What is the intended (“correct”) way to insert the value for an electrolytic capacitor, which has both capacitance and maximum voltage specified?
Typically: “47µF 25V” or “47u 25V”
IF I write “47u 25V” in the value field, the simulation will not understand the value.
If I have only “47u” the simulation works but the voltage value is lost in the schematic.
What should I do?
Or is this a missing feature (handling voltage value of capacitor)?
There are of course other examples, like power rating of resistor (“0,22R 5W”) etc.
This is to some extent inspired by the forum thread below, but I have had the question in my mind for a good while without getting to the point of actually asking…
There is no “correct” way, or, whatever you decide do do is the correct way for you. There are many different people and each has his own preferences or company policies. Some try to cram everything into the value field (including tolerances and size. Others have separate fields for everything.
But now it makes me wonder…
For the people who use database libraries, you can’t just change the value field of a resistor, as it would get out of sync with the database. But I guess that may be part of ERC or some separate BOM checking script.
that’s correct. With DBLibs you just change the part with a different IPN (internal part number) and all the fields magically are updated to the correct db contents.
I understand that is the intention, but what prevents errors from creeping in when a user (accidentally) changes the value field of a resistor in the schematic?
If that happens, then the schematic does not represent the correct part number anymore.
I have never tried KiCad simulation but when I had a need for using SPICE from time to time my simulated schematics were never the same as schematics used to PCB design.
If schematics are separate you have no the problem you ask.
In my case (PSpice simulator from 90s) the reason for different schematic was for example adding ESR for electrolytic capacitor and for inductance for simulation but not for designing PCB.
I don’t know may be KiCad symbols for simulation integrate parasitic elements and you need not to use them at schematic for simulation. If so then what I have written is not helpful but may be not.
There’s no patent solution, but you can also overload a schematic with information, making it difficult to read.
All symbols have secondary or tertial parameters, but don’t they really belong in the BOM?
Exactly why is the breakdown voltage for electrolytic capacitors interesting, but not for ceramics? Or resistor breakdown voltage? Or inductor saturation current? Or tolerance? Or temperature coefficient?
You can add information as you like, all the way down to tape-and-reel specs, lead forming and moisture sensitivity level, but is it really needed?
I go to the KISS church on this one, for me it’s enough to know it’s polarised. All the rest is in the BOM (and footprint).
This is a very opinionated post, I know, but to me readability, clarity and understandability come first.
Simplicity is one parameter that can contribute to readability, but sometimes readability also includes getting the information you need or expect or want without having to jump through additional hoops.
Hence it happens that in certain cases you want to insert two parameters into the schematic for emphasis or where it is commonly needed.
The electrolytic capacitor is one example, there are others of course.
• Cap’s can be Ideal or Behavioral
• That parameter is defined in the Kicad panel
• The Value and Sim Field takes only the Value of Capacitance, not Voltage
• You can define Voltage as shown below
What you probably want is to show the Voltage in the REF field.
I agree with you 100% that for some symbols emphasis on a certain feature is needed to understand the functionality (electrolytic voltage is not one of them).
I do that myself on my schematics, but it’s rare. I use simple text labels next to the symbols (the real details are in the BOM). This can be a bit of extra work when moving/dragging a part, but no big deal.
As examples:
Sample-hold amplifier: I’ll add a text to the cap: “PPS”, because it’s significant.
Mains connected circuits: I might add “X2, 600 V” to a cap, showing the viewer that this is special.
“10 W” to a resistor, because that’s also special.
Or “1%” to relevant parts in a precision circuit.
That puts emphasis on the special/critical devices in the circuit, without plastering needless information on the jelly-bean parts.
The nice thing about doing this, is that it’s all ignored totally by ERC, simulation, PCB layout etc.
But it’s a help for you and others who read the schematic.
If you: Schematic Editor / File / Schematic Setup / General / Field Name Templates and then add a field name with for example Note, then you have this “Note” field available in all schematic symbols, it stays with the symbol when you move it, and it shows up in other places too.
Now this Guust field name is available in all schematic symbols. If you for example edit the properties of a resistor, you can add a text string in that field:
All extremely wonderful, but not what I want nor need. I stated that I use the text feature sparingly (eg, a design with 100 symbols, maximum 5 will have additional text). I can manage that myself with no problems, and I do not need to have them linked to the symbol. The very fact that they’re “neutral” and unconnected is a big plus, seeing the compatibility troubles that arise every time a new major version comes out.
If I wanted an extra field, I’d just add it in the symbol properties.
How I learned it in school, is that the shown value in the schematic is the most importuned spec of the part.
With a resistor, for example, the most importuned ting about it is the value, “100k”, than what already can be left out if the current going through it is relevant, or you specified somewhere that all resistor values that do not say other vies are a certain power rating. After the power rating the precision is the next thing, here it is practically the same with the power rating but in the case of resistors it is considered “standard” that if nothing is written the resistor is at least a 5% resistor, if not better. If it is importuned for the application even the Voltage rating or the Temperature Coefficient is specified, these are at least the values that I know of that can be specified with resistors.
With electrolytic capacitors it is considered to be “standard” to specify what voltage rating they have because with them the voltage rating can be rather low and when you design a circuit you what to make sure that it is clear that there should be at least this voltage rating.
It is also the case sometimes that there are companies that say “We want that every resistor has these values, every capacitor has these, …”, this can be for procurement or any other reason, but it is the case.
The service manual for my amplifier goes to the other extreme. All that’s shown on the schematic are the reference descriptors, e.g. Q409, and you have to refer to a parts list where all the characteristics of the part are tabled.
There’s no reason why you can’t store all the fields you want for the part, and a database backend will make this easier. No data is lost, just selectively displayed.
For my own schematics I think showing the refdes and value suffice so that I can do a quick mental analysis of the circuit. Displaying more fields than that just clutters up the schematic. Which is not to say you can’t present those separately. Perhaps some special parts might display annotations like “1 of matched pair” or “0.1% tolerance”.
The other reason why you should not overload the value field with lots of information is from database practice where stuffing comma (or space) separated values in a field is a poor man’s substitute for separate fields. Suppose one day you decide to ask the database how many ⅛W resistors you use, then you have to write a bespoke search expression.
