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Me Here e6f425ee6f PM_K-1 hardware: Stage 1b -- Hi-Z instrument DI buffer + line/inst select relay 
OPA1641 non-inverting DI buffer (1Mohm in, +12dB) + TQ2SA DPDT relay that both
routes the jack tip (line receiver vs DI buffer) and selects the output. Default
de-energized = LINE (common case, fail-safe). Driven by the shared ULN2003 via
net K1_DRV from GPIO SEL_LINST.

Pinouts verified from datasheets before capture (per the no-guessing rule):
- OPA1641 (TI SBOS484D): 1=NC 2=-IN 3=+IN 4=V- 5=NC 6=OUT 7=V+ 8=NC.
- ULN2003A: GND=8, COM=9, in 1-7 / out 16-10.
- TQ2SA (Panasonic TQ-SMD): pole1 COM=3 throws 2/4, pole2 COM=8 throws 7/9
  (from contact-resistance terminal pairs). NC/NO orientation + coil pins (1/10)
  follow the standard single-side-stable diagram -- flagged in-file for a final
  connection-diagram cross-check (not over-claimed).

ngspice stage1b_di.cir confirms +12.04dB gain, flat across the audio band.
ERC 0 errors; netlist 0 errors.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
2026-05-30 19:56:55 -05:00
..
circuits PM_K-1 hardware: Stage 1b -- Hi-Z instrument DI buffer + line/inst select relay 2026-05-30 19:56:55 -05:00
sim PM_K-1 hardware: Stage 1b -- Hi-Z instrument DI buffer + line/inst select relay 2026-05-30 19:56:55 -05:00
Containerfile PM_K-1 hardware: Stage 1 input receiver as SKiDL (code-defined schematic) 2026-05-30 19:43:07 -05:00
README.md PM_K-1 hardware: reproducible EDA container (KiCad 9 + ngspice) 2026-05-30 19:17:54 -05:00
run.sh PM_K-1 hardware: reproducible EDA container (KiCad 9 + ngspice) 2026-05-30 19:17:54 -05:00

README.md

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

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)