4 layers30 × 23.5 mm

NIMRS-21Pin Decoder
CDFER/NIMRS-21Pin-Decoder
An open source 21-Pin DCC Decoder for model trains
89 parts21
KiCad boards from 1 GitHub repository tagged “model-trains”, the most starred first; open any of them in PCBKit.

CDFER/NIMRS-21Pin-Decoder
An open source 21-Pin DCC Decoder for model trains