Build Your Own Custom Chips
in C, Rust or AssemblyScript
Define your own integrated circuits with the Wokwi-compatible Custom Chips API. Write the chip in C, Rust, or AssemblyScript; Velxio compiles it to WebAssembly and runs it on the canvas like any other component — driven by Arduino, ESP32, or RP2040 firmware.
Wokwi-compatible API · Free & open-source · WASM-powered, runs in your browser
What can you build?
Custom chips fill the gaps between built-in components. If a real IC isn't on the shelf, build a behavioural model and your firmware never knows the difference.
Sensor stand-ins
Mock a temperature, pressure, or IMU sensor that responds over I²C — useful when you don't have the part yet but want to develop the firmware.
Protocol bridges
Build a UART-to-I²C bridge, an SPI shift register, a digital-to-analog wrapper, or a custom level translator.
Custom logic
Glue logic, state machines, address decoders, debouncers — anything you'd otherwise wire up with discrete gates.
Behavioural ICs
Re-create the externally-visible behaviour of a real IC (a 7-segment driver, a stepper controller) without simulating its analog internals.
Test fixtures
Inject signals on schedule, capture pin transitions, validate firmware against expected pin-level behaviour.
Reusable libraries
Save the chip to your account, import it into other projects, share with the community.
What the API gives you
The Velxio Custom Chips runtime is fully Wokwi-compatible, with extras for the SPICE and multi-board environment.
Pin I/O
Read pin state, write digital high/low, configure pull-ups, react to edges with pin-watch callbacks.
Attributes
Read user-configurable chip attributes from the property panel — values, strings, numbers — and re-read on change.
Timers
Schedule callbacks at microsecond resolution. The runtime fires them aligned to the simulator clock.
I²C bus
Connect to any wire that's part of an I²C bus, respond to start/stop conditions, acknowledge addresses, send / receive bytes.
SPI bus
Bidirectional SPI with chip-select handling. Implement a shift register, an SPI memory, or a sensor with one byte-stream callback.
WASI shim
A small WASI shim lets your C/Rust chip use standard-library calls (printf, string ops, math) without a heavy runtime.
Frequently Asked Questions
- What is a custom chip in Velxio?
- A custom chip is a user-defined integrated circuit. You write the chip's logic in C, Rust, or AssemblyScript — Velxio compiles it to WebAssembly, instantiates it on the canvas like any other component, and drives its pins from the simulator.
- Which API does Velxio use?
- Velxio implements the Wokwi Custom Chips API — the same API used by Wokwi — so chips you write for Velxio are portable to Wokwi and vice versa. Velxio adds a WASI shim so you can use standard library functions in your chip code.
- What can I build?
- Behavioural models of real ICs (sensors, decoders, level translators, protocol bridges), custom digital logic, sensor stand-ins for hardware you don't have yet, and protocol-level mocks for testing firmware. Chips can drive pins, read attributes, register timers, and bridge to I²C / SPI buses.
- How do I share or reuse a chip?
- Save the chip to your Velxio account and reuse it across projects. The chip definition includes its pin layout, attributes, and the compiled WASM — drop it onto any project canvas like a built-in component.
- Do I need a backend to run my chip?
- No. Compiled chip WASM runs in the same browser tab as the rest of the simulation. Pin updates, attribute reads, and timer ticks are all local.
- Can my custom chip talk to an Arduino?
- Yes — that is the typical use case. Wire its pins to Arduino GPIOs, SPI, or I²C lines and the firmware on the Arduino interacts with your chip exactly like a real IC.
Build your first custom chip
Open the editor and create a chip in seconds — pick C, Rust, or AssemblyScript.
Launch the Editor →