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# kisim — run KiCad schematics or plain netlists in ngspice from Python
`kisim.py` is a single-file simulation framework with no project knowledge. It:
1. exports a `.kicad_sch` to a SPICE netlist with `kicad-cli` (or takes a plain
ngspice netlist — `.cir`/`.spice`/`.net` — and uses it as-is),
2. edits the netlist (instance parameters, source waveforms, regex substitutions),
3. runs `ngspice -b`, and
4. hands the results back as numpy arrays addressed by the schematic's own net
and device names — e.g. `r.v("+28V")`, `r.i("V1")`, `r.p("Q2")`, `r.at("i(v1)", 0.1)`.
It also carries test-case and worst-case helpers (`Case`, `run_cases`,
`corners`, `tol`, `Wave`, `stim`, `worst`) and caches runs keyed on the
generated netlist.
**The module docstring in `kisim.py` is the full API reference.**
## Environment
Everything runs in the `kicad_work` micromamba environment:
```sh
micromamba create -n kicad_work -f environment.yml
micromamba activate kicad_work
micromamba run -n kicad_work python my_sim.py
```
Required on the system (not in the env):
- `kicad-cli` — schematic → SPICE netlist export (KiCad ≥ 7; developed on 10.0.6).
Only needed for `.kicad_sch` inputs.
- `ngspice` — the simulator (developed on ngspice-47)
## Usage
From a script in a project folder one level under this one:
```python
import sys
from pathlib import Path
sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
from kisim import KiSim
sim = KiSim("my_sim.kicad_sch", tran="10u 400m")
r = sim.run() # -> results/run.cir + run.raw (cached)
print(r.v("+28V")[-1], r.i("V1").max())
r.plot(["+28V", "i(V1)", "Q2:power"])
```
`save=[...]`, `power=[...]` and `currents=` control what gets probed — worth
using for big vendor models, where thousands of internal nodes make huge, slow
raw files.
## Example
`examples/` is a small runnable demo:
- `rc_lp.cir` — a plain ngspice netlist: 5 V step into 1 kΩ + 100 nF
- `rc_lp.py` — runs it with kisim and plots V(in)/V(out)
```sh
micromamba run -n kicad_work python examples/rc_lp.py
```
## Notes
- `results/` directories (sim output, plots) are gitignored; rebuilt by running
the sims.
- Initially developed for the ASPECT+ payload board sims (2026).
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