@othernick,

Through no fault of your own, your simulations is not showing what should actually be happening in your circuit.

It might be what you think you expect but it is very definitely not correct to the simulation schematic that you have drawn!

In trying to answer your question it has uncovered a major bug in EasyEDA simulation.

Please stop working on your simulation - and therefore the PCB that you wish to create from it - until either:

1. the issues identified in the following Bug Report have been resolved or;
2. you have read, understood and redrawn your schematic in accordance with, the recommendations at the end of the Bug Report below:

https://easyeda.com/forum/topic/Problems-with-VCC-vs-5V-netflags-in-simulations-654c82ac3a9a4aad98156b6e59da1991

Hi!

Are you feeding a known DC voltage to V2? If so, then do it with a voltage regulator.

For example:

You want to insert +3.3V into V2. Then you just build a voltage regulator circuit that inputs 5V from your power supply and outputs 3.3V.

Regards,

Markus Virtanen
HW / Electronics Designer

@othernick, @markus_jidoka,

Using a regulator is one option.

Another cheaper option us simply to set the required potential divider ratio and connecting it between the +5V rail and ground

I am also a bit puzzled by whether your choice to connect V1 from VCC to the input is guided by your original design requirements or by the simple fact that you found it was necessary to do that to get your (broken) simulation to give you the output you expected.

To clarify:

"Another cheaper option is simply to set the required potential divider ratio and connecting it between the +5V rail and ground."

That assumes that your 5V supply is from a regulator and so is controlled to something like a +/-3% or better tolerance.

@Markus_ee Thank you for your suggestion, I will try the voltage regulator, I would have 5V there.

@andyfierman
The PCB was ordered about two weeks ago (when I got the desired simulation results) and it is expected to arrive in the next days. I am very confused by your comment: "it is very definitely not correct to the simulation schematic that you have drawn". Would you please try and be more specific? An example of what I would get instead would help, the link you sent is not enough for me to understand what's going on. I couldn't be aware of the "bug of the system" you mentioned, as I mainly work offline on the project, so how does it woow if my system won't give me the results that I simulated? Will I get a refund?

To VCC was connected to V1 to simulate an external sinusoidal input I will have (for AC).

Important to mention that in the schematic I have actually printed I have substituted vcc+v1 and vcc+v2 by vcc supply flag only and inserted a pin header to connect to external sources, like I did now here to show you https://easyeda.com/editor#mode=sim,id=fb3873960883413b855ad2eb1bfb2f15|08559fc18e1c4d448e55baf80f489ce1 . (similarly for other power sources)

@g.lat,

Until you correct the power supply connections (or EasyEDA fix the voltage source auto-assignment bugs) as I have described above and clarified what voltage the VCC net should be, you are wasting your time because as I have explained: your simulation is not showing you what the circuit actually does.

In this project:,

https://oshwlab.com/andyfierman/lm358-v-divider



Sheet 1 is your simulation as originally given at the start of this topic.

Sheet 2 is the simulation with the power supplies corrected to avoid the EasyEDA auto-assignment bugs and assuming that the supply you have labelled as VCC should be +5V.

If you run them you will see that the simulation results are not the same.

Your original sim:

which gives the following WaveForm results:

This is the same circuit but with the voltage sources for the supply rails explicitly (i.e. manually) assigned:

which gives the following WaveForm results:

If you do File > Export Netlist > LTspice for This Sheet... and compare them, you will see that there is only one (auto-assigned, -5V) voltage source in the netlist for sheet 1 whereas there are three correctly manually assigned for sheet 2.

The relevant part of your original netlist showing only a single -5V supply with the positive supplies of the opamps connected to a net called +5V but which has no voltage source supplying it:

The same part of the netlist for the corrected circuit showing all three supplies in place:

Apologies, this is the right link https://easyeda.com/editor#id=e7732ac4929f4f55b93c384b814b52f5

OK, thank you for the explanation. So it won't work with the schematic I showed now either? Is there a procedure for this now? Will I get a refund based on what happened?

@g.lat,

Your new link is not public.

Please see:

https://easyeda.com/forum/topic/How-to-make-a-Project-public-and-share-the-links-to-it-9f006513b84b412580910905b0281d20

https://easyeda.com/editor#mode=sim,id=08559fc18e1c4d448e55baf80f489ce1

@g.lat,

This simulation schematic has also ended up wrong due to the incorrectly auto-assigned supplies.

You have however not specified the voltages that you expect to be applied to VCC and VCC2 so it is not clear what you expected the simulation output to be anyway.

Also, neither this or the earlier schematics would appear to be the one from which you created the PCB which you have submitted for fabrication. Since that schematic has not been made public, it is not possible to comment on the status of the PCBs you will receive with respect to the schematic from which they were created.

It is not clear if your PCB design was completed before or after you started your simulation schematics.

@g.lat,

Two of your earlier posts arrived while I was working on the example to show you so I missed your questions and further the information in them.

I understand that you created a PCB based on the results of your simulations and that it was submitted for fabrication about a week before you posted about your simulation here.

" I couldn't be aware of the "bug of the system" you mentioned, as I mainly work offline on the project, so how does it woow if my system won't give me the results that I simulated?"

Working on or offline makes no difference.

The error in the netlist is a result of the EasyEDA auto-supply assignment process and due to the bugs in it, it would not detect - and so you would not have seen - any indications or warnings about it anyway.

"Will I get a refund based on what happened?"

Once we can clarify your original design aims and whether the schematic that you converted to PCB and then submitted for fabrication, will meet those design aims then that will be a question for EasyEDA Support. At the moment it is not possible to decide if the physical board will "work" in your application because you have not sufficiently specified what that application is. All we have established is that the simulation schematic does not give you the results that you expect which is not the same thing.

"To VCC was connected to V1 to simulate an external sinusoidal input I will have (for AC)."

Sorry but I still don't understand what you mean here because you have not specified or described the external circuitry, signals and supplies to which this board is to be connected clearly enough.

@andyfierman I have totally run the simulations before going through the order, many times, to make sure to get the same result. The only thing I have done on the sketch I simulated before converting to PCB was substituting the sources with VCC, because I am going to connect externally anyway. Isn't this correct? Thanks for sharing a way to simulate the bug, I will use it now to obtain what I want. But is there a way to overcome it and get instead the result I had? Because in that case I could order different parts (resistors/op amps) and still use that PCB.

@g.lat,

"The only thing I have done on the sketch I simulated before converting to PCB was substituting the sources with VCC"

Not sure that's true because when I open your project:

https://easyeda.com/g.lat/voltage-divider-x2inverting-amp_copy



and try to convert it to PCB it is missing the LM358 footprints:

So it seems that the schamatic that you converted to PCB is not the one that you have made public.

Maybe you are not sure, but I am, 100% that it is not in the way you are describing the problem now. I have specified above that this https://easyeda.com/g.lat/voltage-divider-x2inverting-amp_copy was an example to show you the way I substituted VCC+V1 and VCC+V2 when converting the PCB, not even the pin header is the right one over there.
I can't share my project as public, so I won't. You are basically saying that I can't be refunded because maybe my PCB won't work for other reasons, is it? But this doesn't matter, because in that case I wouldn't have asked for a refund. What actually matters is that I have printed my PCB based on the results that I got from this https://easyeda.com/editor#mode=sim,id=fb3873960883413b855ad2eb1bfb2f15 simulation and that I won't have the expected results on that part because of the bug of your system. I think it would be more than fair that either you make sure I will be refunded, or at least you suggest here a solution to "overcome the bug" providing a way that would give me the solution I was expecting. And I didn't even ask to charge on you the extra parts I would need in this last mentioned case. I am not asking anything more than fair here, there was a disservice based on which I would be the one losing out. And this is not right.

I really appreciate your help and I also understand your position. But there must be a solution here for the the issue I experienced.

@g.lat,

No one has said that you cannot get a refund.

What I have pointed out is that due to a bug in EasyEDA,  the simulation results you obtained - and from which you then decided that you had a schematic suitable to convert to a PCB - are incorrect. The reason they are incorrect is because the spice netlist generated from the schematic and used in the simulation is different from what the schematic shows due to the incorrect auto-assignment of the various supply voltage sources.

I have also said that before starting a discussion with EasyEDA Support about the possibility of a refund, is that you need to find out if the boards that you have already ordered will or will not work in your application.

In order to do that you need to state exactly:

1. What the voltages are that are applied to the netflags that you have most recently labelled as VCC1 and VCC2;
2. What the signal source is (is it really a voltage source or is it actually more like a current source?);
3. How it is connected to the input of the amplifier chain (is it really connected between  one of the VCCs and the amplifier input?);
4. Verify that the simulation results that you obtained from the original (broken) simulation represent what you actually require from the inputs and supplies you specify above;

If you do that then I  can run the corrected sim schematic and try to recalculate the resistor values to generate the required output from your specified inputs.

I understand that you do not want to make the schematic public but what would be helpful would be if you add me to your team so I can see it privately then have a clear picture of what sources and loads you are actually dealing with.

Then, after that, if your boards cannot be made to give the required outputs with a few resistor changes then we can present the results in support of your case in requesting a refund or a set of replacement boards.

OK, I will DM you the details and add you on the project. Thanks @andyfierman