examples: runnable RC low-pass demo on a plain netlist (no KiCad)

rc_lp.cir + rc_lp.py: 5 V step into 1k + 100n, prints V(out) at one
time constant and writes a plot. README updated for netlist support;
results/ output dir ignored.

1 files changed, 18 insertions, 5 deletions

diff --git a/README.md b/README.md
index da5996c..b44856e 100644
--- a/README.md
+++ b/README.md
@@ -1,8 +1,9 @@
-# kisim — run KiCad schematics in ngspice from Python
+# 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`,
+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
@@ -26,7 +27,8 @@ 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)
+- `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
@@ -49,8 +51,19 @@ r.plot(["+28V", "i(V1)", "Q2:power"])
 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/*.raw` and regenerated `results/*.cir` files are gitignored; they
-  are rebuilt by running the sims.
+- `results/` directories (sim output, plots) are gitignored; rebuilt by running
+  the sims.
 - Initially developed for the ASPECT+ payload board sims (2026).