Updated for the actual speaker on the bench (GRS 3FR-4, not the
Adafruit 1314 we initially specced — same 60 mm M3 mounting pattern
but a much deeper magnet). Reference doc renamed and rewritten with
the new specs.

Geometry consequences:

* Speaker posts grow from 22 mm to 44 mm to position the frame plate
with 1 mm of clearance below the magnet (vibration isolation; the
alternative of resting the magnet on the plate would couple bass
into the nightstand surface).
* Chamber inner height grows to 46 mm (44 mm post + 2 mm foam tape
on top of the frame, compressed against the cover underside).
* Speaker frame extent goes from 78 mm to 95 mm (the GRS is wider
across the mounting ears), so the chassis grows to ~107×162×49 mm
assembled.

Cable clip rework:

* Was a closed rectangular tunnel centered on the back wall — over-
engineered (the goal was strain relief, not a zip-tie pass-through)
and conflicted with the centered back snap-fit tab.
* Now an open L-shape (post + cap), positioned ~14 mm from the side
wall to clear the snap tab. The cable drops in from above during
assembly and rests in the L corner — post on the chamber-interior
side, cap extending toward the side wall, cable contained on three
sides with the open side facing the wall.
* Cable notch in the back wall and matching notch in the back edge
of the bottom plate shifted to match the L-clip's X position.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Reorganized so the bottom plate is the structural foundation and the
chassis ("cover") is purely cosmetic. Cover comes off without tools,
exposing all internals at once.

* Speaker mounts to four tall posts on the bottom plate (60 mm M3
pattern), with self-tap pilots at the post tops. No more screw holes
through the cover's top panel. Foam sealing, if it turns out to be
needed, becomes a foam donut on top of the speaker frame compressed
against the cover underside during assembly.
* USB cable routes internally. The connector lives on the Atom inside
the chamber; cable threads through a printed strain-relief tunnel
a few cm in front of the back wall and exits through a small notch
at the bottom of the back wall, matched by a notch in the plate's
back edge so the exit sits flush with the bottom of the unit.
* Cover retention is snap-fit. Four tabs on the plate carry hemi-
spherical bumps that catch in detent recesses on the chassis inner
walls. M3 screws and bosses are gone.

Post height, cable diameter, and snap-bump diameter are param-tunable
guesses to be dialed in after a test print.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

The assembled nightstand unit gets a printable shell. `make enclosure`
renders three STLs to `enclosure/build/`: the chassis (open-bottom shell
with integrated top), a separate bottom plate that screws on with four
M3 self-tap screws, and a translucent snooze cap. The chassis houses
the Atom Echo press-fit onto a daughterboard via M5's 5+4 "Atom Stack"
header pattern, a MAX98357A I2S amp, and the Adafruit 1314 speaker.
Snooze cap on the front-top half presses the Atom's button via a
captive plunger; speaker fires up through a perforated grille on the
rear-top half; USB-C exits a cutout in the back wall.

Layout decisions worth flagging for future archaeology:

* Speaker fires up — less directional, more room-filling for a
nightstand. Snooze cap on the near (front) half of the top, grille on
the far (rear) half.
* No internal divider between the snooze and speaker zones — single
shared chamber so the USB-C cable can route from the front-mounted
Atom straight to the rear cutout. White noise through a 3" driver
doesn't need a sealed speaker chamber.
* Press-fit on the 5+4 side headers as the only Atom mount — no screws
on the Atom itself. M5's mechanical drawing shows two M2 mounting
holes on the bottom face, but they aren't externally accessible on
the actual unit (covered by the label sticker).
* Bottom plate screws into corner bosses with M3 self-tap into PLA;
four register tabs on the plate keep it laterally aligned during
assembly before the screws snug.
* 1.5 mm fillet on visible top + side edges; cap top has a 1.5 mm
spherical dome for tactile cue in the dark.
* Daughterboard is hand-soldered protoboard, not a custom-fab PCB.
Standoffs at the four corners of a 38 × 38 footprint for now; will
re-tune once a real piece of perfboard is on the bench.

The reference docs needed several corrections that fell out of measuring
the actual hardware (photos of the bottom, back, and top-right faces
added under `reference/atom-echo/`):

* Bottom face has the 5+4 press-fit headers + a male HY2.0-4P GROVE in
the middle.
* USB-C is on the back face, not the top.
* The onboard NS4168 speaker grille shares the top face with the
button, not the front.
* Planned MAX98357A wiring: I2S DIN moves from G21 (which isn't exposed
on the Atom's external pins) to G25.
* Stale PAM8302 references in the Adafruit 1314 doc updated to
MAX98357A — that path was the rejected analog-amp architecture.

References:

* https://docs.m5stack.com/en/atom/atomecho
* https://www.adafruit.com/product/3006 (MAX98357A breakout)
* https://www.adafruit.com/product/1314 (3" 4Ω speaker)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>