Hello !
I would like to make a small converter using an Epcos RM8 ferrite transformer. This transformer use a coil former with 12 pins.
My schematics has a primary made of 4 winding (2 winding with center tap) (so eight pins) and a secondary with a center tap (so 3 pins).
I’ve, using the Epcos datasheet, designed a footprint for the 12 pins of the coil former. And numbered them from 1 to … 12 
So far so good.
I draw the schematics using “Transformer:TRANSF7” as the symbol. It was the only one having the correct number of pins available in the libraries. Those pins are all “equivalent” as far as I can tell. And I can’t force Kicad to use one side of the coil former for all the primaries winding and the other side of the coil former for the secondary. This gives me trouble when starting to draw the PCB because all connections get mixed up in the netlist.
Could you please tell me how to draw a transformer symbol with the pins numbered and actively linked to the one on the footprint I designed ?
Many thanks in advance for your help and answer to a real newbie !
Have a nice and bright day !
The simple solution is to create your own schematic symbol… if the pinout of “TRANSF7” looks good, then use that as your starting point.
All KiCad’s default libraries are read-only, because they can be changed with updates of KiCad.
I agree with Paul.Blitz to make your own schematic symbol for this transformer, but you do not have to start from scratch.
The grand view of things is:
- Start the KiCad project manager.
- Start the Symbol editor.
- Symbol Editor / File / New Library
- Type in some name, [Save], choose “project” in the "Add To Library Table popup.
- type “transfo” (from transformer) in the search box.
- Double click on some of the transformer symbols to find one you like best.
- Right click on it’s name and copy it.
- Right click on your new library and “Paste Symbol”
You have now made a copy of a default symbol in a personal library and you can study how it is build, and change what you wish. Pins can be added, moved, renamed, etc.
Also make sure to edit it’s properties:
Symbol Editor / Edit / Properties
The “Value” field is what is used in the library as it’s name. Have a close look at the other fields in the properties window. If anything is listed in the “Aliases” tab, it’s probably best to remove these for your custom transformer.
For more info about library management or creating custom symbols, look at the official documentation (either from the “help” menu or from the main KiCad website) and the FAQ part of this forum.
OK. I will try to do it. I hope it is not too difficult to have the link between the pin number in the symbol linked to the pin number in the footprint.
Thanks for the reply.
Edit : Did the new symbol. Put it in the personal library. I’ve numbered the pins from 1 to 10 (I only need 10 even if the coil former has 12 pins). I turned the signals to “bidirectional” because I thought I may need this if one day I try to simulate the wiring ? is it wise ?
Thanks for your help.
I don’t use ERC, but I think bidirectional is a type for digital ICs pins that can be input or output. I would use passive for all transformer pins.
Passive would also be my choice.
For more insight to how the pin types interact, look at the ERC matrix:
Eeschema / Inspect / ERC / Options (tab)
Thank you for your insight.
I’ve turned the pins “Passive”.
For now it makes no difference because I do not intent to simulate this little circuit.
Have a nice day !
Congratulations with your first custom schematic symbol.
For some strange reason many people who start with a PCB program are very shy when it comes to making custom schematic symbols or footprints. It seems they rather spending looking hours for some online source, and theno find something that almost resembles what they want, is from some conversion program which also delivers only half usable parts for KiCad.
For me it was the other way around. When I was looking for a new PCB program, the quality and ease of use of the schematic symbol editor and Footprint editor were important factors in deciding for KiCad. I find good editors more important than big libraries. (Although with KiCad, the included libraries have become of such good quality that I do not have to make many parts myself. anymore).
Well, drawing the footprint for the coil former was not difficult at all as Epcos shows the pins in a grid pattern of 2.54 mm pitch. I only had to copy it in the footprint editor of Kicad ! Easy enough for a beginner…
Once I got the footprint, I was able to see it would be usable in the PCB editor. And when i discovered the pin number problem, editing the symbol became the only way to go. But I did not know how.
When I decided to move to KiCad I spend months on defining my symbols and footprints to have a minimum (about 100 footprints) to start working. I use only my symbols and footprints.
For such things as custom transformers and other special components you need custom symbols and footprints.
For the vast majority of components however, there is no need whatsoever to do so. KiCad’s libraries are quite good, and I use them for almost all my parts. But I do not trust them, implicitly, but still check them before ordering PCB’s. Especially schematic symbol to Footprint pin mapping, and packages such as SOT-23 which are always troublesome because of lack of standardization.
Agree, but…
I prefer smaller symbols as I prefer to have my schematics fit at one page.
I could’t find the way to get documentation pictures as we use since ‘always’ using KiCad footprints so I have to modify each of them a bit.
Bigger differences I noted in SMD diode footprints. At such footprints I collect them from many manufacturers and do my own that (in my opinion) are good for all of them. Typically I get a little bigger pads in both (internal and external) directions. That is because of our small quantity of production I specify for each component as many equivalents as I can.
BTW, the pin type doesn’t have to do with simulation. AFAIK it is only used for the ERC and is related to the ERC matrix screenshot that Paul posted.
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