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.

2 files changed, 30 insertions, 0 deletions

diff --git a/examples/rc_lp.cir b/examples/rc_lp.cir
new file mode 100644
index 0000000..58d1f57
--- /dev/null
+++ b/examples/rc_lp.cir
@@ -0,0 +1,5 @@
+* RC low-pass: 5 V step into 1 kohm + 100 nF
+V1 vin 0 PWL(0 0 1n 5)
+R1 vin vout 1k
+C1 vout 0 100n
+.end
diff --git a/examples/rc_lp.py b/examples/rc_lp.py
new file mode 100644
index 0000000..0a79b60
--- /dev/null
+++ b/examples/rc_lp.py
@@ -0,0 +1,25 @@
+#!/usr/bin/env python3
+"""Example: run a plain ngspice netlist with kisim -- no KiCad involved.
+
+    micromamba run -n kicad_work python examples/rc_lp.py
+"""
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
+
+import numpy as np
+
+from kisim import KiSim
+
+sim = KiSim("rc_lp.cir", tran="1u 2m")   # .cir input: used as-is, no kicad-cli
+r = sim.run()                            # -> results/run.cir + run.raw (cached)
+
+tau = 1e3 * 100e-9                       # R1 * C1
+vout = r.v("vout")
+print(f"5 V step into 1 kohm + 100 nF: tau = {tau * 1e6:.0f} us")
+print(f"V(vout) at 1 tau: {np.interp(tau, r.t, vout):.3f} V   (1 - 1/e of 5 V)")
+print(f"V(vout) settled:  {vout[-1]:.3f} V")
+
+r.plot(["vin", "vout"], title="RC low-pass: 5 V step", file=sim.workdir / "rc_lp.png")
+print("plot:", sim.workdir / "rc_lp.png")