m8 — 2×4 LEGO Macropad & SPI Testbed
Status: Prototype Tested
2×4 Ortho (8 Keys)
74HC595 + 74HC589 Shift Registers
SPI E-Ink + I²C OLED + Clickable Encoder
QMK
The m8 (m4×2) is an 8-key hardware development testbed designed to validate scanning a switch matrix via chained 74HC595 (column output) and buffered 74HC589 (row input) shift registers over hardware SPI while sharing the SPI bus with a WeAct SSD1680 e-ink display, alongside an I²C OLED screen and a clickable rotary encoder.
The circuitry validated on this board directly informed the architecture of m65 Rev 10/11 and m66 Rev 2/3. See Not Enough Pins? for the full schematic analysis of this SPI bus-sharing circuit.
KiCad Project & Hardware Files
Full schematics, PCB layouts, and Gerbers are available in the GitLab repository:
