Chime hardware: BOM and updated Zero W variant

[exddc]

What

• Adds hardware/chime/bom.md with parts, status, rationale, and harness lengths.
• Rewrites the rpi0w_lsm104f8 variant: J8 pin map, reserved and free pins, audio straps and output levels, firmware interface, enclosure, and assembly.
• Updates wiring.yml and the regenerated wiring.svg: soldered loom, C1/C2 at amplifier VIN, twisted speaker pair, lengths.

Why

Chime had no real BOM and its hardware docs were a thin snapshot. Chime stays on the Pi Zero W: its load is light and the existing image already targets it, so one variant covers every build. This freezes the interfaces so housing work can proceed without re-picking parts.

Follow-up

• mqtt_topics and ring_topic must match ring/<unit>/pressed/<n>; the default ring/pressed does not.

Resolves TW-453.

[linear-code]

TW-453

[pullfrog]

ℹ️ No critical issues — one small inconsistency inline.

Reviewed changes

Reviewed the Chime hardware docs update: the new BOM, the Pi Zero 2 W variant spec, and the restructured WireViz source.

• Assembly BOM — adds hardware/chime/bom.md with part status, rationale, harness cut lengths, and a procurement allowance.
• Zero 2 W variant — adds variants/rpi02w_lsm104f8/README.md with the J8 map, reserved and free pins, config.txt, audio output levels, firmware requirements, enclosure, and assembly steps.
• Wiring source — wiring.yml splits the loom into W1 power (24 AWG), W2 I2S (26 AWG), W3 twisted speaker pair, and W4 VIN–SD strap in place of the old loops; wiring.svg is regenerated.
• Shipped baseline — rpi0w_lsm104f8 becomes the record for shipped Zero W units (Dupont jumpers, no C1/C2).

I checked these against the code: the free-pin list is complete. The audio table matches the datasheet formula (dBFS + 2.1 dB + 9 dB). The defaults for volume_ring, volume_notifications, ring_topic, and heartbeat_topic match schema/chime_config.json. The linear volume / 100 scaling matches the software fallback in chime/src/audio/aplay_audio_player.cpp, which is the path the max98357a card takes because it has no mixer control.

  ^{｜ Fix all ➔ ｜ Fix 👍s ➔ ｜ View workflow run ｜ Using Claude Opus ｜ 𝕏}

[pullfrog]

✅ No new issues found.

Reviewed changes

Since the prior review, the separate Zero 2 W variant has been dropped. Chime now has one Pi Zero W variant.

• Single variant: Folded the rpi02w_lsm104f8 content into variants/rpi0w_lsm104f8/README.md, which covers power rails, the J8 map, reserved and free pins, config.txt, audio levels, the firmware interface on openchime_rpi0w_defconfig, the enclosure, and assembly.
• BOM: Changed P1 and PSU1 to the Zero W and removed the "verify Zero 2 W fit" status on the body.
• Top-level README: Removed the "Shipped baseline" row and the "Both variants" wording.
• Wiring drawing: Changed the J8 note from "Zero 2 W" to "Zero W" and regenerated wiring.svg to match.

Nothing under hardware/chime/ still refers to rpi02w or the Zero 2 W. The J8 table, the free-pin list, and wiring.yml all use the same pins. One thing to be aware of: the docs no longer describe how earlier builds differ (Dupont jumpers, no C1/C2). That seems deliberate.

  ^{｜ View workflow run ｜ Using Claude Opus ｜ 𝕏}