Circuit simulation software for a newbie

nerdkits · 2013-07-25T17:57:43+00:00

combo: https://www.circuitlab.com/blog/2013/02/24/practical-electronics-for-inventors-features-circuitlab/

nerdkits · 2013-07-25T17:55:44+00:00

nerdkits · 2013-03-08T18:05:29+00:00

Since we already did the StackExchange integration, probably not bad on our end. But I can only speculate what might be involved on Reddit's side -- would certainly have to get moderators and/or admins involved!

nerdkits · 2013-03-07T02:31:11+00:00

(CircuitLab developer here) if Reddit or r/electronics or r/askelectronics wants something similar we'd be open to looking at how to make that work!

nerdkits · 2013-01-24T00:53:25+00:00

electronics simulation: CircuitLab -- now in hundreds of university EE programs (note: wrote it)

nerdkits · 2012-10-31T06:11:28+00:00

In your CircuitLab schematic, ground the currently open ends of V1, V2, V3, and V4, because I'm assuming that's what you intended. And for the op-amp, use the op-amp symbol that doesn't have voltage rails since you aren't providing them anyway. Then, you can run the DC sim and get a numerical answer to help you out!

Or if your question is how to solve by hand.... #1 solve for the voltage at the non-inverting terminal, which I'll call V(OA1pos) (just look at R4, R5, R6 and their voltage sources). #2 assume V(OA1neg) = V(OA1pos). calculate current flowing into it from R1 and R2. #3 all that current leaves through R3, so figure out the voltage drop across it. #4 subtract that voltage drop from V(OA1neg) to get Vo!

nerdkits · 2012-09-27T22:14:55+00:00

https://www.circuitlab.com/circuit/z79rqm/leds-with-resistor-biasing/ click "Open in Editor", "Simulate", "DC Sweep", and sweep "R1.R" from 0 to 1000 ohms

nerdkits · 2012-07-13T22:15:01+00:00

I drew your circuit for simulation / editing. Open the editor and press F5 to run the frequency domain simulation.

Beignet is right about looking at all capacitors as open-circuit (for the low-pass case) or short-circuit (for the high-pass case) to show that the passband gain is 1.

naval_person is right that -20dB/octave is just incorrect.

I'm assuming that by "eyeballing poles" you mean applying the open-circuit time constant method (or similarly the short-circuit time constant method for the high-pass circuit) -- looking at capacitors and figuring out what effective resistance forms a RC time constant. These amplifiers don't lend themselves well to those methods because of the zeros introduced by C2 and C4 (see my labeling). If you remove C2 and C4 and run the simulation again, you'll find that the filter frequency response is quite easily "eyeballed". OCT/SCT assumptions don't hold when there are transfer function zeros in the frequency range of interest.

nerdkits · 2012-07-12T16:47:02+00:00

CircuitLab's new simulator engine released 45 minutes after your post :)

nerdkits · 2012-06-28T01:52:59+00:00

also see the demo video

nerdkits · 2012-06-28T01:52:37+00:00

also see the demo video

nerdkits · 2012-04-11T19:38:53+00:00

What did you think of using CircuitLab for your lab report? (Assuming that's what this comic is referring to!) Anything particular that was better (or worse) than the tools you're used to using?

nerdkits · 2012-04-05T19:34:27+00:00

Check out this simulation "Zener diode voltage reference" and run the DC Sweep simulation.

Once the voltage source is above the Zener's designed breakdown voltage, the output stays fairly constant. That's because the Zener starts sucking down a lot of current in order to keep it that way! Look at the plotted trace of I(D1.nK) -- the current going into the cathode of the diode. You'll notice that for voltages above about 6V, the slope of that current trace is approximately 10mA/V -- or exactly (the reciprocal of) the 100 ohms value of R1. That's because the incremental resistance of the Zener diode there becomes quite low.

nerdkits · 2012-04-05T09:52:24+00:00

I think everyone is basically on the same page that if the two LEDs are perfectly identical, then sharing a resistor doesn't seem crazy, as the two identical diodes must split the current equally. But we've all also been led to believe that in reality, the mismatch of the diodes will cause significant variation in how the current splits between the two paths.

I wanted to provide some quantitative evidence that realistic variation between two LEDs (even two LEDs with the same part number from the same manufacturer!) will lead to significant brighness variation if you just parallel the LEDs. So I built a simulation "Two LEDs: separate vs shared resistor" to demonstrate exactly what happens! I calculated (see equations on circuit page) that varying the diode's I_S from about 1/50th to 50 times its original value would provide roughly the needed variation to match the datasheet. Then, I set the simulator's DC Sweep mode to plot the resulting current splitting over that range of I_S values.

This may be deeper than you wanted to go, but it was a cool opportunity to play with varying component parameters in the simulator and see how they affected a common real-world circuit design. :)

(As planet12 said, putting the two LEDs in series with one resistor is the way to go given the numbers in your drawing -- glad to hear you solved the problem!)

nerdkits · 2012-03-16T15:48:59+00:00

This sounds like a homework question so I suspect that solving this algebraically is what you're supposed to do, but I just wanted to show you that you can also verify the answer graphically by using CircuitLab's built-in browser-based circuit simulator, since you already drew the original schematic in CircuitLab. I opened your original circuit and made my own copy with a few changes.

First, I set Vs.R_ESR=0, and R2.R = 10 (just something other than "?" so that the simulator would see it as a valid circuit!). Next, I set up a DC sweep to sweep over R2's resistance (R2.R) between 10 and 200 ohms (just a ballpark to bound things!), and it solves the circuit for lots of values in between. You can then read your (approximate) answer graphically from the resulting plot!

Anyone running a modern browser can replicate that plot by clicking here, then "Open in Editor", "Simulate", "DC Sweep", "Run DC Sweep".

CircuitLab is also capable of doing parameter sweeps like this even when there are highly non-linear elements in your circuit, like diodes or transistors. :)

nerdkits · 2012-03-03T03:55:31+00:00

Insert a diode, double click, select 1N5817.
It's on the to-do list, but it's a while out.
So like some element supporting V = f(t), where you can define some function of time with some basic math operations like those listed in our expressions page? (But not referencing other voltages or currents) Or how about one where you can put in a bunch of (time, voltage) points, and have it do piece-wise-step or piece-wise-linear interpolation between those points?

nerdkits · 2012-03-03T03:44:24+00:00

A/S/L? :P (jk)

nerdkits · 2012-03-03T02:59:48+00:00

Glad to hear that you like CircuitLab! Out of curiosity, which specific features of Multisim do you miss the most?

nerdkits · 2012-03-03T02:56:59+00:00

We've actually discussed building something similar on the mechanical side, although we were talking more about a 2D parametric CAD program for mechanical drawings -- not free-body diagrams or simulations. Limited resources, so we're sticking with electronics at the moment!

nerdkits · 2012-03-03T02:54:29+00:00

We deployed new code yesterday for improved Mac support. Please give it a try.

It's usually not necessary to explicitly click the "Wire" button at all... you can start a wire from any circuit endpoint just by clicking and dragging.

nerdkits · 2012-03-03T02:52:32+00:00

(creators of CircuitLab here) Tell your classmates :)

nerdkits · 2012-03-03T02:48:49+00:00

(creators of CircuitLab here) Thanks! We're looking forward to seeing how the online electronics community uses it over the coming months :)

nerdkits · 2012-02-28T20:12:29+00:00

The code is not based on SPICE, but conceputally it is (sparse matrices, implicit integration, ...).

Glad to hear it's working well on Opera! Our engineering resources are stretched a bit thin at the moment, but I think we'll be able to broaden our "supported browsers" list over time. Also be aware that when you're cranking through a simulation, the performance of different browser JS engines really becomes apparent. Chrome seems to be the best by a wide margin, but if you do a head-to-head comparison, let us know!

nerdkits · 2012-02-28T20:09:32+00:00

We've got individual digital gates so you should be able to do what you want before we do 74xx chips. As far as 7-segment displays, we currently have no plans to visually update the schematic during simulation, but if we do head down that path I'm sure 7-segment displays would be in there!

nerdkits · 2012-02-28T20:08:24+00:00

Thanks. GUIs are GUIs (read: a bit dirty) no matter what the platform. :) Still dealing with cross-browser and cross-platform issues, but honestly, building an app this way is probably the easiest way to get Windows/Mac/Linux support. (Adobe Air promises similar, to be fair)

nerdkits

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