My personal micro pad for general shortcuts and game development, I am using 3 x 3 keys matrix and 9 diode (so it just needs 6 gpio pins) and 3 extra keys to switch between three different channels , so in total the micro pad can have a total of 3x9 = 27 output. It is based on XIAO RP20400

BOM
# XIAO RP20400
# 12 x MX-Style switches
# 12 x Blank DSA keycapss
# 9 x Through-hole 1N4148 Diodes
# 4 x M3x16mm screws
# 4 x M3x5mx4mm heatset inserts

Schematic

PCB


Case


Final Look