PM_K-1 hardware: reproducible EDA container (KiCad 9 + ngspice)

Pinned toolchain under hardware/eda/ so the design can be checked/simulated
identically in the future (system KiCad is 7.0, which has no CLI ERC):
- Containerfile: Ubuntu 24.04 + KiCad 9 (PPA) + ngspice + python3.
- run.sh: build-if-needed + run with the repo mounted; lands in hardware/kicad.
- sim/input_loading.cir: ngspice deck proving the line(25k) vs instrument(1M)
  input-loading decision — Hi-Z preserves a +16dB pickup resonance the 25k load
  flattens to -3dB.

Verified: KiCad 9.0.9, ngspice-42, ERC runs clean (0 violations) on
pm_k1_core.kicad_sch.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

hardware/eda/Containerfile

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+# Reproducible EDA toolchain for the PM_K-1 core board.
+#
+# Why this exists: the system KiCad is 7.0 (no CLI ERC). This pins a known,
+# rebuildable environment so the design can be checked/simulated identically
+# years from now — fitting for a device meant to outlive its tools.
+#
+#   KiCad 9  -> schematic capture, CLI ERC/DRC, netlist/PDF/Gerber export
+#   ngspice  -> SPICE simulation of the analog audio circuits
+#   python3  -> scripting / BOM / skidl-style helpers
+#
+# Build/run via ../eda/run.sh (or: podman build -t pmk1-eda:9.0 .)
+FROM docker.io/library/ubuntu:24.04
+
+ENV DEBIAN_FRONTEND=noninteractive
+SHELL ["/bin/bash", "-o", "pipefail", "-c"]
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        software-properties-common ca-certificates gnupg && \
+    add-apt-repository -y ppa:kicad/kicad-9.0-releases && \
+    apt-get update && apt-get install -y --no-install-recommends \
+        kicad \
+        ngspice \
+        python3 python3-pip python3-venv \
+        git make && \
+    apt-get clean && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /work
+CMD ["bash"]

hardware/eda/README.md

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+# PM_K-1 EDA environment
+
+A reproducible container with the tools to design, check, and simulate the core board —
+so the work doesn't depend on whatever happens to be installed on a given machine, now or
+in 50 years.
+
+## What's inside
+- **KiCad 9** — schematic capture + PCB layout, and a CLI (`kicad-cli`) that can run
+  **ERC** (Electrical Rules Check) and DRC, and export netlists/PDF/Gerbers.
+- **ngspice** — SPICE simulator for validating the analog audio circuits before we commit
+  copper (op-amp stages, filters, input loading, etc.).
+- **python3** — scripting, BOM munging, optional code-defined-schematic helpers.
+
+## Why a container?
+The system KiCad here is 7.0, whose CLI can't run ERC (that arrived in KiCad 8). Rather than
+fight the host, we pin a known toolchain. Anyone — including future-you — rebuilds the exact
+environment with one command.
+
+## Use it
+```bash
+cd hardware/eda
+./run.sh                                   # interactive shell, lands in hardware/kicad/
+./run.sh kicad-cli version                 # confirm KiCad 9
+./run.sh kicad-cli sch erc pm_k1_core.kicad_sch   # run ERC on the schematic
+./run.sh ngspice -b ../eda/sim/input_loading.cir  # run a simulation (cwd is kicad/)
+```
+`run.sh` builds the image on first use, then mounts the whole repo at `/work` (so KiCad sees
+`hardware/`). Use `RUNTIME=docker ./run.sh …` to use Docker instead of Podman.
+
+## Layout
+```
+eda/
+  Containerfile      # the pinned toolchain (KiCad 9 + ngspice + python)
+  run.sh             # build-if-needed + run with the repo mounted
+  sim/               # ngspice decks (SPICE simulations of the analog circuits)
+```

hardware/eda/run.sh

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+#!/usr/bin/env bash
+# Build (first time) and run the PM_K-1 EDA container with the repo mounted.
+#
+#   ./run.sh                 # interactive shell in hardware/kicad/
+#   ./run.sh kicad-cli sch erc pm_k1_core.kicad_sch
+#   ./run.sh ngspice -b sim/some.cir
+#
+# Override the runtime with RUNTIME=docker ./run.sh ...
+set -euo pipefail
+
+IMG="pmk1-eda:9.0"
+EDA_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"   # hardware/eda
+REPO_DIR="$(cd "$EDA_DIR/../.." && pwd)"                  # repo root
+RUNTIME="${RUNTIME:-podman}"
+
+if ! "$RUNTIME" image inspect "$IMG" >/dev/null 2>&1; then
+  echo ">> building $IMG (first run, a few minutes)…" >&2
+  "$RUNTIME" build -t "$IMG" "$EDA_DIR"
+fi
+
+# Mount the whole repo so KiCad/ngspice see hardware/ ; land in hardware/kicad.
+flags=(--rm -v "$REPO_DIR":/work:Z -w /work/hardware/kicad)
+[[ -t 0 && $# -eq 0 ]] && flags+=(-it)
+exec "$RUNTIME" run "${flags[@]}" "$IMG" "${@:-bash}"

hardware/eda/sim/.gitignore

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+*.csv

hardware/eda/sim/input_loading.cir

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+* PM_K-1 : input loading -- line receiver (25k) vs Hi-Z instrument buffer (1M)
+*
+* This is the circuit-level proof of a decision we made by hand: why a guitar/bass
+* needs a HIGH-impedance input. A passive pickup is inductive, so the load impedance
+* it sees shapes its tone. Plug it into a low impedance and you damp its resonance
+* and lose treble + level; a high-Z buffer preserves it.
+*
+* Pickup model: open-circuit source + winding resistance + inductance + self-capacitance.
+* Plus a typical ~300 pF guitar cable. We drive two identical pickup+cable networks
+* from one ideal source and load them differently, then compare.
+*
+* Run:  ngspice -b sim/input_loading.cir   (from inside the EDA container)
+
+.title PM_K-1 input loading: line 25k vs instrument 1M
+
+Vpu  src 0 AC 1
+
+* --- Branch A: LINE input, ~25k receiver impedance ---
+RdcA  src a1 6k
+LpuA  a1  a2 3
+CpuA  a2  0  150p
+CcabA a2  0  300p
+RinA  a2  0  25k
+
+* --- Branch B: INSTRUMENT input, 1M Hi-Z buffer ---
+RdcB  src b1 6k
+LpuB  b1  b2 3
+CpuB  b2  0  150p
+CcabB b2  0  300p
+RinB  b2  0  1meg
+
+.ac dec 100 10 100k
+
+.control
+run
+meas ac a_1k  find vdb(a2) at=1000
+meas ac b_1k  find vdb(b2) at=1000
+meas ac a_peak max vdb(a2) from=1000 to=20000
+meas ac b_peak max vdb(b2) from=1000 to=20000
+echo
+echo "  Level @1kHz   : line(25k)= $&a_1k dB   inst(1M)= $&b_1k dB"
+echo "  Resonant peak : line(25k)= $&a_peak dB   inst(1M)= $&b_peak dB"
+echo "  -> the 25k load drags the signal down and flattens the pickup's natural peak;"
+echo "     the 1M input preserves level and tone. Hence the switchable Hi-Z front end."
+wrdata ../eda/sim/input_loading.csv vdb(a2) vdb(b2)
+.endc
+.end

hardware/kicad/.gitignore

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 # KiCad generated/derived outputs
 *.pdf
 *.net
+*.svg
+*.rpt
 *-bak
 *.kicad_prl
 fp-info-cache