Have You Ever Changed a Circuit Only to Make the Schematic Look Better?  - Page 1
Forum section: electronics / projects

author: niconiconi
author_rank: Frequent Contributor
timestamp: September 23, 2019, 12:04:48 pm
content: It happens to me as a hobbyist, that sometimes one piece of my circuit simply doesn't fit into a specific location of the schematic elegantly. Occasionally, instead of redrawing the whole schematic or the symbols, I find myself doing minor changes to the electrical design itself, not for any electrical/technical reason, but simply to make the schematic looks better. An example would be using an alternative pin on the microcontroller (despite the program is already written), changing the combination of some resistors or capacitor in an alternative way that still works, or even changing the topology if it's something non-critical. (*)I wonder if somebody here has done something similar, I'd like to hear your experience.(*) Unfortunately, when you move to the PCB routing stage, you'll often find yourself changing the schematics again for routing reasons, and this largely undo the improvements of your schematics you did previously, so two efforts cancels each other in terms of aestheticsOn the other hand, the end outcome is still better than doing nothing.

author: tggzzz
author_rank: Super Contributor
timestamp: September 23, 2019, 12:14:13 pm
content: The PCB should be laid out in a way that allows thecircuitto work correctly.The schematic should be laid out in a way that allows areaderto understand how the circuit is designed to work. That implies using standard conventions, not "random convenient" placement of symbols!Back annotation from PCB to schematic is normal.

author: Seekonk
author_rank: Super Contributor
timestamp: September 23, 2019, 12:18:03 pm
content: Yes. A manager once told me, The optics of a project are everything.

author: Bud
author_rank: Super Contributor
timestamp: September 23, 2019, 01:13:28 pm
content: I never change circuits (even never thought about that) but i make every effort to make schematics easily readable.

author: ConKbot
author_rank: Super Contributor
timestamp: September 23, 2019, 01:30:41 pm
content: I design open source hardware so all my a schematics are just a jumble of ICs with netlabels and a few resistor dividers with net labels anyway. /s

author: ejeffrey
author_rank: Super Contributor
timestamp: September 23, 2019, 04:41:06 pm
content: At the schematic capture stage I treat the schematic readability as a heuristic for easy/good layout. So I would flip gates or pins around to get clean signal flow assuming that will help me at layout time. Once I start layout it is normal to find that some of those choices were not optimal and go back and change them.Other than that I'm not sure what you mean? Like you have a schematic that is ready for layout or you have already started layout and you go moving pins to make it prettier? No I wouldn't do that. Waste of time unless you screwed up in the first place :-)

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 23, 2019, 04:42:33 pm
content: Quote from: niconiconi on September 23, 2019, 12:04:48 pmNot really.There are many ways of improving the readability of schematics. Flip/mirror parts as required, sometimes create new symbols if that really fits better.Also don't hesitate to use labels for signals, instead of running crossing wires all over the place. Too much is too much. You need a sensible compromise when it comes to direct connections.Labels have an added benefit of 'self-documenting' a signal's purpose. Of course it requires basic common sense and experience. Don't put labels on ALL signals either. That would in turn become unreadable.Apart, obviously, from fixing design issues, the PCB layout phase is the only one worth modifying a design for from an electrical POV.

author: langwadt
author_rank: Super Contributor
timestamp: September 23, 2019, 04:51:37 pm
content: Quote from: ConKbot on September 23, 2019, 01:30:41 pmjust write the net list by hand

author: tggzzz
author_rank: Super Contributor
timestamp: September 23, 2019, 04:53:07 pm
content: Quote from: SiliconWizard on September 23, 2019, 04:42:33 pmActually, do hesitate. Too many people follow ConKbot's "suggestion"If you want a concrete example of how it wastes people's time, I know of far too many people that have been screwed by this example from a Tektronix 485. They replace C911 (a 15V tant on a 13V line, doh), and miss theotherson that line(They areverydifficult to find).QuoteLabels in that case can help.The key is to think about how the mythical intelligent engineer that isn't familiar with this circuit will be able to (mis) understand it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 23, 2019, 05:49:40 pm
content: Yes, constantly.I excuse the fact that I'm idly poking at the schematic or layout, by the fact that it gives me a distraction, a hands-on review of sorts, contemplating as I go.I've seen some real stinkers: wires and components off-grid, floating net labels, schematic-as-netlist (pins end in stubs with net labels, very little is actually graphically connected), text fields (designators, values, etc.) overlapping other graphics, labels/notes/headings out of sync with the circuit as-drawn, etc.I try not to reorganize existing schematics -- which could cause confusion to those expecting relative consistency between revisions of a design. So, pushing sub-circuits around on a sheet, or between sheets.On the layout, of course it's a lot more work moving around whole sections, so I don't go out of my way to do that. But I will every so often spot an opportunity to shove components and buses around, maybe vias. The saved space can be nice for future revisions. Mind that moving around components and pads may conflict with existing test fixtures!Tim

author: rrinker
author_rank: Super Contributor
timestamp: September 23, 2019, 09:04:43 pm
content: I did this. Again, only at the PCB stage. The schematic was neat enough. Laying out the circuit to prototype on a breadboard worked ok, and once I had the code good, it all worked as expected. Then I went to draw a PCB for it. No matter how I tried arranging things, I had far too many lines trying to cross over one another to make a neat and orderly PCB. I realized in looking at what was happening, that if I changed the pin usage a bit on my micro, I could get clean shots from the pins to the pullups/component being controller/external connector. Bingo, much cleaner PCB layout, and all I had to do was change some initialization code at the beginning to swap the pins around.I never felt a schematic should reflect any sort of physical layout of the circuit. Maybe that's the wrong way to go about it, but I use the schematic to display the logical connection of components in a neat and organized fashion. An input jack on the schematic may be on the left side of the sheet, but on the actual PCB maybe it's on the bottom, or the right side of the board. (ok, maybe not a great example, being in a left to right oriented country, I would tend to want the inputs to be on the left and outputs on the right of the actual PCB). Plus things get modularized in the schematic, not everything has 'wires' going to it, sometimes there are just tags. When it all fits on one page, I just put it on one page, but for something more complex, perhaps the power circuit would be on one page, the main processor and I/O on another, and output circuits on a third page. Just to keep it organized.

author: IDEngineer
author_rank: Super Contributor
timestamp: September 23, 2019, 09:28:43 pm
content: Arrrggg... I HATE labels on signals (when they're used as substitutes for actual lines on the page). Particularly on a multipage schematic. You never know when you've found all of the connections! It would be more acceptable of the schematic/layout application auto-appended to the label an indication of this/quantity (example: "clock 3/5" meaning this is the third of five references to that label), because then you'd know if you'd missed one and how many total implicit connections there are to that common "point".Another pet peeve is ground/earth symbols that point up. Yes, I've seen that. Multiple times. I always wonder if the person was (mis)using that symbol while trying to indicate something OTHER than ground/earth/common, or if they were just incredibly unbelievably lazy. Bottom line, it makes the schematic less clear when they use a very well known symbol in some nonstandard way... what exactly are they trying to convey? Do you dare presume they knew what they were doing? (If they're misusing symbols like that, the answer is obviously NO.)Quote from: rrinker on September 23, 2019, 09:04:43 pm100%agree, and the way I've solved this for years now on embedded MCU systems is that, for any given connection to the MCU, I provide a list of acceptable pins to the PCB Designer. They can then optimize pin assignments. I personally review each and every PCB layout before boards get prototyped, so I have the final say, but my Designers have told me that this is an INCREDIBLY helpful technique for them. Unless we're dealing with a parallel bus or something similar, the code usually doesn't care what I/O pin is used for a given function and there's no impact on cycle time. But it makes the Designer's job a lot easier, and I get far cleaner layouts as a result. There have been a few boards where the Designer has flat-out told me they were able to slash the layer count solely because I didn't force them to use specific pins. That pays dividends in reliability and economy on every unit.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 24, 2019, 04:25:10 pm
content: Quote from: IDEngineer on September 23, 2019, 09:28:43 pmThat's what ERC is used for. I would personally never design a moderately complex circuit, especially if it's multi-page, without running ERC. And I have a strict NO UNCONNECTED PIN policy. If you want to leave a given pin NC on purpose, you explicitely flag it as such, and ERC will then ignore it. This way an unconnected signal is unlikely. With some EDA software, you can even define your own additional ERC rules that would be adapted to your specific design. Very handy. I would not rely on eye-checking a schematic only unless it's very simple (which of course doesn't mean I only rely on ERC either. Don't twist logics here). To each their own methods.It's kind of funny how this labels thing is almost as debated and as controversial as "spaces vs. TABs", or other topics of this kind. Everyone will usually stick to their ideas with a force.As any method, it requires common sense and consistency to be usable, and then everyone pretty much has a different notion of what good style is. But just because you have once seen horror schematics with labels doesn't mean you should never use any. That's sometimes where it becomes a bit religious.

author: mikerj
author_rank: Super Contributor
timestamp: September 24, 2019, 04:35:43 pm
content: Quote from: IDEngineer on September 23, 2019, 09:28:43 pmOn schematics drawn in Pads every label has a list of pages where that label is used. Even better, on a schematic PDF generated by Pads you can click a label and it will jump to the next location that label is used. Not a cheap tool however.

author: taydin
author_rank: Frequent Contributor
timestamp: September 24, 2019, 05:00:22 pm
content: I think this disagreement about label use is because limitations of ECAD tools. For example, if the schematic capture program would be able to very nicely highlight a net so you see EVERYTHING attached to it (even in multi page, multi hierarchy designs), this label discussion wouldn't really happen, and everybody would be using labels. But it's really hard to get net highlighting to work in multipage, nested subcircuit, hierarchical designs.