Digital command control

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Digital Command Control or DCC is a scheme for allowing independent control of multiple trains on the same track or layout (contrast with block control in which the layout is broken up into electrically isolated sections) using common rail technology.



DCC was developed and refined by the NMRA working with a consortium of manufacturers over a number of years starting in the 1980s. Maerklin (Germany) and Digitrax (USA) were among the manufacturers involved. For more info consult

Principle of operation

  • DCC uses a high voltage constant supply to the tracks with a control signal superimposed. The signal is digital and is realized by using pulse trains of voltage variation. Each pulse train is a message, which is addressed to a particular receiver in the header packet, and then contains the command (change to speed x, operate accessory, etc) and a trailer packet.
  • A DCC Controller generates these signals and superimposes them on supply voltage. Controllers can have handheld parts and base stations, etc, as with conventional MR controlers.
  • Each locomotive or powered unit is equipped with a receiver (or decoder). This receiver is wired across the rail pickups and watches for messages addressed to it. It interprets the message and controls the motor and accessories in accordance with the commands given (thus, the motor is no longer directly connected to track voltage)

Applicability to LEGO trains

A number of trainheads have carried out experiments or applications of DCC. These include performing surgery on the 9V motor unit and installing a DCC receiver (possibly with an accessory lead powering the 2x2 electrical pad on the top), controlling resulting trains using commercial DCC equiment, and more radically, (and closer to the purist heart, programming an RCX to function as a DCC controller, or even, a DCC receiver to operate trackside accessories (remote turnouts, lights, signals, etc)

External References

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