Electronics > KiCad

Help sorting out libries, symbols and footprints

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I've been playing around with KiCAD for a few years now and mainly using the standard libraries along with some symbols and footprints I have had to make myself. I saw a YouTube video a while back where the person used a different approach... he copied each symbol to his own symbol library and then duplicated for each value of that component used ie. every resistor value had its own symbol. I can see this being useful in that I buy SMD parts by the 100, its a good chance that I will always use the same 10k resistor with the same datasheet, footprint, manufacturer part number, source link etc etc. It seems that it would be useful to have all this info entered once into the symbol fields instead of having to enter it for each project if I were to use the default library symbol. Each symbol then had some smaller text that contained relevant data for the circuit.

Not sure if this makes sense. I can't find that YouTube video that got me thinking about using this process. How do others make use of the default library symbols? I am about to get serious in my use of KiCAD and want to make the right decisions up front so I don't to go and rework schematics if I change my mind later.

Let's say you have a separate symbol for every E24 resistor value, perhaps also a set to cover 1/8W and 1/4W. Does the footprint count in this? OK, so you have another lot of symbols for 0603, 0402, PTH. That's a lot of symbols, but you only have to do it once.

Now, some time later you figure your zig-zag line resistor symbols should actually be of the box sort. That's a lot of symbols to go in and change! Or, you could use a common symbol, change it once and every resistor magically matches.

IMO, using a common symbol where possible makes a lot of sense. Over in Other Products the trend is to have specific parts in the parts library (as opposed to generic parts that you sort of the detail when placing), but they still use common symbols.

I was thinking that individual symbols linked to a specific component value, part# would make the BOM easier to manage. I buy 10K SMD resistors by the 100's so I will be using that exact part# for some time.

It might. If you were talking, say, micros or something reasonably functionally unique then there are positives for doing that. But for jellybean parts such as resistors... selecting the actual manufacturer and supplier is best left to point to buying, probably. You don't really care where they come from so long as they match the headline value and tolerance specs, and if you specify, say, Vishay via RS, are you really going to create a new component to replace that when you come to order and find RS don't have any and anyway Yageo via LCSC is far cheaper?

IMO, it would be better to have the part detail relevant specs (value, tolerance, size, etc) and include a unique part reference of your own devising. It's that part reference that makes it to the BOM, and your parts database manager then generates the appropriate purchase request. It will know what to buy from where depending on MOQ, other parts (better to get them all from one place if you can to reduce shipping costs), availability and spot price. Of course, you might not have that bit of your system yet so it will be manual work, but you'd have to do that at the start using the scheme you suggest, and then again at the end when you find the part you specified isn't available from the disty now you're three weeks down the line.

If you're buying jellybeans by the 100's, that doesn't change much. In fact, it can make it worse - I do the same and some of the rarely-used parts last forever. Almost. When they do run out, often I find the supplier part number is no longer recognised, so all the buying info is obsolete and I need to resource them. Not a problem for me because the BOM gives my part reference and I just fix what that resolves to, but if I had to go back to the schematic to replace those symbols, then check the layout isn't affected (it shouldn't be, but you never know and it's better safe than sorry), then regen the BOM... no, don't want to go there ;)

phil from seattle:
I dunno, that seems like a lot of work. To change a resistor or cap value, you have to change actual symbol?

I use a disti field in my symbols.  You can just plug the disti part number in via the Edit Symbol field tool in Eschema. I use LCSC so have that set up.  Then when I have, for example, 20 10K  603 resistors in a design, I just plug in the LCSC number once where they show up on the same line. I usually pull up previous BoM and crib the part numbers from that. Then when I build the BoM, it has the disti number right there.  If you use JLCPCB there is a custom BoM script that produces the BoM in their format.  No Muss/Fuss. I think there are scripts for other assembly houses as well. Totally beats having to massage a BoM by hand for part number or format.


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