Aarivpad

AarivPad - My 3x3 Mechanical Macropad + EC11 Rotary Encoder + OLED

Try the Live Interactive 3D Hardware Workbench & KMK Simulator: https://aariv.me/hackpad/

I designed and built AarivPad for the Hack Club Stardance Hackpad mission. It is a custom 3x3 mechanical macropad powered by a Seeed Studio XIAO RP2040, an Alps EC11 rotary encoder with push-button switch, a 0.91" 128x32 SSD1306 I2C OLED status display, and four SK6812 MINI-E reverse-mount addressable RGB underglow LEDs.

Alongside the complete KiCad 8 schematic, 2-layer routed PCB, JLCPCB Gerber archive, parametric OpenSCAD enclosure STLs, and CircuitPython KMK firmware, I also built an interactive browser workbench at https://aariv.me/hackpad/ so you can test all 9 keys across all 3 macro layers, spin the EC11 encoder, inspect the 2-layer copper traces, and orbit the exploded 3D CAD assembly directly in your browser.

Why I Built This

Whenever I am working across terminal Git sessions, KiCad PCB layout, and media playback, I constantly find myself reaching for awkward multi-finger keyboard chords (git status, git diff --stat, git log --oneline -n 15, switching tmux panes, or toggling KiCad copper layers and track widths).

I wanted a compact desk companion that sits right next to my mouse and gives me:

1. Nine tactile mechanical switches arranged in a standard 19.05mm (0.75") 3x3 grid for single-press macros.
2. A physical EC11 rotary encoder at the top-right corner so I can scrub timelines, adjust volume, or zoom in and out of KiCad/CAD viewports with tactile detents.
3. A crisp 128x32 SSD1306 OLED screen at the top-left so I never have to guess which macro layer (L0: GIT/DEV, L1: MEDIA/RGB, or L2: KICAD/CAD) is currently active.

Features & How It Works Under the Hood

1. 3x3 Anti-Ghosting Switch Matrix + Peripherals on 11 GPIOs

Because the Seeed Studio XIAO RP2040 exposes exactly 11 user GPIO pins (D0 through D10), fitting 9 switches, a quadrature rotary encoder + push button, an I2C OLED display, and an addressable RGB LED chain required careful pin budgeting:

• Columns (COL0..COL2): Wired to D0 (GPIO26), D1 (GPIO27), and D2 (GPIO28).
• Rows (ROW0..ROW2): Wired to D3 (GPIO29), D6 (GPIO0), and D7 (GPIO1) through nine 1N4148W SOD-123 switching diodes (D1..D9) oriented COL2ROW so pressing any combination of keys simultaneously never causes ghosting.
• Hardware I2C0 (SDA / SCL): Reserved D4 (GPIO6) and D5 (GPIO7) for the 0.91" 128x32 SSD1306 OLED display at address 0x3C.
• EC11 Encoder & Underglow Chain: Quadrature channels ENC_A and ENC_B connect to D8 (GPIO2) and D9 (GPIO4), while D10 (GPIO3) handles the encoder push switch (ENC_SW) and drives the 4-pixel SK6812 MINI-E RGB underglow chain.

2. Three-Layer KMK Firmware (firmware/code.py)

I wrote the firmware in CircuitPython using KMK (kmk_keyboard, Layers, EncoderHandler, RGB, and adafruit_displayio_ssd1306):

• Layer 0 (GIT / TERMINAL): Single-key macros for git status -sb, git diff --stat, git add -A && git commit, git log --oneline -n 12, git pull --rebase, git push, tmux pane split, terminal clear, and layer cycle (DF(1)). Rotary dial scrolls terminal history line by line.
• Layer 1 (MEDIA / RGB): Play/Pause, Next/Previous Track, Mute, RGB Hue/Animation toggle, Brightness step, and Window Snap shortcuts. Rotary dial controls system volume (VOL+ / VOL-).
• Layer 2 (KICAD / CAD): KiCad track routing (X), via placement (V), copper layer flip (F.Cu <-> B.Cu), DRC inspector, 3D viewer launch (Alt+3), and measurement tool. Rotary dial zooms the canvas in and out.

3. 2-Layer 68mm x 84mm PCB & Parametric OpenSCAD Enclosure

• KiCad 8 PCB (pcb/aarivpad.kicad_pcb): Routed on a compact 68.0mm x 84.0mm two-layer board with 1.6mm FR4 thickness, rounded 3.0mm corners, four M2 mounting holes (4.0mm inset), 0.25mm signal traces (0.50mm power rails), and stitched GND copper pours on both F.Cu and B.Cu.
• 3D-Printable Case (cad/aarivpad_case.scad): Includes a heat-set M2 bottom tray (bottom_case.stl), a 1.5mm/3.0mm clip-in MX switch plate (switch_plate.stl) with a framed viewport over the OLED and clearance for the EC11 bushing, and a knurled 6.0mm D-shaft knob (encoder_knob.stl). Total print weight is ~58g PLA - well under the 300g Printing Legion limit.

What Was Tricky to Build

1. Fitting 9 Keys + OLED + EC11 + RGB onto the XIAO RP2040's 11 Pins: A direct-pin wiring approach would have needed 9 (switches) + 2 (I2C) + 3 (encoder) + 1 (RGB) = 15 GPIOs, which exceeds the XIAO RP2040's 11 pins. Scanning the 9 switches as a 3x3 diode matrix reduced the switches from 9 pins down to 6 (3 cols + 3 rows), leaving D4/D5 free for hardware I2C and D8/D9/D10 free for the EC11 encoder and RGB chain.
2. Preventing Mechanical Interference Between the OLED Header and Top Switch Row: On a tight 68mm x 84mm board, placing the XIAO RP2040, the 0.91" OLED module, and the EC11 rotary encoder along the top header zone required carefully offsetting the OLED center to (22.0mm, 14.5mm) and the EC11 shaft to (52.5mm, 14.5mm) so the top switch row (SW1..SW3 at Y = 34.0mm) clears both the OLED PCB edge and the 18mm knurled encoder knob with zero keycap rub.

XIAO RP2040 Pinout & Matrix Wiring

Bill of Materials (Hackpad Kit Compatible)

Repository Structure & How to Explore It

• Interactive Browser Workbench: Open https://aariv.me/hackpad/ (or open index.html locally) to test the 9-key KMK macro simulator with Web Audio mechanical switch clicks, rotate the EC11 encoder, inspect the 2-layer PCB traces (F.Cu, B.Cu, F.SilkS), and orbit the 3D exploded CAD assembly.
• KiCad 8 Design Files: Open pcb/aarivpad.kicad_pro in KiCad 8 to inspect the schematic (pcb/aarivpad.kicad_sch) and routed PCB (pcb/aarivpad.kicad_pcb). Fabrication-ready Gerbers are zipped at pcb/gerbers/aarivpad-gerbers.zip.
• 3D Enclosure CAD: Open cad/aarivpad_case.scad in OpenSCAD or slice cad/bottom_case.stl, cad/switch_plate.stl, and cad/encoder_knob.stl directly in Bambu Studio / PrusaSlicer.
• Firmware: Copy firmware/code.py onto your XIAO RP2040's CIRCUITPY drive with the kmk and adafruit_displayio_ssd1306 libraries installed.

License

MIT.