IO4 Quad Optical/IR Detector baseboard
Derived from Geoff Bunza's SMA Detector, published in his column in MRH as "SMA23 – A New DCC & DC Car & Loco Detector – Differential Absolute Position Detector (DAPD)"
This version eschews "small" in favor of a remote mountable IO4 baseboard that can be mounted near the point of use, and then use sensors disguised as ties for the sensor electronics themselves.