Absolut-CAS — the drop-in board

KiCad project for the NumOS Casio Port. It replaces the original board inside a stock Casio fx-82 / fx-991 with an ESP32-S3, a colour screen interface and a oem compatible keypad matrix — reusing the calculator's own shell and buttons.

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Components

• U8 — ESP32-S3-WROOM-1. Does everything/core MCU.
• U7 — TCA9555DBR (16-bit I²C expander, SSOP-24). Reads the keypad matrix, so the whole keypad costs the MCU two pins instead of fifteen.
• S1 — 40-pin 0.5 mm FPC connector. This is what the ILI9341 2.4" 320×240 panel plugs into.
• U5 — TP4056-42-ESOP8. Li-ion charge management for battery.
• Q1 — DMP3099L P-channel MOSFET, plus a battery protection pair on SOT-23. Power Path
• LDO — TPS73733DCQR. Regulates the rails.
• J2 — USB-C 16P connector, USB 2.0 only, 5.1k CC pull-downs on R3/R19.
• J4 — JST PH 2-pin. Battery connector.
• J3 — Micro SD socket (footprint CONN_TF-01A_HRO). Fitted. Doesn't work. See status.
• B1/B2 — two tactile push buttons. D5/D6 — LEDs. D4 — 1N5819. D1–D3 — SOD-123.
• Passives are all 0603.
• **Camera Header for an OV2640 Module
  • will use an fpc-connector based smaller ov2640 in v2 and have it embedded in unit rather than external.

The board itself

• 4 layers: F.Cu, In1.Cu (GND Plane), In2.Cu (signal), B.Cu
• 1.6 mm.
• Outline: 65 × 94 mm as drawn in the board file.
• Every component sits on B.Cu — the whole board mounts bottom-side-up behind the keypad.

What it can actually do

• Runs NumOS: CAS maths, natural display, graphing, apps, and a Game Boy emulator.
• 320×240 colour screen instead of a 7-segment LCD.
• Wi-Fi on board. The AI and notes features need it.
• Rechargeable Li-ion over USB-C. Untethered.
• Keypad-only input. No touch.
• OTA firmware updates are the eventual goal.
• Drop-in: same shell, same buttons, same feel.

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Files

Path	What it is
Cfx-port.kicad_pro	Project settings.
Cfx-port.kicad_sch	Root schematic. Just holds the three sheets.
Cfx-port.kicad_pcb	The board. 95 footprints.
keypad.kicad_sch	Keypad matrix and the TCA9555 expander.
power-ic.kicad_sch	Charger, LDO, protection, USB-C.
esp32-s3-pinout.kicad_sch	Module pinout and connectors.
production/	Fabrication outputs. See below.
jlcpcb/	Order output folder. gerber/ and production_files/ are empty.
plots/	Cfx-port__Assembly.pdf.
packages3D/	3D models. Downloads/ holds the vendor STEP files.
Cfx-port-backups/	Dated zips. The project's own footprints live here in Library.pretty.
KicadConductivePads/	Third-party pad footprints. Own LICENSE, own nested .git.
.history/	KiCad autosaves. Contains its own nested .git.
.portability/	KiCad's own backup manifest.
DRC.rpt / ERC.rpt	Design rule and electrical rule reports.
Cfx-port-all-pos.csv	Pick-and-place data.
fp-lib-table / sym-lib-table	Footprint and symbol library pointers.
NeoFX.kicad_sym, sch_data.json, fp-info-cache, fabrication-toolkit-options.json	Support and scratch.
untitled.kicad_sch, Cfx-port.kicad_sch_old	Old copies, not part of the project.

Everything else in this folder is KiCad scratch — ~*.lck locks, zero-byte tmp*.rpt, #auto_saved_files#, .step, and model.stl.[sS][tT][eE][pP] (a broken filename from a shell glob that got committed). Safe to ignore.

Status — v1

• Board ordered August 2026, delivered, built, partly tested.
• Working: keypad, calculator maths, boot, Wi-Fi.
• Broken: the SD slot. Fitted and dead. Board decision 2026-10-01 — no SD in v1, it comes back in v2.
• This is a first PCB. Nothing here is physically validated beyond "it boots".
• v2 is roughly a month out. No promises.

Known issues and cleanup before the next order

• The reports are stale. DRC and ERC are dated 2026-07-31 / 2026-08-02, older than the last board edit (2026-10-03). Re-run both before trusting them.
• Last DRC: 0 violations, but 59 unconnected pads.
• Last ERC: 0 errors, 5 warnings — two library symbol mismatches and three power pins not driven by any output power pin.

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Credit

Keypad pad footprints come from KicadConductivePads by nataliethenerd — public domain (Unlicense), sizing loosely based on the Game Boy Color and Pocket pads. Everything else in this folder is AbuPaad's Keypad pad footprints come from KicadConductivePads by nataliethenerd — public domain (Unlicense), sizing loosely based on the Game Boy Color and Pocket pads. Everything else in this folder is AbuPaad's