Zen Circuit Lab vs Falstad CircuitJS
CircuitJS is the best tool there is for understanding a circuit on paper. Zen Circuit Lab is for building one from parts you can buy, with the mistakes that cost money shown before you make them. Import a Falstad circuit and carry on.
Facts about Falstad CircuitJS are from its public pages and documentation at the time of writing; tell us if something is out of date. Nothing here is a ranking: the two tools are for different jobs.
Side by side
| Zen Circuit Lab | Falstad CircuitJS | |
|---|---|---|
| Price | Free, no account needed (an account only keeps progress across devices) | Free |
| Runs on | Browser, desktop or laptop; lessons work on a phone | Browser, and a downloadable offline version |
| Simulation | Electrical solver (modified nodal analysis) for analog and digital: every voltage and current, parts that heat, trip and burn | Analog and digital simulation with animated current flow; a very large library of circuit elements |
| View | 2D bench with a schematic view; 3D view of the bench, breadboard and perfboard | Schematic only |
| Breadboard | Yes | No |
| Parts | 293 parts modelled on real products, each with a datasheet card | Hundreds of ideal and semi-ideal elements: every passive, diode, transistor, op-amp, logic gate, transmission line |
| Microcontrollers | ESP32 (WROOM, S3), Arduino Uno and Nano, Raspberry Pi Pico 2, LILYGO T-SIM: Arduino C++ sketches run by the lab's own compiler (not cycle-accurate firmware) | No |
| Analog solver | Yes | Yes |
| Solar | Panels, PWM and MPPT controllers modelled on EPEVER, Renogy and Victron, inverters | No |
| Batteries and BMS | Cells and packs with real capacity and curves; BMS boards modelled on real products | Ideal sources |
| Instruments | Multimeter, clamp meter, oscilloscope, function generator, LCR meter, electronic load, logic analyser | Scope on any element, with many views |
| Perfboard and PCB | Perfboard and PCB layout and routing, run on the same solver | No |
| House wiring | House wiring with breakers, RCD, outlets, appliances | Elements only; no breakers, wiring or codes |
| Learning | 193 lessons, 7 courses, 66 guided builds with test sheets | A big library of example circuits |
| Sharing and import | Share links; import Falstad, Wokwi and SPICE; export SPICE | Share links and import/export text; open source |
| Source | Not open source | Open source (GPL) |
Where Falstad CircuitJS is better
- Nothing beats it for seeing how a circuit works: the moving dots show current in every branch at once.
- The widest library of circuit elements, including things like transmission lines and tunnel diodes.
- Open source, tiny, instant, and it has been trusted for decades.
Where Zen Circuit Lab is better
- Real products instead of ideal elements: a TP4056, an EPEVER controller, a Daly BMS, an LM2596 module, each with a datasheet.
- Microcontrollers programmed in C++, and the circuits they drive.
- Breadboard, perfboard and PCB, courses and guided builds with test sheets.
- Falstad files import straight onto the bench, so you can keep both.
Open Zen Circuit LabFree, in your browser, no account needed.