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S88 Feedback Module

S88 Feedback module

Note: In addition to Information on Feedback Modules, this page details Electronic Project(s) that offers similar functionality to commercial products


For the control of the trains and the signals in a model railroad, the computer has to know in which section of track are located the trains, for that, it needs to know which sections are occupied.

One way of detecting if a section is occupied is with the use of Occupancy detectors.  Occupancy detectors provide a “feedback” signal that is connected to a feedback module that informs to the command station and this to the computer.

The two most common Feedback systems on the market is RS  and S88.

For Computerized control we need to connect the Feedback Modules to a PC by means of an interface.

Also the feedback modules can be connected directly to the PC by means of GenHSI interface for the S88 or the RS2PC interface for the RS.

The DCC_Gen command station uses the S88, the signal of the occupancy detector arrives to one of the inputs of the S88 feedback module (it is connected to ground) and DCC_Gen reads it every certain time, for that this modules have a R-S flip-flop for every input.

You can connect to DCC_Gen up to 8 S88 modules (128 inputs) one module next to other, JP1 module connector connected to the JP2 connector of the next one, the first JP2 is conencted to DCC_Gen, that will be the 65-66 module number as Lenz, the next one 67-68 and so on


I have build S88 modules like the S88 Interface web, this is the schematics with common components:

Every input goes to an R-S flip-flop (4044) to memorize the ocupation until the command station reads it, the reading is done with serials registers (4014) so it can be chained different circuits.

This is a photo of a finished PCB:


Support files:

Download the design of the printed circuit board

Read this manual on how to use the S88 with the occupancy detector as example.

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