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DCC History
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History of DCC
Contents |
[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 Fifties 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] 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.
Another compatible system called CTC-16e appeared in 1984. Again, designed for people to build themselves. A later, enhanced version was called CTC-80.
[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.
Dyntrol uses a supersonic carrier, with modulation of the duty cycle to transmit information to a pre-programmer 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.
[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] KATO Digital Control System
A proprietary digital system that appeared in the late 1980s. Discontinued in 1992.
It was capable of up to 100 addresses, and could be controlled by a computer using an RS232 serial connection. It also offered a 'horn' function.
[edit] Onboard Sound and Control
The Onboard system offered 10 channels, with a constant 12VDC on the track. It used tones to control the locomotives. A base system was about $200 (1979).
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.
[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.
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.
[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. (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 system was advertised for $300, 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.
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] 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.
[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. Hornby pricing: Hornby advertisement, March 1981, Model Railroader.
