AustNTrak T-TRAK Control Unit
By Terry Nathan, AustNTrak

As our club’s inventory of T-TRAK modules has grown over the years and we have become more involved in large regional shows, our need to control large layouts has become more critical. Our old toolbox-mounted unit with a Digitrax Zephyr and a single DC power pack were clearly not able to handle the multi-club layouts that accommodate multiple trains and are made up of multiple independent inner loops. It was time for us to find a way to control everything, including the DC trains, with a central system using wireless throttles.

So we needed to rethink our control unit. Our list of requirements was pretty clear:

• Multiple circuits that are easily switched between DC and DCC operation
• The ability to accommodate wireless throttles for both DC and DCC
• An interface to JMRI to facilitate programming and smartphone throttles
• Enough capacity to handle dozens of engines and throttles
• A portable package that could be transported easily and setup quickly

Our club chose Digitrax as a standard years ago, primarily because of its share of the market and local availability of components. While other neighboring clubs use various other systems, we decided to stay with that as our base system because most of our members either had Digitrax systems of their own or had Digitrax wireless throttles for use with our existing system. But to serve the other clubs that we often set up with, we needed to have the ability to include JMRI Wi/fi throttles as well. This would involve a computer interface and a Wi/fi network in addition to the Digitrax wireless network that we already had in our old system. By having a JMRI computer talking to the DCC system, anyone with a smartphone or tablet can download the free JMRI app for their device and use it as a fully functional throttle on the layout.

And as our layouts have grown, the need to provide wireless throttles for all tracks, even those operating in DC mode, has become more obvious. We decided to build decoders into our control unit which would allow the DCC throttles to control trains that did not have their own decoders. This allows the track to be powered with the analog output of the decoder while providing the operator with a seamless control mechanism that allows him/her to use the same wireless throttle for both DC and DCC trains.


The task of building the control unit was handed to me and the first challenge was to find a container large enough to handle all the components, yet portable enough to travel and store easily. I quickly realized that the system would not fit into a toolbox or briefcase as I had used in my previous unit. So I turned to the T-Kit carriers we use to transport and store our modules in. The carriers have removable trays that are large enough to handle a Triple module that is up to 14” deep. By using one of those trays, I was able to accommodate all the components and cables in a format that fit into our existing carriers and remains easy to pull out and set on a table (or the top of the carrier) for use.


So I went about assembling the pieces to create a control unit. First I needed a DC power supply that could handle all the functions we envisioned for even the largest layout. Because we were already a Digitrax operation, I decided to stay with that product line and selected the model PS2012 which provided 2 circuits capable of a total of 20 AMPs of regulated DC power. One circuit is used to power the DCC controller and the second circuit to provide a 12V DC accessory power bus for use in module accessories such as lighting, layout sound systems, and animation.


I then installed a Digitrax DCS200 command station for the master controller. With an 8 AMP capacity and the ability to handle 120 engines and 120 throttles, I felt that this unit would provide ample capacity for even the most challenging setups. The output from this unit is fed through a Digitrax PM42 power management card to split the power into 4 independent circuits and to provide protection to prevent damage in case of shorts. The picture also shows the PR3 computer interface, but more on that later.


The 4 circuits of track power are color coded (Red, Yellow, Blue, and Green) and each is connected to a 3 position double pole/double throw switch. The switches provide the selection between DC and DCC, with an off position in the middle (convenient while transitioning between different modes of operation). In the DCC position, the circuit is routed directly from the circuit breaker to the track bus (and then out to the track). But in the DC position, the DCC circuit generated by the command station is routed to a Digitrax DG583S 5 AMP decoder (those small boards on the left) for conversion to an analog DC output. This is then fed out to the track bus and on to the track as a standard DC current. So the engine on the track gets an analog DC current, but the operator has the ability to control that circuit as a standard DCC system. I simply took the decoder and mounted it in the control unit instead of inside the engine – the best of both worlds at the flick of a switch.


The output is transmitted to the track through 4 wire track buses which plug into the back of the control unit using PowerPole connectors. The track buses actually consist of two 12 gauge zip cables, each carrying one of the 4 circuits from the control unit. The buses are configured with 2 circuits each because each T-TRAK module is assumed to have 2 tracks. The Red circuit is common to all the bus feeds because it is assumed that the outer track is continuous throughout the layout. But because of the use of Junction modules and the creation of inner loops, each leg of the layout may require a unique circuit for its inner track. So the bus connections are configured to have a common Red circuit for the outer track, and then one of 3 independent circuits (Yellow, Blue, or Green) for its inner track. This allows for up to 3 independent inner loops on the layout. As we have seen already, that is not always enough for a large layout – at our most recent train show, we had 8 inner loops in addition to the continuous outer loop. But there is a limit to how much we could pack into a single control unit, so the system is limited to 4 circuits, and any loops beyond that have to be controlled locally with separate power packs or command stations.


From the operator’s perspective, the system is operated using either a Digitrax duplex radio throttle or a JMRI Wi/fi throttle app. The Digitrax system utilizes a UR92 radio transceiver mounted on a 4’ mast that screws into a base on the control unit. There is also a Digitrax UP5 panel mounted lower on the mast to allow operators to plug into the network to initialize their throttles and to provide a connection point to the Loconet cabling inside the control unit. To handle the operators using JMRI Wi/fi throttles, there is also a Cisco wireless access point mounted on the mast. The mast itself is nothing more than some PVC pipe with standard electrical boxes mounted on it to house the Loconet panels.


To drive the JMRI system, a Raspberry Pi computer is included which interfaces through a Digitrax PR3 unit. The Raspberry runs JMRI’s Panel Pro software which is the server that the smartphone throttles talk to. It then interfaces to the PR3 through a USB connection. Thanks to a great deal of help from Steve Todd (creator of Engine Driver among other things) for configuring the Linux operating system on the Raspberry, we now have a completely self-contained system that requires no operator intervention to drive our JMRI-based throttles.


So the result of all this is a very ordinary looking box with a rather complicated interior. The user interface of the control unit itself is simply 4 color coded switches to determine whether the track is to be operated under DCC or as a standard analog DC circuit. Once that is determined, the operator simply dials in his train id (#11, 12, 13, or 14 for DC operation), and runs his/her train using their throttle of choice.


Future enhancements that are planned are to add at least one booster to the system to provide more power for those very large layouts we anticipate for the future. And with the booster another 4 circuits will be added to reduce the need for remote power packs.

This project was actually relatively easy to construct once I determined the components to be included and the container to put them in. It is simply a matter of finding a way to fit all the pieces into the box. Then you get a big roll of Velcro, several terminal strips, and start putting the puzzle together. A couple of things you should always include if you are building one of these for your club are, an on/off power switch for the whole system, and some ventilation if your power supply is mounted in a closed compartment. The components are all readily available and the JMRI software makes everyone welcome on the layout.

Earlier this year we used the system to power the largest T-TRAK layout ever put together, so we know it can handle a lot of trains. But as with any layout, the control unit is only part of the solution. A strong bus system with frequent ties to the track is essential in any size layout.

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License