Feedback modules often are referred to after the method of how their sensors work.
YaMoRC offers 4 types of feedback inout sensors:
Current Sense: Inputs that measure the current that flows from rail to rail caused by e.g. a loco's motor, headlamps etc. Also passenger cars with interior illumination or freight wagons with conductive wheel axles. Usage: Track (section, block, turnout) occupation detection. OPTO: Inputs that are galvanically isolated from the module electronics by means of an optocoupler. Having this isolation, enables two different power sources to be used for module and e.g. tracks. GND: This is the most simple input type. It detects feedback when the input is connected to ground (GND). The module provides a so called pull-up resistor to turn the feedback off in case the input is left "open". An important note to this type of input is, that for detecting track events, it cannot be used with boosters that uses so-called H-Bridges! RailCom: This type of input is able to detect messages coming from the loco sent by a RailCom enabled decoder. The module translates those messages in feedback messages to the command station. It is mainly used to detect which loco (address) is present in a stretch of track. For vehicles without a RailCom enabled decoder, this type also works as a Current Sense input.