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How to Read a Schematic
- mbell 7y agoA question: How many people are there out there that understand what these devices are whom are in need of a(nother) symbol reference?
- SlowRobotAhead 7y agoI’m always having to double check where arrow (body diode) is on a Pch vs Nch mosfet... so... at least one. I think the market of people just learning that would like a nice reference like this is probably larger than the number of people who would complain about educational resources being availble. :)
- userbinator 7y agowhere arrow (body diode) is on a Pch vs Nch mosfet... P points to N. This general rule applies to the symbols for diodes, BJTs, UJTs, JFETs, and other semiconductor components too.
- topspin 7y agoNot many I suspect. What I'm sure of is that you can't learn to interpret schematics using a symbol reference. A circuit is a composition of components that follow a number of idioms that must be understood to grasp the intent.
- rramadass 7y agoI am actually quite disappointed with sites/books which talk about circuit "schematics". They are all too basic. What i am looking for is a book which a) Will take a non-trivial schematic for an actual product and walk me through deciphering it b) Will show me a actual PCB and derive its schematic from it. This is kind of like trying to understand the architecture of a system given its codebase and documentation. While there are lots of books which walk you through understanding software (eg. Linux Kernel) i have not found one which will do the same for electronic schematics. As a person self studying Embedded/Electronics systems, i find this a big drawback for real-world understanding. Perhaps some experts here can chime in with suggestions on how i can acquire such a skill.
- ryandrake 7y agoI agree. While nice, this article is like a “how to read a program” article that lists the language’s keywords and what they mean, and stops at that. It’s great that I know what several flavors of resistor look like. Fine. But how do I know this circuit blinks lights in succession and that one produces a sine wave?
- tlb 7y agoI learned to read schematics by doing it. It helps to have the schematic, a working device, and an oscilloscope so you can probe waveforms on the PCB in locations that seem interesting in the schematic. Modern devices have the most interesting parts inside chips, so it's easier on an older device like a 1970s Hi-Fi amplifier. They were designed to be repairable, so they often came with schematics (!) and had corresponding labels on the PCB. Reverse-engineering a PCB back to a schematic is painful, for the same reason that converting object code back to source code is: the schematic is nicely organized for human comprehension.
- rramadass 7y agoI actually had a project where i was given a) Prototype PCB for driving a pump (status unknown, no software for the MCU) b) A badly done schematic with no proper functional delineation c) Gerber files and asked to make it all work. I had to quickly ramp up on basic Electronics (am a software guy with no EE/Electronics background), learn to read the schematic, identify the inputs/outputs, map them to the requisite pins on the MCU and program it accordingly. While i did write the MCU firmware and got everything to work by myself (pat on back :-), the process was frustrating. No doubt much of it was standard "learning process" due to my lack of knowledge/experience but i was distinctly annoyed at my difficulty in understanding the schematic and mapping it to the components on the PCB for effective debugging. And of course, some of the component values on the schematic did not match the ones on the actual PCB leading to more painful debug sessions. It was "trial by fire" and i am happy to say that i passed, if i do say so myself. But still a very long way to go to catch-up with the industry professionals :-)
- spectramax 7y agoI totally agree with you. There is a deeper problem I think across the board, whether it is electronics books or programming tutorials, mechanical engineering, etc. For example, no one teaches you the way you see in this particular segment of an old EEVBlog episode [1]. Please watch this clip as Dave dives deep into how a simple 555 chip works at the transistor level, breaking down into modules and explaining how each module works. What we need is a book that does the following: Break down REAL circuits from the wild, explain each module in isolation, then explain how it fits into the larger system. No one does this, not in my 15 years of experience in engineering. It is the same everywhere regardless of the subject, teaching is difficult thing to master. 3Blue1Brown is a rare exception, a unicorn of a guy. Richard Feynman's physics lectures are also an example. Programming books are littered with content pages that list: 1. Variables, 2. Loops, 3. Conditionals, 4. Strings, 5. Functions, 6. Objects,..I am already asleep. YAWN. This is a wrong way to teach people how to program. I couldn't emphasize it enough. Most people won't remember what all these things are and they'll lose interest as they grind through this mindless mess of syntax that they have never seen before. Instead programming should be taught by building a goal to automate something. Start out by hard coding everything, then introduce variables. Add functions to make your code modular. Then introduce objects, etc. As you build through a program...a real fricking program! with a real goal!. [1] https://youtu.be/U6qZPx4uD0g?t=2344 https://youtu.be/U6qZPx4uD0g?t=2344
- metaphor 7y agoIn all seriousness, the absolute crap that manifests from schematics developed in Eagle coming out of the open source community is a personal pet peeve. An example of almost everything you shouldn't be doing with respect to at least the following can be found here: color, symbology, scale, reference designators, typeface, labeling, orientation, functional grouping, density, overlap, flow, etc. It's a shame there's zero reference to industry standards like IEEE Std 315 and ASME Y14.44. Abuse of color is probably the one thing that really drives me nuts. I'm of the opinion that if electrical intent cannot be cleanly and unambiguously conveyed in black and white, it's garbage. I secretly wish EEs in general exercised the same level of meticulous attention to detail and pride that designers in the typeface community do, in the same vein as this comment[1]. [1] https://news.ycombinator.com/item?id=19608359 https://news.ycombinator.com/item?id=19608359
- ultrarunner 7y agoHaven't ever popped open anything that came in an Amazon box? At least with OSHW you can submit corrections to bring into compliance with any standard you find relevant. Better than firing off a sternly written letter to China (or HN).
- metaphor 7y agoThe OSHW community has every right to distribute crap schematics, but it isn't immune to criticism. For the record, I haven't opened an Amazon box of my own purchase since 2016 (dropped that like a bad habit after 10 years of Prime patronage), although I'm admittedly failing to see what the relevance of Amazon and China have to do with this discussion. I don't contribute to the OSHW movement because, quite frankly, if I can't buy the custom hardware solution I need, I'll design it myself.
- Taniwha 7y agoyou can print out your eagle schematics in B/W if you like, it's not hard - just click the "monochrome" box in the print dialog
- 7y ago
- Ace17 7y agoToo bad, the article only deals with how to recognize individual components (like a french dictionnary that would be entitled "how to read french").
- fake-name 7y agoOne thing to be aware of: spark fun's schematics are generally flaming crap, along with most arduino stuff. > Sometimes, to make schematics more legible, we'll give a net a name and label it, rather than routing a wire all over the schematic. Net labels are the anti-readable-schematic. They're basically the electronics equivalent of GOTO. This is total bullshit. People use net-labels when they don't want to bother spending time to make their schematic flow properly, or they're doing something dumb like drawing their schematic symbols with the pin-positions from the physical IC. Good schematics should make the overall operation of the system easy to discern. You should have a consistent signal-flow (generally left-to-right, though the opposite also works). More complex systems should also use a hierarchical design with the interfaces between logical sections being clearly defined.
- zrobotics 7y agoVery true. About the only time I find net labels acceptable is buses (otherwise the multiple lines clutter the schematic) and multi-sheet connections. Can't find it now, but back in around 2005 I found a basic 555 circuit for beginners with every connection to the chip besides power & ground being a net. IIRC, the pins weren't even laid out to match the chip. Every time I run across a spark fun schematic I have flashbacks to that. Which is a real shame, since the company's goal is to educate newbies. And it isn't impossible, Adafruit generally does a good job of this.
- deleted 7y ago[deleted]
- snops 7y agoI think you are being quite harsh, net labels are fine for embedded/digital stuff, which generally consists of quite separate functional blocks with few, easily reasoned signals between them (e.g. power + I2C). A lot of Sparkfun's products fall into this category. The Arduino Uno by contrast uses routing too much in my opinion, and is quite hideous: https://www.arduino.cc/en/uploads/Main/arduino-uno-schematic.pdf https://www.arduino.cc/en/uploads/Main/arduino-uno-schematic... If you look at say laptop or SoC development board schematics, they are full of net names, and they certainly aren't using physical pin positions. In fact quite the opposite, one physical device is often split into multiple schematic symbols (e.g. supply rails are one symbol). For the overall system, they use a block diagram or hierarchical schematic. Here is the BeagleBone schematic, which I think makes good use of net labels, e.g. the BAT connection on page 2: https://beagleboard.org/static/beaglebone/BEAGLEBONE_SCHEM_A3.pdf https://beagleboard.org/static/beaglebone/BEAGLEBONE_SCHEM_A... I will agree with you on net names for analog systems, such as audio amplifiers or complex power supplies. There, net names can quite often be misused, as you need to keep more connections in your head when trying to understand a circuit, and it is much harder to remember all the net names than see a direct connection.
- Taniwha 7y agoSome hints on how to get to the meat of a circuit: The most important thing is to learn what to ignore, stuff that has to be there to help a circuit work, but that don't tell you much about what it does - ignore all the power stuff - in particular capacitors oriented with the two lines horizontal are usually decoupling capacitors, ones oriented the other way tend to carry interesting signals - learn to find and ignore the biasing resistors around transistors Rules of thumb: - outputs of transistors are usually inverted from their inputs if taken from the collector/drain - signals usually move from left to right - chips vaguely have inputs on the left and outputs on the right (or pins that work together grouped together)
- Taniwha 7y agoForgot one of the most obvious: - Positive voltages tend to be above negative voltages in a schematic (ground is usually more negative than the power rail) nodes between them on the page tend to be between those voltages
- JoachimS 7y agoThe text shows US and international symbols for things like resistors. But when it comes to logic gates don't mention the IEC standard gate symbols. Like these: https://commons.wikimedia.org/wiki/Category:IEC_Logic_Gates https://commons.wikimedia.org/wiki/Category:IEC_Logic_Gates
- Doxin 7y agoI'm fairly sure no one uses those, I've never seen them in the wild anyways, and I live in a country where they use the international symbols otherwise.
- JoachimS 7y agoI'm fairly sure they are being used. I see them in the wild quite often.
- GlennS 7y agoI love this use of "in the wild". The electronics jungle. Intreprid explorers peering through the gaps between the cables.
- moftz 7y agoSimulink uses similar symbols to IEC, they just write the actual name of the operation, like "AND", rather than the logic symbol, "&".
- g3ph4z 7y agoOh wow, I just found it few weeks ago. It was really helpful for me.
- harryking 7y agoVery nice piece of information it would help all those studying out electronics there.
- spalt 7y ago"I understand how to read a schematic!" - John Hammond
- deleted 7y ago[deleted]
- cr0sh 7y agoProbably already mentioned, but looking at the "schematic symbols" - I noticed they didn't mention the (usually international) form of values - ie 2k5 - meaning 2.5k. Also - they show symbols for potentiometer and variable resistor, but they don't show how if you connect the wiper to one end of the potentiometer, that means "variable resistor" (and is how you usually make one - unless using the potentiometer as an actual rheostat, which means connecting between one end and the wiper, leaving the other end free; electrically it's equivalent to not leaving the wiper floating with respect to the other end, but in a real rheostat, there is no "other end" to connect with - not without modification of the rheostat). Then the battery symbols - and this isn't on them, but more the "standard"; yes, positive is the long side for a series of cells - but on virtually every standard consumer battery cell (C, D, AA, AAA), which end is the positive end? Yep - the one with the "bump" or "short end". Even on the 9 volt battery, the smaller terminal is the positive end. The only time things are "proper" are with coin cells, where the positive end is the flat plate (usually with writing), with the negative being the smaller plate surrounded by the edge of the positive plate on the other side. Knowing humans, though, I wouldn't be surprised if there was a coin-style cell where that was reversed... I expect, though I don't know, that the battery stuff is the result of history (much like how positive and negative aren't really correct per physics as to how current really "flows"). I'm sure there's more weird stuff in Sparkfun's tutorial; it seems mainly geared for an American audience, and also toward older-styled symbols (like you'd find on schematics from the 1960s-80s). Most of the newer style haven't changed too dramatically - but there are some differences (they did note the resistor differences - but I've seen some others). I'll have to read this in more detail later...
- iheartpotatoes 7y ago'.' and ',' generally can be rubbed off or overlooked if the font is too small or if printed on paper/plastic, etc, hence the more reliable notation you mentioned.
- gnode 7y agoI have more experience in reading analogue schematics, and I imagine this is less challenging in purely digital electronics, but to me understanding a schematic is really more about identifying the causal flow of information / signals, by recognising familiar patterns (amplifiers, filters, resonators, etc). This article is more an alphabet chart.