EEVblog Electronics Community Forum
Electronics => PCB/EDA/CAD => KiCad => Topic started by: sausage on January 28, 2022, 08:06:37 am
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Hoping someone might be able to give me some advice on open source USB through-hole connector models.
I can see in the standard KiCAD library that there is very little for USB connectors and the ones there are SMD. I can also see vendors like Digikey and SnapEDA that sell models commercially.
I have been modelling my own USB-A and USB-B connectors to suit parts that I purchase off Aliexpress and I would be very pleased to contribute these back to the community in some fashion as I go. But before I embark on doing too many more models, am I wasting my time? Are a lot of these models for Chinese connectors already freely available?
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If you cannot find them on SnapEDA, maybe have a look at 3dcontentcentral? You could publish yours there, too, if you don't find these models elsewhere.
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Have a look at the Wuerth website, e.g.
https://www.we-online.com/catalog/en/COM_TYPE_A_HORIZONTAL (https://www.we-online.com/catalog/en/COM_TYPE_A_HORIZONTAL)
Under downloads they have the step file. (No KiCad footprints yet, unfortunately.)
Ben
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Thank you both for these.
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Both sites were pretty handy for getting down the models. What I am actually seeing is a few very similar models of USB connector (which is great - almost a standard), but missing footprints.
So I've started making some and will contribute those around as well. Probably on the 3dcontentcentral, though possibly on gitlab.
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My opinion and experience is that anyone designing any non-trivial PCB with an EDA tool like KiCad had better be ready, willing, and able to create any needed parts (symbols and footprints) whenever necessary. The lack of a usable part in a library should never hold up design. I'm saying this not because I think anybody cares about my opinion, but as advice to beginners: learn to make schematic parts and PCB footprints as needed. It's a normal and natural part of the process.
3D models might be a different matter. ;D
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My opinion and experience is that anyone designing any non-trivial PCB with an EDA tool like KiCad had better be ready, willing, and able to create any needed parts (symbols and footprints) whenever necessary. The lack of a usable part in a library should never hold up design. I'm saying this not because I think anybody cares about my opinion, but as advice to beginners: learn to make schematic parts and PCB footprints as needed. It's a normal and natural part of the process.
I agree with this and would like to add that footprints and symbols you find online for free are useless. Not most of them but all of them. Making your own is the only solution so learn to be good at creating your own symbols and footprints. 3D models OTOH can be found for most parts and are not critical for the PCB manufacturing /assembly process so it doesn't matter if they are slightly wrong.
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Check github/ and gitlab first to avoid duplicating effort unnecessarily. These are probably the largest repositories of odd Kicad resources that people have made and used. That's where I found Kicad footprints for through-hole USB-C connectors that I use. It sometimes takes careful search and filtering - based on knowing the textual representation for symbol and footprint libaries, and to weed out software libraries for interfacing with components.
Edit. Also the pull-requests against official kicad libraries that got rejected for reasons other than quality and correctness.
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Really appreciate the insight. And yes, good advice to accept that doing custom footprints is part of the job, which is good experience overall.
I agree with this and would like to add that footprints and symbols you find online for free are useless. Not most of them but all of them.
@nctnico I'd like to dig a little more into what you said here. You are saying that all free footprints are useless, which is a blanket statement, however could you elaborate on exact why this is the case? Is it because it is very likely these footprints will contain measurement or alignment issues once printed and the part simply doesn't fit as intended? I would expect that as long as the footprint measures expectations and the model of the intended part fits, I should be able to trust the footprint rather than sinking a couple of hours creating a new one.
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I agree with this and would like to add that footprints and symbols you find online for free are useless. Not most of them but all of them.
@nctnico I'd like to dig a little more into what you said here. You are saying that all free footprints are useless, which is a blanket statement, however could you elaborate on exact why this is the case? Is it because it is very likely these footprints will contain measurement or alignment issues once printed and the part simply doesn't fit as intended? I would expect that as long as the footprint measures expectations and the model of the intended part fits, I should be able to trust the footprint rather than sinking a couple of hours creating a new one.
The problem is that with online footprints you don't know who created them and for what kind of process. Think about thermal reliefs for the pads, copper clearances, pad sizes on inner layers, annular rings, having mechanical holes as connected or not, etc. Some of those are things that are specific for the kinds of projects you do (PCB tolerances / geometries). Also some manufacturers specify holes which are way to large or too small. You have to check those.
Last but not least some are very sloppy with drawing silkscreen outlines. I learned that the hard way a couple of decades ago. As a junior engineer I had designed a board using the library made by the head engineer. When I wanted to put the board together it turned out the transformers (which I places in a row) didn't fit.Turned out the head engineer had drawn some kind of rectangle without taking the actual size into account. On top of that the transformers had a notch on the cases making the fitting even worse. The head engineer told me to check the components next time to which my reply was that I wanted to be able to rely on the library being correct. We both had a good point.
I do get your point about making components is extra work but with some practise you can churn out symbols and footprints really quick. It takes me far less than an hour to make a footprint for a USB connector; likely less time compared to searching and checking an existing footprint. Over the years I have created a vast library of footprints (not for Kicad) but for every project I need to create one or two new footprints. It is inevitable nowadays.
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Really appreciate that, thanks @nctnico.
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If we're talking about 3D models specifically, most manufacturers do have them available for download for their parts.
However, far too often, their legal departments told them to make them available under some unnecessarily restrictive or ambiguous license terms. As such, projects that need to be "open source clean" like KiCad can't really include them in the official libraries. So you basically have to just add them to your own project, then update a copy of the footprint to reference them.
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That's what I usually do. I harvest 3d models from 3dcontentcentral, SnapEDA or manufacturer libraries and the standard package models that come with KiCAD cover the rest.
For me they're just eye candy, but if you really need them e.g. for import into a mechanical CAD, for mating or collision tests, it's mandatory that they're exact.
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What has been interesting going through this process is the sheer amount of USB connector configurations available. I'm only talking USB-A (Horiz THT), B Mini (Horiz THT) and B Micro (Horiz SMD).
Every vendor places the binding posts, and the pins in slightly different positions.
So it's entirely feasable that if you can't get exactly the same USB connector again, you *could* end up having to respin a board based on one component alone.
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What has been interesting going through this process is the sheer amount of USB connector configurations available. I'm only talking USB-A (Horiz THT), B Mini (Horiz THT) and B Micro (Horiz SMD).
Every vendor places the binding posts, and the pins in slightly different positions.
So it's entirely feasable that if you can't get exactly the same USB connector again, you *could* end up having to respin a board based on one component alone.
Yep. Even from the same manufacturer the pins can be different. In some cases making the holes bigger or slots wider is all what it takes.
OTOH it is possible to find connectors that have standard footprints across vendors but you have to check the mechanical drawings carefully. It is not an advertised feature.