PPolySim OS

Block Diagram Simulator

Wire up sources, gains, integrators and transfer functions on a live canvas and watch the Scope respond — a browser-native alternative to Simulink, with real continuous-time RK4 under the hood.

Block Diagram SimulatorLive

Controls

A browser-native alternative to Simulink. Wire up sources, gains, integrators and transfer functions, then watch the Scope. Feedback loops solve because integrators break the algebraic loop.

Presets

Click a block on the canvas to edit its parameters.

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▶ Run in Python

Data Inspector

IntegratorRK4 (fixed-step)
Step size0.01 s
PresetFirst-order lag
Blocks3
Wires2
State variables1

Effective dynamics

Reading this result: A first-order lag: the output chases the step input, reaching about 63% of the final value after one time constant (τ=2.00 s) and settling to the input amplitude after roughly 5τ ≈ 10.0 s. Increase τ and the rise slows; decrease it and the output snaps to the step almost immediately.

Runs locally in your browser — free forever. Scale to the cloud when reality gets heavy.

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How it works

This is a block-diagram simulator in the spirit of Simulink, running entirely in your browser. Every block carries the semantics of a control-systems primitive: sources (Step, Sine, Constant) generate signals, algebraic blocks (Sum, Gain, Saturation) transform them instantly, and state-holding blocks (Integrator 1/s and first-order Transfer Function 1/(τs+1)) carry memory. On each fixed step the solver evaluates the algebraic blocks in dependency order, then advances every integrator and transfer-function state with a fourth-order Runge–Kutta (RK4) step. Because those state blocks introduce a delay, closed feedback loops are solvable — that is exactly why a PID loop or a mass–spring–damper works — while a pure algebraic loop with no integrator is flagged as unsolvable. Load a preset to see a correct wiring (first-order lag, closed-loop PID, harmonic oscillator, mass–spring–damper), tune the gains and time constants to watch rise, overshoot and settling change in real time, then export the exact system as runnable SciPy Python. It is an alternative to Simulink for learning and quick modelling — not a replacement for a validated production toolchain.

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Frequently asked questions

Is this Simulink alternative block diagram simulator tool really free?
Yes. Block Diagram Simulator runs entirely in your browser using your device's own compute, so local use is free forever. You only pay Compute Tokens if you scale a job to the cloud.
Do I need to install anything?
No. Everything runs client-side in a modern browser — no downloads, no license, no account required to start.
Can I save or share my simulation?
Create a free account to save projects, and use a shareable embed or minted DOI to publish a live, interactive version anywhere.
How accurate are the results?
The solver uses established numerical methods, but results are for research and educational purposes and should be validated against experiment or professional review before you rely on them.