Understanding Schematics - Page 1
Forum section: electronics / beginners

author: SilverHawk
author_rank: Contributor
timestamp: February 27, 2016, 03:12:54 am
content: Im a beginner and just started my degree in EEE, i was wondering how does someone learn to read a schematic and understand what does the circuit do. Please tell me is it just based on experience or if you can actually develop this skill .Just as an example, understanding this circuitThanks

author: ataradov
author_rank: Super Contributor
timestamp: February 27, 2016, 03:30:50 am
content: Quote from: SilverHawk on February 27, 2016, 03:12:54 amExperience is developing a skill. No one is born with understanding of how to read schematics, or do anything, really.Quote from: SilverHawk on February 27, 2016, 03:12:54 amFor this one, it would be beneficial to redraw it in a sane way. There is a reason why there are standards for capturing the schematics. They are there, so others could read them.On this one, for example, it is not clear where there are joints and where are simple intersections.EDIT: Or, I guess, they all are joints, except for one on the left.EDIT: This looks like some bank of filters. It is hard to say more without knowing where this is taken from.

author: SilverHawk
author_rank: Contributor
timestamp: February 27, 2016, 03:43:38 am
content: Sorry i forgot to say this is schematic for a wafeform selector , part of my labs

author: ataradov
author_rank: Super Contributor
timestamp: February 27, 2016, 03:48:43 am
content: Quote from: SilverHawk on February 27, 2016, 03:43:38 amYeah, it looks like something educational.It does distort input signal in different ways. The actual effect depends in the type of input signal. For pure sine wave it would depend on frequency and input amplitude. Amplitude will matter only for the transistor part.Just keep in mind that stuff like this  never appears in a real world.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 27, 2016, 03:49:51 am
content: There are as many ways as there are people. I would suggest the following approaches as a starting point for you.First, simplify things. For example in your circuit, draw the circuit using only one position of the switch. In the top position of the switch this allows simplification of the circuit to only two components, the two resistors on the left (assuming the source impedance of the earlier stage is low enough that the other components don't load it) and is merely a divide by two in amplitude.Identify inputs and outputs and power sources. Work from these points looking for elements that you recognize. This might be a passive divider like the example above, or a simple amplifier like the transistor in the circuit. The transistor is set up as a gain stage with R9 as the load transistor. The power supply comprises the battery and adjacent capacitor.Look at remaining components in terms of the their effect on already mastered elements.

author: Nerull
author_rank: Frequent Contributor
timestamp: February 27, 2016, 03:51:16 am
content: Quote from: SilverHawk on February 27, 2016, 03:12:54 amA schematic doesn't tell you what a circuit does, just how its built. It tells you what parts it contains, and which parts are connected to which.Understanding what a circuit does is an entirely different skill to being able to simply interpret a schematic. If you want to do that, you need more information. How is it used? What sort of signals does it operate on? How do the components effect that signal?Over time you will learn to recognize various types of circuits and what they're for, if you work with them. If you've never seen it before and have no other explanation, working it out may not be easy.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 27, 2016, 04:01:37 am
content: First, you must learn what all the different symbols mean. It is like learning to read. First you must understand the alphabet or letters or symbols used for the language. Then you can start to learn individual words and what they mean. Then you can learn the meaning of whole sentences of words combined together in different sequences.Do you know what all the symbols in the schematic mean? You must know that before you can proceed. Then you can look at how they are connected together to work out a general concept of what the circuit is doing. Just as you can work out the meaning of a sentence from which words are used and what order they appear.As @CatalinaWOW said, you can start by analyzing each separate stage or section of the circuit. That assumes you have identified inputs, outputs, power, reference (ground), etc.For example the first two resistors (image is too fuzzy to make out the reference names) appear to form a simple voltage divider for both AC and DC. And C7/C4 make an AC voltage divider. And R4/C5 make a low-pass filter as do R5/C6, etc.It would also help somewhat to have the ccontext of what "stage 1" is, and what kind of signal you are expecting from it.

author: onlooker
author_rank: Frequent Contributor
timestamp: February 27, 2016, 05:04:10 am
content: The lazy way to help the understanding and save from the calculation is to do a spice simulation.For example, for a 1kHz square wave input, the 1st output will show a square wave; the 2nd shows a sort of "saw tooth" wave; the 3rd a "triangle" wave and the 4th a "sine" wave. Or it is for an educational demo of the effects of a multi stage rc low pass filter.The voltage divider and the transistor are just to bring all the output amplitudes to a comparable scale.

author: SilverHawk
author_rank: Contributor
timestamp: February 27, 2016, 06:36:02 am
content: Thanks for all the replies guys, i really appreciate it , feel free to add any more tips if anything comes to mind, @Richard Crowley, Yes i can understand the schematic at least in terms of identifying the components and the stage 1 input i believe is from the signal generator with a 1 v peak 2 peak square wave .So from what i can understand is the easiest way is to understand what a circuit does is to know the functions of basic configurations of circuits and piecing together the each section like what @Richard Crowley and @CatalinaWOW has said. Any other tips are welcome guys .Once again thanks for the fast replies

author: tggzzz
author_rank: Super Contributor
timestamp: February 27, 2016, 10:08:01 am
content: Quote from: SilverHawk on February 27, 2016, 06:36:02 amBasically, yes.There are certain configurations of components that occur over and over again, because they work well and perform a standard generically-useful function. (Classic examples are op-amp amplifiers, filters etc). You can find whole books describing some of these "design patterns" ( a useful term from software engineering). Recognising such patterns relies heavily on their being drawn on the schematic in the traditional way.However, never underestimate the ability of people to obfuscate their schematics by placing the components in a strangevisualconfiguration. Why do they do that? Pig ignorance, or laziness, or ran out of space on one side of the paper, or (especially) Spice schematics which function correctly but...

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 27, 2016, 03:52:14 pm
content: I would add that understanding of a circuit comes in layers.A basic understanding of functionAn understanding of the range of conditions under which this function is obtainedAn understanding of the precision of performing the functionAn understanding of unintended or parasitic other functionsAnd so on. It may be true that no one completely understands any circuit.

author: Alex Trofimov
author_rank: Contributor
timestamp: February 29, 2016, 11:37:19 am
content: In my experience, there is only a few basic theoretical things:1) correct drawings;2) Ohm's law and3) Kirghof's laws.I myself learned this mostly from me father's electronics magazines when I was a boy.The slightly more advanced staff includes some more math:1) reactive impedance;2) complex impedance;UPD: 3) understanding in principle the work of transistors and an op amp,but it all is in frame of the first ones. These I learned much more in past, after the university with the work.And that's it. Actually there is of course some nisch staff, but you should learn it only if you actually work on it.So, the 99.99% of real work here is developing intuitive apprehension. And you better prepare yourself, it will be hard as hell.I think, what gives it is experience, reading datasheets, application notes, thinking a lot and UPD: watching EEVBlog.I think it's relevant here, so I will mention that I'm an Electronics Design Engineer with almost 5 year experience, involved in measurement equipment developing.

author: Philfreeze
author_rank: Regular Contributor
timestamp: February 29, 2016, 11:53:13 am
content: Quote from: CatalinaWOW on February 27, 2016, 03:52:14 pm+1 for this. This is exactly how it is.With practise you will get to learn the different amplifier circuits and it will get easier and easier to understand the function of each block and the whole schematic.To understand the other things though you will almost always have to do some more or less complicated math and simulations.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 29, 2016, 12:59:25 pm
content: I think the response from @onlooker is spot-on. With a fixed-frequency square-wave input, the various selections put out various wave-shapes.

author: SilverHawk
author_rank: Contributor
timestamp: April 19, 2016, 03:29:03 am
content: Can anybody tell me what the Transistor is used for in this circuit as i have seen other RC integrators being built without it, and also why is another low pass filter needed at the right most end of the circuit .Input: 1khz 8v pk-pk square wave

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 19, 2016, 03:44:40 am
content: Quote from: SilverHawk on April 19, 2016, 03:29:03 amYour own diagram says it is BC548. Or perhaps we don't understand your question?QuoteThere are MANY different circuits which implement the integration function.QuotePerhaps it provides a smoother approximation of a sine wave.

author: SilverHawk
author_rank: Contributor
timestamp: April 19, 2016, 03:58:09 am
content: question , is R11/C2 is also a low pass filter ?,if not then what is is used for, if yes then why do you use the transistor at that particular filter ?

author: Stonent
author_rank: Super Contributor
timestamp: April 19, 2016, 11:41:46 pm
content: Quote from: SilverHawk on February 27, 2016, 03:12:54 amDid your class come with a textbook?

author: Audioguru
author_rank: Super Contributor
timestamp: April 20, 2016, 01:34:49 am
content: The resistor R9 and capacitor C10 at the right side are not a lowpass RC filter. The resistor is the collector load for the transistor and the capacitor is the battery's bypass. The transistor circuit is an inverting amplifier.

author: Audioguru
author_rank: Super Contributor
timestamp: April 20, 2016, 01:38:52 am
content: Quote from: Stonent on April 19, 2016, 11:41:46 pmI was wondering, where is the teacher? Why isn't the teacher teaching the students about these things?