Circuit Bench

Build circuits and test CircuitPython in VS Code, without a physical board. The simulator runs real CircuitPython 10.3.1 compiled to WebAssembly, set up to behave like an Adafruit Metro M0 Express, so your code.py can move to a real board unchanged.

Get started

1. Run Circuit Bench: New Project from Example from the Command Palette.
2. Open code.py, then run Circuit Bench: Run on Simulator.
3. Use Circuit Bench: Set Up CircuitPython Autocomplete for suggestions as you type. This needs the Python extension.

Each project is a folder holding code.py, your circuit in circuit.json, and a lib folder. Opening circuit.json shows its circuit diagram. To move a project to another computer or hand it in, see Export and import.

Build a circuit

Hover over a pin to see its name and everything connected to it. Select a part to give it a label, which shows on the canvas, in the diagram and in the parts list. For a value that is not in a resistor's list, type it, such as 4.7k or 2M2. Add a Note from the Tools list to leave text on the canvas.

Run it

Press Run. While it runs, press parts on the canvas, or use the controls on the right. The Serial console shows print() output: click it and press Ctrl+C to stop your program and reach the REPL.

Problems warns about mistakes that would matter on a real board. A part being damaged smokes on the canvas, and a part that is only wired wrong gets a warning sign. Hover over the part to read why, or click the problem to select the part. Parts with no connection to the board or a battery turn grey, because the simulation cannot reach them.

Multimeter

Add a Multimeter from the Tools list and wire up its red and black probes. Click it while the program runs to change what it measures, or use the buttons on the right.

Parts

Boards, breadboards, resistors, capacitors, diodes, LEDs, RGB LEDs, transistors, MOSFETs, buttons, switches, potentiometers, rotary encoders, joysticks, keypads, touch pads, photoresistors, thermistors, force sensors, TMP36, DHT11/22, DS18B20, HC-SR04, PIR, sound and water sensors, IR receiver and remote, MPU-6050, MCP9808, DS3231, buzzers, servos, DC motors, steppers, relays, NeoPixels, 7-segment displays, LED bars, 8x8 matrices, character LCDs, SSD1306 OLEDs, 74HC595, L293D, batteries, multimeters and notes.

Differences from a real board

• Python runs much faster than on a real M0, so slow code can look fine here.
• Timing is close, not exact. Short sleeps can run a few milliseconds long on Windows.
• Memory limits are an estimate, so a program near the limit may behave differently.
• Parts are simplified. Capacitors do nothing at DC, and the display contrast pin is ignored.
• USB keyboard, mouse and MIDI output is accepted, but nothing shows it yet.

Export and import

Press Export in the builder or run Circuit Bench: Export Project, then choose what to save.

To open a project package, press Import or run Circuit Bench: Import Project Package, then choose a folder. It creates a new project folder and opens it. A package only holds project files: it cannot include VS Code settings or tasks, it cannot write outside the new folder, and nothing in it runs until you press Run, which only runs it on the simulated board.

Packages saved as .metrosim by earlier versions still open.

Circuit diagram

Press Diagram in the builder, run Circuit Bench: Show Circuit Diagram, or open circuit.json to see the circuit as a schematic. It shows how parts are joined rather than where they sit, so breadboards disappear and only the board pins in use are drawn. Power and ground are marked at each pin instead of being wired across the page.

The diagram only shows the circuit, and it updates as you build. In the builder, press 2D view to go back to building. In the circuit.json tab, press Edit circuit to open the builder, or Show JSON to see the file as text. Hover over a wire to light up everything joined to it. Wires that cross without a dot are not connected.

Parts need no diagram symbol: each one is drawn as a labelled block. To draw a part with its own symbol, add it to SYMBOLS in webview/diagram-art.js.

To work on the diagram outside VS Code, serve the extension folder over HTTP and open test/diagram-preview.html?example=dimmer.

3D view

The 3D view button shows the circuit in 3D. Students still build in the 2D canvas, but while a program runs they can click parts in 3D just as they do in 2D: press a button, flip a switch or change the multimeter's mode. Dragging anywhere else turns the view. Smoke, warning signs, grey parts and notes only show on the 2D canvas. Close the view to free its memory.

Parts need no 3D model: each one gets a body from the largest shape in its 2D art, with that art on top. To model a part by hand, add it to BUILDERS in webview/scene3d.js.

three.js 0.186.1 is kept in webview/vendor/three, copied from the npm package's build folder with its licence. It loads the first time the view opens.

Licence

MIT. The extension includes third-party software, listed in THIRD_PARTY_NOTICES.md.