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Run your model railway with Command 28  Silicon Chip Part 1: How would you like to run as many as 16 locomotives on your layout, all at the same time? And would you like to be able to do it without masses of wiring in the layout and the need for separate speed controllers for each locomotive? You would? – then read on. Design by BARRY GRIEGER F While this photo shows just seven locomotives, the Protopower 16 Command Control system to be described in this series of articles can control up to 16 locomotives simultaneous­ly. OR MANY MODEL RAILWAY enthusiasts, the enjoyment comes from the variety of prototype operations that can be built into a layout, irrespective of home or a club. Some modellers enjoy mainline running of interstate freights and passenger trains. Others enjoy yard and industry switching, engine terminal service and branch line operation. Still others enjoy the make-up and splitting-up of trains at terminals. But the enjoyment can rapidly turn to frustration and disillusion when it comes to wiring a layout for operation of more than a single cab for train control. “Single cab” means single loco or single train in model railway jargon and if you want multiple locos you need “multiple cab” operation, with a separate controller for each locomotive. In addition, each locomotive can only run in a block section of the layout. Now block wiring for multiple cabs can become very compli­cated, especially if you want say, five or six locomotives oper­ating simultaneously. For 16 locomotives, the wiring would be extremely complex and it is doubtful if anyone would attempt it, even on a large club layout. Fortunately, there is an alternative approach that offers simple layout wiring while allowing you to run as many as 16 locomotives or trains independently and simultaneously. The solution is Command Control. OK, would you really want to be able to control 16 locomo­tives simultaneously? Well, why not? You want realistic opera­tion, don’t you? Consider, for example, if you had a large double loop of track which means that you can run trains in both directions at the same time. That double loop could have several stations and stops along the way and you could have, say, four separate trains running and stopping on the east (direction) track and the same number of trains on the west track. And you might have a few locomotives running on spur lines and a few working on shunting duties in marshalling yards. You can see how the number of loco­motives starts to climb, can’t you? Of course, this range of operation is nothing like as com­plex as a real full scale railway but even so, it would Control January 1998  29 require a huge amount of wiring, a lot of speed controllers and probably quite a few people to run it as well. With Command Control, the wiring is greatly simplified, you don’t need block sections and you only need one power supply. History of Command Control For too long, Command Control for model railways has been out of reach for the average Aussie modeller, for a number of reasons. In the early 1980s, Keith Gutierrez paved the way in North America with his “CTC-16” system. It is a digital propor­ tional command control system and was published in detail in “Model Railroader” magazine. A few years later, the next genera­ tion system, “CTC16e” was published. Since then, there have been other systems such as “Dyna­trol” by Power Systems Inc, “CTC-80” by Keeler Rail Specialties, “Zero 1” by Hornby and “PMP 112” by Pressed Metal Products. Unfortunately, not many of these systems were compatible and due to the physical size of the electronic components used, they were only suitable for HO and larger scale locomotives. As the benefits of command control are realistic prototype operation and easier layout wiring, the National Model Railroad Association of America in due course proposed a set of standards for Command Control. These standards were based upon the Lenz System of Europe and the concept of Digital Command Control was born. Today, DCC is gaining popularity due to the small size of the receivers (decoders) – so small, in fact, that they can be fitted into N-scale locos. This has recently motivated Keith Gutierrez to publish his “EasyDCC “ command control system in “Model Railroad­er”. So DCC has brought freedom for the modeller but at a price. The technology is brilliant but being based upon microprocessors and surface mount components it represents a field that many railway modellers don’t want to venture into. Over the next few months, we will publish a Command Control system. This will enable the average modeller or electronics hobbyist who has a collection of wide bodied locomotives like Athearn, Life-Like, Bachmann, Powerline and Lima, to build their 30  Silicon Chip Brief Specifications •  Can control up to 16 separate locomotives. •  Consists of four easy-to-build parts: Throttles, Command Station, Power Station(s) & Receiver/Decoders. •  Receiver/decoders fit inside locomotives (HO & larger scale). •  Provision for momentum (inertia), braking & constant brightness headlamps. own system, understand how it works, construct their own decoders and make any repairs themselves. What is Command Control? Command Control is quite different from any conventional model railway speed control. A conventional speed control or throttle varies the voltage and voltage polarity to the track and thereby varies the speed and direction of the locomotive. By contrast, Command Control maintains a constant voltage with fixed polarity across the track at all times. Superimposed on this constant track voltage is a serial data stream with blocks of 16 pulses, one pulse for each of the 16 locomotives which can be used on the system. These pulses have an amplitude of about 5V peakto-peak and so form a very “robust” data stream which will not be subject to interference from the commutator hash of typical model locomotives. The serial data is fed to every locomotive on the track. Each locomotive has its own decoder so that only it responds to the speed and direction commands of its particular handheld throttle control. The locomotive decoder drives its own pulse amplifier to drive the locomotive at the right speed, slow or fast, and in the right direction, forward or reverse. The serial data stream on the track is similar to, but not the same as, the serial data transmitted to radio-controlled model aircraft, cars and boats. In radio controlled models, the serial data stream is used to control servos and the speed of the engine in just one model. In this Command Control system for model railways, the track serial data stream is used to control the speed and direction of up to 16 model locomotives. (Editor’s note: for a good explanation of radio control principles, see the November & December 1997 issues of SILICON CHIP). Protopower 16 Protopower 16 is my version of the original CTC 16 command control system designed by Keith Gutierrez in January 1980. This system was made obsolete by the demise of the Signetics NE544N chip used in the decoders. Protopower uses a Plessey ZN409CE decoder which is still available. Fig.1 is a graphical representation of how the system works. Only one locomotive and one throttle is shown, to keep things simple. (1). The handheld throttle settings for speed and direction of the specific locomotive are fed to the command station. In this case we have shown throttle number 5. (2). The command station takes the speed and direction informa­tion from each throttle and in turn inserts it into one of the 16 channels in the serial data stream. (3). The command station checks all 16 throttle inputs approx­imately 100 times per second for speed and direction data and sends the resulting serial data stream to the power station. (4). The power station then combines this data stream with a constant 11.2V DC to form a composite voltage of about 16V DC. (5). A preprogrammed receiver/ decoder installed inside each locomotive receives this voltage, decodes the programmed channel from the serial data stream and then extracts the speed and direction data to power the electric motor in the locomotive according to the original throttle settings. (6). If more than one throttle is being used at the same time, then each preprogrammed decoder inside a locomotive will only react to its own channel. Other channels or locomotives won’t do anything. Therefore, it is possible to have two locomotives within centimetres of each other, each under separate control. This means that head-on and tailend collisions and other aberrations are quite possible! Fig.2a shows the special composite waveform present on the track at all times. Fig.2b shows how the pulse Fig.1: this is a graphical representation of a Command Control system for model railways. The speed and direction settings from each handheld throttle are feed to the command station which produces a serial data stream. The pulses of the data stream are superimposed on the constant voltage to the track and fed to all locomotives. Each locomotive has its own receiver/ decoder to drive it at the correct speed and direction. January 1998  31 Fig.2: this is a representation of the serial data stream super­imposed on the constant track voltage. It (a) consists of blocks of 16 pulses separated by a sync pulse pause. Depending on the width of each channel pulse, it may be decoded as a command to (b) stop the loco; (c) run at maximum reverse; or (d) run at maximum forward speed or any speed setting in between. must be installed inside each locomotive. If you have 16 locomotives, you will need 16 receiv­er/decoders. If you have more than 16 locomotives, you will still need one receiver/decoder for each loco and this means that more than one loco will be assigned to some channels. So if you have 50 locomotives and you want to be able to run them all (not simulta­neously, of course), you will need 50 receiver/ decoder PC boards. (2). Each locomotive will be labelled on the underside with its channel number. Two identical locomotives assigned to the same channel can be used for “double heading”. (3). The PC board is to be cut if necessary and joined with flexible wiring to enable the circuitry to be fitted into the restricted spaced inside the body shells of locomotives. (4). Constant brightness for locomotive headlights is standard. (5). Changing receiver channels is a simple matter. A locomotive assigned to one channel can be easily changed to any other chan­nel. (6). Each receiver has a maximum current rating of 1A DC. Critical parts width of a specif­i c channel determines the speed and direction. The Protopower 16 System consists of simple throttles, the command station, the power station and the receiver/decoders. (1). This is the brains of the system and incorporates a master digital oscillator, a triggered ramp generator, a pulse width modulator, digital switching of analog throttle data, multiple line driver outputs for connection to power stations/auxiliary power stations, and a throttle power supply. composite voltage and has a current rating of 5A. If each of your locomotives draws a maximum of 1A and you want to operate 16 locos, then you will need more power. Up to four more power stations can be added to the system. (2). These additional power stations are used to divide your layout into divisions (blocks). Each division is connected to its own power station and separated from other divisions by a gap in the rails. Since each power station is fed the same serial data signal from the command station, each division has an identical composite voltage signal on the rails. Each locomotive can cross the gap in the rails and continue to run without hesitation. As far as the receiver/decoder is concerned, it sees identical signals and it will behave as if there were no gap between divi­sions. Such blocks or divisions in a large layout have a number of uses, one of which is to enable short circuits or open circuits to be more easily pinpointed. Power Stations Receiver/decoders Throttles (1). Each throttle is wired directly to a specific channel (locomotive). (2). Simple throttles have only two parts – a directional switch and a potentiometer. (3). Each throttle needs four wires to connect it to the command station. (4). Throttles incorporating momentum (inertia) and braking can be easily built into the simple design. Command Station (1). The power station produces the 32  Silicon Chip (1). A receiver/decoder PC board While most of the circuitry involved in the Protopower 16 system uses standard readily available parts, each receiver/decoder has three critical parts and you may want to order them to ensure that you have a reasonable number on hand for your layout. The parts are as follows: (1). A 14-pin DIL Servo Control integrated circuit, ZN409CE, made by Plessey. These are available from Farnell Electronic Compon­ents, order code 407.574. Phone (02) 9645 8888. They are also available from RS Components, product code 304-813. Phone (02) 9737 9966. (2). A top-adjusted, sealed, single turn 1kΩ 0.5W cermet trimpot. These are available from Farnell, order code 107.617 or from RS Components, product code 187-955. (3). A .015µF or .018µF 5% NPO ceramic disc capacitor (.018µF preferred). These are available from Crusader Electronics (Sydney & Melbourne), order code C333C153J1G5CA for .015µF or C333C183J1G5CA for .018µF. Next month we will describe the circuit and construction details for SC the Command Station.