+ Velxio 2.5
+
+ Arduino meets SPICE in your browser
+
+ + Real-time analog circuit simulation via ngspice-WASM, wired to Arduino, ESP32, and + Raspberry Pi Pico. Resistors, capacitors, op-amps, transistors, live ammeters and + voltmeters — co-simulated with your firmware. Free, open-source, no install. +
+From digital-only to full circuit emulation
++ Velxio 2.0 simulated your firmware perfectly. Velxio 2.5 simulates the circuit around + it — with the same ngspice engine used by professional EDA tools, running entirely in + your browser tab. +
+ +Not a linear approximation
++ Velxio solves the full Modified Nodal Analysis every tick. Non-linear devices — + diodes, BJTs, MOSFETs, op-amps with saturation — behave like the real thing, not + like textbook idealisations. +
+Real firmware. Real circuit. Same canvas.
+
+ GPIO pins drive SPICE nets as voltage sources. ADC inputs read solved node
+ voltages. analogRead() returns what the circuit actually produces —
+ not a simulated shortcut.
+
100% browser, 100% offline
++ ngspice compiled to WebAssembly via the open-source eecircuit-engine. No server, no + cloud, no account. Works offline after the first load. Your circuits never leave + your machine. +
+100+ SPICE-accurate components
++ A complete electronics catalogue — passives, semiconductors, logic, instruments — + every one of them modelled with real ngspice device cards, not behavioural stand-ins. +
+ +{section.title}
+-
+ {section.items.map((item) => (
+
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Hybrid digital + analog co-simulation
++ Most browser simulators run either your firmware OR a circuit — never both together. + Velxio 2.5 solves them on the same clock. +
+Drive a motor from an Arduino pin
++ Pin HIGH → MOSFET gate → drain current through a real inductive load → back-EMF + through a flyback diode. All SPICE-solved. Scope the gate and drain voltages side + by side. +
+Read a sensor through a real op-amp
+
+ Photodiode → transimpedance op-amp → ADC. Adjust the lux slider and watch
+ analogRead() respond through the actual amplifier stage — saturation,
+ slew rate, and all.
+
Debug with live instruments
++ Drop an ammeter between any two nodes, a voltmeter on any net. The oscilloscope + captures digital pins and analog nodes together. No "what if" — just + measurements. +
+40 new analog & hybrid examples
++ Pre-wired circuits you can open in one click — from textbook fundamentals to realistic + Arduino+analog systems. +
+Fundamentals
++ Voltage divider, RC low-pass filter, RC high-pass filter, LR circuit, capacitor + charging, RLC resonance, Wheatstone bridge. +
+Diodes & rectifiers
++ Half-wave rectifier, full-wave bridge rectifier, Zener regulator, clamper, + clipper, voltage doubler. +
+Op-amp circuits
++ Inverting amplifier, non-inverting amplifier, summing amp, differential amp, + integrator, differentiator, Schmitt trigger, comparator. +
+Transistor circuits
++ Common-emitter amplifier, transistor switch, Darlington pair, MOSFET driver, H-bridge, + current mirror. +
+Arduino + analog
++ PWM-driven LED with RC smoothing, Arduino-controlled MOSFET motor driver, opto-isolated + relay, photodiode + op-amp + ADC pipeline. +
+Sensors
++ NTC thermistor bridge, photoresistor light meter, photodiode transimpedance, + potentiometer dimmer, flame detector. +
+The outcome
++ Velxio 2.5 closes the loop between firmware and hardware: the same tool that runs your + sketch now solves the circuit around it. +
+Teach & learn electronics
++ A free, browser-based SPICE playground for students — with the added benefit of + driving real microcontroller firmware. No license, no install, no lab booking. +
+Prototype before soldering
++ Validate analog front-ends, power stages, and sensor pipelines end-to-end before + you order a single part. The scope and DMM are already on the bench. +
+Still 100% open source
++ AGPL-3.0 on GitHub. Built on ngspice, eecircuit-engine, avr8js, rp2040js, QEMU, + and wokwi-elements. Fork it, host it, extend it. +
+Built on open-source
++ Velxio 2.5 stands on the shoulders of decades of electronics tooling. Huge thanks to + the maintainers of every project below. +
+ngspice
+The open-source SPICE circuit simulator — powers every analog solve in Velxio 2.5
+eecircuit-engine
+ngspice compiled to WebAssembly — the bridge that makes browser SPICE possible
+avr8js
+AVR8 CPU emulator in JavaScript — Arduino Uno, Nano, Mega, ATtiny85
+rp2040js
+RP2040 emulator — Raspberry Pi Pico and Pico W
+wokwi-elements
+Web Components for electronic parts — LEDs, buttons, sensors, displays
+Velxio
+This project — free, open-source Arduino + SPICE co-simulator
+Try Velxio 2.5 now
+Open the editor and start simulating — firmware and analog circuit, same canvas, zero setup.
+ trackClickCTA('velxio-v2-5', '/editor')} + > + Launch Simulator + + + + +