The Modular Signal System (MSS) An Overview In 2005 Gregg Fuhriman developed the Modular Signal System, designed to allow Automatic Block Signals to be easily installed on nodular layouts. Two important features of the MSS are the use of a combination of optical and current detection to eliminate the requirement for resistance wheel sets, and the Modular Signal Buss for connecting modules. Signal Detection To add a signal system to a model railroad it’s necessary to have some way to detect trains. The prototype uses the all metal wheels of cars and locomotives to “shunt” the rails and provide an electrical path between the rails. One approach to detection on a model railroad is current detection, an electronic circuit placed in series with the feeder to the track which can sense the flow of electricity to the train. This works fine for locomotives, but since model cars have insulated axles they will not be detected, and the block will clear as soon as the locomotive exits. The usual time consuming solution is to replace at least on wheel set on every car with a resistance wheel set that will draw enough current to activate the current detection. Others have tried to activate model signals using optical detection. Some optical detectors rely on room light, but these are finicky and unreliable. There are good detectors, using reflective infrared light. These use an infrared LED to generate an invisible beam that is reflected off the bottom of the train and detected by a phototransistor. These work great, but are limited to detecting the presence of a train at a single point on the layout. Before the MSS no one had found a way to reliably relate the point detection to the blocks a signal system uses. How Does the Modular Signal System Work? Let’s look at how the MSS combines current and optical detection to eliminate the need for resistance wheel sets. In fig. 1 the train has just entered block B. Optical detector AB has detected the train, and current detector B has also detected the locomotive, both setting Block B to occupied.

BLOCK A

BLOCK C

BLOCK B

Current Detector B

Optical Detector AB

Current Detector B

Optical Detector BC Current Detector B

Fig. 1 In fig. 2 the train has cleared optical detector AB, but current detector B detects the locomotive and keeps Block B at occupied.

BLOCK A

Current Detector B

BLOCK C

BLOCK B Optical Detector AB

Current Detector B

Fig. 2

Optical Detector BC Current Detector B

In fig. 3 the locomotive has left Block B, and the standard insulated cars are not detected by current detector B, but Block B is properly kept at occupied by optical detector BC.

BLOCK A

Current Detector B

BLOCK C

BLOCK B Optical Detector AB

Current Detector B

Optical Detector BC Current Detector B

Fig. 3 In fig. 4 the train has now left Block B and all three detectors have cleared, as has Block B. Note that optical detector AB really only serves to keep Block A occupied until the train has cleared. Optical detector AB also becomes necessary for Block B with a train moving to the left.

BLOCK A

Current Detector B

BLOCK C

BLOCK B Optical Detector AB

Current Detector B

Optical Detector BC Current Detector B

Fig. 4 The Modular Signal Bus The Modular Signal Bus is designed to allow the quick and easy connection of signaling between modules. It uses standard 8 pin RJ45 Ethernet cables and connectors, which are readily available from computer networking suppliers. The MSS standard takes advantage of the cross-over cables to eliminate the problem of left and right (or East and West) ends of the modules. Both ends of each module are wired the same, and the cross-over cable takes care of correctly connecting outputs to inputs. The beauty of the bus is that the user doesn’t need to understand what each pin and wire does, it is plug-and play, just connect the module and it works. Modules built to this standard can be quickly connected together in any combination and still have a working Automatic Block Signal (ABS) system that is acceptably close to prototype operation. The following drawings show the pin assignments and color code for the Modular Signal Bus, as well as the wiring for applying it to modules, both unsignaled (called Crossover Modules), and signaled modules (called Cascade Modules).

1 Adv Apr In 2 Approach In 3 Adv Apr Out 4 Blk Occupied 5 Ground 6 Approach Out 7 Reserved 8 Reserved

ORN/WHT ORN GRN/WHT BLU BLU/WHT GRN BRN/WHT BRN

Adv Apr In 1 Approach In 2 Adv Apr Out 3 Blk Occupied 4 Ground 5 Approach Out 6 Reserved 7 Reserved 8

GRN/WHT

ORN/WHT

1 Adv Apr In 2 Approach In 3 Adv Apr Out 4 Blk Occupied 5 Ground 6 Approach Out 7 Reserved 8 Reserved

GRN

ORN

ORN/WHT

GRN/WHT

BLU

BLU

BLU/WHT

BLU/WHT

ORN

GRN

BRN/WHT

BRN/WHT

BRN

BRN

Crossover Cable Wiring

MSS Bus pinnout and color code for straight-through cables

GAPS

Other than Main Track feeds do not go through detector.

1000 OHM All Main Track feeders must be through detector.

DCC Track Power

Optional direct connection

LOGIC

GND 1 2 3 4 5 6 7 8

LOGIC

GND

BLU

WHT/BLU

WHT/BLU

WHT/BLU

BLU

DCC Track Power

CUR. DET.

Adv Apr In Approach In Adv Apr Out Blk Occupied Ground Approach Out Reserved Reserved

CUR. DET.

CONTACTS TIED TO SWITCH POINTS LINED FOR MAIN

BLU GRN/WHT

ORN/WHT

GRN

ORN

ORN/WHT

GRN/WHT

BLU

BLU

BLU/WHT

BLU/WHT

ORN

GRN

BRN/WHT

BRN/WHT

BRN

BRN

Crossover Cable

1 2 3 4 5 6 7 8

Adv Apr In Approach In Adv Apr Out Blk Occupied Ground Approach Out Reserved Reserved

Adv Apr In Approach In Adv Apr Out Blk Occupied Ground Approach Out Reserved Reserved

1 2 3 4 5 6 7 8

GRN/WHT

ORN/WHT

GRN

ORN

ORN/WHT

GRN/WHT

BLU

BLU

BLU/WHT

BLU/WHT

ORN

GRN

BRN/WHT

BRN/WHT

BRN

BRN

Crossover Cable

Detecting Main Track Switches Crossover Module Wiring

1 2 3 4 5 6 7 8

Adv Apr In Approach In Adv Apr Out Blk Occupied Ground Approach Out Reserved Reserved

GAPS

IRDOT

OPTICAL DET.

GND

LOGIC

CUR. DET.

GND

YEL IN

RED IN

SIGNAL LOGIC

GND

RELAY

GND

RED IN

LOGIC

GND

YEL IN

SIGNAL LOGIC CUR. DET.

Adv Apr In Approach In Adv Apr Out Blk Occupied Ground Approach Out Reserved Reserved

1 2 3 4 5 6 7 8

ORN/WHT ORN GRN/WHT

ORN

BLU

BLU

GRN

ORN

WHT/BLU

ORN

BLU

DCC Track Bus

WHT/GRN ORN

WHT/GRN BLU

BLU BLU/WHT

BRN

ORN GRN/WHT BLU BLU/WHT GRN

GRN BRN/WHT

ORN/WHT

GRN

Signaled Module Wiring (a.k.a. Cascade Module) All Main Track switches must have detection to their block.

BRN/WHT BRN

1 2 3 4 5 6 7 8

Adv Apr In Approach In Adv Apr Out Blk Occupied Ground Approach Out Reserved Reserved

LOGIC

LOGIC

CUR. DET.

GND

GND

LOGIC

CUR. DET.

GND

CUR. DET.

DCC Track Bus

GAPS BOTH TRACKS

SIGNAL LOGIC

GND WHT/BLU

RED IN

WH/GRN

GND

YEL IN

Sig. Pwr.

YEL IN

SIGNAL LOGIC

SIGNAL LOGIC

RED IN

GND

RELAY

GND

YEL IN

SIGNAL LOGIC

RED IN

CONTACTS TIED TO SWITCH POINTS LINED FOR MAIN. FROG WIRING NOT SHOWN.

IRDOT

OPTICAL DET.

ORN/WHT ORN GRN/WHT

BLU

GND

YEL IN

RED IN

ORN

BLU

GRN

BLU/WHT GRN BRN/WHT BRN

1 2 3 4 5 6 7 8

Adv Apr In Approach In Adv Apr Out Blk Occupied Ground Approach Out Reserved Reserved

1 2 3 4 5 6 7 8

ORN/WHT ORN GRN/WHT BLU BLU/WHT

GRN ORN

ORN WHT/GRN WHT/BLU

BLU

GRN

Adv Apr In Approach In Adv Apr Out Blk Occupied Ground Approach Out Reserved Reserved

BLU

4PDT 12V RELAY

ORN/WHT ORN

WHT/GRN

WHT/BLU

GRN

GRN/WHT BLU BLU/WHT GRN

BRN/WHT

BRN/WHT

BRN

BRN

Single Track to Double Track Module

1 2 3 4 5 6 7 8

Adv Apr In Approach In Adv Apr Out Blk Occupied Ground Approach Out Reserved Reserved

Parts Sources for the MSS Signal Logic: Tractronics Inc. AutoBlock and AutoSearch Signal Logic, Signal Products at http://users.rcn.com/weyand/tractronics/ttinchom.htm Atlas

HO Signal Control Board, Signal System at http://atlasrr.com/ also available through dealers.

Infrared Detector: Heathcote Electronics

IRDOT-2DEW Products at http://www.heathcote-electronics.co.uk/ Also available from Micro Mark http://www.micromark.com/ search for IRDOT-2DEW

Current Detectors: Any current detector that has an open collector output is suitable, for DCC the NCE BD20 works well and requires no power input. See http://www.ncedcc.com/ Available from any DCC supplier. RJ-45 (CAT-5 network) Cable Supplies: Many sources, I use PCH Cables Inc., http://www.pchcables.com/ RJ-45 couplers are listed separately with Keystone Jacks.

Look under Network Cables and Supplies (left side)

Other Parts: Tie replacement IR sensor pair, Mouser Elect. http://www.mouser.com/ 1N 4006 general purpose diode, Mouser PN 625-1N4006-E3/73 4PDT 12 VDC relay, Mouser PN 653-MY4-DC12 Barry Draper Feel free to contact me for advice on the MSS, [email protected]

Part number 828-OPB704WZ