PRODUCT OVERVIEW

Circuit simulation capabilities

resistor.dev is a browser-based workspace for building circuits, observing their behavior and learning how component choices affect the result.

Open Circuit Lab

AVAILABLE NOW

Build, simulate and inspect

Visual circuit editor

Place components, wire electrical nodes, save circuits locally or to your account, and start from curated examples.

Measurements and waveforms

Inspect voltage, current and power on components and use a four-channel oscilloscope for signals over time.

Two simulation engines

Use Fast educational mode for immediate experiments, or Engineering accuracy mode powered by ngspice in WebAssembly.

SPICE model import

Import supported .model cards and simple .subckt models, assign them to a compatible component and map pins when necessary.

Engineering tools

Use the multimeter, current clamp, parameter sweep, tolerance analysis, thermal estimates and UART, I²C or SPI decoding.

Named electrical nets

Name connection points IN, OUT, VCC or GND. Equal names connect without a drawn wire; GND is the common reference. Block names stay local. Names follow measurements, recorded signals, breadboard connections and KiCad export.

Circuit checks before running

Review disconnected terminals, reference ground, floating networks, source shorts and model compatibility. Jump to a component or wire from the report. Errors block startup; warnings can be accepted for intentional configurations.

Portable simulation projects

Export a saved SPICE calculation as one .resistor file containing its circuit, embedded models, original results and oscilloscope settings. Import it on another device and inspect it without recalculating.

From simulation to hardware

Create a BOM, use the breadboard view and export a KiCad netlist as a starting point for a real design.

MODELS AND LIMITS

Choose the model that matches the question

Fast educational mode is designed to make circuit behavior understandable and immediate. It includes illustrative component limits and selected effects such as battery sag and incandescent-lamp heating.

Engineering accuracy mode follows the imported SPICE model. For a transistor with an assigned model, its SPICE parameters control the simulation; the generic educational gain field does not override it. Pin order can be inferred from a direct transistor subcircuit card, and can be corrected manually when the model documentation requires it.

ENGINEERING ROADMAP

Analyses in development

Transient analysis (.tran) is available in Engineering accuracy mode. The following analyses are planned and are not presented as available today:

Operating point (.op) — DC voltages and currents for checking a transistor bias point.
DC sweep (.dc) — output response while a source or parameter changes.
AC, transfer function and poles/zeros — frequency response, gain, phase and stability work.
Noise, sensitivity and distortion — identify performance limits and the parameters that matter most.
Temperature sweep — compare a circuit across specified ambient temperatures.

Start with an example, then change one thing at a time

Use the learning pages to open a relevant circuit, observe the baseline, adjust a component value and compare the measurements. This makes the assumptions behind a simulation visible.

Explore learning resources