OhmPy

Open-source electronic circuit simulator — analog, digital, and mixed-signal.

Documentación en español

OhmPy is a schematic-capture and simulation environment built with Python + PyQt6. Its custom MNA (Modified Nodal Analysis) engine solves DC, AC, and transient analyses from the same netlist, with virtual instruments (a multimeter, two-channel oscilloscope, and function generator) integrated into the canvas.

• DC analysis — linear and nonlinear (Newton–Raphson), with source stepping for circuits containing diodes, LEDs, BJTs, MOSFETs, and op-amps.
• AC analysis — frequency sweeps with cached LU factorization at each frequency point.
• Transient analysis — adaptive time steps with LTE error control for linear and nonlinear analog circuits.
• Digital engine — event-driven binary simulation with propagation delays.
• Mixed signal — internal bridges couple shared analog and digital nodes during co-simulation.

The engine API additionally exposes digital models such as XNOR, buffers, registers, memories and standalone A/D bridge classes. They are not all wired into the schematic editor.

• Multimeter — DC/AC voltage, current and resistance readings between two schematic pins.
• Oscilloscope — two differential channels with configurable time base and vertical scale; it can also read the optional serial hardware stream.
• Function generator — sine, square and triangle waveforms with amplitude, frequency and offset controls.

• Digital circuit analyzer — truth tables, SOP/POS minimization and automatic construction of a gate circuit.
• Resistor calculator — color code ↔ value conversion and E12/E24/E96 series.
• Power triangle — P, Q, S, and power factor for AC analysis.
• SPICE interchange — import and export R, C, L, independent sources and diodes in .cir, .net or .sp files. Imported node names are preserved; subcircuits, models and expressions are intentionally left untouched.
• Themes — support for customizable JSON themes. See themes/README.md to create your own.

Requirements: Python 3.10 or later; Windows, Linux, or macOS.

git clone https://github.com/pabdan2003/OhmPy.git OhmPy
cd OhmPy
python -m venv .venv
# Windows
.venv\Scripts\activate
# Linux/macOS
source .venv/bin/activate
pip install -r requirements.txt
python main.py

To create the distributable macOS application, install the optional build tool and run:

python -m pip install ".[build]"
sh scripts/build_macos.sh

This produces dist/OhmPy.app and dist/OhmPy-<version>-macOS.dmg. Distribute the DMG and ask users to drag OhmPy.app to Applications. For each new release, build it with an increased version in pyproject.toml; replacing the existing app in Applications updates it in place, without duplicating the application. User preferences and custom themes remain in ~/.ohmpy.

Before distributing outside a small trusted group, sign and notarize the app with an Apple Developer certificate; otherwise macOS will show a security warning on first launch.

For macOS, download the .dmg asset from the release, open it, and drag OhmPy.app to Applications. The current build is for Apple Silicon (M1, M2, M3, M4, or M5); an Intel macOS build is not available yet.

1. Start OhmPy with python main.py.
2. Choose a category and component, then click the canvas to place it.
3. Connect pins by clicking one pin and then another.
4. Double-click a component to edit its value.
5. Click ▶ SIMULATE; OhmPy automatically detects DC, AC, digital, or mixed-signal mode.

Open any project in examples/ with File → Open. They are small, working circuits intended both for learning the editor and checking that a release still behaves correctly.

LED DC simulation	BJT DC operating point

Digital logic	Low-pass Bode plot

from ohmpy.engine import Resistor, VoltageSource, MNASolver

solver = MNASolver()
circuit = [
    VoltageSource("V1", "in", "0", 10.0),
    Resistor("R1", "in", "out", 1000.0),
    Resistor("R2", "out", "0", 1000.0),
]
result = solver.solve_dc(circuit)
print(result["voltages"]["out"])  # 5.0 V

OhmPy/
├── main.py                  # Entrypoint (opens the main window)
├── ohmpy/                  # Main package
│   ├── circuit_analyzer.py  # Simulation-mode classification and mixed-boundary detection
│   ├── spice.py             # Basic SPICE import/export
│   ├── theme_manager.py     # Theme loading and persistence
│   ├── engine/
│   │   ├── mna.py           # MNA solver (DC, AC, transient)
│   │   ├── components.py    # Analog component models
│   │   ├── digital_engine.py# Event-driven digital simulator
│   │   ├── bridges.py       # Analog ↔ digital converters
│   │   └── mixed_signal.py  # Mixed-signal simulation coordinator
│   └── ui/
│       ├── scene.py         # QGraphics scene and netlist construction
│       ├── items/           # ComponentItem, WireItem
│       ├── dialogs/         # Instruments and configuration dialogs
│       └── style.py         # Theme, fonts, and visual constants
├── themes/                  # JSON themes (data)
├── examples/                 # Ready-to-open .csin circuits
├── firmware/                # Protocol and firmware examples for a physical probe
└── tests/                   # pytest suite (engine, editor, SPICE, and project I/O)

pip install -r requirements-dev.txt
pytest -v

Pushes to main and pull requests run the suite on Python 3.10, 3.11 and 3.12 through GitHub Actions (see .github/workflows/ci.yml).

• Migrate tests to pytest + GitHub Actions CI.
• Bode plots (magnitude and phase) for the existing AC analysis.
• FFT in the oscilloscope.
• Basic SPICE netlist import/export (R, C, L, V, I, D).
• Reusable subcircuits (selection encapsulation).
• Undo changes using snapshots.
• Redo, duplicate, alignment/distribution, grid snap, and manual wire corners.
• Optional migration from snapshots to QUndoStack.
• Persistent probes on the schematic.

Contributions are welcome. Before opening a pull request:

1. Read docs/architecture.md to understand the separation between engines and global conventions (signs, units, node names).
2. Run the existing tests and add the ones relevant to your change.
3. For engine changes, include a validation case against a known analytical solution.
4. For visual changes, attach before-and-after screenshots.

Quick package maps:

• ohmpy/engine/README.md — purpose of each engine file.
• ohmpy/ui/README.md — purpose of each UI file.
• themes/README.md — JSON theme format and how to create one.
• firmware/README.md — binary protocol for the physical oscilloscope probe.

Distributed under the MIT License.