KB69: Nemo Junction - Connecting BD4 to the SE8C

This article was last updated on Nov. 28, 2011, 5:47 p.m. | Print Article | Leave Feedback

BD4 Output

Each BD4 is situated between the PM42 Power Manager and the railroad.

The DCC signal passes from the DCS50 Zephyr, through the Power Manager, through the BD4 to the track to the locomotive.

When a locomotive (or equipped car) is present in a track segment, the BD4 also sends out occupancy information, in two ways.

Occupancy Information Output


The LED1 10-pin header is for testing the status of power to the rails and block occupancy with the LED indicator which is included with the BD4.

The LED1 can also be used for panel indicator lights using LED's.


The DS1 10-pin header of each BD4 is connected to the SE8C.

Outer Loop Connections
Pins 1, 3, 5 and 7 of the DS1 are the respective outputs for detection blocks 1, 2, 3, and 4 of the Outer Loop.

Using a section of ribbon cable and a socket from the SDCK - Signal Driver Cable Kit, the BD4 is connected to the SE8C.

A segment of ribbon cable is cut to the distance from the BD4 to the 44-pin edge connector of the SE8C.

One end of this cable is fitted with a 10-pin socket from the SDCK.

The SDCK socket is then connected to the BD4 so that Pin1 corresponds to the brown wire, making it easy to identify the different DS1 connections of the BD4 at the 44-pin connector of the SE8C.

The Nemo Junction Outer Loop's BD4 is connected to pins 5, 7, 9 and 11 of the SE8C's 44-pin edge connector; on the SE8C pin-out diagram, these are identified as "DS01", "DS02", "DS03" and "DS04".
The ground connection of the Outer Loop's BD4 (Pin 2, or 4, or 6, or 8, or 10) is the common wire of the BD4 and is connected to pin B (-VE sensor return) of the SE8C's 44-pin edge connector.

The corresponding wire colors, if Pin1 is connected to the brown wire:

  • Pin 1 - Brown
  • Pin 3 - Orange
  • Pin 5 - Green
  • Pin 7 - Purple

The -VE sensor return connection can be made with Pin 2 - Red.

Here, a completed cable:

Inner Loop Connections

The same process is repeated for the Inner Loop BD4, which is connected to pins 13 ("DS05"), 15 ("DS06"), 17 ("DS07") and 19 ("DS08") of the SE8C 44-pin connector.

In this way, the Detection Sections for both the outer and inner loops of the railroad now feed track occupancy information to the railroad's LocoNet via the SE8C.

A computer program will take that information and apply signaling operation logic.

This is how a railroad signal interlocking operates.

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