What does 'Alias' do in 'Edit Component Properties' in the Part Library Editor?

[Nick_Collier]

I have just started learn KiCad today. I want to add a TL074 op-amp to my schematic, it is not in the my library so I selected a LM2902 which is there. I noticed in the Part Library Editor, the LM2902 has a list of aliases which can be seen by pressing Edit Component Properties. One of the aliases is TL074, but I can only add or remove alias entries from the list. I don’t know how to select TL074 to be ‘active’ for my op-amp. I not sure exactly what I mean by ‘active’. I guess as a minimum requirement it should change the annotation on the schematic to TL074.

[dchisholm]

@Nick_Collier

. . . I want to add a TL074 op-amp to my schematic, it is not in the my library so I selected a LM2902 which is there. I noticed in the Part Library Editor, the LM2902 has a list of aliases . . . (including) TL074 . . . [/quote]
Does the LM2902 appear in more than one file in your Symbol Library table? In the EESchema “Choose Component” tool, I found the TL074 near the bottom of the list under the “linear” library. There are a few hundred opamps in the list, so you may need to send your forefinger out for lubrication before you finish clicking the down-carat to scroll through all of them.

If there is an “LM2902” symbol in another library that is listed BEFORE the “linear” library, it will take precedence. If “TL074” is not an alias of this higher-precedence “LM2902” symbol, then “TL074” will not show up in your schematic.

[quote]. . . I guess as a minimum requirement it should change the annotation on the schematic to TL074.

That is essentially what the “Alias” feature does: makes a symbol which can have any of the “Value” properties found in the “Alias” list, while (almost) all of the other information remains identical (e.g., symbol shape, pin names, pin numbers, footprint, SPICE model, etc). The only symbol-file information that is unique to each “Alias” entry are the “Description”, “Keywords”, and “Documentation File Name” entries.

Dale

[Nick_Collier]

Thanks, i found the TL074. My list appears to be the same as yours. So if i add an entry to the aliases list, that will make a new component appear in the library that has all the same properties of the parent component, only with different annotation? I guess this is useful for different components that have identical pinouts, like the various quad op-amps.

[dchisholm]

Yes, you have the right idea. At the least, it saves storage space in the symbol libraries.

I don’t know the history of the feature. I can speculate that it originated as a way to accommodate parts with different identifying numbers, that are fully interchangeable in both electrical and mechanical details - such as the National LM741 and Fairchild uA741 opamps. It’s also useful when parts come in interchangeable packaging, but different tolerances or performance grades - like the OP27A and OP27G. As you said, it’s most often used as a way to catalog components that have the same pinout and footprint details even though they may not be interchangeable in a broad sense. I.e., for purposes of laying out and routing a PC board there isn’t much to distinguish an LM2902 from a TL074, but I certainly hope you wouldn’t just plunk the '2902 into an '074 socket without first doing some circuit analysis!

Dale