• Modular Signaling System Debugger

Modular Signaling System Debugger



As a debugger for the Modular Signal System, the MSS-DEBUG monitors signals on the occupancy bus as well as sends occupancy signals to test installations.  It's useful for bench testing signal installations on a module when no larger MSS network is available, or for figuring out why an MSS installation isn't working correctly.  The MSS-DEBUG requires 3x AAA batteries to provide operating power and includes a 1' straight-through ethernet cable for attaching it to an adjacent MSS node.


  • Diagnostic LEDs indicate status of MSS signal lines:
    • Local Block Occupancy
    • Approach Occupancy In (to node)
    • Advance Approach Occupancy In (to node)
    • Advance Occupancy Out (from node)
    • Advance Approach Occupancy Out (from node)
    • Diverging Approach In/Out (to/from node)
  • Switches for toggling each signal line to test module response
  • 12V bus pull-up voltage for testing bus segments without pull-ups (e.g. MSS-CROSSOVER module)
  • Compliant with the Modular Signal System 2.0.1 standard
  • Powered from 3x AAA batteries


3.25"(L) x 1.9"(W)

Many thanks to Gregg Fuhriman and other contributors for the development and release of the Modular Signal System specification.


The complete gEDA design files are available on GitHub.

User Manual


  • $25.00

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