 2012, 11:33:16 pm
content: QuoteNope! On the plus side though, you say you prefer programming, and this is a tool for programming. The R-Pi is basically a very low power computer... you can hook it up to a tv and decode movies/music, browse the web, and do things like that. You can program it like you can program an ipad, but I don't believe there are any user programmable logic pins like there are in an Arduino. The R-Pi is much higher level than Arduino

author: Legion
author_rank: Frequent Contributor
timestamp: May 01, 2012, 11:41:53 pm
content: I know it has a set of GPIO pins. But I'm looking at the Arduino and it looks awesome. It seems to be a lot closer to what I'm interested in. I found this old book called "Build Your Own Z80 Computer". They really mean build, right down to the circuit board. Arduino looks kinda similar, minus all the soldering. Can you use Assembly language with it?

author: ivan747
author_rank: Super Contributor
timestamp: May 02, 2012, 12:27:41 am
content: Quote from: Legion on May 01, 2012, 11:41:53 pmYes, but it's not what it was intended for. It will work, but don't expect to find a big community of AVR assembly programmers working with Arduinos out there. Nowadays assembler is not very used unless something critical demands it (edit: not very used when higher level languages like C can be used instead). In fact, I mostly do digital electronics with microcontrollers and I still haven't had to learn PIC assembly.

author: vxp036000
author_rank: Regular Contributor
timestamp: May 02, 2012, 12:41:50 am
content: Analog design and programming require two entirely different ways of thinking. Programming is based on logic. Circuit design is based upon mathematical models of physics. Without a strong understanding of the math and physics behind circuit components, you will have a difficult time progressing much beyond a superficial understanding and the ability to regurgitate circuits. I strongly suggest picking up a book on circuit analysis, small signal modeling, etc.I think a major limitation to teaching yourself electronics is that all the concepts build upon each other. Just understanding a simple audio amplifier requires rudimentary knowledge of Kirchoff's laws, semiconductor physics, and small signal analysis. There is a reason why most practical circuits aren't taught until third year in many universities. You're trying to understanding upper level engineering concepts and skipping the basics.You might consider starting with op-amp based designs. A basic understanding of ohms law and some math is good enough for something like an inverting amplifier, summing amplifier, etc.Quote from: Legion on May 01, 2012, 09:37:29 pm

author: m12lrpv
author_rank: Regular Contributor
timestamp: May 02, 2012, 01:01:34 am
content: I too struggle to "read and understand" a circuit but the tool that most helped me to overcome that was LTSpice.When I see a circuit that I want to understand the first thing I do is model it up. Then I probe the hell out of it, seeing how each part of the circuit affects the next part and all without actually having the physical circuit.It allows you to experiment with the components, to see how the use of specific component values can be critical to the whole circuit.I still have problems with purely theoretical circuits which have no component values on them but I'm learning enough to be able to guess at the necessary starting values.Understanding an existing circuit is one thing. Designing your own is another.Which is why another great resource for learning how circuits work is Dave's blogs. When he designs he does it from start to finish and explains what he's doing all the way through. He doesn't just slap up a final schematic and then skim over what it does.Seeing how Dave approaches circuit design really helps me to approach a design task the right way. It's an invaluable resource that you just cannot get from the printed word.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 02, 2012, 01:26:45 am
content: Build something!It won't work!You will learn a lot more about circuitry while you are trying to fix it!

author: vxp036000
author_rank: Regular Contributor
timestamp: May 02, 2012, 01:34:06 am
content: This is great advice. You'll learn what simplifying assumptions are valid and which one's aren't. I think a lot of the theory doesn't start to make sense until you actually design and build your own. You find things like: oh, it's a really bad idea to use breadboard for high frequency circuits because the parasitic capacitance is too large, don't try to make a ring oscillator out of discrete inverters expecting the resonant frequency to be consistent between different circuits, and so on.Quote from: vk6zgo on May 02, 2012, 01:26:45 am

author: IanB
author_rank: Super Contributor
timestamp: May 02, 2012, 01:38:21 am
content: Quote from: vxp036000 on May 02, 2012, 12:41:50 amI cannot readily agree with this philosophy. To say that programming is based on logic is a grossly naive and incomplete way of thinking about programming. Programming is actually about producing suitable conceptual models of the process you are trying to achieve and then combining these conceptual models in a structured way to produce an outcome you desire.Which is really what most engineering design is about, including electrical circuits. You develop (learn) conceptual models of the various circuit elements you might employ, and then you combine these elements in a structured way to produce the outcome you desire.Fundamentally you should be trying to see the similarities in everything you examine, rather than the differences. You make much more progress by exploiting similarities observed and transferring the insight gained to different but similar systems, than you make by seeing everything as different and requiring unique learning.The history of engineering is in fact a story of observing how to fit outwardly different systems into common patterns of understanding and thus reducing the number of uniquely different things you have to learn about.

author: pickle9000
author_rank: Super Contributor
timestamp: May 02, 2012, 02:14:18 am
content: Try looking at a datasheet for a cd4011b (texas instruments pdf). The internal schematic is there ans well as the logic. Remember even digital logic is made up up transistors and such (analog circuits). These diagrams will give you a much better idea the blocks that make up a circuit. A flip flop (like a 4013) is pre microprocessor but will give you insight on how computers can countPlaying with a simple logic IC's and op amps are a good way to understand blocks.I think programming is a good start, but willingness to ask questions is by far your biggest asset....mike

author: CampKohler
author_rank: Contributor
timestamp: May 02, 2012, 02:45:05 am
content: Like anything else, you start with the simple and work up to the more complicated. This forum is an example of how others can help you understand one thing at a time, and with the 'Net, you no longer are confined to buddies within traveling distance like in the good ol' days. But then that is balanced by the fact that everything is getting more and more complicated. (It's awfully hard to ask a question of someone if you have to draw them a schematic with parts that have a hundred pins on them.)I wonder what it would look like if you graphed two curves, one showing increasing communication simplifying passing information over distance and the other, showing the necessity for passing growing amounts of data to communicate the increasing complexity of today's problems. Somehow I think they don't balance out; it's tougher nowadays to understand everything. Will electronics even be comprehensible by mere mortals in a hundred years? Or will we just understand modules that use standard inputs and outputs and only the robots will know what goes on inside them?

author: Legion
author_rank: Frequent Contributor
timestamp: May 02, 2012, 02:52:07 pm
content: Thanks for all the advice. I'll keep working at it. I managed to get a copy of Multisim Utilboard from National Instruments. Hopefully that'll be useful.

author: w2aew
author_rank: Super Contributor
timestamp: May 02, 2012, 09:54:04 pm
content: Quote from: Legion on May 02, 2012, 02:52:07 pmProbably the toughest thing to get your head around in analog circuits is the concept of feedback, I don't think there's a good programming analogy for basic analog negative feedback.FWIW - I "visualize" the operation of analog circuits by mentally visualizing voltage levels at various nodes (this node goes up, so this on goes down, and current flows this way as a result, etc.) It's much the same way as an oscilloscope shows you voltage levels/changes.Start small, with series circuits, then parallel branches, then dip your toes in the feedback waters.......and, keep at it! It will put you way ahead of curve! It always intrinsically bothers me when I see someone use a half-million transistor uC to blink an LED, but can't do the same thing with a handful of discrete components.

author: A-sic Enginerd
author_rank: Regular Contributor
timestamp: May 04, 2012, 10:54:03 pm
content: The combination of what TerminalJack and vxp036000 said hits the nail on your mental block:- first and foremost, SW always runs sequentially. Hardware always runs in parallel. You have to view it as things happening all over the place all at the same time. This is true for both digital and analog. One of the most complex problems I had to solve for a digital design dealt with taking data off one 128 bit interface, masking off any unused bytes, do an endian swap on it, pack it together with bytes from previous accesses, and endian swap it all back around and write it to a fifo......in a single clock cycle. Ya just gotta think different and get your head around the idea of looking at a snapshot of time and what is the state of everything at that instant.- second, as mentioned, when it comes to analog you have to realize you're dealing with mother nature. You're interfacing to the natural world and the natural laws of physics are always analog. Nothing is ever black / white, one / zero. For me (coming from a strong digital background) I have found it easiest to take the afore mentioned 'snapshot' of the circuit, then slowly take a very small step in time and see how the circuit responds (a little Einstein type thought experiment). Start chaining those steps together and you'll then start to get the feel for what's happening in the circuit. And yes, it can take a lot of hours to get a handle on this for even the simplest of circuits.Many EE's I know are able to best get a handle on circuits when they start doing the heavy math for them. Lots of calculus flying around. I always had an issue with that personally. I could always do the math easy enough, and like you I could understand the principles of the individual components easy enough, but when you started getting really knarly mathematical analysis of the circuit, I could never quite make the 'intuitive' connection between what the equations were saying and what the circuit is really doing. (just food for thought)

author: vxp036000
author_rank: Regular Contributor
timestamp: May 04, 2012, 11:07:16 pm
content: This hits the nail on the head. It's also important to recognize that even when you do the math, you're only halfway there. Now it's a matter of figuring out what the math means. In some applications, this is very straightforward. But, in oscillator design, for example, the math may not make sense until you start plotting the equations. What happens when I change the frequency, tweak some component value, etc.Simulators are sometimes good for this kind of thing, but also can lead to pitfalls. I once took a working oscillator design of mine and put it in a SPICE simulator. It didn't even oscillate. So much for the simulator. I've found the same to be true even for simple circuits, like audio amplifiers. That's when I learned to create my own models for circuits (usually just with some back of the hand calculations) instead of relying on some SW package. At least doing it myself, I know how the circuit is being modeled. It's hard to say what assumptions the simulator makes.Quote from: A-sic Enginerd on May 04, 2012, 10:54:03 pm

author: IanB
author_rank: Super Contributor
timestamp: May 05, 2012, 12:50:05 am
content: I think a lot of this stuff depends on how your brain is wired.I first started reading electronics magazines and learning about circuits when I was 11 or 12. The school library had a subscription to Everyday Electronics magazine. We used to hang out in the library in breaks between lessons and I used to grab every new issue and read it when it came out. This was long before I had even heard the word calculus, but EE magazine was not aimed at experts and it had a good way of explaining things at an everyday level. For me the working of circuits was never complicated at a basic level because I was born an engineer and could readily appreciate what was going on. You really don't need mathematics to wire up a transistor as a switch and figure out how it works, or to figure out what logic gates do. If you come at things at a young enough age, intuition leaps huge chasms of understanding.I had the fortunate experience of learning about electronic circuits way before I even had a clue how a computer worked or how to write programs for one. So I got to make the leap from hardware to software. From that perspective, computers were amazing. You mean you don't have to create a physical circuit to solve a problem, you just tell the computer what to do by typing letters on a keyboard and it does it? How can this be? What magic is this?So to bring this back to the beginning, I disagree with people who say you should understand the parallel nature of hardware. It's not the case at all. All of engineering is enabled by fitting a complex reality into abstract models that are easier to deal with. Any EE will tell you that electronic circuits consist of functional blocks that are connected together with cause and effect and a sequential flow of information (or signals, or power) between them. For instance a radio receiver has a section to pick up the signal, a section to amplify the signal, a section to discriminate and pick out the bit of the signal that is wanted, a bit to filter out the unwanted parts of the signal, and a bit to amplify and deliver the selected bit that is wanted. I'm not an RF engineer, so radio engineers please don't jump on me. I simplified, OK? But if you can't see the sequential and logical arrangement in something like that, you are screwed.If you want to be an engineer, don't over complicate things. Complexity hurts your brain. Learn how to boil things down to the essentials and only introduce complications when they are needed to solve the problem at hand.

author: vxp036000
author_rank: Regular Contributor
timestamp: May 05, 2012, 01:20:20 am
content: There absolutely is a signal flow, even for us RF gurusIn fact, that's the easiest way of analyzing a circuit, by breaking into functional blocks. I have a signal source here, I send it through a buffer stage to a power amp, and voila, I have a simple RF transmitter. Once you understand the building blocks of amplifiers, oscillators, filters, and matching networks, putting them together is trivial, because you simply model the loading of the next stage of the circuit as a lumped impedance.

author: vxp036000
author_rank: Regular Contributor
timestamp: May 05, 2012, 01:47:29 am
content: One other important point, that hasn't been brought up yet, is that no one in their mind models mixed signal / analog circuits in the time domain. The math gets to be ridiculous. So, we look at the frequency domain, treating the signal as an amplitude with some phase. Nothing else matters. Now, modeling your impossibly difficult RF circuit becomes trivial high school level algebra.

author: deephaven
author_rank: Frequent Contributor
timestamp: May 05, 2012, 09:37:15 am
content: Quote from: vxp036000 on May 04, 2012, 11:07:16 pmOscillators sometimes need a tiny push to make them start. In the real world, there is always a little noise around which is often all that's needed to make them start. Your simulation may have worked if you had introduced a little 'nudge' signal to get it started.

author: dfnr2
author_rank: Regular Contributor
timestamp: May 09, 2012, 02:37:33 pm
content: Quote from: vxp036000 on May 05, 2012, 01:47:29 amThat statement reveals some bias :-) There are plenty of very interesting and useful nonlinear analog circuits that are applied and understood in the time domain. Even among linear applications, I can think of some examples that require careful attention to time, frequency, and even spatial domains all at once, in order to do anything useful.Dave

author: gnosis
author_rank: Newbie
timestamp: May 10, 2012, 03:21:44 pm
content: Quote from: Legion on May 01, 2012, 08:12:08 pmI'm also just starting out in electronics, and quickly learned that the overwhelming majority of online sources of educational material are very much lacking compared to professionally written books.The main problem with most of the amateur instructional material is that there usually aren't enough thoroughly explained examples and exercises. It's doing lots of exercises (with reference to well-explained theory and examples) that really gets me to finally understand the material.The best amateur online tutorials tend to do a decent job of explaining the theory, and maybe come up with an example or two, but very rarely do they give you as many (solved) exercises as a well written textbook.To pick a good textbook, I usually head over to the local university library and browse through their electronics section. 99.999% of the stuff there is way over my head, but they do have a decent selection of introductory material, and from that the best I've found is: "Electric Circuits Fundamentals" by Thomas L. FloydSome of their other textbooks also looked good, but I don't have a note of their names on hand at the moment. I'm using the 2004 (6th edition) of the Floyd book. I've found that the more recent textbooks are generally the better ones. They tend to have color illustrations and color photographs, vs the two-tone illustrations and b/w photos in textbooks from earlier days, and that helps -- when they are put to good use, which good textbooks will do. Though not exclusively true, I've found that more recent textbooks also tend to have more exercises and examples than older textbooks. The newer ones also often have CDROMs and websites with supplementary material that could potentially be helpful (though I admit I haven't really looked in to those myself yet).Something else I imagine could potentially help a lot is playing around with circuit simulators that are designed for educational use. I've had a fair bit of experience with using them in some other (non-electronics) field, and they really helped. I still need to find some good ones for electronics, though.One more thing that's definitely helped me is to read lots of different explanations made by different people of the same thing, and looking at lots of similar (but not identical) circuits.For example, recently I've gotten interested in linear power supplies, and started reading through every article and tutorial I could find on them. Soon, I started to see the similarities in the various circuits. Eventually, it sinks in and starts to make sense.

author: marcosgildavid
author_rank: Contributor
timestamp: May 24, 2012, 05:47:33 pm
content: Hi,I have a similar problem, I'm starting in electronics coming from a software background.My mind seems to be "conditioned" to see circuits as programs which makes everything more confusing for me to understand...Anyway, thing I learned that make the process of circuit analysis more simple.Analyze the AC and DC parts separately (this works for transistors and simple circuits) the final result is the sum of both with some extra magicSome people mentioned looking at parts of the circuit as functional blocks, this is true and it helps.It works just like a function in a program: signal in -> magic -> signal out and it helps to simplify things.Sometimes, things just don't make sense at all, for those cases there are books, Google and ForumsAnd, has with all programming languages (and almost everything in life) practice makes perfect.Happy hacking.