kisim — run KiCad schematics or plain netlists in ngspice from Python

kisim.py is a single-file simulation framework with no project knowledge. It:

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),
edits the netlist (instance parameters, source waveforms, regex substitutions),
runs ngspice -b, and
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:

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:

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 — a 5 V step into an RC low-pass:

rc_lp.cir — a plain ngspice netlist (1 kΩ, 100 nF)
rc_lp.py — runs it; then sweeps R1/C1 tolerance corners of the step response (corners + run_cases), reading τ and the pole (f−3dB) off each transient; then cross-checks the transient results against the control model H(s) = 1/(1 + sRC) with scipy.signal — analytic step overlay, poles and a Bode plot

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).