How Atari can Control Model Trains

1. Two Hobbies

Since my early ages, I have one certain hobby - model trains in all possible forms and sizes. Before I was three, my father bought a small scale TT (1:120) model of railway on a hinged panel. Later, when my younger brother learned to crawl and stand, he was inflicting physical damage on the model landscape. That's why my parents sold the model railway eventually.

Very soon they discovered that without model trains, they would have hard times with me. So they bought me a starter set of trains and rails of the H0 scale (1:87), that I still have today. Gradually, I have been buying more tracks, cars and locomotives.

The other great hobby began when I was 11 years old and my father bought our first Atari.

Since then, I have significantly expanded my collection of both the H0 model trains and Atari computers. I kept pursuing both hobbies in turns. Until very recently, I had no clue that these two hobbies can be connected...

2. Analog versus Digital

Model trains with analog controls mostly work as follows: The engine of the locomotive is connected by one wire to the left rail and by another wire to the right rail. The more voltage in the rails, the faster the locomotive goes. The polarity determines the direction of the travel.

It is crude and efficient. There is an obvious catch. This way of controlling affects all locomotives present on the railway. All of them are either moving in the same direction or hold their positions.

This is useful for one or two locomotives. When we want to operate more of them all at once, it is very limiting. Therefore, in 2018, I came to conclusion that analog control is no longer the way to go.

Is there another way? Since 1990s, there is a standard for digital control - Digital Command Control - DCC.

Although the basic principles of DCC are simple, a full description would exceed the available space in FLOP. Please consider the following paragraphs a simplified introduction to the DCC area. Detailed information is available on the internet (e.g. [1] and [2]).

Every locomotive must have installed so-called decoder. It is a microcomputer on a small PCB. The sizes of these PCBs begin at 1 square centimeter.

The decoder is connected between the lead wires of the locomotive and the electrical contacts of its engine. A constant voltage is applied to the tracks (usually 12 to 14 V). The control unit modulates this voltage by control signals for all decoders.

Apart from supplying power, the track serves as a communications bus. Every decoder has its own (unique) digital address. The address is used to determine if the signal received through the track is meant for the particular decoder.

According to the received command, the decoder applies the required voltage to the locomotive's engine with desired polarity. This way, (almost) any number of trains can be going to various directions at various speeds.

Apart from controlling the engine, the decoder can perform other functions - e.g. switching the lights, either external or internal (if the car is equipped with these). Other possibilities include electrically controlled couplers or steam generators of the steam locomotives.

Most of the modern locomotives are ready for digitalization. They have a connector to which a PCB is connected. The PCB connects the pins so that it connects the engine and lights with the rails for typical analog operation. After buying a decoder, it is enough to remove the PCB and install the decoder instead.

In addition to the locomotive decoders, there are also so-called function decoders without motor controls. These are useful for controlling illumination in standalone cars (or buildings in the model railway), or operating the switches equipped with electric switch motor.

3. Control Units

When I came to conclusion that I do need to digitize my fleet of trains, I had to decide which way I will control my railway and what device will modulate signals sent to the tracks.

Standalone control centers are available. These are approximately as big as a set top box. Their price (including accessories) is typically over 10,000 CZK. Another option are miniature computers (for example Raspberry Pi). Special modules providing functions of a control center are manufactured. Here, the price is around 5,000 CZK. DCC interfaces connected to ordinary PC through USB are available too. The prices begin at several thousands of CZK.

Various controllers for operating the trains are connected to the control center. They can be special instruments resembling TV remotes. With computer-based systems, one can connect through a network and use a web or desktop user interface. Some solutions allow using touch screen devices.

A strong enough power supply is connected through the control center to the tracks (typically several Amperes). One traction vehicle requires around 0.5 A (consumption comparable with analog operation).

I almost inclined to buy a control center connectible through USB to a PC. I mention that to Honza, and he just casually replied: "I believe that I read somewhere that the model trains can be controlled by Atari". He sent me a web link [3] the very same day.

4. A-Track - Contact

I checked out the web and indeed, A-Train Systems today supplies its software for PC with USB DCC interface, however, in the past, the company offered their A-Track solution for 8-bit Atari computers. At the web (in the Download section) a documentation including photos of the devices [4], screenshots [5] and product manual [6] are still available. The software itself is missing and so is the price of the hardware.

Without much hesitation, I used the contact form at the web and asked if it is somehow possible to get the SW and HW for Atari. In few days, I got an answer from the UK from Terry Chamberlain, a helpful old gentleman pleased by my interest in the old product.

Terry told me he was not maintaining Atari version for more than 10 years. However, if I am really interested, he would find the SW and check his attic to see if there is some HW left. Naturally, I replied that I am interested.

After few days, Terry got back to me with good news. To his e-mail, he attached two disk images with the software. Also he told me that he has found a complete HW set including the following:

The only item missing was a power supply. Terry could have sent me some, but I would have to change the plug to the continental one. Moreover, the weight of the PSU would have significantly increased the shipping costs.

Terry proposed the price to be the price of the parts. He also offered he would give me all technical documentation (including schematics) and the source code of the software.

Although the price was somehow higher than I expected, the offering of the documentation and source code greatly outweighed it. That's why I sent Terry the agreed amount + shipping cost through PayPal and kept waiting.

5. A-Track - Commissioning

To shorten the waiting, I took the liberty of appropriating decoders for 2 new locomotives already fitted with a DCC connector. I realized there are more DCC connector types.

Despite the initial struggle, I managed to buy the right connectors and place them in the locomotives. Just to give you an idea, the prices of the decoders are between 500 and 1200 CZK if not considering decoders with sound, where the prices start at 2000 CZK per piece. These are not supported by A-Track anyway.

The next quest was to get some PSU. A-Track requires alternating current on input with voltage of 15 - 16 V. It passes maximum of 4 A to the railway, but the PSU can be stronger (excess currant is not used) or weaker (handles fewer trains, of course).

At the beginning, it would have appeared that getting the needed PSU is a problem. Then it turned out one can use a PSU with 2 secondary windings - 2x 8 V. If connected properly, it becomes 1x 16 V.

So, I bought Indel TST100/002 2x 8 V /6.25 A for 579 CZK. I placed the PSU in a plastic case. I connected a cable with 230V plug to the input leads. To the output leads, I connected a pair strong enough that wouldn't melt at 4 A.

In the meantime, I've got a shipment from the Great Britain. A moment of suspense when unboxing and ... it was not a brick. Seriously, I've got the A-Track set for Atari.

Terry took some extra effort to prepare and send me an itemized TODO list to commission DCC locomotives using A-Track written for dummies (seemingly under the impression of our e-mail communications).

I have wired everything together. Following the TODO list, I configured a locomotive for A-Track. Then I placed the locomotive on the railway and, full of expectations, sat in the front of the computer. I pointed to the button for increasing speed and tensely watching the locomotive I pressed Return and ..... Yes, the locomotive got going!

3rd February 2019 13:32 CEST, A-Track fulfilled my dream that I didn't know I could even have. I am controlling my model trains with my Atari.

So much for emotional outbursts, let us take a look on how A-Track works.

6. A-Track - Description of the HW

6.1 DCC Interface

The foundation of the A-track system is the control unit (DCC interface) enclosed in a metal box with many connectors, 3 indication lights and 2 switches. The unit is connected to Atari through the system bus (PBI - XL models or ECI - XE models). The control unit is internally divided to two parts - logical and power.

The logical part draws power from the Atari PSU, while the computer draws power from the control unit. The logical part is connected to Atari with a data cable.

The power part is powered by the previously mentioned PSU: 15 - 16 Volts / 4 or more Amps. The logical part translates commands from the computer to pulses. The pulses are modulated to the electric currant that is applied to one of the terminator pairs.

The first terminator pair is used for so-called programming track. It is a standalone (a short one is enough) track where one places a single locomotive, so one can read (verify) or write (program) contents of the locomotive decoder (Control Variables - CVs).

The other terminator pair is connected to the model railway where there can be almost unlimited number of trains with decoders.

The control unit has just two switches. The main power switch and mode selector. The mode selector selects either normal operation or programming. It selects to which terminator pairs the current is applied.

6.2 Handheld Controllers

The trains can be operated using paddles connected to the second joystick port. This way, one can control only two trains at a time. The paddles have only one button too, not enough for additional functions.

That's why Terry invented a bus to which one can connect up to 8 handheld controllers (HHC) that he designed. These handheld controllers have one potentiometer, 4 switches and 4 buttons.

The potentiometer controls speed. One of the switches chooses direction. Other switches and 3 buttons handle additional functions (e.g. illumination).

The 4th button (like the paddle button) initiates emergency brake. This is very useful function that immediately stops all trains on the railway. It is handy in case of derailment or to avert an imminent collision.

6.3 Network Driver

The control bus is managed by a Network Driver. The driver is connected to the second joystick port (instead of the paddles) and draws power from another cable connected to the control unit.

The control bus has 8-wire cables with RJ 45 connectors. Twisted cables (e.g. UTP) are not recommended. There are almost no limitations on the topology - linear, star or combined.

This is of a great use for bigger model railways with cables underneath. One can place RJ 45 sockets to suitable locations and connect the controllers as needed.

6.4 Mouse

If you ask why the A-Track set includes an ST mouse, then it is because the software can take advantage of it. Of course, all functions are accessible with keyboard, yet an ST mouse connected to the first joystick port is supported too. Detailed information on the hardware is available in [4] and [6].

7. A-Track - Description of the SW

One monolithic program is used to control A-track. The program requires DOS because it is processing configuration and data files. The last version is 2.2 released in 2004.

The vendor ships two floppy disks. One disk contains A-Track with DOS 2.5, the other one with SpartaDOS. You can use whatever suits you or you can create another disk with your favorite DOS.

After loading, the program firstly prompts you for a file with a list of configured trains. The file extension is ITL (ITem List).

7.1 The Main Screen

The main screen displays list of the decoders (i.e. locomotives etc.). Items can be added or deleted. For each item, one can request control (control screen) or modification (programming screen).

At the top of the screen, there is a hidden menu that can be activated with keyboard or mouse. The menu allows to load or save ITL files, edit preferences etc.

7.2 The Control Screen

The control screen has controls organized in 3 columns. In the left column, one can choose if a locomotive is controlled from the computer or by one of the controllers. The middle column allows to change direction and speed of the travel. The right column allows extra functions to be switched on or off. Indication of the current speed and direction of the travel is at the bottom of the screen.

7.3 The Programming Screen

The programming mode allows reading and writing values of the decoder. Every decoder stores several tens of values (so-called Configuration Variables - CVs). These values determine various properties, for example decoder address (something like MAC), maximum speed, the default direction of travel, connection of the lights with functions on the handheld controller.

Most of the decoders also store a CV that holds so-called acceleration curve. This is an increasing sequence of values, which (if used), better simulates the behavior of a real locomotive when changing speed, especially during start-up and braking.

Modern decoders (especially those with audio) tend to have more than 100 CVs. A-Track only supports 96, resulting in certain limitations. The basic functions are fully preserved, though.

8. Conclusion

It is great! And it works. I recommend this to all atarians passionate about model railways.

However, in order not to set false expectations, I believe it is necessary to point out some important facts:

I believe the enthusiasts won't be discouraged by these troubles and after some time, our Atari gatherings will have a corner dedicated to model trains.

Bohdan Milar


[1] https://www.vlacky.com/dcc/
[2] https://en.wikipedia.org/wiki/Digital_Command_Control
[3] https://www.a-train-systems.co.uk/
[4] https://www.a-train-systems.co.uk/download_files/A-Track_HardwarePics.pdf
[5] https://www.a-train-systems.co.uk/download_files/A-Track_Screenshots.pdf
[6] https://www.a-train-systems.co.uk/download_files/ATrackUserGuide22.pdf
[7] Interview with Terry Chamberlain, FLOP 65