would some kind person on this forum show me with a schematic view how the dual lm339 comparator should be shown on the schematic editor so that the pcb editor will display correctly. I have tried various combinations of using the power supply (unit c) on the comparators. The last effort was with the + supply on one symbol and the - on the other symbol. This so that I could have the + rail at the top and the - rail at the bottom of the schematic.
Doesn’t appear to come out properly on the pcb editor. There must be one and only one display on the schematic which will be correct on the pcb editor.
Its a pity that kicad can’t show the complete dual comparator like they show moc3041N.
These are the three different ways of representing the LM393 for your schematic (of course, all items can be flipped in both X & Y axes). All are correct.
U1 all separate, U2 A & C joined, U3 B & C joined.
Note, on U3 the Ref. & Value have been hidden.
To get the correct footprint, double left click any of the three parts in the IC, then associate the correct footprint you desire for the PCB.
Some examples are below:
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Hi, I see that my way of putting v+ on one symbol and v- on the other must not be correct.
In your all separate, u1c wouldn’t have a footprint would it? It is just where the power supply attaches to the chip. Your power supply components can be attached to 8 and 4.
Can I separate in u1c v+ from v- so that I can fit a + track at the top of the schematic and a - track at the bottom. Much better for fitting all components together without overlap of tracks. I found I could separate them for putting v+ on u1a and v- on u1b. This did not seem to be correct on the pcb editor.
Your statement of incorrectness is incorrect! OK; I have not seen it done that way, and it is probably not conventional… But I do not think it is WRONG.
Layout of the schematic is for your eyes to see clearly. This is some relationship but making the schematic clear to your eyes does not insure a clean layout and vice versa. U1 is one package, U2 is one package, and U3 is one package in the example by @jmk.
There are other ways: You could also use a symbol which shows both comparators in one package like this
But probably shrink the pin names and move them inside the rectangle.
It is all a matter of what works best for you…
If you are designing the circuit yourself, then use a symbol which you like best for clarity in indicating circuit operation. (I like something like JMK’s U3)
If you are copying a circuit which you got from elsewhere, then you might want to find or make a symbol which closely resembles that which you are copying. It is not difficult to edit or make symbols in KiCad.
Is correct, but not common (I have never seen it).
It is hard to understand what you mean.
u1 would have a footprint. But u1 as whole IC meaning u1a+u1b+u1c they together have a footprint.
If you write about u1c alone then it depends on logic interpretation. u1c symbols a part of footprint - does it mean it have footprint or not. One can say: yes, other can say no.
From one point of view - of course. The power to this IC is connected through pin 8 and 4.
But what exactly is power supply component in your sentence. This symbol being a power supply of this IC or other that this IC elements like power supply regulators that are connected to this IC. I don’t understand this sentence.
Yes.
Make a copy of this symbol and edit it:
- to contain 4 parts (two op amps, and one v+ and one v-), or
- to contain 2 parts (one op amp with addition of v+ and second with addition of v-.
But it is not common to use + track and - track at schematic. Common is to use power symbols and not doing a mess at schematic with power wires.
The idea of 3 parts of this symbol is that you can place u1c somewhere else (in the corner of your schematic) and you have no power mess in the schematic itself. When you read a schematic trying to understand its working, in most cases you are not interested how it is powered.
Hello again @petercl14
Below is a schematic using 1½ LM393s that I copied from a data sheet. The layout is designed to be easy to read and understood by humans. It is a completely abstract version of a product.
Underneath the schematic is a rough PCB layout of the exact same circuit. This is a real life version of the schematic that, when assembled, will do the real life job of the schematic. Note how difficult it is to try to understand the purpose of the PCB by looking at it. Understanding the purpose of the PCB is why Schematics exist.
This PCB layout was created for Through Hole Components on a single layer PCB deliberately because I am assuming this is the type of circuit you wish to attempt.
Please note the difference between the schematic and PCB. Also note that there are no jumpers or split power supplies anywhere, simply because the two drawings belong to totally different concepts… one is real life and the other is purely abstract. Please try to understand the different concepts involved with Schematics and PCBs.
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That doesn’t look right to me. On the pcb layout you have 2 lm393. This is a dual comparator with 8 pins. Only one should be on the pcb layout.
There are 3 comparators in use on the schematic and 1 unused one so the count is correct.
yes I would like to get this symbol in the schematic but there is no symbol like that. A schematic using the real dual comparator would be much easier to use in getting a pcb layout… Your comments assume that you can get that rectangle symbol because you are talking about shrinking the pin names to be inside the rectangle.
How specifically do I get that symbol on my schematic?
You seem to obsessed with having symbols in the schematic that resemble the physical part. Are you coming from some wiring system for beginners like Fritzing?
You have to overcome this conceptual hurdle of yours and accept that the layout will nearly always look nothing like the schematic but is exactly the same circuit, topologically speaking. Laying out a PCB is not easy to start learning but KiCad has all the tools you need.
To answer your question directly, the way to “get symbols” is to make them yourself. It is not difficult and I do it much more often than using symbols from others.
But…I am guessing that you do not have a good understanding of circuit operation. (??) Please excuse me if I am wrong. The point is that symbols as shown in @jmk’s post are meaningful to a design engineer or anyone who wants to understand circuit operation. While you do not lose all of that with a symbol that more closely resembles the package, this second option (for a dual or quad comparator such as LM393 or LM339) will generally be more difficult to read by someone who wants to understand circuit operation.
Perhaps if you took a dive into your circuit operation you would have better appreciation of why schematic diagrams look the way they do, and why they do not look so much like the pcb layout.
??? !!!
Schematic is not to be looking like pcb layout. POINT.
The schematic like one shown by @jmk will look identical if it uses dual or four comparators packages because they both will work the same way.
If you draw it using symbol containing 4 comparators inside it will be very hard to understand how it works.
Some of those old manufacturer schematics did it that way instead of having separable units. They are hell to read. I guess those were the days when there was a lot of attention on the IC parts.
Even back in the valve days, sometimes you would see a part of say a combo triode-pentode drawn with incomplete envelopes to indicate that it was only part of the valve.
Here’s an ECL86 example from the Internet: http://www.valvewizard.co.uk/ecl86pcb.jpg
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I have an excellent understanding of circuit operation Bob. I have used ltspice simulations first to get the circuit correct instead of building it first and then finding out it doesn’t work for some reason. And of course the simulation uses the same symbols as in the kicad schematic.
But in the case of kicad you are using a real dual comparator with 8 pins for example. When you build your circuit board these pins have to be connected to tracks on the circuit board. Tracks lead out of the pins. That is why in designing a circuit board it would be a lot simpler to use a rectangle with 8 pins for the actual schematic symbol. For simulation yes use the 3 pin symbols.
This is where kicad has gone wrong. They want to do simulations and at the same time make a circuit board. The two are incompatible. If you want to do simulations use ltspice. If you want to make circuit board tracks you have to use the real life components.
If you are designing your circuit board by hand you are using the real life symbol. The same goes for software design.
No. Pads from footprints connect to tracks.
No. The THREE are incompatible.
There are Simulations, Schematics and PCB.
Three different workloads.
Three different results.
@BobZ posted a nice drawing of a component as an idea for you.
You won’t find a drawing like this in the Kicad libraries because it is neither a symbol (no pins) nor a footprint (no pads). It is a nice outline drawing of a component.
Hardly to believe after reading:
What you have written after seeing a schematic containing 4 comparators.
Distinguish between pins and wires at schematic and pads and tracks at PCB. It will be easier to understand what you are trying to say and if your thought are at schematic or at PCB.
During designing circuit board (PCB) we all have rectangle with 8 pads and we all agree that using this rectangle is the only way to go when designing PCB. But this have ABSOLUTELY NOTHING to how schematic should look like.
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I disagree, and I think that millions of design engineers working since about 1971 would probably disagree. In 1971, I was a college sophomore who began as an intern in a work-study program. That work introduced me to TTL logic. The 7400 IC was a quad two input NAND gate, and I hand wired a breadboard based on the schematic diagram. The schematic diagram symbols were 4 gates drawn individually. They were not drawn in a package enclosure. (Thank you @m852 for providing this example for the LM339.) There is nothing wrong with such a symbol, but most design engineers find it more difficult to think and design with that sort of symbol than with the comparators drawn individually.
You may infer that I have been design engineering for almost 50 years. I have often used schematics with (symbols showing individual comparators or op amps or logic gates). Most of the time, I can design the board (or hand wire a breadboard) and it will work properly when I apply power. No need to use simulation for functionality of many of my designs. I will bet that MANY members of this forum have had similar experience.
Often in life, my opinion has been the odd one out for something or other. But here you are going against the proven experience of MANY engineers over MANY years. Of course other EDA programs are using similar symbols; nothing odd about KiCad in this regard. You are certainly entitled to your preferences, but any assertion that KICad is wrong in this regard does not carry much credibility.
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It all depends on the requirements in my country there is a GOST standard in Europe, this is usually IPC if there are no requirements, then you can draw as convenient as possible … Below in the picture, for example, the designation of microcircuits and other parts according to GOST and I personally do not like readability and there are more strict Although DRC is used to it, this is a requirement for registration and is not a mistake if there are no clear tasks …
If you want to do simulations use ltspice
Sadly i cannot use you suggestion on my machine.
Thankfully ngspice exists and, hopefully on the next release, KiCad will be able to import and simulate ltspice’s stuff on all supported OSs out of the box.