Signaling and Detection System

An Eastbound freight approaches a Medium Clear (RGR) Signal at BOB Tower. Note the crossover thrown ahead and the Restricting (RRY) Signal on the siding.

Some advanced signal aspects used on the Garden State Northern.
Approach Medium (YG) seen at Middletown preceding RYG at DOUG Tower.
Medium Approach Medium (RYG) seen at DOUG Tower preceding RGR at BOB Tower.
Approach Slow (YRG) seen at PETE Tower approaching the Hidden Yard.

Garden State Northern signal aspects are modeled after the NORAC system.

A view of the center portion of the dual widescreen monitors that display the virtual Dispatcher’s Panel. The switch levers across the top row throw the turnouts directly above and the traffic levers below them set the signals.

It all began at the Club business meeting held on June 16, 2000 when DCC Bob Savino asked for and the Club approved $200 to purchase detectors and detector motherboards from JLC Enterprises. These componenets were part of a state of the art Dr. Bruce Chubb designed C/MRI (Computer Model Railroad Interface) signaling and detection system. The Hidden Yard was in desperate need of detection and so Bob wanted to start there. Two kinds of detectors were purchased. One was the DCCOD (DCC optimized detector) which only worked for DCC. The other OD (optimized detector) was the more common anti-parallel diode design which required a constant bias on the track. Bob spent the next couple of years testing these detectors in his basement at home and working with some other C/MRI components he had purchased. By 2002, he had an old PC talking to the components and both detectors working. Bob was not at all happy with the ODs because the diodes distorted the DCC signal and had to be replaced with fast recovery types. The Club was still using DC as much as DCC and so the superior DCCOD was not really an option at this point. The signaling system was not going to work without reliable detectors and so everything went into a box and sat for nearly three years.

The Thanksgiving 2004 Open House was the last show operated with conventional DC. At the business meeting held on September 24, 2004, Bob had asked the Club if it wanted to run the show with DCC like it had been running its operating sessions. The Club voted no because there were still not enough DCC locomotives and it would have been too confusing to change the operating scheme at that time. In March 2005, the Club finally decided to switch the shows over to DCC. Bob went home and dusted off the box of C/MRI componenets. He could now forge ahead with the DCCOD detectors.

The next major breakthrough came when it was discovered that a Virtual Dispatcher’s Panel could be written in software using Visual Basic. The Club had no room to physically fit a panel large enough to control the entire railroad. A real panel would have been at least 5 feet long. Bob, using some templates provided by JLC Enterpriese, spent several years writing and fully customizing over 7000 lines of Visual Basic code to create the Dispatcher’s Panel.

The first components, finally installed on the layout in 2009, became Node Zero, consisting of an IOMB motherboard, SUSIC serial interface card to connect the Club’s PC to the node, a couple of DIN32 input and DOUT32 output cards, DCCOD optimized detectors for DCC, and several ODMD optimized detector motherboards. DCC Bob Savino used a recycled computer power supply, which provided very clean +5 Volts and +12 Volts, to power all of the boards and later added fuses to protect the fragile components. Signaling had finally arrived at the Hidden Yard and the two interlockings on either side of it.

Three years later and after the purchase of several Super Mini Nodes, additional Detector boards, and signals around the railroad, the Club had essetnailly completed its fully functioning prototypical system. Repeater boards continue to be added up near the ceiling to make hard to see signals easier to view for operators. Additional turnouts and lock relays continue to be added to the Computer, giving the Dispatcher more control.

GSN Signaling System by the Numbers
Block Detectors70
Sensed Turnouts (some are PC Controlled)40
Signal Masts (with 1, 2, or 3 Heads)94
Signal Heads284
Maxi Nodes1
Mini Nodes7

Behind the Scenes (Under the Layout)

A look at Node 0, the central hub of the signaling and detection system, located beneath both the west throat of the Hidden Yard and Steam Facility. In the top left corner is the IOMB motherboard with one SUSIC Super Mini Node card, two DIN32 input cards, and five DOUT32 output cards. Below that is a small card which converts the RS232 signal from the computer’s serial port to RS485. This RS485 serial bus connects to the SUSIC card of Node 0 and then goes on to all the other Super Mini Nodes around the layout. Down the middle are two racks of output RJ45 connectors for all of the signals at Soggy Bottom, both ends of the Hidden Yard, PETE Tower, and the east end of Albatross Yard. Top right is three rows of DCCOD detectors covering that same territory. Along the bottom are the power fuses and power terminals feeding +5 Volts, +12 Volts, signal ground, and track common rail ground to the various cards at Node 0. The computer power supply that runs the entire system is mounted on the back side of the white plywood. There is also a separate unregulated +12 Volt supply for the various control relays.

Node 5 before it was installed at Middletown. The C/MRI Super Mini Node board is top center. Signals will plug into the RJ45 jacks at the top left. Tortoise switch machines are controlled by the relays at the bottom left. This small circuit board contains two sets of relays, one being a lockout relay and the other actually operating the Tortoise machine. The screw terminals terminals at the top right accept inputs from the contacts on the Tortoise machines so that the C/MRI system knows the position of every turnout, regardless of how it was thrown. Detector boards plug into the motherboard on the bottom right.

Node 1 after it was installed at WJ Tower. Note the LEDs on the Super Mini Node indicating communication back to the PC and one of the Detectors with a red LED showing a block occupied. This node handles detection for WJ, BOB and DOUG Towers, and all the blocks in between. This was done to save wiring. However, BOB and DOUG Towers each have their own nodes supplying outputs to all their respective signal heads.

A bench test of the Signal Bridge that is now installed going westbound approaching PETE Tower. The RJ45 cable from a Node plugs into this Signal Board which is typically mounted right under the Signal. The transistors on the board drive the LEDs on the Signal and the potentiometers allow the LEDs to be fine tuned to blend and make a nice amber (yellow). These boards were designed and built to solve several issues by standardizing the interface between the C/MRI and the actual signals. The Club needed to come up with a way to add load resistors for the LEDs, provide yellow adjustment, and simplify installation and wiring beneath the layout.

A detailed look at a typical Occupancy Detector and Motherboard. This brilliant design by Dr. Bruce Chubb makes use of a pulse transformer. The yellow wire wrapped around the black transformer is the primary winding and ground return for one track circuit. It is not physically connected to the signal circuit, thereby providing total electrical isolation. When DCC current flows through the track, it induces a voltage in the transformer secondary causing the Detector to show occupied. These Detectors are DCC only. The potentiometer adjusts the sensitivity of the circuit and the red LED on the end shows occupancy. The Detector also has built in time delays that simulate the massive track circuit relays found on the prototype (half second on, two seconds off).