The MorBus connects at left. The board is completely powered via the MorBus interface.
The left four connectors in back provide 16 digital outputs. Each connector carries four digital outputs, 5 volt power, and ground. The outputs are either 5 V or 0 V, and can be shorted to power or ground indefinitely without damage. The outputs have 150 Ω impedance both high and low, so can drive LEDs directly to either power or ground.
The right two connectors in back provide eight digital inputs. Each connector carries four digital inputs, 5 volt power, and ground. The inputs are passively pulled high, so switches can be connected directly between any input and ground. 50 ms debouncing provides reliable detection of switches without false events. The passive pullups are weak enough so that ordinary digital logic signals can be received. Such digital logic can even be powered from the 5 volts and ground provided by each connector. The digital inputs are protected to withstand over ±20 volts indefinitely without damage.
The outputs of an Olin's Depot OC1 occupancy sensor only requires a direct connection to ground and four digital input lines. No other electronic parts are required.
Prototypes were demonstrated working at the NMRA HUB Division model
railroad show on 6-7 December 2014 in Marlborough MA, and at the Amherst
Model Railroad Society model railroad show on 24-25 January 2015 in West