LTSpice is Terrible - Page 1
Forum section: electronics / beginners

author: BlackHecilopter
author_rank: Contributor
timestamp: June 06, 2025, 07:14:41 pm
content: I've never seen a bigger pile of junk. Sure you can eventually almost get it to do what you want but the entire experience is like pulling teeth.

author: TimFox
author_rank: Super Contributor
timestamp: June 06, 2025, 07:18:44 pm
content: Another topic using words like “ridiculous” and “terrible” to complain about something, but this one gives no examples of what the poster dislikes in LTSpice, which is a free program.(Personally, I use AimSpice, which is an old fashioned version of Spice using unfashionable line-based syntax.)Is there a symbolic meaning of the misspelling of the username?

author: BlackHecilopter
author_rank: Contributor
timestamp: June 06, 2025, 07:27:07 pm
content: The currents are backwards. Current through the resistors and the voltage source is negative. LTSpice appears to use electron flow.When I simulate the circuit in a normal tool like Falstad, the currents are correct.If you've never used a normal simulation program, here's a free one to try.https://www.falstad.com/circuit/Now place these two tools inside your head and compare them. See what I mean?

author: BlackHecilopter
author_rank: Contributor
timestamp: June 06, 2025, 07:31:30 pm
content: Here's another one that's not completely insane from a users perspective (i.e. Micro-Cap)https://gotroot.ca/spectrum/www.spectrum-soft.com/download/download.html

author: Benta
author_rank: Super Contributor
timestamp: June 06, 2025, 07:34:18 pm
content: Why start a thread like this at all?Primal Therapy would probably give better results.

author: BlackHecilopter
author_rank: Contributor
timestamp: June 06, 2025, 07:37:40 pm
content: Valid complaints about the tool is my therapy.

author: BlackHecilopter
author_rank: Contributor
timestamp: June 06, 2025, 07:42:50 pm
content: See attached images

author: BlackHecilopter
author_rank: Contributor
timestamp: June 06, 2025, 07:47:23 pm
content: Can someone verify if -3 mA is the correct current? Apparently, I'm too dumb.

author: floobydust
author_rank: Super Contributor
timestamp: June 06, 2025, 07:51:19 pm
content: I've never seen a bigger pile of gold.LT Spice is fabulous but it requires some IQ to interpret results, also includes tests for patience and humility, sanity.Significant digits possibly to blame. It might be 1 for the current and 8 for the dissipation.So the current really is 3.3mA but to 1 SD is 3mA.

author: BlackHecilopter
author_rank: Contributor
timestamp: June 06, 2025, 07:53:35 pm
content: Why's LTSpice have a minus sign?Falstad seems to work fine.Plus it took me two seconds to make the circuit in Falstad versus 15 minutes in LTSpice.I spent 15 minutes in LTSpice to get the wrong answer for a circuit that a 5th grader could figure out.

author: tooki
author_rank: Super Contributor
timestamp: June 06, 2025, 08:03:59 pm
content: Quote from: BlackHecilopter on June 06, 2025, 07:14:41 pmThe user interface could really use some work (especially the Mac version, whose interface was deliberately hobbled by the “my way or the highway” developer, who lamented the “mistake” of adding a toolbar to the Windows version). It behaves contrary to most modern software, and that’s a bad thing IMHO. It’d also be easy to fix, without making it hard to use for the millions of existing users.On the other hand, once one gets used to said oddball interface, it’s fabulously fast to work in. If I need to draw a schematic to post here on the forums, I’ll do it in LTspice because there’s no other tool I can do it in so quickly.I’m a fairly light user, downright inexperienced compared to some of the expert users here on the forum.The only thing I really miss in LTspice compared to some other simulators (like TINA and Falstad) is interactive simulation, where you can change the state and values of things while simulating. In LTspice you have to plan the state or value changes in advance and then have it run the simulation. And unless I’m sorely mistaken, LTspice doesn’t do digital logic simulation at all.In school, we used LTspice with one instructor and TINA with another.

author: Victorman222
author_rank: Regular Contributor
timestamp: June 06, 2025, 08:08:19 pm
content: Isn't the minus sign just because of the "polarity" of the resistor? Try rotating it 180 degrees. Microcap has that for sure. CircuitJS is nice and simple, but for more complicated stuff it is very slow or doesn't work at all

author: floobydust
author_rank: Super Contributor
timestamp: June 06, 2025, 08:14:39 pm
content: I think part of the problem is the corporation that now owns it, doesn't want to any spend dollars to improve it. So bitching about the program - it's not the programmer's fault."Change the logos and splash screen and leave it, we have no budget for it otherwise." This is what I believe keeps it as academic software, something not for noobs.Of course there are many improvements that could happen. But who's paying for that?As someone who started out using Spice on a command line with text file input, I'm happy

author: Benta
author_rank: Super Contributor
timestamp: June 06, 2025, 08:20:16 pm
content: Quote from: BlackHecilopter on June 06, 2025, 07:42:50 pmPosting a partial screenshot with zero information is futile.

author: BadeBhaiya
author_rank: Regular Contributor
timestamp: June 06, 2025, 08:21:47 pm
content: Quote from: BlackHecilopter on June 06, 2025, 07:14:41 pmYou should have a look at the alternatives...

author: joeqsmith
author_rank: Super Contributor
timestamp: June 06, 2025, 08:24:32 pm
content: Quote from: BlackHecilopter on June 06, 2025, 07:47:23 pmEE 101?https://spinningnumbers.org/a/conventional-vs-electron-current.html

author: BlackHecilopter
author_rank: Contributor
timestamp: June 06, 2025, 08:28:40 pm
content: The resistors might be backwards in the circuit in LTSpice. Why the developer wouldn't add plus and minus to the resistor symbol is beyond me.Micro-cap at least shows positive and negative polarity.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 06, 2025, 08:29:09 pm
content: Google AIQuote

author: BlackHecilopter
author_rank: Contributor
timestamp: June 06, 2025, 08:37:44 pm
content: Quote from: joeqsmith on June 06, 2025, 08:29:09 pmLTSpice uses conventional current flow. Got it.The resistors are backwards. That one wasn't obvious.I really didn't know someone could put resistors in backwards. Anyone know how to tell if the resistors are in backwards or not? I don't see any markings.

author: tggzzz
author_rank: Super Contributor
timestamp: June 06, 2025, 08:39:16 pm
content: Quote from: BlackHecilopter on June 06, 2025, 07:14:41 pmI'm surprised you can get get it to do what you want; heckle-opters of any colour have great difficulty using keyboards effectively.Or have you been reading the thread, and wish to experiment?https://www.eevblog.com/forum/supporters-lounge/word-salad-users-(unintelligible-techo-jargon)-is-it-acceptable/

author: TimFox
author_rank: Super Contributor
timestamp: June 06, 2025, 08:41:38 pm
content: In general, Spice assigns node numbers (e.g., 1 and 2) to each component.In actual Spice, the syntax isRXXX N1 N2 VALUE, or an exampleR21 11 12 180for a simple resistor (reference R21) connected between nodes 11 and 12, with value 180 ohms.N1 and N2 define the polarity of current flow through the component.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 06, 2025, 08:44:13 pm
content: I guess I don't really see what your complaint is about regarding the direction of current flow.World's simplest circuit:Notice the polarity*; it's in the direction of "conventional" current flow (i.e., positive to negative), not the pointy-headed physicist's current flow. And the current shown on the plot is positive.(*I know you can't see it since my screen capture didn't include the LTspice ammeter cursor, but it was pointing downward in the "conventional" direction. And BTW, resistors have no polarity in LTspice, which is as it should be.)As others have pointed out, plenty of other minor complaints with LTspicee. (Mine is that even though the app prompts me that my installation is out of date and offers to let me download a new version, when I click "OK" it fails to do so because it can't parse some .gz file.) But those quibbles are outweighed by the program's usefulness (and the fact that it's free).

author: joeqsmith
author_rank: Super Contributor
timestamp: June 06, 2025, 08:48:16 pm
content: Quote from: BlackHecilopter on June 06, 2025, 08:37:44 pmpay attention to the direction of the arrow when you measure the current. Try flipping the resistor in the circuit and see how it effects the arrow.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 06, 2025, 08:49:26 pm
content: Quote from: TimFox on June 06, 2025, 08:41:38 pmAll I can say is thank [insert name of deity here] that we don't have to use LTspice in text mode like in the Olden Days.If we did I would never use it. I'd rather program a microprocessor through front-panel switches than subject myself to that nonsense.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 06, 2025, 08:50:25 pm
content: Quote from: joeqsmith on June 06, 2025, 08:48:16 pmResistors have no polarity in LTspice, just as they don't in Real Life.

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: June 06, 2025, 08:53:01 pm
content: Quote from: BlackHecilopter on June 06, 2025, 07:53:35 pmHyperbolenounexaggerated statements or claims not meant to be taken literally.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 06, 2025, 08:53:30 pm
content: Quote from: Analog Kid on June 06, 2025, 08:50:25 pmThe probe will track the resistor. Simple test to run if there is any question.

author: BlackHecilopter
author_rank: Contributor
timestamp: June 06, 2025, 08:54:01 pm
content: QuoteAre you 100% sure? See the image

author: Analog Kid
author_rank: Super Contributor
timestamp: June 06, 2025, 08:56:11 pm
content: Goddamnit, I was wrong: wrong, wrong, wrong.Resistorsdohave polarity in LTspice.WTF? ? ? ?Any way to fix that, by messing with the R model?Resistorsshould nothave polarity, right?

author: BlackHecilopter
author_rank: Contributor
timestamp: June 06, 2025, 08:57:51 pm
content: It appears they do in LTSpice. I'm shocked as well.Micro-Cap appear to have polarity as well. Micro-Cap actually shows you, see image.I honestly had no idea. Is there a way to change this or tell? This can be really confusing

author: IanB
author_rank: Super Contributor
timestamp: June 06, 2025, 09:01:12 pm
content: Quote from: BlackHecilopter on June 06, 2025, 07:47:23 pmOf course −3 mA is the correct current inside the voltage source. It is going from − to +. Positive currents go from + to −.You should probably think more and complain less.I'm not going to read the rest of the thread where others have probably said the same thing before me.

author: TimFox
author_rank: Super Contributor
timestamp: June 06, 2025, 09:03:52 pm
content: Quote from: Analog Kid on June 06, 2025, 08:49:26 pmAnd in my occasional prayers, I rejoice that even in this wicked millennium, I am still allowed to use Spice in text mode, which I find easier to write and debug.It ain't that hard!It is easy to check for the resistor polarity in text mode.I started with Spice in Hollerith days, but it is much easier with modern text editors.At work, I used PSpice, but I switched to AimSpice.You may do as you please.

author: DimitriP
author_rank: Super Contributor
timestamp: June 06, 2025, 09:08:48 pm
content: Quote from: BlackHecilopter on June 06, 2025, 07:14:41 pmIt's 2025. Get used to it, don't use it or get over it.Quietly.

author: BlackHecilopter
author_rank: Contributor
timestamp: June 06, 2025, 09:10:53 pm
content: Quote from: IanB on June 06, 2025, 09:01:12 pmNow do the resistor

author: Zero999
author_rank: Super Contributor
timestamp: June 06, 2025, 09:19:48 pm
content: Quote from: BlackHecilopter on June 06, 2025, 08:57:51 pmYou appear to be ignorant. This is not an insult, but based on your statements, which indicate a lack of knowledge.It's true, resistors don't have polarity. It doesn't matter whether the current is positive or negative, but the simulator needs to know which way to connect the probes, when measuring the current. Well it doesn't measure the current, but calculate it of course, but it still needs to know the sign, in order to calculate the correct current.Have you ever done nodal analysis before? If you haven't or have not done it for awhile, I suggest you look into it.Although I picked it up fairly quickly, I know many have trouble with LTSpice's user interface. You do know, it's possible to draw the circuit in another program, generate a net list and simulate it with LTSpcice, you know? You might think that's silly and wonder why anyone would do that? The answer is, lots of the good things in LTSpice are inside its SPICE engine, which is nothing to do with the user interface.I've dabbled with Micro-Cap before. I used it a bit at a former employer, but haven't used it for many years.Falstad is just an educational aid. It's not intended as serious simulator. I dislike the Falstad UI and find it harder to use than LTSpice, but that's just personal preference. The fact is, LTSpice's engine is superior to Falstad. Again, I'm not knocking Falstad. It's an excellent educational tool. Being able to visualise the currents and voltages is very helpful, especially for beginners.

author: IanB
author_rank: Super Contributor
timestamp: June 06, 2025, 09:27:04 pm
content: Quote from: BlackHecilopter on June 06, 2025, 09:10:53 pmI write simulation software for a living. It is inevitable that resistors will have polarity in a simulation tool. However, I will agree that the directionality should be indicated somehow on the symbol.

author: TimFox
author_rank: Super Contributor
timestamp: June 06, 2025, 09:31:10 pm
content: Or use a text mode version of Spice, where polarity is indicated by the syntax.

author: Zero999
author_rank: Super Contributor
timestamp: June 06, 2025, 09:38:52 pm
content: Quote from: IanB on June 06, 2025, 09:27:04 pmFor the benefit of the OP, not just resistors, but capacitors (including the small ones which aren't polarised in real life) as well as inductors are polarised in SPICE. They have to be, for the same reasons mentioned above.It's possible to modify the resistor symbol and add signs to indicate the direction of current flow.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 06, 2025, 09:58:36 pm
content: Quote from: IanB on June 06, 2025, 09:27:04 pmIs it, though?Look at wires, which are another component*in Spice: they have no polarity.Couldn't the resistor model be made so that the component has no polarity? Wouldn't that make more sense?*Well, I know that wires aren't components in the same sense as resistors, caps, etc.: they're just network connections. But still.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 06, 2025, 10:10:41 pm
content: Quote from: TimFox on June 06, 2025, 09:03:52 pm[Dana Carvey old man voice]Yes, back in the day we had to walk 10 miles each way to the lab through 3 feet of snow. Not only that, but on days when the card punch stopped working, we had to take out our pocket knives and punch the cards by hand. It took a half hour for each card., and the cards were a bloody mess.And we liked it!

author: Ian.M
author_rank: Super Contributor
timestamp: June 06, 2025, 10:20:53 pm
content: Resistors *need* to have polarity to be consistent with the underlying SPICE3 compatible engine. Consider a capacitor charging/discharging from an AC source through a resistor. The direction of the current is obviously significant. LTspice defaults to placing a resistor with vertical orientation, and positive current flow from top to bottom. (If so placed, the top end is the first node on the SPICE line.)The problem happens when you rotate a resistor to make it horizontal. The convention is for schematic signal flow to be (whenever possible) left to right, but LTspice only has a rotate clockwise menu command/keystroke/icon, so to end up with its first node on the left you have to rotate three times.

author: IanB
author_rank: Super Contributor
timestamp: June 06, 2025, 10:25:34 pm
content: Quote from: Analog Kid on June 06, 2025, 09:58:36 pmTechnically, wires/connections are nodes in the nodal analysis. Conceptually they are a "point" in the system where all currents in and out add up to zero. The current leaving an upstream component could have a negative sign, and the current entering a downstream component would have the same magnitude but a positive sign. So now the current could either be positive or negative according to your measurement perspective (i.e. which way round you want to look at it).The same is true in real life. You can change a positive sign to a negative sign on your DMM just by switching the probes around. Which one are you going to choose? It's really up to you, since the circuit itself does not change. It's only the measurement perspective that changes.

author: TimFox
author_rank: Super Contributor
timestamp: June 06, 2025, 10:31:01 pm
content: Quote from: Ian.M on June 06, 2025, 10:20:53 pmAgain, despite the whining of some who don't like old things, this polarity orientation of two-lead components (resistors, capacitors, inductors, etc.) is straightforward in text Spice files, but potentially confusing in the graphic interface that generates the lines in the underlying Spice file that is computed by the program.

author: PascalNE
author_rank: Regular Contributor
timestamp: June 06, 2025, 10:31:18 pm
content: When I was making a node based (similar to spice) circuit simulator last year for my A level coursework I could never get my algorithm to work without resistor "polarity". It's nice to see it's an issue even in one of the most advanced circuit sims.Mine also ended up being much better in command line mode GUIs are hard

author: Analog Kid
author_rank: Super Contributor
timestamp: June 06, 2025, 10:43:23 pm
content: Quote from: Ian.M on June 06, 2025, 10:20:53 pmYes, of course the direction of current is significant.But I still don't see why that requires resistors to have polarity. The direction of current is inherent in the configuration of the circuit, the connections between a voltage source and ground. But if the current is flowing through a resistor, why doesn't Spice just let it flow depending on the source and ignore any polarity for the component itself? Same as the conductors connecting the components; Spice ignores all physical orientations there and treats the conductors as polarity-agnostic.I can well understand why all capacitors are polarized.Now, since I'm totally ignorant about how Spice operates internally, there may be a good reason it needs to treat Rs as polarized, but i just don't see it. Maybe someone can explain this.

author: Circlotron
author_rank: Super Contributor
timestamp: June 06, 2025, 10:45:34 pm
content: QUCS makes LTSpice look better.

author: tggzzz
author_rank: Super Contributor
timestamp: June 06, 2025, 11:15:23 pm
content: Quote from: Ian.M on June 06, 2025, 10:20:53 pmI don't know why the OP didn't show a more explicit example: one voltage source, two resistors in parallel with one resistor rotated 180degrees. Yes, the current in one will show +ve and the other -ve, but both will be consistent with the mouse tooltip shown when selecting the current.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 06, 2025, 11:31:52 pm
content: Quote from: BlackHecilopter on June 06, 2025, 07:47:23 pmThe minus is nothing to do with Electron Flow, it is a "bug" in LT Spice.Using EF, the figure for "I" would simply be "3ma", with no sign attached.People brought up on "Conventional" Current Flow tie themselves in knots, adding negative signs to things which are unnecessary.

author: IanB
author_rank: Super Contributor
timestamp: June 06, 2025, 11:44:14 pm
content: Quote from: vk6zgo on June 06, 2025, 11:31:52 pmAs I mentioned above, it is not so much a bug, as a consequence of current flow conventions. Conventional current is assumed positive when it is flowing from + towards −.Inside a battery (for example), the current inside the battery is flowing from the − terminal to the + terminal, so it is negative. This is reflected in the voltage drop due to internal resistance: since the sign of the current is negative, the terminal voltage decreases as the current increases in magnitude.

author: fourfathom
author_rank: Super Contributor
timestamp: June 07, 2025, 12:04:30 am
content: Quote from: Analog Kid on June 06, 2025, 08:50:25 pm[ I hadn't read through the entire thread before posting this...]I hadn't realized this, but yes, the displayed current polarity through a resistor depends on the resistor orientation. Obviously the simulations work, and I've just compensated for polarity if I need to plot (say) power, using V*I. Here's a circuit with two resistors in parallel, one "right side up" and the other rotated 180 degrees. And yes, the displayed current-arrows do match the plotted current polarity.I would say that criticism is warranted here, but it's certainly not going to stop me from using LTSpice.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 07, 2025, 12:06:42 am
content: Quote from: BadeBhaiya on June 06, 2025, 08:21:47 pmMy alternative would be a piece of notepaper & a pen.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2025, 12:10:04 am
content: Quote from: IanB on June 06, 2025, 11:44:14 pmI think they just want to know why in 2025 that the tools are not smart enough to handle these cases for you. Again, when probing current, the probes polarity (indicated by the direction of the arrow) does track the polarity of the resistor, but you have to pay attention.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2025, 12:13:30 am
content: Quote from: vk6zgo on June 07, 2025, 12:06:42 amThat's way too much work, unless you are doing something really simple like making a 50 ohm terminator for a scope...

author: BlackHecilopter
author_rank: Contributor
timestamp: June 07, 2025, 12:43:31 am
content: How does Falstad handle not having polarity for resistors?

author: IanB
author_rank: Super Contributor
timestamp: June 07, 2025, 12:58:59 am
content: Quote from: BlackHecilopter on June 07, 2025, 12:43:31 amHard to know. Make an H-bridge out of resistors, and inspect the resistor forming the horizontal. Now, by varying one of the vertical resistors, you can make the current flow either way through the bridge resistor (left-to-right, or right-to-left). How will Falsted show you the direction of current in that bridge resistor? If it flows one way it should be positive, and if it flows the other way it should be negative, right?

author: ledtester
author_rank: Super Contributor
timestamp: June 07, 2025, 01:07:50 am
content: Quote from: BlackHecilopter on June 07, 2025, 12:43:31 amIt does have a polarity for resistors.Here is a circuit with two resistors:(Falstad Two Resistor Circuit)If you open a scope on the 500R resistor you'll see that the voltage and current are both negative.You can achieve this by simply using the "Swap Terminals" option in the right-click menu for the resistor.

author: themadhippy
author_rank: Super Contributor
timestamp: June 07, 2025, 01:11:59 am
content: QuoteThe yellow dots change direction

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 01:15:59 am
content: Quote from: joeqsmith on June 07, 2025, 12:10:04 amQuote from: fourfathom on June 07, 2025, 12:04:30 amSo apparently we're not the only ones who are just a bit flabbergasted that this tool is still this primitive at this late stage of the game. (Except for a few old fogies who insist "a slide rule and paper were good enough for grandpappy and they're good enough for me".)Nobody has answered my question yet: are polarized resistors a necessity in (LT)Spice because of how the internal "engine" is constructed? Or is it just a matter of engineers who use it not being bothered by this "feature" and just learning to live with it without complaining?

author: ledtester
author_rank: Super Contributor
timestamp: June 07, 2025, 01:28:20 am
content: Quote from: Analog Kid on June 07, 2025, 01:15:59 amYes - when performing nodal analysis you need to assign a direction (also called an orientation) for all of the current variables.That is, if you have two nodes, say A and B, and define I to be the current between them, you also have to indicate if positive current means flow from A to B or from B to A. That's why in nodal analysis you draw an arrow for current variables. The arrow indicates the direction of positive current flow.Either choice is valid and will result in the same solution - up to a minus sign, of course.You can create a resistor symbol which also indicates which end is the "positive" end and which is the "negative" end and then you can decide the orientation of the current quantities for yourself - but most of the time it isn't necessary.

author: BlackHecilopter
author_rank: Contributor
timestamp: June 07, 2025, 01:31:32 am
content: Does PSpice produce the same result as LTSpice?

author: BlackHecilopter
author_rank: Contributor
timestamp: June 07, 2025, 01:45:29 am
content: Quote from: ledtester on June 07, 2025, 01:07:50 amI see that.Strange that the small pane in the lower right corner still shows the correct current when the resistor is clicked/selected.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2025, 01:53:53 am
content: Quote from: Analog Kid on June 07, 2025, 01:15:59 amI doubt you will find too many details about the inner workings of LTSPICE or the whys of the designers decisions.Going back to my Berkeley SPICE (which evolved from CANCER), they also appeared to have a polarity in their resistor model. This was from 1975. The source code should still be available along with complete documentation describing the history, math, development. I suspect most modern SPICE applications evolved from that effort.https://ptolemy.berkeley.edu/projects/embedded/pubs/downloads/spice/Even the original DOS based PSPICE's resistor model also had a polarity.QuoteSee page 214https://www.seas.upenn.edu/~jan/spice/PSpice_ReferenceguideOrCAD.pdf

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2025, 01:55:03 am
content: Quote from: BlackHecilopter on June 07, 2025, 01:45:29 amFlip the 500 ohm resistor on the X axis (mouse right click, select flip).

author: ledtester
author_rank: Super Contributor
timestamp: June 07, 2025, 01:58:17 am
content: Quote from: BlackHecilopter on June 07, 2025, 01:45:29 amFrom my testing the current value shown there is always positive -- consider the circuit with the voltage source is a square wave alternating between +5 and -5:(Square Wave Circuit)

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2025, 02:05:50 am
content: Quote from: ledtester on June 07, 2025, 01:58:17 amOdd that your's will not flip polarity when you flip the resistor.

author: BlackHecilopter
author_rank: Contributor
timestamp: June 07, 2025, 02:07:50 am
content: Quote from: ledtester on June 07, 2025, 01:28:20 amWouldn't it make sense for the spice tool to show the orientation as well?

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 02:29:38 am
content: Quote from: BlackHecilopter on June 07, 2025, 02:07:50 amNo, because now you'd have something that doesn't exist in the real world, a polarized resistor.If I had a vote on the matter (which I don't), I'd urge the developers to just get rid of that polarity once and for all, so it made no difference how a resistor is oriented.

author: BlackHecilopter
author_rank: Contributor
timestamp: June 07, 2025, 02:32:07 am
content: Quote from: Analog Kid on June 07, 2025, 02:29:38 amI completely agree with that.

author: IanB
author_rank: Super Contributor
timestamp: June 07, 2025, 02:50:24 am
content: Quote from: Analog Kid on June 07, 2025, 01:15:59 amIt is a necessity because real, physical resistors are directional in the same way.As an experiment, construct a Wheatstone bridge and place a resistor in the bridge. When the bridge is unbalanced current will flow through the resistor and it will have a voltage across it. Measure that voltage with your DMM. Is it positive or negative? Now swap the probes around and measure again. You can see, by deciding which way round is positive, you have decided the polarity of that resistor. One end is "+" and the other end is "−". If you like, you can now put sticky labels on each end of the resistor according to your measurement. Henceforth, you can now always place the red lead of your DMM on the end labeled "+" and the black lead on the end labeled "−". This will give you the sign of the voltage across (and the direction of current through) that resistor. If you unplug the resistor from the circuit and reverse it, you will find the sign of the voltage you measure will have changed polarity.If you consider this to be strange, imagine you only have access to the resistor on the outside of a black box, and any other circuitry is hidden inside the box. You are asked to determine the voltage across the resistor, and whether it is positive or negative (i.e. which way is the current flowing?). You will find it is impossible to do this unless you label the resistor somehow. (The positive current is flowing from "this end" to "that end".)The situation is exactly the same with circuit simulators. All two terminal components like resistors, capacitors and inductorsmustbe labeled with a "+" end, and a "−" end, in order for reported currents and voltage differences to make sense.

author: ledtester
author_rank: Super Contributor
timestamp: June 07, 2025, 02:50:58 am
content: Quote from: BlackHecilopter on June 07, 2025, 02:07:50 amIIRC some circuit analysis programs do have a polarized resistor (and capacitor and inductor) symbol.However, note that the choice of current orientation is usually not of any significance.- it does not affect voltages- it does not affect power calculations- everyone will agree on the absolute value of the currentIf you want to know the current through a resistor in your preferred frame of reference, you can always plot (V(A)-V(B))/R where by positive current you mean current flowing from node A to node B.Or, just flip the resistor symbol around.Or, just plot -I(R) instead of I(R).

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 02:57:24 am
content: Quote from: BlackHecilopter on June 07, 2025, 02:32:07 amNonsense. The resistors in Spice are not polarized, although of course diodes are.The sign convention for current direction is tied to the order of the node numbers, but the resistor itself is just like real resistors, where the voltage across it is proportional to the current through it, with the appropriate direction.If the polarity of current is important to your simulation, you must define which direction through the resistor is positive.In Spice, there are nodes and components. Nodes have voltages, which by default are with respect to the reserved node 0 (ground), but voltages can be defined between two nodes.Cirremts flow through components, such as resistors and inductors.There are no wires: if your calculation requires the current through an actual wire in your design, you can insert either a small-valued resistor or a voltage generator set to zero, and measure the current through it.This is why I personally prefer text for the Spice files over graphical representations: these features are obvious in text but confusable in the graphics.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 03:01:17 am
content: Quote from: IanB on June 07, 2025, 02:50:24 amYabbut, that has nothing to do with thecomponentbeing polarized: it's a result of how the probes are attached to the component to measure V or I. Right?Tell me this: does it make any difference which end of a wire connecting two components is connected between them? (Assuming you could flip a wire end for end the way you can a resistor.) No, of course not.Your explanation is unsatisfactory to me.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 03:02:24 am
content: Quote from: TimFox on June 07, 2025, 02:57:24 amOK, Grandpa.

author: IanB
author_rank: Super Contributor
timestamp: June 07, 2025, 03:05:42 am
content: Quote from: Analog Kid on June 07, 2025, 03:01:17 amThen read it again. You have a wire, with current flowing through it. Someone asks you which way the current is flowing in that wire? How are you going to answer that question unless you put some kind of label on that wire with an arrow, or label each end of it with something like "A" and "B", or "1" and "2"?

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 03:10:25 am
content: Quote from: Analog Kid on June 07, 2025, 03:02:24 amJust because something is newer doesn't mean it works better.Otherwise, posters here would not be confused about the direction of current through a resistor.As things evolve, oftentimes convenience wins against accuracy, which does not make it better; perhaps it makes it terrible.As mentioned above, voltmeters and ammeters are "polarized", in the sense that they have red and black test leads.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 03:12:21 am
content: Quote from: IanB on June 07, 2025, 03:05:42 amThe program should be smart enough to figure out that if I flip that wire (or that resistor) end for end, the current still flows the same direction through it, say from top to bottom, even though the wire/resistor has been flipped. Can you not see that?The "problem" of numbering and ordering nodes internally is not something that I, as a LTspice user, should ever be exposed to. (Unless one wants to go back to the old text-based, non-GUI way of doing things.)

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 03:16:21 am
content: Quote from: Analog Kid on June 07, 2025, 03:12:21 amAgain, nonsense.Of course the current flows in the same physical direction, but you won't know which direction unless you define "red" and "black" somehow.For DC circuits, that direction is important.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 03:51:30 am
content: OK, lety me try to make this really, really clear:Say a guy has made the World's Simplest Circuit in LTspice:Notice the node numbers on the resistor, which do not appear on the schematic display.Current (conventional) obviously flows from top to bottom as shown.But then our guy flips the resistor end-for-end for some reason:currentstillflows from top to bottom, even though the nodes are now reversed.I'm saying that the program should be smart enough (remember, the reason we use computahs is that they do things that are supposed to be smart) to figure out that yeah, they guy flipped it but so what? current still flows north to south, so I'm not going to change that when he puts his mouse pointer there and clicks; it'll still show downward-flowing current, and I'll just make whatever adjustments to my internal data structures are needed to compensate.Don't tell me this isn't possible, in this year of our lord 2025.

author: IanB
author_rank: Super Contributor
timestamp: June 07, 2025, 04:10:03 am
content: Well, look at the diagram below. From left to right, it is the same electrical component, with the same current flow, but rotated progressively on the schematic diagram. The current is flowing from top to bottom on the left, but what on the right? Since it is the same circuit, with the same component, wired the same way, then surely the current must be flowing from bottom to top by the time we get to the right? So what is the program going to do here?

author: MathWizard
author_rank: Super Contributor
timestamp: June 07, 2025, 04:10:24 am
content: Voltage sources provide power, if they uses the same current direction convention as resistors, it would imply the Vsource is also consuming power, like the resistors.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 04:12:29 am
content: Quote from: IanB on June 07, 2025, 04:10:03 amIt doesn't make any damn difference how the component (resistor) is oriented;all that matters is how it's connected to the rest of the circuit.Sheesh. It ain't rocket surgery.

author: IanB
author_rank: Super Contributor
timestamp: June 07, 2025, 04:16:42 am
content: Quote from: Analog Kid on June 07, 2025, 03:51:30 amQuote from: Analog Kid on June 07, 2025, 04:12:29 amDo you see any contradiction in your posts? First you say orientation matters, and then you say orientation doesn't matter.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 04:25:27 am
content: Quote from: IanB on June 07, 2025, 04:16:42 amI'm saying that the final result should be that orientation doesn't matter, even if the program has to do some internal adjustments for orientation if the user flips a resistor; the direction of current flow (top to bottom, regardless of node numbering) shouldn't change, and neither should the indicated direction of current flow should the user mouse over and get the "ammeter" cursor; it should indicate the same direction.As far as I can see this behavior is a bug. Of course orientation does matter for components like diodes, but current should still be indicated as flowing through them in the same direction even if they are flipped.

author: tggzzz
author_rank: Super Contributor
timestamp: June 07, 2025, 07:13:34 am
content: Forget circuit simulators for a moment.Go back to your school or university days when you were being taught KCL and KVL and nodal analysis. (You did do that, didn't you).Do it again, step by step, for a simple circuit, where you write down the V and I equation for each component separately plus the equations representing how they are connected together. Solve those simultaneous equations to get the voltage and current for the component of resistance.Now, for that component change the sign of V and I, and resolve.Ditto change the equations representing how it is connected in the circuit.What difference doand don'tyou see?That should convince you the issue is more fundamental than any circuit simulator!

author: iMo
author_rank: Super Contributor
timestamp: June 07, 2025, 07:47:14 am
content: In order to better spend your valuable time - here is the page where you may certainly post your claims:https://ez.analog.com/design-tools-and-calculators/ltspice/There are the current developers of the LTspice sitting and answering..

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 08:05:20 am
content: Quote from: tggzzz on June 07, 2025, 07:13:34 amNope, sure didn't.I tried one semester at the College of Engineering, discovered that math (polar notation, etc.) made my head hurt and went back to the College of Business. Learned later about Kirchoff, etc., but never studied it formally.Nodal analysis? Nope as well.QuoteY'know, that's all very nice, but I'm now convinced more than ever that my complaint about LTspice is completely valid, and moreover that it could be cured by just a bit of code.My feeling is, though, that it won't be and we'll just have to continue putting up with this inconvenience.I will say that I don't agree at all with the subject title of this thread; I don't think LTspice is terrible at all. Just has a few warts.

author: tggzzz
author_rank: Super Contributor
timestamp: June 07, 2025, 08:45:06 am
content: Quote from: Analog Kid on June 07, 2025, 08:05:20 amNo. Full Stop. (Or "Period" for leftpondians).All engineering simulators, including circuit/EM/FEM/climate/communications/etc, arebased on solving mathematical equations.If you don't understand maths, youcannotunderstand what is "under the surface" and in particular you cannot understand the code doing the grunt work. Hence any suggestion that it is "just a bit of code" is ignorant nonsense.It is as useful as if I told someone creating drugs that they "just need to change the peptide sequence", or if I told an aeronautical engineer that "it just needs a bit of string and bent metal added".Sorry to be so blunt, but that reality has to be faced. N.B. there's nothing inherently wrong with not understanding maths any more than there is anything wrong with having a reading age of 13. But that isprovidedthe limitations of the impediment are understood sufficiently that people are sufficiently humble that they avoid Dunning Kruger territory.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 07, 2025, 11:19:36 am
content: Hi,Here are a few test circuits that illustrates the behavior of resistors in LTspice:In all cases the resistor are in series, so the current is identical.The program reports, correctly in my opinion, that the current in some of the resistors is negative.This is because SPICE, and I believe all versions of SPICE, assign positive and negative terminals to all components.This includes capacitors and inductors.The model was created by rotating some of the resistors to change the direction of the current flow.Placing the mouse over a component, will be display the current probe. The arrow shows the direction of current measurement.Examples:andandRegards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 07, 2025, 11:42:39 am
content: Quote from: floobydust on June 06, 2025, 08:14:39 pmI disagree with this idea. LTspice24 was a complete re-write of the LTspice application. There is tremendous efforts to add legacy Maxim and legacy ADI models to the LTspice libraries. This has been confirmed by some friends within ADI.LTspice and other implementations of SPICE, are powerful tools. To master these tools takes a little time. There are lots of video on YouTube and many examples on this forum.Regards,Jay_Diddy_B

author: tggzzz
author_rank: Super Contributor
timestamp: June 07, 2025, 11:51:57 am
content: Quote from: Jay_Diddy_B on June 07, 2025, 11:42:39 amYes. Too many people don't put in the time and thought to gain understanding.Some people will never be able to understand, just as some people never understand arithmetic. Being innumerate is like being illiterate; neither should be trumpeted nor be a source of inferiority - both are sad.

author: G0HZU
author_rank: Super Contributor
timestamp: June 07, 2025, 12:06:52 pm
content: If you have had enough of LTSpice, the free version of Simetrix is generally nicer to use than LTSpice and the circuit size limits are quite generous. Simetrix has its own niggles and limitations but it is much quicker and easier to draw circuits, the libraries are easier to access and the graphs are much nicer. It's generally much more intuitive to use although it is quite dated now as the Simetrix GUI hasn't really changed much in over 25 years.Having been a career long user of various simulation tools at work, I find LTSpice to have the worst user interface by some margin. The graphs are poor, the GUI and libraries are generally a mess and the circuit editing is quite awful. However, behind all this mess is a very powerful and versatile tool.It is free and you can't expect too much because of this.

author: Circlotron
author_rank: Super Contributor
timestamp: June 07, 2025, 12:08:09 pm
content: +1 for Simetrix.

author: tggzzz
author_rank: Super Contributor
timestamp: June 07, 2025, 12:22:20 pm
content: Quote from: G0HZU on June 07, 2025, 12:06:52 pmWhat is the quality and extent of the model libraries? That's, arguably, the single most important attribute of any simulator.After all, if the models are inadequate and give poor results, nobody cares if the GUI is pretty!

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 07, 2025, 12:29:31 pm
content: Seems the terms "polarity" and "polarized" are causing confusion.Resistors in SPICE are not "polarized" in the sense that they are asymmetric or nonlinear. But SPICE requires that the terminals of the resistor (and all other components) be uniquely defined, so a resistor must have a terminal 1 and a terminal 2.Voltage across the resistor is defined as V(1) - V(2). Current through the resistor is defined as current into terminal 1 and out of terminal 2. This is per conventions older than computers.Think of it like using a DMM to measure voltage or current. The DMM is linear and has perfect symmetry in its behavior. But to be useful, it has to have its "polarity" defined (i.e. a positive/red probe and a negative/black probe). Otherwise you have no way to tell what the sign of the actual current or voltage is from your measurement.

author: G0HZU
author_rank: Super Contributor
timestamp: June 07, 2025, 12:41:12 pm
content: It's easy to add models to the Simetrix library. Just drag a manufacturer's model file into the Simetrix window and it automatically adds it to the library. LTSpice obviously supports lots of components and ICs but for general use, it's easy to add model libraries to Simetrix. It's also very easy to modify or tweak the model within a simulation. So things like internal capacitance of a BJT or its other parameters can be adjusted with just a couple of mouse clicks.I've used LTSpice quite a few times, but only when there's no alternative, i.e. if it involves a specific IC from AD/LT or if someone sends me an LTSpice project file.It's generally best to use the manufacturer's models rather than anything bundled with the app unless there's no alternative or if the simulation is just a casual thing.

author: rsjsouza
author_rank: Super Contributor
timestamp: June 07, 2025, 12:59:01 pm
content: Quote from: tggzzz on June 07, 2025, 08:45:06 amI was suspecting the critics might be in this category. This thread reeks of too much willy-nilly clicking and too little basic circuit knowledge, with a tad of arrogance. The tool is computationally powerful and uses an WYSIWYG interface to help with the drawing of a circuit, but it will not teach you circuit analysis. It will output simulated behaviour based on what you tell it to do (garbage in, garbage out).The core confusion in this thread is one abstraction that is added when compared to the "real world": the ability to measure currentinsideparts. In the real world you don't know the current of a resistor "R1", but instead use an external ammeter in series and measure it - if the current is negative as to what is expected, you simply reverse the ammeter and try again. Therefore, the "polarity" of parts does not exist.For someone experienced in circuit analysis (the target audience of such tool), the signal of a measurement is entirely dependent onhowthe measurement is being done - i.e, where is the reference. This experience also brings a sane skepticism about any results put out by such simulations and their limitations when compared to the real world - models and calculations are simpler than the actual physics of elements.In summary, power is nothing without control and a basic core knowledge.

author: tggzzz
author_rank: Super Contributor
timestamp: June 07, 2025, 01:25:10 pm
content: Quote from: G0HZU on June 07, 2025, 12:41:12 pmYes, but the key question is not which button to press (it takes me <10 minutes to learn that), but which manufacturers provide libraries that will work with Simetrix. It sounds as if LTSpice libraries don't, which is a significant limit since there is a wide range and their quality is (by and large) decent.Background: >40 years ago a simulator manufacturer approached my company to produce libraries for standard logic components. I, of course, asked what aspects they wanted to simulate and what tests would be sufficient. The answer was no tests were necessary.Upon questioning, it became apparent they were salesmen who merely wanted to be able to tick a box (in an RFI) currently preventing them from making a sale. I recommended "no bid", and that was acceptedMany analogue libraries are like that too

author: tggzzz
author_rank: Super Contributor
timestamp: June 07, 2025, 01:32:47 pm
content: Quote from: rsjsouza on June 07, 2025, 12:59:01 pmJust so.A simple indication of that is some people thinking there are "wires" in a Spice circuit. There aren't, of course: there are nodes connecting model components.If you want a wire, you have to create your own model of your wire. Sometimes that is critical to whether or not the Spice circuit usefully represents reality, as illustrated in this "two component audio buffer/amplifier":https://entertaininghacks.wordpress.com/2024/03/16/practical-traps-with-a-one-transistor-audio-amplifier-solderless-breadboards-and-oscilloscopes/

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 02:30:21 pm
content: To end my replies to this thread:LTSpice and similar packages are a graphical interface that converts a schematic diagram to a Spice file, runs the Spice calculation, and has a further interface to facilitate “measurement” of voltages, currents, waveforms, etc.Since LTSpice and similar packages are provided by IC manufacturers, they include a useful library of Spice models for their parts.Apparently, misunderstandings about the interface gave rise to some misconceptions:There are no “wires” in Spice corresponding to the lines in the schematic, in the sense of a component through which you can “measure” current, only nodes where you can “measure” voltage. Current can be measured through components such as resistors or voltage generators.Components in Spice have syntax for their connections that determine the “polarity” of current through them in the calculations. It looks like the interface in LTSpice can be confusing for that question.I used to do this stuff for a living. I rarely needed Spice for DC calculations, but often used .AC analysis for magnitude and phase for active and passive circuits, for frequency response and feedback stability calculations.Getting the current and voltage “polarities” correct was essential to get the phase right.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2025, 05:03:47 pm
content: Quote from: Analog Kid on June 07, 2025, 03:51:30 amYou would think they would have have such basics sorted after 50 years. I have a version of SPICE that is close to 30 years old. It require you to place a special current probe device from the library into your schematic to measure current. Or you can type in the equation. But that fancy LTSPICE current probe does not exist. The current probe, like the resistor has a polarity. And like the resistor, will show you the direction based on orientation.

author: G0HZU
author_rank: Super Contributor
timestamp: June 07, 2025, 05:08:19 pm
content: Quotehttps://www.simplistechnologies.com/webinar/2023/04/27/using-ltspice-schematics-and-models-simetrix#:~:text=Since%20version%209.1%2C%20SIMetrix%20can,special%20LTspice%C2%AE%2Dinvented%20devices.Simetrix is a decent alternative to LTSpice if the user can't tolerate the LTSpice GUI. The free version has generous circuit size limits and nearly all the features of the full version.I've been using Simetrix since version 2 (late 1990s?) and it is now up to version 9.The standard opamp library in Simetrix contains about 1000 device models including AD and LT parts. However, I'd still recommend the use of the latest models from any manufacturer for any critical work.

author: Zero999
author_rank: Super Contributor
timestamp: June 07, 2025, 05:19:26 pm
content: There's lots of discussion surrounding resistors, but what about the direction of the current through the voltage source?SPICE uses conventional flow, so current flows out of the positive terminal of a device must be negative.Another reason, is it gives correct results for power calculations.If the voltage or current source is providing power, then the sign must be negative. When calculating enthalpy change of a system, the sign is negative if energy is being lost from the system to another place and positive, if the system is gaining energy. Exothermic reactions have a negative sign and endothermic reactions have a positive sign.If a battery is being discharged, then the sign for power should be negative, because it is losing energy.If a battery is being charged, then the sign for power should be positive, because it is gaining energy.Here's a simulation showing two batteries connected together via a resistor. Note the signs. The battery being discharged has a negative current and the battery being charged a positive current.Battery charging sim.asc(0.69 kB - downloaded 30 times.)Another thing to note is in SPICE, a voltage source of 0V is often used an ammeter, so current flowing into the positive terminal must give a result with a positive sign.

author: fourfathom
author_rank: Super Contributor
timestamp: June 07, 2025, 05:34:19 pm
content: My beef with LTSpice (other than the UI pan/zoom/component-placement, and disappearing mouse pointer) is just the resistor polarity issue. Trust me, I understand about conventional current flow, etc, and in simulation the need for a circuit element to have identified nodes. That's just fine.But when I am working with the LTSpice schematic and simulator I wish that the indicated current polarity wasn't dependent on the resistor orientation. The resistor node names are not displayed on the schematic, and even if they were, when I want to see the current through a resistor I don't want the polarity to depend on the resistor orientation. Instead I want it to show current flow as if I put an ammeter in series with the resistor. I don't need to see what's going on "under the hood" with the simulator.

author: Zero999
author_rank: Super Contributor
timestamp: June 07, 2025, 05:45:23 pm
content: Quote from: fourfathom on June 07, 2025, 05:34:19 pmThat's easy to fix.Save the attached file to:\LTspice\lib\sym\res.asyres.asy.txt(0.42 kB - downloaded 40 times.)Disclaimer: backup the existing res.asy file first.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 06:54:44 pm
content: Quote from: fourfathom on June 07, 2025, 05:34:19 pmThank you for kinda/sorta agreeing with me on the whole "resistor polarity" issue.Yeah, yeah, I do understand the whole thing of current flows through a circuit and how their polarities are important for a proper analysis of that circuit, despite whatever innumeracy I may suffer from.But that stuff ought to be handled within the software so that what we're presented with, graphically, is minimally confusing, here in the year of our lord 2025.Otherwise it's back to the slide rules and pencil and paper.Speaking of which, a question for @TimFox: when you use SPICE in text mode, do you first at least draw out the circuit on paper so you can label the nodes? or is it all in your head? (If the latter, then you ought to be hailed as some kind of genius in my book.)

author: showman
author_rank: Contributor
timestamp: June 07, 2025, 07:23:30 pm
content: Quote from: TimFox on June 07, 2025, 03:16:21 amIs this not the key question here. Before solution, unless it is a trivial problem, neither you nor LTSpice knows how to define red and black. But after the solution, what it could do is to postprocess the results such that the current is positive and flows from higher to lower potential. Similarly how you'd do KVL+KCL analysis on paper where you first assign arbitrary current directions and then when you get negative, you'll say that it actually flows in the opposite direction compared to your initial guess. LTSpice could in principle do that too as it knows the voltage at each node.Whether it really matters though is another question and I'd say the answer is no. I'll borrow the Wheatstone bridge example. Say LTSpice says you have 1 mA through the resistor inside the bridge. That alone still does not say whether it goes "left to right" or "right to left" so you need some indicator for that, which LTSpice gives you when you hover the resistor or look at the voltages yourself. And in that case does it really matter if it is 1 mA from left to right or -1 mA from right to left? I wonder what kind of problems people who complain about this are actually solving?

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 07:24:23 pm
content: Quote from: Zero999 on June 07, 2025, 05:45:23 pmNice.How 'bout if one makes a new component, call it, say,R_Polarized, so one has both the standard R and this new one?I don't know how to do that.

author: fourfathom
author_rank: Super Contributor
timestamp: June 07, 2025, 07:58:37 pm
content: Quote from: Zero999 on June 07, 2025, 05:45:23 pmThat's (it looks like) a fix to not showing the resistor polarity/node names. Which could be useful. But I shouldn't need to care about that -- in my schematics a resistor is a resistor, and positive (conventional) current flows from the more positive end to the less-positive end.In truth, while this is an interesting discussion, and explains things that I had wondered about (a little bit), I'm happy enough with LTSpice as it is. I know which direction the currents flow in my simulations, and if needed I can compensate for the displayed values.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 08:03:53 pm
content: Quote from: fourfathom on June 07, 2025, 07:58:37 pmYes.I invite anybody to try to refute this eminently sensible point.

author: tooki
author_rank: Super Contributor
timestamp: June 07, 2025, 08:19:59 pm
content: It is sensible. But that doesn’t mean it’s practical or possible.Consider a motor as a load in a full H-bridge motor driver. The motor has a + and - wire. But which one goes on the left and right connections of the bridge? Electrically, the left and right halves of the bridge areabsolutely identical. When the bridge is energized one way, current flows from left to right. The other way, from right to left. But there is no inherent polarity to either direction. Yet in a simulation, you absolutely would expect the current to be displayed as negative in one of the directions, since it can’t be correct for it to be positive inbothdirections!

author: showman
author_rank: Contributor
timestamp: June 07, 2025, 08:36:16 pm
content: Quote from: tooki on June 07, 2025, 08:19:59 pmOf course it can be positive in both directions. For you to interpret the results correctly, the simulator just needs to give the direction together with the absolute value of the current. For example Falstad does it visually by moving the "current dots" in different directions and at the same time displaying the absolute value of the current (I'm not talking about the scope, but when you hover a component). From the simulator perspective it is of course easier when it fixes the direction arbitrarily, but this is in principle not required even internally, let alone how it presents the results.

author: IanB
author_rank: Super Contributor
timestamp: June 07, 2025, 08:39:29 pm
content: Quote from: showman on June 07, 2025, 07:23:30 pmThis is missing a rather important aspect. Although LTSpice can be used to analyze DC resistor networks, that is not its main purpose. That's much too trivial. LTSpice is used to analyze complex circuits in the time domain and the frequency domain where AC components dominate. If it is a clocked circuit or a harmonic filter there may not even be a DC operating point.

author: fourfathom
author_rank: Super Contributor
timestamp: June 07, 2025, 08:40:21 pm
content: Quote from: tooki on June 07, 2025, 08:19:59 pmI will grant you this point -- it's a good one.

author: showman
author_rank: Contributor
timestamp: June 07, 2025, 08:42:08 pm
content: Quote from: IanB on June 07, 2025, 08:39:29 pmI totally agree. That's why I asked what kind of problems people are actually solving with LTSpice that whether the current in a resistor is positive or negative matters so much.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 08:43:24 pm
content: Quote from: tooki on June 07, 2025, 08:19:59 pmPractical? That's up to the owner of the software (Analog Devices).Possible? C'mon, it's a piece of software, which can always be made a bit smarter. (If "practical", of course.)

author: fourfathom
author_rank: Super Contributor
timestamp: June 07, 2025, 08:49:23 pm
content: Quote from: IanB on June 07, 2025, 08:39:29 pmYes, of course. But so what? I do time-domain design, and lots of L/R/C filter design using LTSpice (frequency domain unless I want to look at voltages / current waveforms). But there is always a DC operating point, since you have to have a ground reference somewhere in the circuit.

author: fourfathom
author_rank: Super Contributor
timestamp: June 07, 2025, 08:51:31 pm
content: Quote from: showman on June 07, 2025, 08:42:08 pmFWIW, I never said it mattered much. It's just annoying.

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 08:53:18 pm
content: Quote from: Analog Kid on June 07, 2025, 06:54:44 pmFor non-trivial circuits, especially with active devices, I draw out the circuit, fill in the reference designators, put in the values, and number the nodes before using a simple text editor (actually, the one built into AimSpice) to generate the file in Spice format. Like other proprietary versions of Spice, AimSpice has a post-processor that can generate sensible graphs with respect to time or frequency (as required), but I usually use it to generate a .csv file and then graph it in Grapher (Golden Software).Question for you: when doing a linear .AC analysis (frequency response), how do you check that your phase angles are correctly defined (equivalent to the infamous polarity questions)?

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 08:55:07 pm
content: Quote from: Analog Kid on June 07, 2025, 08:03:53 pmHow do you know before doing the simulation which end is more or less positive?If you know that in advance, you probably didn't need Spice to work out the DC voltages in the circuit.

author: showman
author_rank: Contributor
timestamp: June 07, 2025, 08:55:30 pm
content: Quote from: fourfathom on June 07, 2025, 08:51:31 pmOk, lets say you do filter design with AC (or even transient) analysis. Do you have a specific example where it is particularly annoying whether a positive current in a resistor flows from left to right or a negative current from right to left?

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 09:20:31 pm
content: Quote from: TimFox on June 07, 2025, 08:55:07 pmGoddamnit it, Tim:OK, here goes again. The World's Simplest Circuit®™.Now how in the world can there be any doubt whatsoever which end of that resistor is more positive than the other?No matter which way it's "oriented"?I mean, the top of the damn thing is connected to the positive terminal of the voltage supply.How much more explicit do you need this to be?I swear, Tim, discussing things with you is like trying to argue with a Talmudic (or worse, an Islamic) scholar who knows every verse of the Torah (Q'uran) by heart.

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 09:23:07 pm
content: Oh, for heaven's sakes!I wrote" How do you know before doing the simulation which end is more or less positive?If you know that in advance, you probably didn't need Spice to work out the DC voltages in the circuit. "Emphasis added.

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 09:25:53 pm
content: That trivial circuit takes up very little space in text mode:V1 1 2 DC 1.0R1 1 2 100orR1 2 1 100Except that you need to connect something to node 0 (reserved) or Spice will not calculate it.Therefore, doV1 1 0 DC 1.0R1 1 0 100orR2 0 1 100

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 09:27:58 pm
content: Quote from: TimFox on June 07, 2025, 09:23:07 pmOK, I guess we were arguing at cross-purposes there.But don't you see how my illustration pretty much puts the final nail into the coffin of the argument that (LT)Spice's nonsensical treatment of resistor "polarity" is natural and necessary?

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 09:29:06 pm
content: Here is an example of a simple passive circuit that does not need to be drawn out, since it is easy to see what is whereV1 10 0 AC 1.0R1 10 20 100C1 20 30 100pFL1 30 40 1uHL2 40 0 10uHC2 40 0 10pFR2 40 0 1000Obvioously, node 40 is the output and the text file is easy to read. It ain't hard!

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 09:29:15 pm
content: Quote from: TimFox on June 07, 2025, 09:25:53 pmThanks but no thanks. You ain't gonna convert me to using the simulator in that primitive way.Life's too damn short for that.

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 09:31:45 pm
content: Quote from: Analog Kid on June 07, 2025, 09:27:58 pmIf LTSpice determines <Node 1> and <Node 2> from the orientation of the part, that could work if the user understands the connection.Spice will determine the polarity (+ or -) of the current through that part based on those two nodes and their location on the line.If that resistor is feeding the base of a transistor, the polarity of the current through it is important.

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 09:35:13 pm
content: Quote from: Analog Kid on June 07, 2025, 09:29:15 pmAnd that's an example of a circuit too simple to require Spice.Remember that the "IC" in Spice is there because it was designed originally to analyze complicated circuits in ICs.As I have posted elsewhere, a German visiting professor asked a question to get a simple answer, and when an enthusiastic student suggested an over-complicated method, he replied "You could also pull on your pants with tongs."

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 09:39:51 pm
content: Quote from: TimFox on June 07, 2025, 09:31:45 pmDamnit, of course the polarity of current through each and every part of a circuit is important!Nobody here's arguing any different.You're missing the point, which in this thread has always been simplythe representation of current flow through a component (resistor) that's needlessly dependent on that component's physical orientation in the on-screen schematic diagram.You seem hopelessly wedded to the idea of SPICE as a solely text-file driven program, where the information given in that network of nodes is somehow immutable.It's not; since LTspice is a GUI program, it could, if the developers so wished, change this behavior, this admittedly only slight annoyance, so thatit wouldn't matter which way a resistor is oriented.

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 09:44:23 pm
content: If you want to show the polarity (in the sense of connecting a voltmeter across the part) without relying on orientation, then one needs to add (for example) + and - at the ends of the part symbol, or an arrow in parallel with the part symbol, and then people will complain that there ain't no such thing as a polarized resistor.The polarity is not a property of the resistor, it is a property of the circuit.I don't care what type of Spice program you prefer, but with my preference for text files these questions are so trivial that I have never had a problem with them.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 09:48:03 pm
content: Quote from: TimFox on June 07, 2025, 09:44:23 pmWhich means, to put it in plain terms, that you don't have a dog in this fight.

author: tggzzz
author_rank: Super Contributor
timestamp: June 07, 2025, 09:52:36 pm
content: Quote from: Analog Kid on June 07, 2025, 09:39:51 pmEr no. LTSpice is a GUI glued onto a text based program.Itwillalways - andmustalways - matter which way a resistor is orientated in the nodal analysis.It might, however, be useful if there was an easy way to select graphical display of current through a component, and then state "I want current flowing through a component in theotherdirection to be regarded as positive". That could be achieved by the GUI post-processing the simulation's output.I'm not entirely sure why, but I've never run into this issue in my simulations.

author: tggzzz
author_rank: Super Contributor
timestamp: June 07, 2025, 09:57:33 pm
content: Quote from: Analog Kid on June 07, 2025, 09:48:03 pmAlternatively that you and black-heckle-opter (the OP who has, as is traditional, disappeared) create a fight because you don't understand the tools and fundamental concepts, and want the world to conform to your misapprehensions.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 09:57:42 pm
content: Quote from: TimFox on June 07, 2025, 09:44:23 pmYes! Yes! Yes! Yes!Agree 1000%.Therefore, since the simulator "knows" (or should know, in any case) that the top of the resistor is more positive than the bottom, no matter which way the resistor is "oriented", when the user mouses over it the current arrow should always point in the correct direction, down.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 10:01:20 pm
content: Quote from: tggzzz on June 07, 2025, 09:57:33 pmSo, do you lump @fourfathom in that same category? Considerthis post of theirs, which seems to agree with me. (And I'm quite willing to stipulate that they know a hell of a lot more about electronics than I do.)

author: rsjsouza
author_rank: Super Contributor
timestamp: June 07, 2025, 10:20:08 pm
content: I just thought about how the orientation of a passive part on a circuit should never be ignored when working with computer-based tools for electronics.Case in point: all the EDA tools I have used make a clear distinction between pins "1" and "2" of every single passive part placed in a schematic and translated to a netlist - invert them and you end up with criss-crossed tracks. I perceive this as having the same fundamental principle: if the pins of a given passive part have zero behavioural/physical difference, the EDA tool should simply swap them at its own discretion*.*Sure, there are auto-placement tools that will correct that, but they act as simply rotating the part as you would be expected to do in LTSpice as well.

author: TimFox
author_rank: Super Contributor
timestamp: June 07, 2025, 10:48:03 pm
content: In this common circuit:the direction of current flow in the two horizontal resistors is important.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 10:55:34 pm
content: Quote from: TimFox on June 07, 2025, 10:48:03 pmYes, agreed; so what does that have to do with the price of tea in China?Does it matter which way those horizontal resistors are "oriented"?

author: tggzzz
author_rank: Super Contributor
timestamp: June 07, 2025, 11:09:08 pm
content: Quote from: Analog Kid on June 07, 2025, 10:55:34 pmApparently it does to some people, but not to an equation solver.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 07, 2025, 11:31:34 pm
content: Quote from: Analog Kid on June 07, 2025, 08:03:53 pmSo in your ideal world, can the current through a resistor ever be negative? Or does it just become positive, but in the other direction?

author: coppercone2
author_rank: Super Contributor
timestamp: June 07, 2025, 11:33:50 pm
content: I agree with the OP it feels like working with some crap metal thats not been deburred, flattened, etc.I don't like the symbols drawings, I don't like the UI, I don't like how it looks, how it communicates with the user, how it draws graphs or basically anything about it.To me its like going to the junkyard district or something, it has what you might need to determine something but its not pleasantmy brain says "please find some way around having to make me deal with this".and it calls stuff primitives. nice psycho word choice thereThe user interface feels like trying to play chess with billiard cues or perhaps pieces of rebar instead of your hands

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 11:38:12 pm
content: Quote from: mtwieg on June 07, 2025, 11:31:34 pmI'm not sure just what your (somewhat troll-ish) question is:If you're asking "can current (in the "conventional" sense) ever flow from negative to positive?" then the answer is "no".If you're asking something else then you'll need to clarify that a bit.

author: IanB
author_rank: Super Contributor
timestamp: June 07, 2025, 11:45:01 pm
content: Quote from: coppercone2 on June 07, 2025, 11:33:50 pmAnd there may be some deliberate logic to this.It is a tool for experts.If the tool was more appealing to novice users, then the support forums would probably get filled up with more questions about unimportant things like this thread, which would be a time drain on a free resource.So it is probably for the good that the tool does not have mass user appeal. If that happened, its owners would probably want to stop supporting and developing it.The target audience for LTSpice is engineers who want to design products using LT parts.

author: coppercone2
author_rank: Super Contributor
timestamp: June 07, 2025, 11:46:11 pm
content: it also means people don't even wanna get into the field after they walk past a 'electronics simulation lab'if you got more creative people in on this field you might not have thread #199192 about a E-load and instead have some project that gets into other interesting disciplines and stuff. Like we need more experts clogging it up about cheaper transistor replacements for street lights

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 07, 2025, 11:46:39 pm
content: Quote from: Analog Kid on June 07, 2025, 11:38:12 pmNot trolling, but I can understand why you might think so.When I read the following:QuoteMy first reaction is "obviously, and this is exactly what happens in every simulator, including LTspice". Though I would rather state it as "current flows into the more positive terminal and out of the more negative terminal".However from the perspective of the resistor itself, whether the voltage and current it sees is positive or negative is arbitrarily based on which of its terminals is assigned pins 1 and 2. This doesn't mean the above statements are false.

author: coppercone2
author_rank: Super Contributor
timestamp: June 07, 2025, 11:50:19 pm
content: and the other problems when people start to get discouraged because of computers, that is you don't have circuits anyone builds made after 1990

author: Analog Kid
author_rank: Super Contributor
timestamp: June 07, 2025, 11:56:39 pm
content: Quote from: mtwieg on June 07, 2025, 11:46:39 pmBut see, here's the thing:It shouldn't matter what the terminals are labeled.Back to the World's Simplest Circuit®™:If the user plunks down the resistor as in the first drawing, with terminal #1 on top, and then later flips it as in the second drawing, the program (LTSpice) should just adjust its internal netlist--something it can easily do, don't you agree?--so that the circuit behaves, in all respects, as it did in the first drawing.None of this violates any electrical or physics principles; it's just a matter of having a user interface that caters to the user instead of the other way around.I think even engineers would appreciate this. After all, they're people too.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 08, 2025, 12:02:31 am
content: Quote from: Analog Kid on June 07, 2025, 11:56:39 pmI think what you're saying is that the GUI simply shouldn't allow you to flip the resistor the other way. It could enforce a rule like "resistor currents are always positive from left to right and top to bottom".Is that basically what you're asking for?

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 12:04:30 am
content: Quote from: coppercone2 on June 07, 2025, 11:50:19 pmI think we all recognize that LTSpice's user interface is badly out of date, certainly in the area you're most objecting to, which is its decidedly 1990s look and feel. Nobody's disputing that.However, to use a well-worn tautology, it is what it is. And it still is a very useful tool. And it'sfree.What the OP brought up here is one of the few actual operational flaws of the program; all the others are mainly cosmetic or somewhat clunky program flow. Not show-stoppers as you make it sound like.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 08, 2025, 12:08:35 am
content: Our first PSPICE was DOS based, had no schematic capture and required a netlist, similar to what we were doing with the VAX and Berkeley's SPICE.For home, I had hacked the key for PSPICE and eventually bought the DOS version of ORCAD. That could spit out a netlist file for PSPICE.A couple months ago a few people had asked to see some details about a homemade arb. One member here was asking about the DC coupled power amplifier. Shown below is the SPICE netlist for it.AmplifierVCC 22 0 DC 30VEE 23 0 DC -30C6 16 0 .47UFR16A 7 12 .5R16B 12 15 .5R10 17 23 1.8KR11 17 20 1.8KR13 19 15 10R18 12 16 10R9 2 3 100R12 21 23 100R14 4 12 100C5 12 17 100UFR3 10 0 10KR8 11 12 10KR1 9 10 1KR4 1 22 1KR7 11 0 1KRLOAD 12 0 2C2 2 1 270PFC4 0 18 4.7UFR5 13 18 6.8KR6 18 23 6.8KVIN 9 0 SIN(0 .5 1000)D1 5 3 D1N4004D2 12 5 D1N4004D3 14 12 D1N4004D4 20 14 D1N4004D5 3 6 D1N4004D6 6 8 D1N4004D7 8 20 D1N4004Q6 15 21 23 Q2N3055Q8 22 4 7 Q2N3055Q1 1 10 13 Q2N4401Q2 22 11 13 Q2N4401Q4 2 1 22 Q2N4403Q7 22 3 4 Q2N5192Q5 21 20 19 Q2N5195.MODEL D1N4004 D+ IS=375.50P RS=1.45 N=1.50 TT=100.00P CJO=26.93P VJ=354.00M+ M=326.00M EG=1.11 XTI=1.00 KF=0.00 AF=1.00 FC=500.00M BV=400.00+ IBV=1.00M.MODEL Q2N3055 NPN+ IS=3.42P BF=522.00 NF=1.02 VAF=43.40 IKF=388.00M ISE=41.82N+ NE=2.40 RB=1.57 IRB=1.20 RBM=42.50M CJE=940.70P VJE=331.00M+ MJE=700.00M CJC=282.80P VJC=450.00M MJC=393.00M.MODEL Q2N4401 NPN+ IS=38.21F BF=404.00 NF=1.00 VAF=104.00 IKF=576.00M ISE=2.18F+ NE=1.27 BR=2.56 NR=1.00 VAR=5.53 IKR=10.00 ISC=1.74P NC=1.21+ RB=126.00 IRB=57.56M RBM=10.00 RE=571.00M RC=3.30 CJE=21.67P+ VJE=750.00M MJE=373.00M TF=636.60P XTF=1.00 VTF=1.00 ITF=1.00M+ PTF=0.00 CJC=10.55P VJC=431.00M MJC=378.00M XCJC=1.00 TR=0.00+ CJS=2.00P VJS=500.00M MJS=500.00M XTB=0.00 EG=1.11 XTI=3.00+ KF=0.00 AF=1.00 FC=500.00M.MODEL Q2N4403 PNP+ IS=29.86F BF=285.72 NF=997.00M VAF=42.56 IKF=716.07M ISE=9.38F+ NE=1.33 BR=8.11 NR=991.96M VAR=6.33 IKR=28.25M ISC=496.40F+ NC=1.31 RB=132.66 IRB=12.72M RBM=1.00 RE=1.81 RC=9.63 CJE=23.70P+ VJE=800.00M MJE=427.56M TF=100.00P XTF=1.50 VTF=1.50 ITF=1.00M+ PTF=0.00 CJC=14.07P VJC=425.30M MJC=376.67M XCJC=1.00 TR=0.00+ CJS=2.00P VJS=500.00M MJS=500.00M XTB=0.00 EG=1.11 XTI=3.00+ KF=0.00 AF=1.00 FC=500.00M.MODEL Q2N5192 NPN+ VAF=35.9 VAR=11.3 IS=1.494E-11 NF=1.03 IKF=4.53 ISE=1.747E-10 NE=1.71+ RB=132.0 IRB=4.751E-03 BR=26.3 NR=1.00 IKR=0.108+ NC=1.47 CJE=1.705E-10 VJE=0.499 MJE=0.345 FC=0.5 VJC=0.492 MJC=0.369 EG=1.11+ BF=1.380000E+02+ TF=7.958002E-010+ CJC=1.522000E-010+ XTB=1+ TR=200.MODEL Q2N5195 PNP+ VAF=33.8 IS=4.796E-12 NF=1.14 IKF=0.863 ISE=6.746E-12 NE=1.47+ RB=100.0 IRB=10.0 CJE=1.592E-10 VJE=0.619 MJE=0.380+ VJC=0.499 MJC=0.332+ RC=0.000000E000+ BF=2.040000E+02+ TF=7.958002E-010+ CJC=1.730000E-010+ XTB=1+ TR=200.TRAN 0.00001 0.001.FOUR 1000 V(9) V(12).OPTIONS ACCT.OPTIONS LIST.OPTIONS NODE.OPTIONS OPTS.OPTIONS NUMDGT =4.OPTIONS ITL1 =100.OPTIONS ITL2 =50.OPTIONS ITL4 =10.OPTIONS TNOM =27C.OPTIONS GMIN =1.0E-12.OPTIONS RELTOL =0.001.OPTIONS ABSTOL =1.0E-12.OPTIONS VNTOL =1.0E-6.OPTIONS TRTOL =7.0.OPTIONS CHGTOL =1.0E-14.OPTIONS PIVTOL =1.0E-13.OPTIONS PIVREL =1.0E-3.OPTIONS DEFL =100U.OPTIONS DEFW =100U.OPTIONS ABSMOS =1.0E-9.PROBE.END

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 12:13:05 am
content: Quote from: mtwieg on June 08, 2025, 12:02:31 amNo, not at all.Sheesh, why is this so hard to get across?What I'm asking for (and I believe the OP and a couple others here who seem to agree with me) is that the GUI definitely should allow you to flip, mirror, rotate any component, including resistors.And after that re-orientation, it should adjust its internal netlist--you know, the internal data structure that actually drives the simulation--to correspond to what the user sees on-screen. Which in the case of re-orienting a resistor, as we're discussing here, means that the simulator behaves exactly as it did before the resistor was re-oriented, since it's a non-polarized component. If the user mouses over it to measure the current through it, the arrow on the "ammeter" cursor should still point in the same direction as before the resistor was flipped or rotated.Does that make sense to you?Of course, the same doesn't apply to polarized components like diodes,exceptthat the ammeter should respond identically as in the case of the resistor (I mean the orientation of the ammeter arrow, not the actual current measured through the diode, which does depend on the diode's orientation).

author: IanB
author_rank: Super Contributor
timestamp: June 08, 2025, 12:51:52 am
content: Quote from: Analog Kid on June 08, 2025, 12:13:05 amI don't think you will understand that until you design and program your own circuit simulator. Once you do that, the light will eventually dawn, and you will realize the problem with what you are asking.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 12:58:07 am
content: Look at it this way:Say you have that stupid circuit I posted built on a breadboard. You put the components in and hook up your ammeter to it to measure the current through the resistor, using jumpers, clip-on probes, whatever: the plus lead to the ammeter goes to the bottom of the resistor, let's say, and the minus lead to the minus of the voltage source, completing the circuit. All fine and dandy.Later for some reason you need that resistor for something else, so you take it out. Then you decide to stick it back in and retest the stupid circuit. (You must be really bored.)So tell us, when you put that resistor back in, do you agonize over which way to insert it in the circuit? (assuming everything else, the meter probes and jumpers, are in exactly the same place). "Let's see: did brown-black go to the left or the right?"No, of course you don't. (Well, unless you suffer from OCD, in which case you have my sympathy.) You just stick it in, and the circuit works exactly as it did before.That's how we think LTSpiceshouldbehave, including the placement of ammeter probes.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 08, 2025, 12:59:58 am
content: QuoteOk so you want the GUI to allow the components to be flipped, but to behave as if they had not been flipped?

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 01:03:18 am
content: Quote from: IanB on June 08, 2025, 12:51:52 amNo, I think you're wrong.If I wanted to I'm sure I could design a user interface (GUI) that would emit the netlist to drive the simulator "engine". If the user flipped a resistor I'd just re-emit a new netlist so that it would behave exactly as it did before.My understanding is that LTSpice is just a GUI overlay on top of the text-based SPICE engine; all it does is generate a netlist. A smart GUI could do that so that changes the user made on-screen would be accounted for and the netlist adjusted accordingly.Of course I'm not about to do any such thing, as it's far too complex a piece of software. Butsomebodycould definitely do it.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 01:08:05 am
content: Quote from: mtwieg on June 08, 2025, 12:59:58 amBingo!We have a winner.(With the usual disclaimer that this doesn't apply to polarized components like diodes, although even there the ammeter needle should still point in the same direction ...)

author: ledtester
author_rank: Super Contributor
timestamp: June 08, 2025, 01:09:39 am
content: Here is an alternate resistor symbol which shows which way the current will be reported:https://electronics.stackexchange.com/a/661590https://ltwiki.org/index.php?title=File:Res.asyOn my Win11 PC I placed it in my Documents/LTspice directory and it picked it up.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 01:13:20 am
content: @Zero999 already posted such a symbol in hisreply #103here.

author: ledtester
author_rank: Super Contributor
timestamp: June 08, 2025, 01:14:20 am
content: Quote from: Analog Kid on June 08, 2025, 01:08:05 amBut what if you flipped the resistor because you want current to be reported with the opposite sign? Now what do you do?

author: MarkusAJ
author_rank: Contributor
timestamp: June 08, 2025, 01:22:04 am
content: Quote from: BlackHecilopter on June 06, 2025, 07:14:41 pmCongratulations, you just opened a can of wormsIn my opinion the developer of the SPICE GUI should take care of auto adjusting polarization for components like resistors, or add explicit warning how to handle components like that.I agree, when user is writing txt script for SPICE it is obvious, but for person who is using GUI for learning purpose it maybe very confusing.This thread is a perfect example!BTW, I’m not trying to criticize Ltspice, nor similar tools, I’m glad that they exist and are freely available.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 01:26:35 am
content: Quote from: ledtester on June 08, 2025, 01:14:20 amFlipping the resistor should result in no change in reported current direction.If you want the opposite sign (why would you want that, anyway?), just flip it mentally or on paper.(Or if this is something that many people would actually want to do, then add a right-click context-menu option to flip the ammeter probes around.)

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 02:14:57 am
content: Quote from: MarkusAJ on June 08, 2025, 01:22:04 amAgree 100%.I just want to state here that while I agree that LTSpice has some obvious defects, including the one pointed out by the OP, it is definitelynotterrible. I'll continue to use it, grateful to its developers and distributors that it exists and is easily obtainable. The defect that has led to the (so far) 7 pages of comments is at most a minor annoyance, and not a show-stopper.

author: tggzzz
author_rank: Super Contributor
timestamp: June 08, 2025, 06:46:02 am
content: Quote from: mtwieg on June 08, 2025, 12:02:31 amTee hee.Given the way beginners (and too many professionals) draw schematics, that would be doomed to failure.

author: tooki
author_rank: Super Contributor
timestamp: June 08, 2025, 09:32:16 am
content: Quote from: showman on June 07, 2025, 08:36:16 pmIf it’s positive in both directions, then you’re changing the direction of measurement.I mean, polarity is literally how direction is indicated. But direction is always relative to something.

author: mikerj
author_rank: Super Contributor
timestamp: June 08, 2025, 10:34:04 am
content: Quote from: Analog Kid on June 08, 2025, 01:03:18 amPerhaps I am missing something, but how could the GUI possibly know the direction of current flow through any component (in order to arbitrarily reverse the netlist node order) before the simulation has been run?

author: tggzzz
author_rank: Super Contributor
timestamp: June 08, 2025, 11:15:47 am
content: Quote from: mikerj on June 08, 2025, 10:34:04 amEven if it could tell, how would it decide which way is "right"?That would understanding the intention in the designer's mind, such as it is.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 08, 2025, 11:16:59 am
content: Quote from: mikerj on June 08, 2025, 10:34:04 amI was thinking a sloppy pre-simulation that's only job was to sort it out then make changes. No concern for convergence, tolerances and such.They could also remove the feature (measuring current through a component) and force you to add a special current measurement component just for this purpose.For me, this has never been a problem but I certainly can understand where the complaints come from.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 08, 2025, 11:40:04 am
content: Quote from: Analog Kid on June 08, 2025, 01:08:05 amSo let's carry this thought experiment further. Let's take that simple circuit from before:You say that you want LTspice to report the current through the resistor I(R1) as having the same sign in both of these circuits (presumably positive), right?Now I've taken that and flipped the entire thing vertically (not just the resistors):Now I ask you, what should LTspice report for I(R1) in this case?

author: tooki
author_rank: Super Contributor
timestamp: June 08, 2025, 11:45:26 am
content: The same, since you also mirrored the current arrows. I think your question is asking what happens if the current arrows weren’t there.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 08, 2025, 11:52:34 am
content: A couple of different SPICE applications. Note current monitor in upper right.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 08, 2025, 11:58:11 am
content: Quote from: tggzzz on June 08, 2025, 11:15:47 amShould always show conventional current. Lock the current probe to one orientation (maybe user select-able, top down/ left right). Should not track the component as it does today. As I said, another option is ditch this feature and force the user to place a current monitor device.

author: ahsrabrifat
author_rank: Regular Contributor
timestamp: June 08, 2025, 12:33:56 pm
content: I found Proteus more user-friendly. But that one is paid. For a free one, you can try KiCad.

author: tggzzz
author_rank: Super Contributor
timestamp: June 08, 2025, 02:03:06 pm
content: Quote from: joeqsmith on June 08, 2025, 11:58:11 amThat's notthe GUI decidingwhich is right, which was the point I was responding to.

author: eugene
author_rank: Frequent Contributor
timestamp: June 08, 2025, 03:44:01 pm
content: Spice has been around for decades. One of the first things I heard about it was "be careful. Don't trust the results unless you understand the results." Now people want to dumb it down to the point that they don't have to understand the results, because, ... um, because they don't want to take the time to understand the results.I'm nothing like an LTSpice guru, but I've been using it for decades and never once (that I can remember) got hung up on the issue that the OP was ranting about. It's just not a problem unless one goes to the trouble of making it a problem. OTOH, one could go to the trouble of learning how the software works instead.Seven pages and what have we learned?

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: June 08, 2025, 04:35:26 pm
content: What at least I have learned is that if someone starts a thread with hyperbole: “LTSPICE is terrible”, instead of politely asking: “There is a LTSPICE behavior that I don’t understand”, then that TS suffers from a serious case of the Dunning-Kruger syndrome.This is only one of many examples, where a TS angrily blames something, instead of acknowledging his/her own ignorance.

author: tggzzz
author_rank: Super Contributor
timestamp: June 08, 2025, 04:36:16 pm
content: Quote from: eugene on June 08, 2025, 03:44:01 pmYup.Since that is true for everything, I wonder where the OP had their education? University of Life, perhaps?QuotePerhaps the OP was trolling, successfully.

author: tggzzz
author_rank: Super Contributor
timestamp: June 08, 2025, 04:37:53 pm
content: Quote from: UnijunctionTransistor on June 08, 2025, 04:35:26 pmIn this case, I have difficulty distinguishing the first post from a (successful) troll.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 08, 2025, 04:41:11 pm
content: Quote from: joeqsmith on June 08, 2025, 11:58:11 amOk, so I'll pose the same scenario to you:So let's carry this thought experiment further. Let's take that simple circuit from before:You say that you want LTspice to report the current through the resistor I(R1) as having the same sign in both of these circuits (presumably positive), right?Now I've taken that and flipped the entire thing vertically (not just the resistors):Now I ask you, what should LTspice report for I(R1) in this case?

author: joeqsmith
author_rank: Super Contributor
timestamp: June 08, 2025, 04:45:49 pm
content: Quote from: mtwieg on June 08, 2025, 04:41:11 pmBy my thanking Tooki's response, you can safely assume I agreed with what they wrote.https://www.eevblog.com/forum/beginners/ltspice-is-terrible/msg5941218/#msg5941218

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 08, 2025, 04:52:27 pm
content: Quote from: joeqsmith on June 08, 2025, 04:45:49 pmHere's what you just said:Quote from: joeqsmith on June 08, 2025, 11:58:11 amTherefore, a current flowing from bottom to top should have opposite sign as a current flowing from top to bottom.Here's what tooki just said:Quote from: tooki on June 08, 2025, 11:45:26 amThese directly contradict each other.

author: fourfathom
author_rank: Super Contributor
timestamp: June 08, 2025, 04:55:09 pm
content: What I learned is that a slightly annoying behavior of LTSpice is apparently an unavoidable feature.Because of the way I create the LTSpice schematics and place resistors, they generally have different indicated current directions when I place them in the vertical or the horizontal orientation. This wasn't something I worried about, I just used my brain (or the "-" symbol in an equation) to deal with any polarity issues. I wish the resistors and other non-polarized components didn't behave like this during simulations, but I do understand the issues here.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 08, 2025, 05:07:49 pm
content: Quote from: mtwieg on June 08, 2025, 04:52:27 pmThat's the idea of being able to select it is so I can have my cake and eat it too. Seems that is too confusing for you to follow.Quote from: fourfathom on June 08, 2025, 04:55:09 pmOr, like me, you could just be aware of it when creating the schematic so it works as you expect when you run the sim.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 08, 2025, 05:12:31 pm
content: Quote from: joeqsmith on June 08, 2025, 05:07:49 pmHonestly it sounds like you want to redefine conventions on a case-by-base basis rather than adhering to a uniform convention.QuoteIt's definitely confusing when someone reacts to a contradiction in their own logic with a nod of approval.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 08, 2025, 05:15:41 pm
content: Quote from: mtwieg on June 08, 2025, 05:12:31 pmOh well.

author: BlackHecilopter
author_rank: Contributor
timestamp: June 08, 2025, 05:24:53 pm
content: So far I learned that in LTSpice, resistors have polarity and current may not always flow from higher potential to lower potential.Two things that don't represent reality.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 08, 2025, 05:29:04 pm
content: MicroCap also allows hovering the cursor over a resistor to measure the current through it. Try flipping the resistor and see if it has any effect.I've been using MicroCap basically since it was given to the public for free. I like that it can show the currents with the cursor rather than having to enter a special component as I have shown. The real advantage over my low end SPICE programs is it has much better support for RF work.

author: eugene
author_rank: Frequent Contributor
timestamp: June 08, 2025, 05:55:18 pm
content: Quote from: BlackHecilopter on June 08, 2025, 05:24:53 pmThe reality is that if you try to write software to perform nodal analysis, you will soon learn that nodes are a necessary part of defining the problem.QuoteYeah, it really always does. The problem is that you are willfully choosing to ignore the education that people here are offering you.https://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effectQuote from: tggzzz on June 08, 2025, 04:37:53 pmMalice is common, but stupidity is way more common.

author: IanB
author_rank: Super Contributor
timestamp: June 08, 2025, 06:09:21 pm
content: Quote from: BlackHecilopter on June 08, 2025, 05:24:53 pmIn LTSpice, resistors obey Ohm's Law:$$i=\frac{(v_1-v_2)}{R}$$If \$v_1>v_2\$ then \$i\$ is positive.But in the real world, currentdoes notalways flow from higher potential to lower potential. There are common cases where current will flow against a potential gradient. If this was not the case, then no electronic devices would work.

author: tggzzz
author_rank: Super Contributor
timestamp: June 08, 2025, 06:19:50 pm
content: Quote from: eugene on June 08, 2025, 05:55:18 pmTrue. Ditto conspiracy vs cockup theories of history.Trolls can choose to mimic Dunning Kruger exemplars. I glanced at the OPs posting history, and couldn't decide either way.The inability of some posters to sit, read, think, understand physics theory and maths is disturbing but not surprising. Not understanding is acceptable, provided it is recognised astheirlimitation and to act accordingly.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 08, 2025, 06:20:37 pm
content: The developer's of Microcap were able to sort out the current flow readout. I wonder why couldn't the the developers of LTSPICE? Maybe Microcap has similar problems and I have not ran into them? To be fair, while I have used it for actual work, I wouldn't consider myself a power user.

author: Zero999
author_rank: Super Contributor
timestamp: June 08, 2025, 07:08:47 pm
content: Quote from: ahsrabrifat on June 08, 2025, 12:33:56 pmI have used Proteus a lot, not for simulation, but for general schematic capture and would rather use LTSpice any day. I find Proteus to be a complete pig to use. It repeatedly gets identifiers wrong, lacks a quick way to flip components and doesn't allow a component to be dragged and dropped onto a wire.Quote from: fourfathom on June 08, 2025, 04:55:09 pmHave you tried looking at the netlist?[ Specified attachment is not available ]The above generates the following netlist:* E:\User Documents\user\Documents\potential dividers netlist.asc* Generated by LTspice 24.1.7 for Windows.R1 in out1 1kR2 out1 0 1kV1 in 0 12VR3 out2 in 1kR4 0 out2 1k.backanno.endI've flipped R3 and R4 and note the polarities are opposite on the netlist?

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 07:41:07 pm
content: Quote from: mtwieg on June 08, 2025, 04:41:11 pmEasy peasy: It should report current flowing in the direction of the arrow.It shouldalwaysreport current flowing in the direction of the arrow.It knows which way current should flow because of how you placed those components on-screen. (It's "smart", see.)Sheesh; why is this so difficult for people to grok?I mean, look at it this way:Let's say for the sake of discussion that you are writing a great new simulator from scratch. You have no constraints on you; you're not basing your app on SPICE or any other existing simulation engine.How would you want resistors to behave? Would you want to make them actas ifthey were polarized?No, of course you wouldn't.[images got attached in the wrong place ...]

author: fourfathom
author_rank: Super Contributor
timestamp: June 08, 2025, 07:47:55 pm
content: Quote from: Zero999 on June 08, 2025, 07:08:47 pmThere's a difference between being annoyed and being confused! I'm not confused. Of course if I look at the netlist the indicated current polarities make sense -- please don't assume that I am stupid. And I agree that the issue is complicated, and perhaps with no perfect solution (one that doesn't annoy me).

author: Zero999
author_rank: Super Contributor
timestamp: June 08, 2025, 08:58:19 pm
content: Quote from: fourfathom on June 08, 2025, 07:47:55 pmPerhaps I'm the one who's confused about what you mean, along with others who somehow want the simulator to guess the 'correct' signs for the resistor nets?Here's a schematic of an AC coupled amplifier, with a positive ground. I've labelled the terminals on each resistor y and y. Can you, or anyone else, list whether x or y on each resistor should be positive of negative? And how did you make that decision?EDIT: Can anyone spot my not so deliberate mistakes on the schematic attached?The corrected version can be found here:https://www.eevblog.com/forum/beginners/ltspice-is-terrible/msg5941840/#msg5941840

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 09:08:02 pm
content: Wellll, some of them are quite obvious, like R5 (y = -, x = +) and R6 (ditto).Others not so obvious, like R4. Which brings up a question:What about resistors where the current flow direction is ambiguous? Or to be more specific, where the current can be expected to flow in either direction? (I don't know enough about op-amp circuit analysis to know whether that's true of R4, but let's say it is for the sake of discussion.)If that's the case, and the program can definitely assume that (bidirectional current flow) about a resistor, then perhaps the ammeter cursor should show a double-headed arrow.What do y'all think about that?

author: Zero999
author_rank: Super Contributor
timestamp: June 08, 2025, 09:24:36 pm
content: Quote from: Analog Kid on June 08, 2025, 09:08:02 pmWhy?And how would you write a program to determine it?QuoteDoes it matter?I say it's arbitrary.A resistor isn't polarised, so the polarity isn't important. The only reason why you need to know the current or voltage is to calculate the power and since current or voltage is squared, P = I2R or P = V2/R, the sign doesn't matter, since multiplying a number by itself always gives a positive number.Lol, I've just noticed. I've made an error on the schematic. Please point it out.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 09:32:21 pm
content: Quote from: Zero999 on June 08, 2025, 09:24:36 pmOK. You know more about this stuff than I do, so let me ask you:For resistors like R1 through R4:Can current normally go through these in either direction?If so, is there any way for the simulator (the SPICE engine) to determine this?Does it matter if the simulator shows this direction when the user mouses over one of these Rs? I suppose not; might just be icing on the cake.But it also might be nice to refine the tool a bit for the sake of reducing confusion.

author: fourfathom
author_rank: Super Contributor
timestamp: June 08, 2025, 09:33:11 pm
content: Quote from: Zero999 on June 08, 2025, 09:24:36 pmV1 voltage source polarity is reversed.Yes, I get it -- the resistor current measurement is made with what is essentially a built-in ammeter, and the ammeter polarity puts the +/red lead on terminal 1. So the current measurement polarity depends on the resistor orientation.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 09:34:26 pm
content: Quote from: Zero999 on June 08, 2025, 09:24:36 pmYour+inand-inlabels are reversed? That's all I can see.

author: Zero999
author_rank: Super Contributor
timestamp: June 08, 2025, 09:42:37 pm
content: V1 is correct. I said "positive ground".The power supply terminals to U1 and U2 are incorrect as well as the inverting and non-inverting inputs to U1. I simply forgot to flip the symbols. It was very sloppy of me.Here's the correct schematic.

author: tggzzz
author_rank: Super Contributor
timestamp: June 08, 2025, 09:46:06 pm
content: Let's try a real example, from the Tek485 signal differential amplifier chain, where the signal is Icfrom the collectors of U650.Which way round should L650 and R650 in the middle of the image be?(For simplicity, consider only pins 9 and 5, and note that Tek have helpfully annotate the endpoint nodes with voltages.)

author: fourfathom
author_rank: Super Contributor
timestamp: June 08, 2025, 09:46:30 pm
content: Quote from: Zero999 on June 08, 2025, 09:42:37 pmOK. I was just looking at the schematic.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 09:59:54 pm
content: Quote from: tggzzz on June 08, 2025, 09:46:06 pmI have no goddamn idea.You never answered my last previous question about bidirectional current flow through resistors. Care to answer it? I think it's relevant here.

author: ledtester
author_rank: Super Contributor
timestamp: June 08, 2025, 10:16:53 pm
content: Quote from: Analog Kid on June 08, 2025, 09:32:21 pmIf V1 is a negative voltage source conventional current will flow in the opposite direction.If it's an AC voltage source it will flow in both directions.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 10:26:23 pm
content: Quote from: ledtester on June 08, 2025, 10:16:53 pmWell, duh. That much I can figure out.What nobody has addressed so far is the simulator's ability to determine current flow direction, given an on-screen schematic (like, say, @Zero999's).

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 08, 2025, 10:52:04 pm
content: Quote from: Analog Kid on June 08, 2025, 07:41:07 pmI assumed those arrows were there to indicate the direction of actual current in the circuit. So you interpret them as being the definition of positive current for the resistor resistor?In a way, SPICE already does this; the arrow is implicitly pointing from terminal 1 to terminal 2. Though LTspice does not actually show the arrow or terminal numbers in the schematic view.Would you be satisfied if it did? Because it is possible, as others have shown:https://forum.allaboutcircuits.com/threads/ltspice-modified-resistor-symbol.188508/

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 11:15:51 pm
content: Quote from: mtwieg on June 08, 2025, 10:52:04 pmJesus fucking Christ.Yes, the arrows are there to indicate actual current flow through the circuit. Why else would we want to have them shown?Meaning thatwhen LTSpiceknowswhich way current will flow through a resistor--which you surely must see it must know in that stupid simple circuit I posted--then it should show that direction. Regardless of the resistor's "orientation" (since resistors are non-polarized). Forget about 'terminal 1" and "terminal 2": in that circuit as I originally drew it, current flows from top to bottom. (And no, I amnotsaying that current should always be assumed to flow from top to bottom, or from left to right: it depends on the configuration of the schematic.) You can flip that resistor nine ways to Sunday and current will still flow in the same direction.Do you have any objection to what I just stated? I don't know how to make it any more plain or simple than that.However, as shown by the most recent posts here, there may be cases where the direction of current may be ambiguous (meaning it may be unknown until the simulation is run), or it may be bidirectional (as in the case of your AC voltage source).I still haven't gotten any responses from anyone suggesting what should be done in such cases. What do you say to this?

author: IanB
author_rank: Super Contributor
timestamp: June 08, 2025, 11:23:36 pm
content: Quote from: Analog Kid on June 08, 2025, 11:15:51 pmNobody cares?Put another way, it's not an issue.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 08, 2025, 11:26:35 pm
content: Quote from: IanB on June 08, 2025, 11:23:36 pmWell, let's say it's a minor issue with some of us here, not just me. (Certainly the OP.)Without putting words in his mouth, I believe @fourfathom shares some of my concerns, even if they haven't pursued this as doggedly as I have.BTW, i might point out that your reply amounts to a null comment. Saying you don't care about something doesn't mean there aren't others who do care. Odd way to respond, methinks.

author: IanB
author_rank: Super Contributor
timestamp: June 08, 2025, 11:45:24 pm
content: Quote from: Analog Kid on June 08, 2025, 11:26:35 pmNo, it's a logical deduction. If you have not had any responses, it means nobody has been concerned enough to respond.

author: ledtester
author_rank: Super Contributor
timestamp: June 09, 2025, 12:05:47 am
content: In this video Kiss Analog demos Microcap on a simple resistor network and at 35:00 he shows how to plot currents:Introduction to MicroCap for Beginners Kiss U107 - part of Kiss University -- Kiss Analoghttps://youtu.be/hUyzhSZL0cA?t=35m00sand all the currents are negative so he shows how to flip the resistors to make the currents positive.Apparently Microcap orients current based on the node numbers.I think this explains the behavior observed inReply #185because rewiring the resistor also swapped its node numbers.

author: rsjsouza
author_rank: Super Contributor
timestamp: June 09, 2025, 12:18:45 am
content: Quote from: fourfathom on June 08, 2025, 09:33:11 pmThat is precisely what I mentioned in my reply before:Quote from: rsjsouza on June 07, 2025, 12:59:01 pmTherefore, this only adds to the necessary caution of using a tool that is not the same as the real world: passive parts have polarity; all parts have built-in 6-1/2 digit DMMs.

author: fourfathom
author_rank: Super Contributor
timestamp: June 09, 2025, 12:25:46 am
content: Quote from: Analog Kid on June 08, 2025, 11:15:51 pmThe current is definitely unknown before simulation is run. That's what simulation does.As for displayed current and my annoyance with it, I hadn't previously thought about the implementation and the complications (and uncertainties) of displaying it the way I might prefer. In most cases I don't actually care about the polarity (since I know how the current is flowing), so the negative current is a minor complication. But in other cases I could make use of the polarity information, so knowing how the resistor current measurement is orientation-dependent is good to know. I guess at this point my annoyance is about the lack of obvious indicated resistor polarity. And yes, I've seen the patches making this info visible, but I guess I don't care enough to bother with that, now that I know what is going on.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 09, 2025, 01:03:20 am
content: Quote from: fourfathom on June 09, 2025, 12:25:46 amYes, of course.Sorry, and my bad for muddying the waters here a little, because I forgot that you can't even use the ammeter until after the simulation has been run, so scratch everything I wrote about uncertainty of currents.But now I'm pretty close to 100% convinced that those of us here who have expressed disappointment or annoyance with LTSpice's unfortunate way of handling current direction through resistors are justified in our criticism.That's because after the simulation runs, which is the only time we get to wield the ammeter tool, the program knows exactly the direction of current flow through each node and component. So our complaint that the indicateddirection of current flowshouldn't depend at all on the "orientation" of resistors is 100% valid (though a minor issue at best). It's really down to that.The final upshot of which is, learn to live with it, because it ain't likely to be fixed anytime soon, or at all.

author: Ian.M
author_rank: Super Contributor
timestamp: June 09, 2025, 01:28:44 am
content: The problem is not so simple. In many cases, the current through a resistor is either zero at the start of the simulation, or reverses one or more times during it. The simulator has no way of telling which way *you* want to be positive current at the time *you* are interested in, so must resort to simple rules to determine that, and the SPICE convention of positive current flowing from the first to second node of the spiceline has the benefit of being easily predictable, so anyone who cares to can place their resistors the way round they prefer, and of being compatible with other SPICE programs so you get numerical results that are directly comparable.The main deficiency is you cant easily confirm that resistors and other non-polarised two lead components have been placed as you expect without either going through the PITA of inspecting the netlist, or running the simulation. If LTspice showed the names/numbers of *all* of a component's nodes while placing it (or possibly on demand for a selected component), not just those made visible in its symbol, it would be much easier to place them the way round you want to get your preferred positive current flow direction.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 09, 2025, 01:38:08 am
content: Quote from: Ian.M on June 09, 2025, 01:28:44 amBut you misunderstand; I don't want the current to be shown flowing through that resistor any way except the way it's actually flowing. Whether up to down or down to up, whatever. Just show me the actual direction of current flow. (Why would I even have a preference in direction here? The current magnitude and direction is what it is.)I just don't want that direction to depend on which way the resistor is "oriented".It should show the same regardless of whether the resistor is "flipped".

author: fourfathom
author_rank: Super Contributor
timestamp: June 09, 2025, 02:37:56 am
content: Quote from: Analog Kid on June 09, 2025, 01:38:08 amBut in a case where the current changes polarity during simulation, or perhaps when you have a simple current-summing (or subtraction) circuit, how do you, or the simulator, choose? It's all kind of relative. During this conversation I struggled with what I want to see vs how the currents are actually flowing, and I now realize that even if LTSpice was smarter than us humans there is no perfect solution. The simulation below showing negative current still bugs me though, but I can (and have been) living with it.

author: TimFox
author_rank: Super Contributor
timestamp: June 09, 2025, 03:20:31 am
content: In my comment a few pages backhttps://www.eevblog.com/forum/beginners/ltspice-is-terrible/msg5940820/#msg5940820I posted the drawing for an elementary Eccles-Jordan flip-flop.Of course, this circuit has two stable states; in each state, one transistor is ON, and the other is OFF.In theory, there is an unstable equilibrium state with both conducting, but any small perturbation will send it to one of those two states.I chose this circuit because it is symmetric, and two resistors (the two drawn horizontally) will have current flowing in both directions, depending on the state.The analyst would probably define positive current in each of those resistors as the direction that turns on the base of the transistor driven by it.Depending on the resistor, that positive direction is either to the left or to the right, so orientation is not a good way to code the direction.I don't care how the GUI does that, since my preferred text files for Spice itself encode it directly by the syntax of the two node numbers, as I have pointed out.You GUI-philes can deal with it in your own way.

author: BlackHecilopter
author_rank: Contributor
timestamp: June 09, 2025, 04:37:41 am
content: Quote from: Analog Kid on June 09, 2025, 01:38:08 amThis is exactly what I am saying. This concept is pretty simple in my opinion.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 09, 2025, 05:15:32 am
content: Quote from: TimFox on June 09, 2025, 03:20:31 amOK, Grandpa, have fun with your slide rule, your trig tables and your quill pen and vellum.

author: fourfathom
author_rank: Super Contributor
timestamp: June 09, 2025, 05:24:12 am
content: Quote from: BlackHecilopter on June 09, 2025, 04:37:41 amBut it's not that simple. If you don't use resistor orientation, for a given resistor should the current be shown as positive or negative? When and why? Define positive current as left-to-right and top to bottom? I can certainly create a schematic where that would be a poor choice. My thinking on this subject has, shall we say, evolved.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 09, 2025, 06:44:17 am
content: Quote from: fourfathom on June 09, 2025, 05:24:12 amAha, I see now: I've been concentrating all this time on the matter of "which way does the ammeter needle point" and completely ignoring the (probably more important) matter of "is that current positive or negative"?(Reminds me of the refrain of that great Les McCann song, "Tryin' to make it real compared to what!?!")OK, so it's more or less arbitrary. How about my earlier idea where instead of flipping the resistor to establish the "polarity" (of the measured current,notof the resistor itself), there's a context menu choice that allows you to flip the ammeter probes around? Then you can have it show the current in the polarity that makes sense to you.

author: gf
author_rank: Super Contributor
timestamp: June 09, 2025, 06:59:33 am
content: Quote from: fourfathom on June 09, 2025, 05:24:12 amIndeed, it isn't that simple. For plotting e.g. I(R1), it makes IMO sense that the reference direction is defined by the component R1 alone, and not by the context of R1 in some circuit, or even by a particular graphical layout of the circuit.Quote from: Analog Kid on June 09, 2025, 06:44:17 amThe reference direction is just a matter of definition, and SPICE is the one who makes the definition. IMO, the definition of positive current direction for two-terminal and N-terminal components already existed in early versions of SPICE (~50 years ago), and I don't believe it has changed in LTspice.The GUI would of course have the option to flip the arrow instead of displaying negative DC values. But then the arrow can no longer serve as indicator for the reference direction, while expressions like I(R1) are still relative to the reference direction. Hard to say what's really better.

author: Zero999
author_rank: Super Contributor
timestamp: June 09, 2025, 07:55:24 am
content: SPICE in general uses the net order of the resistor to determine polarity. It's not specific to any implementation (Micro-Cap, LTSpice, Ngspice etc.). Some GUI front ends handle this better than others. It's an exercise to the reader to figure out or look up how the order for positive and negative.The classic way to measure current in SPICE is to use a voltage source set to zero, as an ammeter. That way the polarity is clear.Consider the following example:Ammeter.asc(1.06 kB - downloaded 16 times.)It generates the netlist below:* \users\SPICE\Ammeter.ascR1 supply x 1kV1 supply 0 12VR2 x 0 1kR3 supply z 200RR4 z 0 1kVAM1 y z 0VR5 y x 100R.op.backanno.endRunning the .op command generates the following output:--- Operating Point ---V(x):8.6087voltageV(y):9.13043voltageV(supply):12voltageV(z):9.13043voltageI(R2):0.0086087device_currentI(R4):0.00913044device_currentI(VAM1):-0.00521739device_currentI(R1):0.0033913device_currentI(V1):-0.0177391device_currentI(R3):0.0143478device_currentI(R5)0.00521739device_currentThe current through VAM1 and therefore R5 is -0.00521739A = -5.21739*10-3 = -5.21739mA. This is what you would measure, if you built this circuit in real life and put your multimeter set to current mode, in place of VAM1, with the probes as per the signs on the schematic.The useful thing about using a voltage source in this manner is it's possible to measure the current through a wire. R5 can be deleted and replaced with a wire, which VAM1 will measure the current through.

author: iMo
author_rank: Super Contributor
timestamp: June 09, 2025, 08:08:12 am
content: LTspice shows you the current direction via a resistor when you hover with the mouse pointer over that resistor..Also you may memorize the "+ and -" of the resistor based on how it is printed out when placed in the schematics..The weird stuff with the currents is caused by the way LTspice handles the Nodes numbering and the notion of the "reference" in the netlist, imho, not with the resistor's parameters itself..

author: Zero999
author_rank: Super Contributor
timestamp: June 09, 2025, 08:50:28 am
content: Quote from: TimFox on June 07, 2025, 10:48:03 pmSorry, I missed that. Perhaps you should have blown it up a bit.Hint: the forum software can scale the image, saving you the bother of using GIMP or M$ Paint. Put width=x in the image tag, where x is the desired with. It works best if x = an integer multiple of the image's original width. Example x = 2* original size.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 09, 2025, 11:43:50 am
content: Quote from: Analog Kid on June 08, 2025, 11:15:51 pmI think I've been extraordinarily patient with reading and writing all replies in this thread. I'd expect the same from you.QuoteIn my last post I literally mentioned two possible interpretations for the arrows:1. They indicate the direction of "actual" current flow (meaning it's not known until after a simulation has been run).2. They indicate the "reference" direction for positive current (defined before any simulation has been run). If after the simulation is run the current is actually flowing in the opposite direction, then the value of that current will be negative. In a way, the arrow indicates to polarity of the built-in "ammeter" used to measure the current.QuoteObviously it would be silly to say that actual current (per definition #1 above) should always flow top to bottom or left to right or whatever. I don't think anyone has suggested such a thing.But I do think some people were suggesting that the reference direction for measuring currents (per definition #2 above) should follow some fixed convention.QuoteI suggested something in my previous post (putting the "reference direction" arrows on the schematic symbols) and asked you if it would be satisfactory.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 09, 2025, 12:32:58 pm
content: Quote from: iMo on June 09, 2025, 08:08:12 amIt should just show conventional current thru the part. Flipping a resistor should have no effect. Note how flipping the resistor in Micro-Cap has no effect on the displayed current.https://www.eevblog.com/forum/beginners/ltspice-is-terrible/msg5941590/#msg5941590

author: tooki
author_rank: Super Contributor
timestamp: June 09, 2025, 12:35:01 pm
content: Quote from: mtwieg on June 08, 2025, 04:52:27 pmNo, they don’t.The directions of current arrows fundamentally show the point of reference for that flow:* if actual current flow is in thesamedirection as the arrow points, then the value of the current flow ispositive* if actual current flow is in theoppositedirection as the arrow points, then the value of the current flow isnegative(This is not a contrivance I made up for the sake of argument; it’s a very real-world issue that crops up when doing circuit analysis, for example using the superposition theorem. The sequential zeroing of all current and voltage sources except one can result in current that flows opposite to the current arrows you initially drew in.)So as long as current arrows are drawn into a schematic, they would override any “default” behavior by the simulator GUI, because the arrows exist to specify the point of reference.It’s analogous to saying “put the red multimeter probe here and the black one here”: absent any specific instruction to the contrary, one normally connects the black probe to ground and measures other points with the red one. But if a schematic says that a particular measurement needs the black probe somewhere else, that overrides the default.

author: Zero999
author_rank: Super Contributor
timestamp: June 09, 2025, 12:42:38 pm
content: If the OP doesn't like the signs suggested, then add an arrow to symbol. Make it small and then it is reduced to a few barely visible schematics when zoomed out so it doesn't clutter schematics, but can be seen zoomed in. If the resistor is connected with the current flowing in the same direction as the arrow (conventional current flow) then the sign is positive, and the sign will be negative if the current flows in the opposite direction.Save the attached to \LTspice\lib\sym\res.asyres.asy.txt(0.49 kB - downloaded 27 times.)Notes: remember to change the extention from .txt to .asy and backup the original file first.

author: tooki
author_rank: Super Contributor
timestamp: June 09, 2025, 01:02:53 pm
content: I think that this sketchy sketch of mine (I swear, my handwriting and drawing are way neater when using pen and paper, compared to the slick iPad screen…) showing the equivalent circuits of the SPICE resistor and ammeter get to the crux of the problem.Note how theentire equivalent circuitactually gets flipped, not just the resistor.

author: Terry Bites
author_rank: Super Contributor
timestamp: June 09, 2025, 01:07:29 pm
content: Oh, its far worse than that.Qspice is future and its a joy to use.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 09, 2025, 01:39:42 pm
content: Quote from: Zero999 on June 09, 2025, 12:42:38 pmWhy does it need any identifier? Micro-Cap doesn't use it and still shows the correct flow when the resistor is flipped.

author: ledtester
author_rank: Super Contributor
timestamp: June 09, 2025, 02:03:00 pm
content: Quote from: joeqsmith on June 09, 2025, 01:39:42 pmDid you see the video I posted in Reply 210:https://www.eevblog.com/forum/beginners/ltspice-is-terrible/msg5942016/#msg5942016The presenter shows how you need to flip resistors using the flip tool in Microcap in order to change the sign of the current. Initially the currents came out negative so he used the flip tool to make them positive.He also explains how Microcap bases the current orientation on the internal node numbers which is why I think your example didn't result in a change of sign.

author: Zero999
author_rank: Super Contributor
timestamp: June 09, 2025, 02:08:42 pm
content: Quote from: ledtester on June 09, 2025, 02:03:00 pmLTSpice also bases the current orientation on the internal node numbers, the same as all SPICE implementations do.Perhaps he just happened to draw the schematic in a way which produced the signs he expected?I can see the lack of node markers on the default LTSpice symbol can cause confusion, but there are fixes for it: either an identifier to the symbol, or run the simulation, then flip the resistors to give the desired polarity. It's not difficult.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 09, 2025, 02:21:27 pm
content: Quote from: ledtester on June 09, 2025, 02:03:00 pmI used rotate.

author: BlackHecilopter
author_rank: Contributor
timestamp: June 09, 2025, 02:30:53 pm
content: Quote from: fourfathom on June 09, 2025, 05:24:12 amIt is that simple. Positive or negative is determined by the direction of measurement. Like in real life. A current direction is assumed when current is measured. Allow changing the current probe direction in SPICE. Like in real life.Conventional current flow defines positive current as current that flows from higher potential to lower potential. Electron flow is the reverse.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 09, 2025, 02:33:39 pm
content: Quote from: Zero999 on June 09, 2025, 07:55:24 amThat's how I would do this with the old PSPICE. My newer tools provide a symbol for current that is marked. I guess a little less confusing. Coin toss...

author: TimFox
author_rank: Super Contributor
timestamp: June 09, 2025, 02:42:12 pm
content: Going back to the Eccles-Jordan circuit I posted, I thought of a very simple way to unambiguously denote current polarity/direction without extra symbols on such a schematic drawing:Place all resistors and other non-polarized two-terminal components vertically, and always define the forward/positive direction of current flow as top-to-bottom, which is natural for a positive power rail at the top of the drawing.Actual circuit function is defined by the connecting wires in the drawing, which are not Spice objects but are converted to nodes by the interface.This will make drawings such as the flip-flop slightly uglier, but perfectly legible.

author: Zero999
author_rank: Super Contributor
timestamp: June 09, 2025, 02:51:00 pm
content: Quote from: joeqsmith on June 09, 2025, 02:33:39 pmIt can be easily added to LTSpice, or just use the existing voltage source, set to 0V, hide the voltage, overlay the letter A onto it and use AMx for the label. Now it looks like an ammeter symbol, with the polarity clearly marked. Job done.Ammeter.asc(1.13 kB - downloaded 18 times.)Quote from: TimFox on June 09, 2025, 02:42:12 pmYou could also make the convention for horizontal positive left, negative minus.

author: TimFox
author_rank: Super Contributor
timestamp: June 09, 2025, 02:53:23 pm
content: I used the flip-flop drawing as an example of the problem with left-right in the two horizontal resistors.

author: tggzzz
author_rank: Super Contributor
timestamp: June 09, 2025, 02:59:54 pm
content: Quote from: TimFox on June 09, 2025, 02:42:12 pmThe traditional schematic "design pattern" for such bistable monostable and multivibrator is to have the C-B coupling resistors/capacitors horizontal.Ignoring schematic design patterns is not a good idea. It makes it look as if the designer is ignorant of the history or operation of the circuit, and makes it difficult for someone looking at the schematic to understand it. Unfortunately such abominations are seen all the time, especially where opamps are involved.One software equivalent is to ignore indentation/formatting conventions and naming conventions; in extreme cases it is a form of obfuscation.Much better for people to understand the fundamental concepts, and work with them rather than rail against them. Butyouknow that.

author: tggzzz
author_rank: Super Contributor
timestamp: June 09, 2025, 03:02:37 pm
content: Quote from: Zero999 on June 09, 2025, 02:51:00 pmYou could make the convention to be that signal flow is from right to left. After all, many people draw schematics right to left, and many languages are right to left.Best to stick to the common "schematic design patterns", just as it is better to follow software program formatting conventions.

author: Zero999
author_rank: Super Contributor
timestamp: June 09, 2025, 03:10:24 pm
content: Quote from: TimFox on June 09, 2025, 02:53:23 pmIt's a non-issue if you just draw it so the left hand side of each resistor is positive.

author: tggzzz
author_rank: Super Contributor
timestamp: June 09, 2025, 03:12:53 pm
content: Quote from: Zero999 on June 09, 2025, 03:10:24 pmAre you sure of that?

author: TimFox
author_rank: Super Contributor
timestamp: June 09, 2025, 03:15:12 pm
content: Quote from: tggzzz on June 09, 2025, 02:59:54 pmI’m not railing. I explained Spice syntax (order of node numbers) and indicated my preference.Many replies indicated a visceral dislike of text and accusations of being archaic.Like I said, requiring vertical resistors makes the drawing uglier.With the normal horizontal resistors (my preferred orientation), I find it natural to define positive current in the C-B resistors as that which forward biases the base, which precludes a left-right definition in this circuit.My suggestion would make this direction unambiguous without “diacritics” on the drawing.For my purposes, when this is important I use Spice text files to avoid possible confusion.

author: tggzzz
author_rank: Super Contributor
timestamp: June 09, 2025, 03:33:58 pm
content: Quote from: TimFox on June 09, 2025, 03:15:12 pmI meant no criticism ofyou.I agree wholeheartedly with that direction for the C-B resistors, since it (1) usefully emphasises the symmetry and (2) usefully makes the overall circuit's currents design pattern congruent with the individual transistor currents design pattern. What's not to like

author: BlackHecilopter
author_rank: Contributor
timestamp: June 09, 2025, 04:36:27 pm
content: Anyone know where ModelFile attribute went in version 24 of LTSpice? That attribute isn't there.

author: Zero999
author_rank: Super Contributor
timestamp: June 09, 2025, 07:28:26 pm
content: Quote from: tggzzz on June 09, 2025, 03:12:53 pmYes. If the user knows that, if the resistor is placed horizontally, the left-hand connection, always gives a positive sign for current, if current flows into it. I can't see it being an issue, so long as the behaviour is known and predictable.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 09, 2025, 07:51:12 pm
content: Quote from: Zero999 on June 09, 2025, 12:42:38 pmThat's not a bad idea. Not a bad idea at all. Won't further clutter a schematic.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 09, 2025, 07:51:30 pm
content: Quote from: BlackHecilopter on June 09, 2025, 04:36:27 pmI'm running version 24.1.1 and it does appear for me

author: Analog Kid
author_rank: Super Contributor
timestamp: June 09, 2025, 07:54:08 pm
content: Quote from: TimFox on June 09, 2025, 02:42:12 pmYeah, no. I appreciate what you're trying to do here, but that restriction would lead to some horrible schematics.

author: tggzzz
author_rank: Super Contributor
timestamp: June 09, 2025, 08:03:45 pm
content: Quote from: Zero999 on June 09, 2025, 07:28:26 pmThis is the circuit TimFox is referring to:or drawn in a more usual wayIf Qbar is high the (conventional) flowsleft to rightthrough R3 into Q2 base.If Q is high the (conventional) flowsright to left throughR4 into Q1 base. nowadays it is remarkably difficult to find a decently drawn BJT bistable multivibrator. Not too surprising, I suppose.

author: Zero999
author_rank: Super Contributor
timestamp: June 09, 2025, 08:11:37 pm
content: Quote from: tggzzz on June 09, 2025, 08:03:45 pmI don't see the issue. Yes, the signs will be different, depending how it's drawn, but it's fine by me, so long as I know the rules beforehand.

author: tggzzz
author_rank: Super Contributor
timestamp: June 09, 2025, 08:21:34 pm
content: Quote from: Zero999 on June 09, 2025, 08:11:37 pmWell of course, duh!But that's not the subject of this thread. In a symmetrical circuit most people would (quite reasonably IMHO) expect to see symmetrical positive currents in R3 and R4.That wouldn't happen with your proposal that "if the resistor is placed horizontally, left-hand connection, always gives a positive sign for current, if current flows into it"

author: TimFox
author_rank: Super Contributor
timestamp: June 09, 2025, 09:02:26 pm
content: Precisely.This problem does not exist with Spice text files and could be handled by adding features to the wiggly resistor symbol in the graphical schematic.Lacking that, the only suggestion I have is the ugly one to draw all resistors vertical.The flip-flop is a simple example of the symmetry problem, but it also exists with feedback circuits and other common simple circuits.(It is not uncommon for all resistors on a PCB to be mechanically parallel to facilitate assembly.)In my own schematics, to keep records of expected voltages and currents for future troubleshooting, I use, for example, "[2.5 V]" and "<1 mA" notations for node voltages and device current directions.I have my own rule that the "<" indicates direction, not inequality.

author: Zero999
author_rank: Super Contributor
timestamp: June 09, 2025, 09:11:17 pm
content: Quote from: Analog Kid on June 09, 2025, 07:51:12 pmHave you tried my file? I forgot to say another thing: you'll probably need to redo it after updating, since the updater will put the standard symbol back. Yes, I know that's irritating. Just keep the file somewhere else, then you can simply copy it again and replace the original.Quote from: tggzzz on June 09, 2025, 08:21:34 pmIt seems like misunderstood the complaint. It silly thing to get upset about. Repeatability should be what's important.

author: Ian.M
author_rank: Super Contributor
timestamp: June 09, 2025, 10:39:54 pm
content: The problem with many of the proposals from those with a less rigorous background in circuit analysis is that they would break backwards compatibility and compatibility (such as it is) with other SPICE programs. It would be helpful if the LTspice software development team could add either a 'preview' nominal direction of current mouse pointer, greyed out before the simulation has been run (as once a suitable analysis has run the current probe mouse pointer takes over) or overlay the symbol from the .asy with a nominal direction of current indicator when placing, moving or dragging two pin parts.However this is unlikely to happen as the LTspice UI is still firmly rooted in the '90s.

author: tggzzz
author_rank: Super Contributor
timestamp: June 09, 2025, 10:49:57 pm
content: Quote from: Zero999 on June 09, 2025, 09:11:17 pmComprehension is more important than repeatability.If you don't understand something, then repeatability merely reinforces the lack of understanding. There are well known jokes based on that point.

author: tggzzz
author_rank: Super Contributor
timestamp: June 09, 2025, 11:02:06 pm
content: Quote from: Ian.M on June 09, 2025, 10:39:54 pmIndeed it is. Arguably it is rooted in its version of a 90s GUI. I'm not going to defend that; it isn't pretty.OTOH, I don't care a foetid dingo's kidney about whether the GUI conforms tothisyear'sfashion(e.g. flat, modern, dark, light), since those change with monotonous regularity and rarely for the better. Over the decades I've learned so many different GUIs that learning another is trivial compared with learning what the application can and can't be expected to do.I do care about about the application's fundamentalcapabilitiesi.e. what it enables me to achieve that I cannot otherwise do. GUIs don't affect that.I leave the eye candy to wannabe web designers; let them obsess over the thickness/colour of lines etc.

author: ledtester
author_rank: Super Contributor
timestamp: June 09, 2025, 11:05:17 pm
content: Quote from: Zero999 on June 09, 2025, 09:11:17 pmIf you place the res.asy file in the same directory as the .asc file it will use it for that .asc file.I just tested this with 24.1.9 on Win11.So you don't have to use it for all schematics and shouldn't have to worry about it getting clobbered when you perform updates.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 10, 2025, 12:02:57 am
content: Quote from: ledtester on June 09, 2025, 11:05:17 pmI asked earlier about adding the new resistor model but also retaining the good old standard one, which was never answered.In other words, add the "new" resistor as a selectable component while leaving the standard, built-in one alone. Any easy way to do this?

author: ledtester
author_rank: Super Contributor
timestamp: June 10, 2025, 12:36:17 am
content: Place the new resistor in your Documents/LTspice directory but call it a new name like "res-with-arrow.asy".In Simulate -> Settings -> Search Paths your Documents/LTspice directory should be listed as the "User files" directory.This directory will be available to all schematics regardless of where the .asc resides.(Note I'm using 24.1.9)The new resistor symbol should be available from the Component selection dialog.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 10, 2025, 01:00:45 am
content: Thanks.I'm on version 4.11 (2011). Guess it's time to upgrade.Hmm;the download pagehas versions for "Windows 10 64-bit and forward" and XP.The XP version might be what i already have.Does anyone know if the Windoze 10 version will work on 7?

author: Zero999
author_rank: Super Contributor
timestamp: June 10, 2025, 07:11:21 am
content: Quote from: tggzzz on June 09, 2025, 10:49:57 pmWhat's your point?I would agree if you're talking about repeating a procedure i.e. mesh analysis, without understanding why, but I'm talking about the behaviour of a piece of software which I just want to behave in a repeatable i.e. consistent manner.Quote from: ledtester on June 10, 2025, 12:36:17 amThe downside is, if you open the file on another computer, which doesn't have your new symbol, it will give an error message and none of the resistors will appear. If you want to post it on forums such as this one, you'll need to attach your new resistor symbol. Either put it with your .asc file in a zip, or append .txt, like I did.

author: Zipdox
author_rank: Regular Contributor
timestamp: June 10, 2025, 05:14:10 pm
content: LTSpice is ancient. That's the main problem. All the keybinds and the user interface follow different conventions than what modern software follows. Other than that it works fine.

author: Zero999
author_rank: Super Contributor
timestamp: June 10, 2025, 05:31:42 pm
content: Quote from: Zipdox on June 10, 2025, 05:14:10 pmFixed. LTSpice's engine is not ancient. It's very modern and up to date. Granted the UI is stuck in the past, although that doesn't bother me.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 10, 2025, 06:38:38 pm
content: So will the Windows 10 ("and forward") version work on Windows 7?I don't want to install it only to find that I have to save and roll back to my ancient but working version.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 10, 2025, 06:50:55 pm
content: Quote from: Analog Kid on June 10, 2025, 06:38:38 pmWhy are you running grandpa's OS in 2025?

author: Analog Kid
author_rank: Super Contributor
timestamp: June 10, 2025, 07:49:40 pm
content: Quote from: joeqsmith on June 10, 2025, 06:50:55 pmBecause I absolutelyhate, detest, deplore, every succeeding version, and it does everything I need it to do.The computah I'm using came with Windows 10 (used) and I couldn't wait to get rid of it.I actually miss Windows XP. And my "scanning station" (film & flatbed scanner, and soundcard connected to stereo) is a Windows 2000 system, since I need SCSI for my film scanner.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 10, 2025, 09:13:33 pm
content: Quote from: Analog Kid on June 10, 2025, 07:49:40 pmOK, Grandpa.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 10, 2025, 09:16:55 pm
content: Quote from: joeqsmith on June 10, 2025, 09:13:33 pmHey, at least you didn't write "OK, boomer".

author: TimFox
author_rank: Super Contributor
timestamp: June 10, 2025, 09:24:29 pm
content: As we say in Chicago, "What goes around, comes around."Your response to my preference for Spice text files:"[Dana Carvey old man voice]Yes, back in the day we had to walk 10 miles each way to the lab through 3 feet of snow. Not only that, but on days when the card punch stopped working, we had to take out our pocket knives and punch the cards by hand. It took a half hour for each card., and the cards were a bloody mess.And we liked it!"

author: Analog Kid
author_rank: Super Contributor
timestamp: June 10, 2025, 09:28:52 pm
content: Quote from: TimFox on June 10, 2025, 09:24:29 pmYes, believe it or not, I actually "sussed out"that that was the exact motivation for Joe's needling here. Now that's a term i would never use in speech.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 11, 2025, 06:16:55 am
content: Quote from: Analog Kid on June 08, 2025, 01:08:05 amI somehow didn't get the Fax back a few years that said that "Henceforth, the 'ideal" resistors that formerly were just a piece of resistance which looked identical whichever terminals you were measuring between will become polarised real devices with an 'inside' where various magic things happened if you didn't put them the right way around."

author: vk6zgo
author_rank: Super Contributor
timestamp: June 11, 2025, 06:38:26 am
content: Quote from: Analog Kid on June 10, 2025, 09:28:52 pmNot quite punched cards, but back in the day, the "powers that be" decreed that staffed TV & Radio Broadcast transmitter sites should send a weekly Telex, reporting all things of interest to the Head Office.To this end, we had a Telex machine & tape reperforator.Typing up the reports with the standard header, & stuff in the body of the report which seldom changed became quite tedious, so we made up short tapes that could be run & incorporated when making the report.The only thing was that these short pieces of tape looked a bit messy lying around the Telex table, so we were agreeably surprised to arrive one morning & find that they were all neatly pinned to the message board.Neat! thought we, & it wasn't till we tried to "run" them that the "oops" factor set in!

author: Zero999
author_rank: Super Contributor
timestamp: June 11, 2025, 07:44:37 am
content: Quote from: Analog Kid on June 10, 2025, 01:00:45 amPerhaps that might explain why the labels in the .asc file you posted in your latch thread are tiny when it's opened in a newer version?You need a recent version of Windoze to run the latest version of LTSpice.It also runs well on Linux, under WINE, a Windoze compatibility layer. I'm like you in I prefer the older versions of Windoze, but I got tired of all the forced upgrading and changes to the GUI, for no reason and often for the worse, so I use PCLinuxOS now, which works well for me. I hardly ever need the command line. I can accomplish most tasks with the GUI.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 11, 2025, 11:40:54 pm
content: Quote from: Zero999 on June 11, 2025, 07:44:37 amWell yeah, but how recent?There's a lot of software that claims to require Windows 10 that runs perfectly well on 7.Anyone know for sure in this case? I'd like to upgrade but don't want to have to go to all the trouble of preserving my current LTSpice installation and rolling back to it if needed. And I sure as hell ain't upgrading to Windoze 10!

author: ledtester
author_rank: Super Contributor
timestamp: June 12, 2025, 01:28:23 am
content: Quote from: Zero999 on June 11, 2025, 07:44:37 amFWIW, I've figure out what in that .asc file is causing the small fonts.The original .asc file (Bipolar latch.asc) may be found in this post:https://www.eevblog.com/forum/projects/help-adapting-a-discrete-toggle-latch-circuit/msg5933824/#msg5933824and all of the WINDOW directives in that file have a last parameter of "0", e.g.:Code:...WINDOW 3 76 121 Left 0...WINDOW 0 0 56 VBottom 0...That parameter appears to be a font size and 0 is the smallest size. A value of "2" is a much more sane value.In addition, the .tran directive is small because of the "Left 0" in this line:Code:TEXT -168 384 Left 0 !.tran 0 4 0 startupAgain, the 0 indicates the font size.The WINDOW directive appears in the .asc file when you move text associated with a symbol - like the component designator or the part number.On my PC the .asc file for a single NPN transistor just after its been added looks like this:Code:Version 4SHEET 1 880 680SYMBOL npn 304 240 R0SYMATTR InstName Q1and after the Q1 designator has been moved it will look like this:Code:Version 4SHEET 1 880 680SYMBOL npn 304 240 R0WINDOW 0 -51 9 Left 2SYMATTR InstName Q1Note that font size 2 is used in the WINDOW directive.Somehow the original Bipolar latch.asc file was generated with font size 0 for the WINDOW directives.Attached is an edited version of the .asc file with the WINDOW directives hand-edited to use font size 2.

author: Zero999
author_rank: Super Contributor
timestamp: June 12, 2025, 07:16:22 am
content: Quote from: Analog Kid on June 11, 2025, 11:40:54 pmTest it. If the installer complains, try extracting the files. There's a tool for extracting all the files for .msi files.If you must use Windows, then you might be able to install WINE under Cygwin, then you'll be able to run the latest version of LTSpice under WINE.https://www.cygwin.com/

author: tooki
author_rank: Super Contributor
timestamp: June 12, 2025, 07:52:39 am
content: Quote from: vk6zgo on June 11, 2025, 06:16:55 amI think the crux of the problem is that while LTspice does ultimately treat a resistor as nonpolarized in terms of simulating the circuit — the circuit works correctly no matter what orientation the resistor has —, the display doesn’t match our intuition. The entire problem is that an ammeterdoeshave polarity, and so when we have it display the current, and we thus (conceptually speaking) enable the ammeter built into the resistor component, the output depends on the ammeter’s polarity. (See the equivalent circuit I drew in an earlier reply.)