Wayne Roderick, 3rd Division, PNR, NMRA (life)

05/29/98 rev 01/15/07

This description of the Teton Short Line control system was first published in the NMRA-PNR Switchlist in 1986- We've revised it to 1998. Little has changed as far as the operators can see, but behind the scenes, electronic support has been vastly improved. In this page we'll try to give you an overall view of the control system as seen by the train crew. We'll also link you to electrical details that you might glean an idea or two from. The TSL control system has two major sub-systems,

The multiple train control system, originally Automatic Cab Control (ACC), currently Digital Command Control (DCC) and the TSL Walkaround Cabs.

An embedded computer has been gradually entwining its tentacles into all aspects of the TSL and making everything simpler, easier and more fun as it does.


Over thirty years of working with air traffic controllers and more with model railroaders, I've become firmly convinced that they like to control planes and trains, but not knobs, switchs, plugs and computers. Years ago before it was the fad, we wired up a contraption with about 200 TTL integrated circuits to hide the cab control system. John Lukesh built one adapting my design to readily available parts and shared it with you by writing 17 pages on it in the March '77 Bulletin. It was "behind-the-panel" and operator involvement was minimal. It let us run trains instead of switch panels. We called our gadget AUTOMATIC-CAB-CONTROL (ACC).

In 1984 we rebuilt the ACC system with a home brew computer using a 6800 microprocessor and junked much of the TTL circuitry. The Thursday night crew knew it was computerized but they couldn't find the computer. They were looking for something with a screen and keyboard. We fooled them, there wasn't any. A keypad on the dispatchers panel was used to make the initial block/cab assignments, then the computer took over to keep the cab connected to the train. We had four cabs and 20 blocks.

It's 1998 and we're not totally atiquated- The dispatchers panel is gone- replaced by full color graphics and keyboard initiation. We can no longer fool the operating crew. The Teton Short Line really does use an embedded computer.

The principles and algorithms desribed in that old Bulletin have stood the test of time and are still in use, although the new version is much more adaptable to growth and change.

It's 2003 and we move forward. As we read the exciting articles on digital command control (DCC) that started in MR Feb 97, it was obvious that the NMRA DCC standards were mature and DCC would overwhelm all other multiple train control systems so we got busy and built our own version of DCC using the TSLs embedded computer. It worked well for several years and then our HO modular club. selected and installed easyDCC. As our local peers fell in love with it, I realized it would be wise to abandon our DIY DCC in favor of easyDCC. We would gain four digit addressing and operator familiarity. I asked Santa for an easyDCC command station- he delivered and we integrated it with the existing cab control system.


Along about 1978, we decided walk-around control was the only way to go. The TSL, is an HO scale bridge route modeling in exquisite detail, the mythical prototype line running North-South along the Idaho/Wyoming border It conveniently connects the Northern and Central trans- continentals. We totally ignore the bears, buffalo and ecologists as we steam through Grand Teton and Yellowstone. This is a lot of mileage, even in HO, so its best to stay with your train as you wander through three rooms in the basement of our Pocatello home.

cab panel
11/07/98 update: Digital Command Control (DCC) is fully implemented. Our proven MUX cab is unchanged except for some labels, the extensive changes were made in computer software. The voltage indication now indicates the 28 DCC speed steps, and simultaneous depressing the WHISTLE and CALL buttons will emergency stop all trains.
Each engineer/crew has a walk-around, hand-held CAB unit. Everything he/they need is in a 5 x 2-1/2 x 1-1/2 inch box with a telephone type coil-cord and three-wire phone plug. Anywhere he finds a jack, he can plug in, 'cause all the jacks are in parallel on kind of a party-line. The party-line connects to a bunch a electronic stuff but the operating crew couldn't care less.
The engineer sees on his CAB: A four digit display showing official railroad "fast-time" or a two digit train number with a two digit voltage or current value, A flashing display warns that the next block is occupied, All segements lit mean a short circuit, Red, yellow & green LED's will soon be in service as in-cab-signals. His controls are: Three level whistle/horn, (not developed), Time or train data selection, Volts or amps data switch, Train (air) brake, Independent (dynamic) brake, Throttle, Direction toggle, Call dispatcher button, Circuit breaker reset. An emergency brake is available, by simultaneous hitting both brakes. The train stops quick enough, but it seems to take forever to pump up the air and get going again!
Behind-the-panel electric stuff interfaces the CAB UNIT to any throttle system desired. Our design has all the good things like momentum, memory & diminishing pulse, but can not be adjusted or tinkered with by the engineer. He sets a braking rate with train air brake control, then refines his rate with short applications of the independent dynamics. A touch of the throttle releases the train brake.
The TSL engineering department says this is a multiplexed control system, because the four hand-held units and the dispatchers control panel share the three-wire data line as they digitally talk to each other and to the hidden electronics that manage everything. It's a walk-around cab system, but we call it the MUX SYSTEM for short. The design and construction of this system simply isn't appreciated by our operating crew. They accept and use it like a common telephone. I guess that's a good indicator of success. The MUX SYSTEM originally was independent of the computer but that is evolving. About 80% of it's hardware has been scrapped and tasks taken over by the computer. Today, the cab system is interfaced with When Digital Command Control (DCC)


Today's embedded computer has progressed from homemade to a Heathkit 8080/CPM-through all the steps to its present 386-PC. The QBASIC program, about 150k bytes, reads the railroad status, runs the ACC, 48 three color signal heads, official clock, reads and writes the MUX SYSTEM issues commands to the easyDCC system and and displays all railroad status info locally and remotely for use by the dispatcher.

The dispatcher now has full color graphics of track occupancy, switch position and signal indications. He can change switch position and lock or unlock them for local use. He can also control track access for maintenance or in/out of service. Click here for computer integration details. including the QBASIC source code..


05/29/98 Where do we go from here. The ultimate in simple operation is the Command-Control (CC). Several interesting systems are now available, but none of them include all the features of our MUX SYSTEM. Fortunately, our computerized ACC can treat the CC system with all its decoder equipped locos as if it were just one train scattered all over the railroad. Thus we simultaneously mix the old with the new. The four MUX CAB units are each mated with a hidden interface circuit card that drives the diminishing pulse throttles. This hardware will be scrapped and the computer will read the cab commands, do simulations, and issue CC commands.

We're not new at this, having previously driven a Dyantrol system with our walkaround cabs, via the computer. The results of the simulation software was exciting but we abandoned it to preserve the principle that " if you were wired to NMRA Standard S-9, you could run on the TSL". We're going to modify that principle from "S-9" to "S-9.1/2".

The TETON SHORT LINE engineering department is working hard on the new DCC conversion.

11/07/98 update: Tomorrow has arrived. DCC is fully implemented. Some label changes have been made on the Cabs, but the operations continue much the same. ACC is gone and now you can run a red block, have cornfield meets and other disasters that ACC tended to protect us from. Now, we're more prototype! Is this progress?

01/19/03 update: Our DIY DCC was fun, but now we have easyDCC integrated with our cab system using the RS232 connection provided. The big easyDCC Installation and Operation Manual (NEED LINK) has about twenty pages devoted to the task.

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