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History of DCC

[edit] The History of Digital Command Control

Basic history of how DCC came to be.

In this article the term "channel" would be equivalent to the DCC concept of "addresses". Unlike DCC, the channels were usually fixed, often at manufacture. The Zero 1 system offered user programmed addresses, as it was a true digital system.

Many of the systems mentioned were analog in nature, using frequency modulation or tones to transmit commands to a decoder or receiver. For simplification, the term decoder refers to the electronics installed in the locomotive, that respond to signals from the control system.

Note: All references to prices are in US dollars, and the date is in brackets. Many are from 1979. For comparison, $100 in 1979 is equivalent to about $290 today (by CPI, 2008).

[edit] The Early Systems

The idea of independent control of two locomotives goes back a long way. During the 1940s Lionel offered a system which employed a tuned circuit. A high frequency signal, created by an oscillator in the power pack, would control the direction of the locomotive. The locomotive would only react to the correct frequency, determined by the tuned circuit. Due to the nature of the electronics available in those days, the system was expensive and unreliable.

Advances in electronics, with the advent of cheaper, smaller and more reliable solid state devices, made even more things possible. It would take about 30 years to go from analog to digital in the form of DCC. The shift from the analog computer to the digital computer drove electronics to the present day's powerful but small microprocessors that make DCC possible.

[edit] Lionel Electronic Control

The system first appeared as the 4109WS Lionel Electronic Set, in 1946. The set included a massive cast metal 671R Turbine (based on the Pennsylvania S2 Turbine locomotive) for motive power, tender with whistle, a boxcar, gondola, ore-dump car and caboose.

While the PRR built only one S2, Lionel built a lot of the model 671 locomotive. The "R" in the part number indicated Radio.

Each could uncouple anywhere, with the press of a button. The set was a technical wonder, and a maintenance nightmare. Troublesome operations and a $75 price tag resulted in the system being discontinued in 1949. A big problem was dirty track and poor rail joints. This was the second majour postwar innovation from Lionel, after the smoke unit introduced in 1945.

The set was withdrawn in 1949, due to high cost and poor sales. These sets do command a good price on the collector market, but are rarely seen in operation.

[edit] Details

The transmitter was built around a 117N7GT vacuum tube that functions as an oscillator and a rectifier. Ten buttons controlled the operation of the oscillator, which produced RF signals from 230 to 350 kHz. This signal, measuring about 3 volts, was superimposed on the 60 Hz AC track power.

Each receiver is a series tuned circuit, with a rectifier and a relay. The receiver is tuned to a specific frequency, which activates whistles, couplers or a dumping mechanism. Two types of receivers were made. One type was for the locomotive, the other for rolling stock. The tender would have two receivers installed, one to operate the whistle motor, the other to control the reversing unit. The other type (of which there were four channels) operated the coupling mechanism, and in the case of the dump car, the dumping mechanism. To dump a load, the user simply held the button down for three to five seconds, which activated a thermal relay, which in turn controlled the unloading mechanism.

The channels were set up as 1/2 for the locomotives, 3 for the caboose, 4, boxcar, 5, gondola, 6/7 controlled the whistle motors, 8 was the dump car, with 9 and 10 being spares. The locomotives and caboose were fitted with RUB receivers, the boxcar was an RU, RUA for the gondola, RUD for the dump car, and the whistle was controlled by a RUC receiver.

The RUB and RUC were considered high frequency units, and the RU/RUA/RUD were low frequency units, channel 1 being the highest frequency. A complete RU-1 receiver was $5.00. Tuning was accomplished with a slug or plunger inserted in the input coil, which formed the primary of a transformer. A $2 tuning assembly completed the receiver.

The setup was like a command station/booster in two units. The transformer was connected to the Electronic Control Unit, and the ECU was then connected to the track. Lionel recommended feeders for long runs of track. The rolling stock was fitted with stainless steel axles to improve conductivity.

The vacuum tube used functioned both as an oscillator, and a rectifier. A 117N7GT is a tube with a 117V filament (no filament transformer needed). It combined a diode and a pentode in the same package, the maximum voltage on the plate and screen was 117V, and it was classed as a Class A Amplifier Half Wave Rectifier. It's power output was 1.2W maximum. Lionel chose this device to simplify the design and keep the cost down.

[edit] ASTRAC

Automatic Simultaneous Train Control

Introduced by General Electric in the mid 1960s. Used FM signals on the track to control decoders in locomotive. The decoders were tuned to a specific frequency. Not digital, but analog in nature. Five channels supported, GE promised improvements in a future version. GE employed Silicon Controlled Rectifiers (SCRs) to control the motor.

Very short life span, GE dropped the system soon afterwards.

Mid 1963 introduction, mentioned in Model Railroader magazine in December, 1963.

[edit] Alphatronics

A refined version of the ASTRAC system, manufactured by Alphatronics.

Featured 10 channels, compatible with ASTRAC, and additional channels were available by special order. A basic two channel system cost about US$300, and decoders were $40 to $50 (in 1979.) Track voltage was about 19V.

[edit] CTC-16

A 16 channel system, superseded by the Railcommand system. Appeared in 1979. Model Railroader magazine published it as a do-it-yourself project.

[edit] CTC-16e

Another compatible system called CTC-16e appeared in 1984. Again, designed for people to build themselves.

The CTC16e featured a dedicated throttle, or a selectable channel throttle which used what was called the T/BUS.

The dedicated throttle was built for a specific channel. The T/BUS throttle featured 16 channels, with a three wire connection to the system bus. T/BUS allowed channels 0 to F, which were digitally transmitted to the command station. The T/BUS throttle featured momentum, braking and throttle memory.

[edit] CTC-64

Another evolution of the CTC-16 concept, with 64 channels.

[edit] CTC-80

A later, enhanced version of the CTC-16 was called CTC-80.

CVP Products was one of the suppliers of CTC-16 systems.

[edit] Dynatrol

Dynatrol, now sold as "Classic Dynatrol" is an 18 channel system, using a track voltage of 13.5VDC, and a frequency shift reversing system. It used audio tones to transmit commands.

Dyntrol uses a supersonic carrier, with modulation of the duty cycle to transmit information to a pre-programmed receiver in the locomotive. Each throttle has it's own oscillator and modulator, which are controlled by the throttle and brake controls. The carrier frequency is determined by a precision resistor installed in a small plug, called a channel plug. Reversing the locomotive is accomplished by phase shifting the carrier slightly.

The system has been on the market since 1980. Dynatrol and Onboard was among the most popular command control systems in use.

A basic direct or non-momentum cab cost about $65, and a full function cab was $75. Recievers cost from $50 to $60 each.

[edit] EMS

EMS was manufactured by Trix in Germany and sold by Walthers in North America. It used a 9.5kHz carrier to control a locomotive with a decoder. It worked with an existing DC control system, allowing both DC (analog) and EMS equipped locos on the same track. A controller and decoder rated at 850mA would have cost over $100 in 1979.

[edit] Onboard Locomotive Sound and Control

The Onboard Locomotive Sound and Control system, by Keller Engineering, offered 20 channels, with a constant 12VDC on the track. It used audio tones to control the locomotives. A base system was about $376 (1986). Wireless throttles were also available.

A typical starter set came with a 5A power supply, a 16 channel handheld controller, two 1A motor controllers and the manual.

Onboard claimed to eliminate the need for control panels and block wiring.

Onboard offered steam locomotive exhaust sounds, bell and whistle. For Diesels, it featured a variable engine RPM exhaust, bell and six chime airhorn sounds, plus constant lighting. Another optional feature was directional lighting.

Another accessory was a signaling system, for use with lights or semaphores.

Techical details:

Motor controllers available in 500mA, 1, 2, and 4A versions, and also for garden railways. Built in memory, with pure DC out at full speed.

Steam Sound unit

Optical exhaust sync (or magnetic for outdoor use), automatic 2 stroke air pump, adjustable 6 chime whistle, bell.

Diesel Sound unit

Exhaust controlled by motor voltage. Selectable 6 chime airhorn, bell.

Reverb unit

Up to 100mSec of delay, with controllable echo repetition.

All sound units featured a 1W amplifier.

Radio

A radio adapter was also available, using a Futaba unit, which was directly usable in large locomotives.

You can use Onboard sound modules with DCC. See the Digitrax Knowledge Base for details. (Operating Keller SU1990 Sound Unit with Digitrax Decoders.)

[edit] Protrac

Protrac was a system announced in 1979 by the Model Rectifier Corp. The Protrac R/C 1 System 7000 controlled two locomotives, only one decoder equipped. It was similar in concept to the EMS system. According to a review in Model Railroader (November 1979), it didn't appear to be radio based. The Protrac 7000 featured a dual control console, which looked a lot like an R/C unit for model airplanes.

A later, promised R/C 2 System 9000 promised eight channels, with radio control for wireless operation.

MRC quoted prices of about $100, and $150. (1979)

[edit] Rail-Command 816

An 8 channel system using a constant 12VDC on the track.

A single tethered cab that could control one locomotive sold for $14. A dual channel unit was $20. The locomotive would continue to run while it's cab is unplugged.

Another part of the system is the throttle-transmitter unit. It was the power supply and signal generation system. Channels were selected by plugging a cab into one of the eight jacks on the unit. Additional power boosters were available to increase the power available. The 4 amp throttle-transmitter sold for $75, and the accessory 8A booster was $50. Receivers cost about $25 each.

[edit] RFPT

The Regulated speed Full wave Positionable Throttle was a 9 channel system using a constant 12VAC track voltage, and high frequency signals to control the locomotive. A basic system was about $200. Handheld throttles were $25 for a single channel or $50 for three channels. The Engine Control Units sold for about $53. (1979)

[edit] Salota 5300

The Salota 5300 was a West German system imported into North America. It used a constant track voltage of 16-18VDC, and offered 5 channels. The Salota Power Deck/Control Transmitter featured 5 knobs that controlled the speed and direction of the 5 channels.

The system was advertised for $300 (including 2 receivers), and decoders were $40 each in 1979.

[edit] Hornby Zero 1

A four bit microprocessor based system able to address and control up to 16 locomotives. Zero 1 used a 32-bit code generated by the TMS1000 microprocessor, transmitted every third cycle of the square wave track voltage. For an 8.33-millisecond interval (60 Hz system), it replaced the track voltage. Because track power is off during transmission, the system was very immune to interference. The code contains an identifying pulse, for up to 16 locos and 99 auxiliaries. Since Hornby was based in the United Kingdom, two different systems were made for 50 and 60Hz power systems. They were not compatible with each other.

The main system consisted of a master unit, with 3 additional slaves (sold separately) that could be attached via a 15 pin edge connector. It also offered inertia, and was capable of supplying up to 4 amps. The slaves made it easier to control multiple locomotives. All sixteen engines could be in motion at the same time (if they didn't pull more than 4A in total). Upon power-up, the Master unit immediately assigned itself to address #1. Any slave units were assigned 2, 3, and 4, respectively. The master unit's keypad was used to assign addresses for the slave controllers, or itself.

The Zero 1 system could operate 16 locomotives, and up to 99 accessory decoders. Due to the 4 bit microprocessor used, only 16 locomotives could be on the layout, or addresses would be duplicated. Any more would have to be stored on an electrically dead track to prevent conflicts.

Zero 1 decoder, coding pads visible on right.

Three wires were used, two connected to the track, and one to the motor. Three wires made installation very easy, as the motor did not need to be isolated from the frame. By making one brush more positive (or negative) than the other, direction of travel was established. Due to the thyristor circuit used to control the motor, the system could be very erratic.

Track power was a square wave, at about 20VAC. Track power came in three phases: Forward, Reverse, and Data. By controlling which of the two TRIACS mounted on the PCB was 'on', and for how long, the motor speed and direction was determined. Data was transmitted on every third cycle. No locomotive without the Zero 1 decoder installed could be on the layout. The constant 20VAC track power would be harmful.

Double heading required both locos facing the same direction. The master controller merged the two locomotives into one, and was not able to determine direction individually.

A Hornby advertisement in the March 1981 issue of Model Railroader listed the prices for a Zero 1 system. The Master Controller unit was $149.95, and the slaves were $49.95. A 'points/accessory module' listed for $49.95, and a loco module was $24.95. (All prices in US dollars.) Zero 1 may not have been available in the North American market until 1980. Hornby stated you could model a large passenger terminal with up to 16 locomotives in operation at once. Poor marketing may have limited the Zero 1's appeal in the North American market, although some model railroads did use it.

[edit] ZTC Controls

ZTC Controls in the UK still supported the system and made improvements to it, but they ceased business operations in September 2008, and have dismantled their website.

ZTC did make DCC decoders that could be programmed to work with a Zero 1 system, and their controllers had a mode that enabled control of a Zero 1 equipped locomotive.

[edit] Kato Digital

The Kato Digital system appeared in the late 1980s and was discontinued a few years later. It had up to 100 addresses available, a primitive sound function, and capability to control switches, either with a controller or a computer via RS232.

The system was proprietary, and decoders would only fit an HO locomotive (due to their size).

Advertisements for a Command Control System by KATO appeared in late 1986. The recievers where shown beside a ruler, ranging from 20 to 90mm in length.

KATO dropped the system in 1992.

[edit] Marklin Digital

Marklin Digital appeared on the market in 1984. This system was designed for use with Marklin's line of Alternating Current HO trains.

Marklin would also introduce another digital system developed by a third party for use with their DC product line.

Although Marklin Digital sold well in Europe, in North America it didn't fare as well.

[edit] Other systems

Other systems that were either on the market or planned in 1979 included the Airfix Multiple Train Control System, and ECM, both from the UK.

[edit] Lenz

Early developer of what became DCC. Decided to publish how their system worked, to encourage others to support it. The NMRA has taken control of the standard, and extended it. NMRA DCC is defined, yet manufacturers are able to incorporate their own features and improvements, providing the result is compatible with the standard.

[edit] Command Control in the 1980s.

The March 1984 issue of Model Railroader had an editorial about Command Control systems.

Their 1983 annual reader survey revealed that about 10% of the respondent's layouts had some form of Command Control system.

The systems in use were found to be:

• Zero 1: 24%
• Onboard: 22%
• Dynatrol: 18%
• CTC-16: 11%
• Other: 25%

As shown, no one system was a clear leader. Analog may have been in the majourity, but the largest installed base was Zero 1, a digital system. None were compatible with each other either.

[edit] The DCC Advantage

Looking over the various systems listed here shows why DCC has succeeded. No two were compatible with each other. They were all unique, and being analog based, compatibility was not really possible. The fact that the systems were expensive and completely incompatible slowed their adoption. Another factor was expandibility. Most of them were limited by the technology available to only a few channels. Unlike DCC, which can have over 100 unique addresses available.

Prior to the introduction of the DCC standard, the NMRA was looking at the confusion in the marketplace and attempting to create a unifying standard for control systems. When Lenz offered it's command control system to any interested manufacturer as an open system, the NMRA examined it and used the Lenz example as the basis for a new Digital Command Control system.

[edit] Notes

Material in this article was taken in part from a review of command control systems published in the November 1979 issue of Model Railroader, written by Andy Sperandeo.

Hornby pricing: Hornby advertisement, March 1981, Model Railroader.

As one can see by the pricing shown, command control systems were quite expensive in 1979, slowing their adoption. DCC, on the other hand, is a lot cheaper, or comparably priced with respect to the analog systems of 30 years ago.

[edit] See also

• Kato Digital info

• Classic Dynatrol Website

• Zero 1 info and manuals