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During the planning stage of my Chicago Railroad I decided that I wanted to be able to control my RR with a computer. Fortunately I discovered it was already being done by thousands of people using Bruce Chubb's Computer Model Railroad Interface (CMRI). Bruce has a PhD in Electrical engineering and is a passionate model railroader. The system was developed for his own need and then became a commercial operation.  The basic's of the system consists of a Universal Serial Interface Card (USIC), a mini computer that deals with communicating from the serial port of your computer to the input and output cards all installed on a motherboard. Each USIC and it's corresponding input/output cards is a node. The advantage of nodes is that you can create an many as you need near the major areas reducing wiring. Each node is connected to the next node with a 4 wire twisted pair cable.

Due to the size and complexity it was necessary to design a back plane with adequate space to serve the node. In addition consideration was given on how to route the wires. My personal philosophy is that wiring should be organized and neat, but not overly done. Note the PC power supply, Rather than drill a bunch of large holes to run the wire to the back, I used 1/2 x 3/4 lumber to make a bar between the planes allowing wire to be wrapped behind.


  This is the start of the first back plane (node 0) of the Florida RR and allows ample room for wiring.

My first node, in Chicago, was considerably overcrowded but it still worked well. It was difficult squeezing in the last few items. I thought is would be a good idea to create a large panel box type of arrangement and keep the wiring to the front like an electrician would wire a service panel. I have since discovered back planes work better.

I bought stick-on cable clamps but they won't stay on so they had to be drilled and screwed in. Later I will show you a better method. The green boards in the middle of the picture are AC block detectors. More on that later.


I have tried to standardize the wiring using the same type of wire for many purposes.

  • #14 Solid red for track busses

  • #14 Solid  bare for track common

  • #12 Stranded blue for cabling track wiring back to the control panel

  • #18 solid red, green, and black for track feeders and CMRI power

  • #14 Stranded bare (Radio Shank antenna guide wire) for logic ground

  • Cat 5/5e (picked up on EBay for $25-35 per 1000 foot spool.

  • Cable clamps made from sawed split drilled PVC plumbing pipe. Very easy to make 96 of them at a time. 

The #12 wire is due to the length of runs rather then amperage. I use the basics even when a smaller size would do allowing me to buy in bulk.

My first Node in Chicago


The picture on the left is my version of a "condensed" CTC panel, that functions like the prototype. I used an 1/8th sheet of plywood and the graphics were printed on a sheet of paper and glued to the plywood. I used standard toggle switches, push buttons, and LED's. I placed the signal levers for the OS sections over/under to save space. My plan is to replace it with a metal graphically correct panel in the future. This is a nice way to have an interim panel for testing your design and running the railroad before it is finished.

The bottom picture is my screen monitor, if you click on it will see some of the non standard ASCII characters I use. I found an old ASCII character editor and used it to improve the graphics. The monitor shows occupancy, direction of travel, cab number, block and turnout numbers, routing, signal repeating, and the condition of the staging areas. Note the connected corners in the staging yard and the special characters in the turnouts ands repeater signals.  I am also using the computer and keyboard as an assignment panel, probably temporarily

Miscellaneous detail pictures

Wiring and cabling details

 Node 1, a different style of back plane.


 Node 0 today.