Do you ever memorize circuits? What if you have to rebuild it?

Discussion in 'General Electronics Chat' started by NathanielZhu, May 29, 2016.

  1. NathanielZhu

    Thread Starter Member

    Dec 5, 2011
    The nature of learning electronics confuses me and I've been in the hobby for a few years.

    When you've designed something nice, what do you do to keep that knowledge?
    - Is it memorized?
    - Is it written down but otherwise forgotten?
    - Do you understand it so well that it becomes pointless to memorize or write down?
    - How complex does your design need to be until you start writing stuff down?

    Since I majored in the natural sciences, most of what I learn comes from memorizing facts. I can then visualize the facts and create a big picture. But the weakness I had with natural sciences is that even though I could picture how things worked, the knowledge was useless practically. At least by itself. But computer science and electronics was the opposite. The knowledge was useful and I can build stuff but I can't explain why something works past, I put this and this together and it just worked.

    Ever since middle school, I've also had a computer hobby where I don't ever memorize facts. I learned by doing. Programming had no facts that I memorized- I just did many projects.

    But doing has always felt very shallow to me. The code worked because it just worked. Or trying many ideas until one worked and then just remembering how it worked but not really getting why.

    Since entering the electronics and mechanical hobby, it seems again that I learned by doing.
    But that makes me wonder, are there any aspects of electronics that's like the natural sciences?

    For example, I'd read the datasheet for 555 timer and it gives me two circuits- astable and monostable schematic.
    Then I'd follow it and build it and everything turns out working fine.

    However, I realized that even though I built it, the knowledge wasn't really mine. I wouldn't be able to rebuild it from memory, and there's nothing I can infer from (like combining simple concepts to recreate complex concepts) that could let me rebuild it. Unless I built the same circuit over and over again until I memorized it, all I would have is a working device but I haven't felt like I learnt anything new.

    Is electronics always like that? Getting stuff to work by halfmindedly following datasheet instructions? If I didn't have the datasheet, I wouldn't be able to build it.
    It's like building without really knowing what's going on just because a piece of paper says if you do this and this, this happens.

    This has been a lifelong question.
    Even doing biomedical research, and I order kits from various companies, it's all a matter mix this and this and it works. Everything is patented and secret so I can't find out what's really going on either. I can use techniques that verify that it worked but I can't know why it worked in the first place.
    Last edited: May 29, 2016
  2. Lestraveled

    Well-Known Member

    May 19, 2014
    At first it seems like that, you build from the data sheet. Then you start remembering the function, not the schematic. Some parts I still remember the pinout to. There are some circuits that are as clear as speaking English.

    You (we) may always need the data sheet but, you will never forget what it does.
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  3. NathanielZhu

    Thread Starter Member

    Dec 5, 2011
    So am I correct in saying, for you, you can build something even though you don't remember what the pinout is? That sounds unfathomable to me. I hope to be able to do that some day.

    At this point for me, I read the same datasheet over and over again. Each time I need to rebuild a circuit even a circuit I've build over and over again, I still need the datasheet. It's like a disgusting cycle where I can never outgrow the datasheet even for common circuits. Maybe my memory just sucks.
  4. WBahn


    Mar 31, 2012
    I generally work with circuits that I design as the result of solving the problem at hand. I generally try to annotate the schematics with notes (often on the second page -- the circuit is only on the first since if I can't fit the circuit on one page it is past time to break it into smaller circuits) so that I and others can understand the circuit years down the road, if needed.

    I'm not a big fan of grabbing a circuit from some book and using it without understanding exactly how it works -- but I also admit that there are times when this approach is reasonable and easily justified.
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  5. WBahn


    Mar 31, 2012
    No. I don't think he's saying that. He said that there as some components that he can confidently recall the pinouts to without referring to the data sheet. That's true for just about everyone -- if you use a part frequently enough, you tend to recall the pinout as well as the key information from the data sheet. But I can pretty confidently say that the vast majority of us make frequent references to data sheets, even when dealing with parts that we have used before.
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  6. Sensacell

    Well-Known Member

    Jun 19, 2012
    I find myself sometimes building breadboard quickies from memory alone, but it's poor practice, I forget to document what I built!

    After a few years you have a few circuit typologies memorized, and a few part pin outs, you can do some in-brain designs with that.
  7. #12


    Nov 30, 2010
    The concept comes first, then the building blocks, then the system, and last, the pin numbers.
    I don't think I know the pin numbers for any chip, but the ways to make a power supply rectifier are so familiar I don't have to look anything up.
    Building blocks include amplifiers, inverters, clippers, oscillators, regulators, filters, counters, conditional switches, latches, feedback loops...
    After some time, your mind has been through so many twists and turns that it becomes like a fluid. You define a goal to its simplest functions, start putting the functions together, and end up with something you've never seen before. That's engineering!

    Then you go back through the circuit and check for exceeding voltage limits, power dissipation, frequency compensation, start-up glitches, fail-safe escape routes, human factors like convenience and stupid-move opportunities.

    Then you add the pin numbers and copy it into your permanent notebook(s) which you carry with you for the rest of your career.
    Then you remember that the pin numbers will probably change when you route a circuit board for that quad comparator you used.

    Nothing is forever, but the basics are used over and over. Some stuff that required a square foot of circuit board in 1970 are now done in a single chip, but the concepts remain. You just turn them different ways to get new circuits.
  8. MrAl

    Well-Known Member

    Jun 17, 2014


    There is a science to electronics, so you can learn if you really are willing to put the effort in. You do have to realize though that for most people this means something like 4 or 5 or more years of college, so if you want to learn on your own you have to cover at least some of that stuff.

    The real key to all this is circuit analysis. There is more, like materials science, but with circuit analysis at least you can figure out how a circuit works, and start to analyze circuits. Make it a goal to be able to analyze all the circuits you see anywhere mathematically, or at least start with say 10 percent of them, or at least the ones that you think are interesting to begin with. For example, if you like audio circuits then start to analyze every audio circuit you can find. You figure out how and why it works and then that knowledge stays with you and eventually you start to realize that you are able to analyze 99 percent of the circuits you see anywhere, and even get a quick idea how they work when you first see a new one without analyzing it exactly.
    I bought a lot of books on analysis and just plain circuits over the years. Back in the 80's i had a book that was bigger than a phone book and had circuits on every page, maybe 3 to 5 circuits on each and every page, and looking at each one i learned to analyze almost every one of them, as well as many in other books. That's how you get to know your circuits as it almost becomes a part of you after you do that many circuits.

    The key is circuit analysis, so you need to learn that first. The simplest methods involve algebra, so you could start there. If you dont know algebra you'll need to learn that, because it is just so tremendously valuable when it comes to circuits. Then pick a general analysis method like nodal analysis, and learn that well enough to be able to do say a 10 node circuit, but even a 4 node circuit will get you started. Once you learn that you can do larger circuits too.

    Ask questions on forums like this when you run into something you dont know. Circuits are very variable and sometimes need special attention of some sort, and you might not realize what that is yet so you need to ask.
    You can also get good books that focus on analysis, not so much construction, because you can understand many circuits without actually building them all up, which would take forever.
    Use a circuit simulator like LT Spice, which is a free download. Learn that well so you can test your knowledge using the simulator. You can also experiment with various components that way without doing too much work.
    Ask yourself questions that can lead to the answers you want. How does this component affect the design...why does a capacitor change the behavior of this circuit...etc.
    You might want to start with the most common circuits first and learn how they work.
    Dont get put off if you cant analyze a circuit right away. It may take several years to get really familiar with many circuits and analysis techniques.

    It's going to take time to become proficient, but after that you can do almost any circuit found anywhere including some circuits that very few people in the world really know everything about :)

    BTW, it's not like you have to memorize circuits, it's more like they memorize you. That's because you'll see the common circuits over and over again so you dont really have to memorize them as they will pop up anyway.

    Also, store your circuits in gif files or other types of files. Start a collection. Keep a backup of all your circuit schematics.

    What i have found over the years with other people is that if they have a true love of circuits then every morsel of information that they find will add to their delight, so that will drive them to continue to learn more and more about circuits. So really it depends a lot on how much you love circuits and electronics. Every bit you learn starts to pile up until you have so much information it starts to become second nature to you.
    Last edited: May 30, 2016
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  9. wayneh


    Sep 9, 2010
    Not on purpose. It's inevitable that you might remember things you work on closely for a period of time, but in my experience it's simply foolish to try to remember details. I know I can't in the long run, and useful details will be lost if I try to rely on memory. Instead I rely on a system. Diagrams, notes to self, and a decent file naming and filing system so that I can find things years later. This applies to all projects, not just electronics.
    One thing I DO try to remember is a critical or enabling detail, such as the existence of a particular technology I might want to draw on in the future. Like that lasers or MOSFETs exist.
    Often, yes. I won't forget that I built an particular circuit (inverter, LED driver, voltage controlled oscillator, etc.), but I won't remember the details, only the function.
    Nope. Understanding and memory are two different things.
    I'm sure that depends on the individual. I'd say anything using an IC instead of discrete components needs to be written down because it's unlikely one can remember a pinout 5 years later. And even a discrete circuit as simple as a "Blinky" oscillator (look it up) sends me looking for a schematic.

    One point of writing things down and filing them is that it clarifies the information in your own head and helps your brain remember things in the first place. So the irony is that, the better your habits for documenting projects, the less likely you are to need the documentation.
  10. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    As many people have said, the functions become memorized more so than the hardware details.

    In electronics, I look at a problem and immediately recall that I need a 4017, some AND gates and a multiplexor.. I can guess at the IC that had AND gates but will look it up. Then I will search for the particular multiplexor that I need. But, I can and often do draw he circuit at a functional level first and then fill in the details.

    In coding, it's all about the functions. There are basic categories of functions that exist in all languages. Data types, operators, flow control... I feel at this point that I could code in almost any language presented to me, because my understanding of the basics are so strong.

    So in these two endeavors, you are working at a higher level, and have those constructs memorized. There are some characteristics of the environment that you will have memorized, such as the voltage range of CMOS ICs or how to wire a transistor as a switch, but what you will find using primarily is at the functional level. The low level detail is available on demand and you take advantage of that fact.

    I've reread your post and in closing want to add, that with learning and experience you WILL understand what it is doing. In coding, I know that comparing two data types may not work because of what is going on inside. You will get there if you want and it appears that you have the natural enthusiasm to make it.
  11. Tonyr1084

    Active Member

    Sep 24, 2015
    For me - listening to, or reading a description of a circuit and how it works is often harder than looking at the schematic (simple schematics I should say). Many times I've looked at a circuit and had difficulty understanding how it functions until someone explains it. Then the circuit becomes more easily understood than the spoken (or written) description of that circuit. After a while a particular circuit becomes a part of my vocabulary (the schematic). Once understood and practiced it is second nature to build up something.

    Many people here are well beyond my abilities and understanding. For them what is elementary is to me like being a sixth grader trying to understand calculus. But as I learn these things and become more familiar with them - rather than "Remembering" how to build a circuit it's easy enough to build and modify a circuit from scratch. For instance: You might learn how to build a PWM (Pulse Width Modulator) using a 555 timer. You may control a light with it. But once you understand the fundamentals of it you might build a motor speed controller without having to have someone go through the whole process with you all over again.

    At first schematics resembled brain surgery to me. Now it's more like a bowl of spaghetti. A bit jumbled but at least it's not intimidating. You'll start with the fundamentals - learning the math. That's the whole key to successfully designing something to do something nobody else has imagined yet. Fundamentals like ohms law are just the starting point. In time you learn AC and DC theory, transistors, gates and eventually processors. In time you learn radio transmission. But all those things rest on the basics of electronics.

    Don't try to remember everything you build - remember HOW to build. Drawings are a great place to start. Sim's help too. Bread boarding a project helps you get it right before you commit it to solder. However, I DO like to keep my drawings. Sometimes I'm away from a particular circuit for a long time and having the drawings can bring those details flooding back into my memory. Drawings are good. Keeping them is wise. Otherwise you may find yourself reverse engineering a digital clock you built a long time ago just to get a schematic out of it.
  12. ISB123

    Well-Known Member

    May 21, 2014
    I tend to relay on modular design. I basically design a simple circuit which I can constantly reuse in my other projects and adopt it for use in other circuits by changing few parameters. Basically something similar to the way military does it.
  13. dl324

    Distinguished Member

    Mar 30, 2015
    There are some things that need to be memorized, such as ohms law, KCL, KVL, or the function of black boxes (such as comparators, opamp gain formula). You can do the same for circuits, but learning the function of every component in a circuit will minimize what needs to be committed to memory.

    For your 555 timer example, learn how the timer works and what each component does and you won't have to memorize the connections for astable and monostable applications. If you understand how the 555 works, you won't need an application note to tell you how to use it.

    I remember some of the pinouts for things I use regularly, the rest I look up as needed. If I don't use something often enough to remember it's pinout, why bother memorizing?
    Last edited: May 30, 2016
  14. hp1729

    Well-Known Member

    Nov 23, 2015
    How do I document it? I use ORCAD, a schematic capture program, free version.
    Do I memorize it? Often. Once you create a schematic it is usually retained pretty well if you understand the circuit, not just copy it.

    usually designing as circuit goes through three stages. First is general breadboard for development. After that I will commit it to a dedicated breadboard for use. There is often changes I might make before I set it to a circuit board and case.
  15. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    To follow your 555 example... That is exactly what I do. I have a concept of what that device can do, that I keep near and dear. The details are too fragile to trust to memory and the data sheet will be pulled to get those facts such as pin outs, part connections and such.

    For entire project I keep documentation. That starts from a schematic (since I think in pictures) which leads to a parts list, and then assembly drawings. Thus I know what things connect to other things and where they are. Those 3 items are the basic any job needs.p

    If I want to keep notes as to why or how things were done they go in another document.
  16. dl324

    Distinguished Member

    Mar 30, 2015
    Here's a recent example.

    I was trying to help someone in the Homework Help forum design a 3 bit odd/even counter. As far as I could recall, I had never seen the circuit for one and had never designed one; but I know how JK Flip Flops work and how to design such circuits. So I drew up the excitation table to check his work, reduced the logic with Kmaps, and simulated in MultiSIM Blue (free version from Mouser that's quite crippled).
    The design was interesting, but not useful; so I won't memorize the circuit. Hopefully I'll remember that I designed one and remember how I did it. Otherwise, I'll design it again from scratch.
    All of my files on the computers are backed up and archived. I have the design steps documented in my notebook and, hopefully, will remember that I did it if I ever have need for it again.
    Pointless to memorize, but the design is in my notebook.
    Anything I can't do mentally gets written down.

    The person asking the question had a mistake in his excitation table (but was close), made some invalid assumptions regarding don't cares, and never posted a circuit. It's been about 10 days since he visited the thread, so I'll post my solution.
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  17. ian field

    Distinguished Member

    Oct 27, 2012
    There are many basic building block circuits that are fairly easy to remember. You can do a fair bit just assembling those together to make bigger systems. As you gain experience, it becomes easy to tweak the design of those building blocks so they work just the way you want.

    To some extent its not too far different to programming - its common practice to write routines for a particular purpose, and also save them in a library for immediate use in future projects.

    A useful but very basic introduction to circuit building blocks can be found in various manuals here;
  18. AlbertHall

    Well-Known Member

    Jun 4, 2014
    When I started out, if you wanted a datasheet you had to request it, and pay for it, then wait until it arrived. Only then to realise that was the wrong chip!
    I still remember the marvellous joy of being able to type in a part number and up comes the datasheet instantly (well, almost instantly. It was dial-up).
  19. ian field

    Distinguished Member

    Oct 27, 2012
    Quite a few datasheets include application examples, but its worth including "application note" in the search term - appnotes are quite different to mere data on a component.

    Terminology varies among different manufacturers - it could be named something along the lines of application examples or bulletin.

    Manufacturers like LT and NS have fairly busy publishing departments. is another handy resource - search databook or data manual. There's a pretty big collection of data manuals from various manufacturers, most have pages of example circuits.
  20. KL7AJ

    Senior Member

    Nov 4, 2008
    A few circuits that are thoroughly embedded in my cranium, for which I need no schematics or pinouts:

    1) 555 astable timer circuit. I can build these in my sleep.
    2) 741 op-amp inverting amplifier
    3) 6146 linear r.f. amplifier
    4) 2N2222 class A voltage amplifier
    5) Pierce, Colpitts, Clapp, or Hartley oscillators, vacuum tube or transistor.

    I never ever tried to memorize any of these.....just a natural part of working with them for 45+ years. :)