Placing two Op Amps in the same footprint

Hi. Newbee to Kicad, but first project went well from schematic to PCB. But i have spent hours and hours here and google and youtube trying to get the two Op-amps, and its power pins, into the same LM393 footprint. But all the time Kicad places two LM393, instead of one. The pin-numbers in schematic are correct. How do i get the two Opamps in the same footprint?

You probably already have . . . what footprint do you have associated with the symbol ? the standard LM393 symbol has units A, B and C.

Why are you hiding the component references?
It looks like you have placed Unit C on Unit B

You have footprint with two LM393 comparators and you want also insert there (or replace them with) two Op-amps? :slight_smile:
The key is to both symbols have at schematic the same reference like U1 with unit marking like U1A and U1B. If power pins are defined as unit C then also U1C.
If you have U1A and U2B then even having right pin numbers they are separate parts and footprints.
But we don’t see their references at your schematic.

What is 47uF1? Is it 47.1uF?
And why it is shorted with wire going through it?

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There are others like zener 12V.1W1


Welcome to KiCAD, Kornman!

FYI your PNP is upside down.

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From your screenshot, it looks like you’ve been experimenting with setting you would have been better of to leave alone until you’ve got some more experience with KiCad.

It looks like the References (RefDes, Reference Designators) of most resistors are missing (hidden?), but there still is an R5 and an R3.

By default each symbol both has visible RefDes, and value fields. These fields have specific meanings. Do not swap those fields or put the wrong data into them.

Your 47uF1 capacitor also appears to be shorted. There is a wire though it, and the junction dots in unexpected locations are also an indication something is not right.

There is a 220 Ohm string close to R5. What sort of object is that? My first guess is that it’s a wire label, because of it’s color and the little square in it’s lower left corner.

Just as with RefDes and Value fields in schematic symbols, there are also different ways to add text strings to a schematic, and the object type you use to add such texts is important.

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The schematic and the footprint are not related UNTIL you assign a footprint to that/those amplifiers. In theory you could assign a 11 pin header to the opamps, of course it will not work but you can see how the association is manual.

I’m using Version: 8.0.2-rc2, release build.
When I add an LM393 I get a different structured dual comparator (the LM393 is a comparator not an opamp).



It would be more creative if it were inside out.

Hi Kornman - when you place the LM393 symbol and assuming it is a through hole component, associate it with a footprint type DIP-8_W7.62mm. This will give you the dual comparator plus power and ground footprint. As others have pointed out, the symbol is a three part symbol - 2 comparators and the power and ground connection.

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Thank you for being patient with a newbie. I appreciate all the advice, and am quickly realizing that I have a lot to learn in KiCad……
I numbered the parts in the LM393 with U2A, U2B and U2C but it still didn’t work, it refused to load into the Netlist. I removed my LM393 completely, and put in a new LM393. Then it already had this numbering U2A, U2B and U2C, but Netlist still refused to accept it.
Strange thing is that the label on the first comparator is “U2A”, but the reference says only “U2”. When i add the “A” in the reference, the Label says “U2AA”. See image. (Sorry, more than one image was lot alowed for a newbe in this forum.)

Shorting the 47uF capacitor was a rookie mistake.
KiCad puts the “ones” after the components labels for some reason…
I renamed the references from R1, C1 to something more understandable, like 4k7, 0.1uF and so on, which might have been a mistake………
I get a lot of other error codes as well, but they seem to be related to me setting out Labels.

The electronics unit itself is already built, on a veroboard, and in operation on a telescopic boom lift. The customer is very satisfied, so I thought I would build it a bit more seriously and make a circuit board. I got the tip about KiCad, but it wasn’t that easy……….

I understand if you don’t bear with me when I have so much to learn…I might give up……

I’m finding this a bit hard to follow, but in your most recent schematic you’ve still put unit C on top of unit B.

I think you might be missing an important concept here. In a traditional schematic with op-amps or comparators, the triangle symbols are shown with the +ve and -ve supply lines coming out of the triangles vertically up and down, just as you’ve drawn for the right hand triangle. It appears that you’ve done that by placing units B and C on top of each other - see how there are two labels next to it: U2BB and U2CC.

This is wrong. All three units should be drawn separately, as shown by @JohnRob. Units A and B are the comparator parts, and should be shown with NO power lines connected. Unit C should be drawn off to one side somewhere convenient, with the power lines (and only the power lines) connected.

KiCAD requires you to treat the power supply feeds to the comparator chip separately from the signal inputs and outputs. So using @JohnRob’s example, you would connect your +ve and -ve supplies to unit C, and just the signal inputs and outputs to units A and B.

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Thank you for your long and good explanairiton. Much appreciated! I will try that this afternoon.

I don’t agree with you. They can be drawn separately but they can also be placed one on another. It depends on designer decision and I always prefer to see how the supply of part is done when thinking about signals going through it.


I have tried to get an overview of the thread so far, but a few points seem to remain unclear:

First, the terminology in KiCad is:
“Symbol” - representation of the comparator 393 in the schematic; this is what we can see in your screenshots above.
“Footprint” - The pattern of copper pads on the printed circuit board to be designed in the Board Editor, that will connect to the pins of the physical component (for example in a DIP8-package containing two comparators and power supply pins Vcc and Vdd).

In this case, the symbol for LM393 in the schematic, when taken from the KiCad standard library, is in three parts as mentioned in previous posts.
In the schematic editor, pick LM393 from the KiCad symbol library, klick first time on the canvas to place unit A, klick a second time to place unit B, klick third time to place power supply pin unit C. Press escape to stop placing symbols.
Now you can right-click any one of the three placed symbol units, choose “Properties”, in the dialog box that opens go to field “Footprint” and klick the empty part of that field, klick the library icon that appears on the right of the field and choose a footprint (for example “DIP-8_W7.62mm_LongPads” if you intend to use a hole-mounted version of the LM393).
Now when you open the board editor, go to “Tools” menu and choose “Update PCB from Schematic” it will give you only one footprint for the LM393 that consisted of the three units A, B and C in the schematic.

It might be that you have inserted the symbols in the schematic by some other method, which has messed up something. You can try making a copy of your project (backup in case something goes wrong), then delete the two comparators and place new ones using the method above.

I hope this might possibly be of some help.


Adding on to what HMK explains above:

The symbol for LM393 is broken up into three different units. These units behave kind of like different symbols (you can move them around independently, etc) but they only refer to one physical part and will only generate one reference in the netlist.

The A, B, C in the reference designator is added automatically according to what unit is selected. So, you don’t type in U2A as the reference, you just type U2, and the A is added automatically.

It is perfectly fine to place the “C” unit for the op-amp on top of the “B” or “A” unit if desired. This is why the “C” unit is drawn as just a few pins, so it is easy to stack on top.

If you do this, you probably want to hide the reference and value fields from the “C” unit and just leave the ones from the “A” or “B” unit:

Can you explain more what you mean by “netlist refused to accept it”? What error message are you getting, or what behavior that you don’t expect?


Kornman added the A, B, and C to the RefDes himself, KiCad then also adds it’s own A, B, and C for the unit, and as a result there are two A’s, and B’s, and that does not work. See this part of his latest screenshot:

Yes, that’s a problem in the latest screenshot, but I’m not sure that’s the only problem / was the original problem that started the thread, so I wanted to check what the situation is after that is fixed.

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I can see I’m in the minority here! :smile: I was trying to emphasise the essential difference between standard schematic practice, and the need in KiCAD to have a separate graphics entity (unit) just for the power lines.

Yes, you can obviously put any symbols you like on top of each other, but I think it could easily lead to confusion for a newbie, and therefore I recommended keeping them separate. When people are as experienced as you guys, there is no risk of confusion and then it’s just a matter of preference.

But for now, it is essential for the OP to understand that there are three entities to the LM393, not just the two comparators, and all three entities must be correctly - and separately - connected. Perhaps I was explaining it unnecessarily - in which case, my apologies to the OP. :grimacing:


Just so it’s clear, there is no specific need in KiCad to do it this way, it’s just the style chosen by the library team for the KiCad standard libraries. If you make custom symbols you can do it a different way if you prefer.