Generic symbols and using Eeschema for a sole purpose

Hi all,

I’d like to start using Eeschema with the only purpose to generate a netlist for Pcbnew. Basically that’s all I want it for.

Traditionally, my personal design workflow is such that most specific part numbers get defined at some point after the PCB design has been done.

In case you think that doesn’t make sense, I’ll give you a most typical example: let’s say I’m working on the design of an analogue acquisition chain, I come up with a design that requires two op-amps, nothing special (just average precision / noise / speed, internally compensated, no rail-to-rail, blah blah). At that point, the only one thing I decide is that I’ll use a dual in a SOIC-8, and I’ll use any of the million part numbers that come with the exact same pinout (which they do for a reason).

That scenario is me all the time. I choose an N-channel power MOSFET, all I care to decide before PCB design is that it’ll be a TO-220 and, again, they all have the same pinout, for a reason.

And the thing is that I do things in that very particular order because I want my design to be flexible, and part number agnostic where at all possible. So I do have a point.

So, what do I put on my schematic??

Specifically for the MOSFET, and my question comes from the fact that I have been looking for a generic but I haven’t been able to find one with 3 pins (the pspice one has 4 pins), do I have to browse the “Transistor_FET” library until I find an N-channel, 3-pin MOSFET that has the footprint I want?? Implying that my files will have a wrong part number. Rather, should I use the pspice one?? Implying that there will be a 4 pin to 3 pin mapping at some stage. Should I create some generics I’d like??? Just take any of the existing symbols, create a copy, and delete most things in it?

Thanks for any comments :slight_smile:

Alex

In the Device symbol library you will find generic symbols which don’t have a footprint attached. Choose the appropriate one. The 3 letter combination GSD etc. tell the order of the pins from 1 to 3, GSD means pin 1:G, pin 2:S, pin 3:D.

Place the symbol in the schematic.

Then open the symbol’s properties from the schematic and change the footprint. Find one that fits for you. Again, they aren’t in a specific transistor library but are named with a generic package name because you want a generic footprint.

The most important thing to check is that the symbol and the footprint have the same pin numbers in the right order.

Edit: don’t browse through the libraries, use the search field and search for nmos in symbols and to-220 in footprints.

2 Likes

This is only one of the possible ways. For the fully generic workflow where every symbol is initially placed without footprint the assign footprint tool (previously known as cvpcb) is most likely the better choice.

See How can i assign a footprint to a symbol?

Fantastic, guys, thanks a lot. It really looked like I was missing something. It turns out that the specific thing I was missing is this library called Device. All I need is there, so I’m over the moon right now. Good point re. the “fully generic workflow” too. Thanks :slight_smile: