Frequently Asked Questions

General

Saving & Sharing Circuits

Schematic Editor

Simulation

CircuitLab Premium Subscriptions & Billing


What is the pricing for the CircuitLab software?

We believe in the need for a powerful, open platform for accelerating electronics and system design, and we're working on developing that for engineers, academic users, and hobbyists around the world. We believe that pricing plans should be transparent, affordable, and should balance the development of the platform with making sure these tools are within reach of the engineers building the world of the future.

CircuitLab offers a variety of renewing and one-time subscription plans via our Get Started with CircuitLab system.

We also offer a variety of site-wide licenses, floating licenses, and group licenses to make CircuitLab accessible to your entire organization.

CircuitLab Student Edition is available for all current students, staff, and faculty at accredited colleges and universities. (A valid EDU email address required.)

We are pleased to offer significantly discounted subscription accounts for non-commercial hobbyist and enthusiast users.


Do I have to create an account to use CircuitLab?

An account is not required to try the editor and simulation tools. You can simply open any circuit page (see example circuits) and click "Open in editor" to get started.

Creating a CircuitLab account allows you additional time to evaluate our free trial version, and allows you to join the CircuitLab community via our Get Started with CircuitLab.


Does CircuitLab run on Windows, Mac OS X, and Linux?

Yes, yes, and yes. :)

See System Requirements.


Does CircuitLab require a specific web browser?

We recommend Google Chrome or Mozilla Firefox.

See System Requirements.


Does CircuitLab run on tablet or touch-based computers, such as the Apple iPad?

CircuitLab works on the iPad via the Mobile Safari browser. For more details, see our Touch Interface Documentation, or our iPad launch announcement and demo video.


Does CircuitLab run simulations on my computer, or on CircuitLab's servers?

All circuit simulations run in your web browser, on your computer. Your simulations will run faster if you have a faster computer, or if you use a web browser with a faster JavaScript engine.


Does CircuitLab work offline?

CircuitLab can be used offline if it has been installed via the Chrome Web Store. See How do I use CircuitLab Offline?


Does CircuitLab require an internet connection to function?

No. If you are using the Chrome browser, and you have installed the CircuitLab Chrome application, then CircuitLab can work without an internet connection. To install the CircuitLab Chrome App go to our app on the Chrome Web Store and click Add To Chrome.

For other browsers, an internet connection is required to run CircuitLab.


How do I use CircuitLab offline?

To enable CircuitLab for use offline:

  1. Log into CircuitLab.
  2. Install CircuitLab from the Chrome Web Store.
  3. Launch CircuitLab at least once while online.
  4. CircuitLab is now ready for use while offline. Go to the Apps tab on your Chrome Web Browser to launch CircuitLab.
  5. Any circuits you make or modify while offline will be synced with your workbench when you come back online.


Are all of CircuitLab's features available offline?

No, but most of them are. While offline you can create, open, save, edit, and simulate your circuits. The only thing you can't do is render the schematics of your circuit (i.e Export to PDF, SVG, etc...). When you come back online though, CircuitLab will sync the changes you have made to your workbench and you will be able to export your schematics.


Yes! You are encouraged to make your circuit public and link directly to the circuit page. This allows people to view your circuit, your notes, make comments (if you choose to enable them), and edit and run simulations with the parameters you've saved.


Yes! We have multiple screenshot sizes available. After you make your circuit public, look for the "Schematic PNGs" section under "Link & Share" on your circuit page.


Can I copy a CircuitLab-generated schematic image and host it on my own blog / webserver / site?

Yes! Of course, we encourage you to also link to the circuit page so your readers can directly jump into the editor and play with your circuit in CircuitLab.


If I open someone else's circuit, and save it, will it overwrite that person's circuit?

No. If you open someone else's circuit, and then save, you will save a copy of that circuit to your own account.


Can I import my schematics from another tool into CircuitLab?

Not at this time.


Can I export my CircuitLab schematics out to another tool?

Not at this time.


How do I add circuit elements to my schematic?

Click once on the item in the Build Box, and then move your mouse to an empty area on the schematic grid and click to place the item. See Build Mode.


Can I use IEC/European style resistor symbols?

Yes. You can edit individual resistors/inductors/potentiometers, or you can choose a default style for all new circuits drawn in your CircuitLab account.


Can I draw text, boxes, etc. over my schematic to add information or keep it organized?

Yes. In the Build Box, scroll down to "Annotation Tools".


How do I set the parameters of a component?

Once a component is placed on the schematic (see How do I add circuit elements to my schematic?), simply double-click it while in Build Mode to bring up a parameter editor box. See Build Mode.


How can I hide particular component text labels if I don't want them to be visible in my schematic?

If you are using the schematic editor for drawing purposes only, and for example want to show a resistor with only its name "R1" but no value, simply edit the parameters of that resistor and leave the resistance field blank. This circuit will no longer simulate, but will display as you like.

For parts like transistors with part models, to hide the part number, you need to de-associate the circuit element instance from the model using the "Edit Individual Parameters" option in the parameter box.


How do I access schematic PNGs and PDFs?

Schematic PNGs and PDFs are generated and hosted on the CircuitLab servers, and are only available after saving your circuit. Once you save, you'll find PNGs and a "Print PDF" button on the circuit page.

A CircuitLab account is required to save and to generate PNGs and PDFs. See Do I have to create an account to use CircuitLab?


Are there any node or component count limits for the schematic editor?

Not at this time.

Currently, the bounds of the schematic drawing area are large but not unlimited.


How can I add a custom IC or connector pin-out to my schematic?

Within the Build Box, scroll down to "Annotation Tools" and find the "Custom Part" button. This will let you specify a number of pins, and name individual pins as desired.

The resulting component is for display purposes only, and will be treated as completely open-circuit from the perspective of circuit simulation.


Are there any node or component count limits for simulation?

Not at this time.

In practice, the limitations of the simulator greatly depend on your circuit, the number of components, and particularly the number of non-linear components like transistors and the topology of how those non-linear components interact with each other. Furthermore, even large circuits should not "crash" the simulator until computer memory limits are reached -- they will just simulate quite slowly. If you're willing to wait for the answers, CircuitLab will try to produce them!


What kinds of expressions can I use when setting numerical parameters?

Basic mathematical operations are supported.

For example, if you have a 100 Ω resistor and a capacitor forming a low-pass or high-pass filter, and you want the corner frequency to be at 5000 Hz, you could use the parameter box to specify the capacitor's capacitance as "1/(2*PI*5000*100)", and the simulator will properly interpret that as approximately 318 nF.

A subset of Expressions for Plotting are available for setting component parameters in the simulator.


What kinds of expressions can I evaluate and plot?

See Expressions.


What assumptions are made in various component models?

See Circuit Elements.


How can I model my favorite BJT, MOSFET, Diode, LED, op-amp, etc. part numbers?

We have some documentation on component models -- see Circuit Elements.

Every parameter has units shown in the parameter box, and additionally has a short description shown at the bottom of the parameter box when that field is active. Combining this information with existing part datasheets and SPICE models available online should allow advanced users to approximate device behavior.

One of the great things about CircuitLab is that it's quite easy to build, for example, a DC Sweep setup to generate the characteristic curves of a BJT, MOSFET, or Diode. Then, you can tweak your model parameters until your CircuitLab-generated curves closely approximate the datasheet curves!

We hope to make adding custom device models easier in the future. Please also let us know about specific part numbers you love on the forums, as we'd like to maintain a useful initial list of component models.


How can I save my custom part settings for re-use on another schematic?

There is no way to save a custom part model at this time, but for now, you can copy and paste an item from one browser window to another and you'll find that all of its parameters will be copied and pasted along with it!


Are arbitrary behavioral sources supported?

Arbitrary behavioral voltage and current sources are currently supported but experimental within the CircuitLab simulator. These are powerful tools, but may cause convergence issues.

To learn more, read about Behavioral Sources and Expressions.


Are piecewise linear (PWL) and piecewise step (PWS) sources supported?

PWL, PWS, PWLREPEAT, and PWSREPEAT functions are available to construct arbitrary voltage and current input waveforms. For example, a voltage source with 'V' parameter set to "PWL(0,0,1,5,4,5,5,0)" will generate a pulse with one-second edges.

To learn more, read about Behavioral Sources and Expressions.


Why won't my circuit simulate?

Do you have a ground terminal? Does each disjoint subcircuit have a ground terminal? Or equivalently, does every node (whether named or not) have some (DC) path to ground?

Are there any places where voltage sources are shorted out? Are any voltage sources connected directly across another voltage source?

Are any current sources left open-circuit? Are there any places where current sources won't be able to sink or source the specified current?

Do multiple circuit elements have the same name (two "R1"'s, for example)?

Do all elements have reasonable and parseable values for all parameters?

Are there multiple digital outputs fighting to drive the same output node?


Why does the DC solver say "Unable to get solution"?

This generally indicates a structural problem with your circuit that the simulator is unable to resolve. When possible, simplify your circuit and try to isolate the parts that make the simulation fail.

See Why won't my circuit simulate?.


Why does the frequency-domain solver say "Operating point solution failed. Aborting."?

The frequency-domain solver creates a linearized, small-signal model of the analog system. The linearization occurs relative to the DC operating point of the circuit. If the simulator is unable to get a DC solution to the circuit, it has no model to linearize.

Before running a frequency-domain simulation, always make sure the DC simulation works and that all elements are properly biased. See Frequency-domain Simulation.

To fix the DC operating point solution, see Why won't my circuit simulate? and Why does the DC solver say "Unable to get solution"?.


Why does the simulator say "Warning: nonlinear convergence failed. Be suspicious of results."?

While the simulator was able to find a circuit solution, it found one that it wasn't "happy with" -- either because the equations did not converge to an adequate level of precision, or because the solution was oscillatory or chaotic. This can happen in a variety of situations, particularly involving high-gain circuits in feedback configurations. You should re-check all transistor connections, make sure adequate paths for base/gate current are provided, all transistors are properly oriented, etc.

This warning should be viewed as telling you that most likely, the simulator's results for this circuit are not correct. If you see this in DC solver mode, be aware that the same warning effectively applies for all other modes as well!


Can I set the initial voltage across a capacitor, or the initial current through an inductor?

At this time, there is no explicit way to tag a capacitor or inductor with an initial charge/voltage or flux/current.

However, the same effect can generally be achieved using a voltage or current source plus a time-controlled switch (switching at t=0).


Why does the time-domain simulation show large, unrealistic spikes in voltages or currents?

As in any circuit simulator, the time-domain simulation of a circuit involves making approximations of the continuous-time equations of the circuit to be discrete-time equations usable by the computer. Sometimes, spikes you'll see correspond to actual physical effects (such as the voltage spike when rapidly switching current through an inductive load). In other cases, they correspond to errors introduced because of the nature of circuit simulation, particularly when adjacent to a non-linear transition like a switch/transistor changing state -- a "glitch in the matrix," if you will. Changing the simulation timestep may alleviate these conditions in some circumstances. In any case, these things happen, and the user must apply good judgment to decide whether the effect is possibly real or not.


Can I use CircuitLab for commercial activities?

Commercial activities include using the software in your employment as an employee or contractor, or any other activity with the intent of commercial gain.

Subscribers of our "CircuitLab Pro" and "CircuitLab Platinum" plans include licensing authorizing use of the software for commercial activities. These plans are available on our CircuitLab for Professionals upgrade page. Limited commercial use of the free trial version of CircuitLab is authorized in order to evaluate the software for purchase. Otherwise, commercial use is prohibited.


Is annual billing available?

Yes, our annual subscription plans offer significant discounts over our monthly plans. You can find these via our Get Started with CircuitLab system.


Are group discounts available for my company?

We will work with your organization to provide a CircuitLab premium subscription for every engineer. Please contact us for details.


Are discounts available for academic users?

We now offer the CircuitLab Student Edition free-of-charge to students, staff, and faculty of accredited colleges and universities. This is available via our Get Started with CircuitLab system.


Can I pay by credit card, wire transfer, paper check, or purchase order?

Credit and debit cards are accepted instantly via our online Get Started with CircuitLab system. Other payment methods require manual processing and may be available for orders over $1,000. Please contact us for details.

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