TIME INVADERS — arcade word clock

A 16×16 word clock with an 8-bit arcade heart: the time reads as words to the exact minute (IT IS TWENTY THREE MINUTES PAST FOUR), but time changes are game events — Pac-Man eats the old time, a cannon shoots in the new one — and the filler letters hide arcade words (INSERT COIN, GAME OVER, plus a hall of fame: SPACE INVADERS, GALAGA, DONKEY KONG, ASTEROIDS, Q*BERT). The enclosure is deliberately subtle — a plain dark slab that passes at a work desk, on raked feet or wall-mounted; the arcade lives in the light, not the shell.

Every pixel is a letter: the attract-mode sprites are drawn by lighting grid cells, like the invader marching over the cannon above.

▶ Try it in your browser — live simulator running the real firmware logic: word grid, transitions, attract mode, hidden words.

What you need

Item	Notes
16×16 WS2812B flexible panel	160×160 mm, 10 mm pitch — the common ~£12–15 one
Seeed XIAO ESP32S3 (or ESP32-S3 "supermini")	either fits the internal locator
Snap-in USB-C power socket, 4P PD pigtail	CHT-TS023R style; 2P/data variants won't power from C-to-C cables
5 V / 3 A USB-C supply	must present 5 V — verify with a meter before connecting the panel
2× 5.1 kΩ resistors	CC1/CC2 → GND at the socket pigtail (skip if built in)
1000 µF electrolytic (≥6.3 V)	across 5 V/GND at the panel pigtail
330 Ω resistor	in the data line to DIN
Schottky diode (1N5817/19/22)	socket 5 V → ESP32 5 V pin
3 mm foam sheet	cut into 14× 8×8 mm pads
4× M3×16 self-tapping screws	shell → faceplate posts (16 mm, not 8 — see DESIGN.md)
74AHCT125 level shifter (optional)	only if 3.3 V data proves flaky

Print it

Sliceable files are committed — no OpenSCAD needed for a stock build:

• build/desk_set.3mf — the desk build in one file: faceplate, shell, lattice, diffuser, and stand feet in both 12° and 15° tilt (print one pair).
• build/wall_set.3mf — the wall build: keyhole hangers baked in, power socket on the bottom edge, no stand.
• build/ also has per-part STLs and exact STEP CAD exports (wordclock_assembly.step is the full assembly) for other CAD tools.

Every part is a plain single-colour print: faceplate, shell, lattice and stand in something dark; the diffuser in white or clear at 100 % infill. Faceplate prints letters-down, shell outer-face-down, everything else flat.

Pick your diffuser first: print part="coupon" (a four-cell sample) plus coupon_diffuser strips at a few thicknesses (t_diff = 0.6 / 0.9 / 1.2, clear and white), try them over a lit LED, set t_diff to the winner, then print the diffuser and lattice.

Customising needs OpenSCAD (free — open wordclock.scad, use the Customizer): the committed files cover the two stock configurations, everything else is a parameter + re-export — mount_type (desk/wall), power_pos (cable entry: back or bottom), keyhole (wall hangers), tilt (stand angle 5–25°), t_diff, or the letter grid itself. ./export.sh regenerates STLs + 3MF sets, ./export_step.sh the STEP files.

Wire it

Four connections plus the supply handshake — see the schematic for the full picture:

• Socket V+/V− → panel 5 V/GND direct (panel current never touches the ESP32), with the 1000 µF cap across 5 V/GND at the panel pigtail.
• Socket 5 V → D1 (Schottky, cathode toward ESP32) → ESP32 5 V pin; grounds common.
• ESP32 GPIO4 → 330 Ω → panel DIN.
• CC1/CC2 → 5.1 kΩ → GND (one each) at the socket pigtail, unless the socket has them built in.

Firmware enforces a per-frame power cap (FastLED.setMaxPowerInVoltsAndMilliamps(5, 2500)) so no animation can exceed the supply — don't remove it. Power-safety details and why each part is there: DESIGN.md.

Full circuit schematic (ASCII)

+=========================================================================+
|                   TIME INVADERS -- Circuit Schematic                    |
+=========================================================================+

POWER

  USB-C Power Pod (snap-in, 4P fast-charge/PD pigtail)
  +-------------+
  |  V+         |----------------------------------------------- 5V RAIL
  |  V-         |----------------------------------------------- GND RAIL
  |  CC1        |--[ R1 5.1k ]--+
  |  CC2        |--[ R2 5.1k ]--+-------------------------------- GND RAIL
  +-------------+

  R1/R2 request 5V/3A from the supply. Omit them if the socket
  already has CC resistors built in (only V+/V- emerge in that case).

  ESP32-S3 SuperMini
  5V RAIL  --[ D1 ]------------------------------------------------ 5V pin
  GND RAIL ------------------------------------------------------ GND pin

  D1: pod 5V -> ESP32 5V pin, cathode (banded end) toward the ESP32.
  Reinstates the isolation the XIAO's own USB port likely lacks (see
  note below) -- without it, don't power from the pod and a flashing
  cable at once.

  On hand: 1N5817 -- genuine Schottky (same 1N581x family as the
  1N5822/1N5819 the BOM recommends), 20V/1A, VF ~0.2-0.45V. Only
  difference from the BOM pick is current rating (1A vs 3A), which is
  fine here: D1 only carries the ESP32's own draw, not the panel
  (panel is fed V+/V- direct, bypassing D1) -- 1A comfortably covers
  the XIAO even during WiFi TX current spikes.


  ESP32-S3's OWN programming USB-C (internal cradle -- the only
  proven way to flash; web OTA is unproven, see Assemble it)

    USB-C connector
     VBUS ----------[ onboard Schottky ]---------------------- 5V RAIL
     GND  ------------------------------------------------------ GND RAIL

  This diode blocks GND RAIL -> VBUS backfeed, but NOT the reverse:
  if a laptop's VBUS sits above the pod's output, the laptop can end
  up sourcing panel current through this small onboard diode. The
  firmware's USB power guard detects a host on this port (via USB
  enumeration) and automatically clamps LED current to a safe budget
  while it's connected -- no extra wiring, but don't rely on the
  diode alone.


LED PANEL (16x16 WS2812B, 160x160mm, 256 LEDs)

  5V RAIL  --+----------------------------------------------------- Panel VCC
             |
         [ C1 1000uF ]
             |
  GND RAIL --+----------------------------------------------------- Panel GND

  ESP32-S3                                            Panel
  GPIO4 -----[ R3 330R ]----------------------------- DIN

  GPIO4 is a build flag (LED_PIN in platformio.ini) -- change there,
  not here, if your wiring differs. Optional: insert a 74AHCT125
  level shifter between R3 and DIN if 3.3V data proves unreliable
  driving the panel from 5V.


All GND labels share a common ground.
All 5V RAIL labels are the same net: fed primarily by the power pod
(V+/V- direct, no diode), and -- only while a host is enumerated on
the programming port -- additionally by that port's VBUS through the
onboard diode (current-limited in firmware when this happens).

Assemble it

1. Flash the ESP32 first — over USB on the bench. The firmware has a web OTA endpoint, but it is unproven: its only real-world use sent a build that turned out to be broken, so OTA itself was never confirmed working. There's no external port on the finished clock, so recovering from a bad update means opening the case to reach the ESP32's USB-C. Until OTA is proven on a bench unit, plan to update over USB with the case open.
2. Faceplate letters-down on the desk → diffuser sheet into the opening → lattice on top of it → panel, wire-exit edge toward the bottom (shortest runs to the ESP32 and socket; firmware's mapping settings absorb whatever rotation this gives).
3. Foam pads on the 14 grid points; wiring lies in the open cavity between them.
4. Shell — with ESP32 (USB-C connector toward the locator's open end), power socket, and wiring attached — then four M3×16 screws.

First power-on: run a test pattern, set the panel mapping (rotate/flip/serpentine) in the web UI, then leave it on attract mode for a few hours and check nothing runs more than warm (the vent sizing is calculated but not yet soak-validated — see DESIGN.md).

Firmware

Lives on the firmware branch (PlatformIO, ESP32-S3). NTP + web UI — animation pick/interval, colours, brightness schedule, timezone, panel mapping — with transition animations (Pac-Man eat, cannon shoot-up, Tetris drop, invader zap), attract mode and hidden-word easter eggs. Works fully offline too: it hosts its own hotspot and can take the time from your phone with one tap (DESIGN.md has the details).

The letter grid

IT K IS A HIGHSCORE Z         rows 0-8: minute words
TWENTY INSERTCOIN             rows 9-12: hour words + OCLOCK
FOURTEEN SIXTEEN A            rows 13-15: arcade hall of fame
SEVENTEEN TWELVE B
EIGHTEEN NINETEEN             hidden arcade words:
THIRTEEN QUARTER S            HIGH SCORE, INSERT COIN,
THREELEVEN TEN ZAP            ZAP/PAC/POW (stacked), GO,
TWONE FIVE HALF PAC           GAME/OVER (stacked),
MINUTES X PASTO POW           SPACE INVADERS, PEW, GALAGA,
TWONE THREEIGHT GO            DONKEY KONG, ASTEROIDS, QBERT, UP
SEVENINE FOUR FIVE
SIX TEN ELEVEN GAME
TWELVE OCLOCK OVER
SPACEINVADERS PEW
GALAGA DONKEYKONG
ASTEROIDS QBERT UP

Words share letters to fit per-minute wording into 16×16 (TWONE = TWO+ONE, PASTO = PAST+TO, …) — the full construction is in DESIGN.md.

More detail

• DESIGN.md — design notes and rationale: power budget, enclosure stack, ventilation, diffuser experiment, offline timekeeping, full BOM component notes.
• DEVLOG.md — the engineering history: every bug, root cause, fix, and how each was verified.
• Concept comparison — the enclosure concepts considered (arcade cabinet vs. subtle wedge); both demo pages are archived in docs/ and mirrored to word-clock-demo for GitHub Pages hosting.