Digital Command Control (DCC) for Model Trains

 Model railroading and specifically model train control is in the process of changing drastically from the past.  Digital Command Control (DCC)  for railway modelers  replaces the Alternating Current (AC) and Direct Current (DC) power controls previously used.  It fundamentally contains a Digital Command and Control station, which replaces the AC Model Trains Transformer or DC power pack that is used in the non-digital or analog world.

The DCC controller generates a digital signal packet, which is capable of communicating with several locomotives on your model train layout.  Each locomotive contains a decoder, which has its own address thus limiting its response to only when the DCC controller sends out the locomotive’s address. A digital instruction code follows the address which controls the locomotive’s speed, direction, sounds, and lighting effects just to name a few. The DCC controller provides these commands via the model train track rails. There are also DCC controllers that are wireless, permitting the operator to walk freely around the model train track layout at the same time. As required, in order to provide adequate current to run several locomotives at once, a Booster device is added to amplify the DCC current.

In addition to locomotive control, DCC digital signal packets can also be used to control stationary devices such as turnouts and other model train accessories in a wireless fashion.   This is a big breakthrough in the model trains hobby. See the following figure, which depicts a typical digital signal packet:

DCC Signal Packet Waveform

If one were to monitor the electrical signal across the train rails with an oscilloscope, the following characteristics should be noted:

1)      The waveform is Bi-Polar with its voltage varying between + 14 volts and – 14 volts. It is symmetrical about zero volts.

2)      It is Pulse Width Modulated in such away as to provide a digital command to the locomotive’s decoder or other device containing a decoder.

3)      It is not a periodic waveform, meaning it does not repeat itself as an AC signal does.

4)      The National Model Railroad Association (NMRA) in association with its DCC Working Group is in charge of the design and manufacturing standards for DCC equipment.  Basically this group controls the critical elements of the electro-mechanical design of a DCC  manufacturer’s products.  Details of these standards can be found on the NMRA website.

5)      The DCC timing and protocol defined by the NMRA and DCC Working Group defines signal levels and timing between the command station and the track.  However, these protocols are combined with a variety of proprietary standards from several manufacturers.  In other words, command stations from one manufacturer might not be compatible with throttles from another.

It should be noted that many manufacturers of model trains have gotten on the DCC bandwagon such as:

Bachmann Trains and train sets

Lionel Model Trains and train sets

Model Power

LGB Trains

Hornby (UK Company)


MTH Trains

Walthers Trains


Athern Trains

Broadway Limited

Rivarossi Model Trains

The above manufacturers will generally supply locomotives that are DCC ready (Have  internal wiring and NMRA compatible connector without Mobile Detector) or DCC installed (Has Mobile Detector installed).  In addition, locomotives are available with or without Sound Decoders.

DCC is basically model train scales independent.  Hence, whatever your interest whether it is HO, O, N, or G scale model trains, you should have no trouble entering the world of DCC. Even Z scale model trains and on30 scale which are not as popular can be operated with DCC.

Another interesting aspect of DCC is its adaptability to computer control. Go to the following link for more information: DCC combined with computer control

DC Locomotive using DCC Controller

It is also possible to run a DC analog locomotive (non-DCC Type) at the same time as a DCC locomotive.  This is accomplished by assigning the DC analog locomotive an Address of 00.  This address will cause the DCC waveform to have what is known as a zero stretched waveform which is basically either a plus DC  voltage to cause the locomotive to move in one direction or a negative DC waveform to cause motion in the opposite direction.  However, because the DCC waveform still has periodic bits ( AC-like voltage swings), some DC motors begin to hum and heat-up while at idle (locomotive not moving).  Therefore, caution is recommended if one tries this technique.

DCC Model Train Wiring Requirements

With DCC operation, it is possible to control many trains simultaneously on the same track. Hence your controller or booster must have the capability of shutting down in the event of a short. Hence, the wire size chosen must not only be capable of supplying several trains, but it must also be capable of turning off the controller or booster if a short is detected at the greatest distance from the booster or controller . The following table depicts the primary track bus wiring vs scale used.

The Track Bus is typically wired to a Terminal Block along with the feeder wires. The smaller size feeder wires are soldered to the rails.  Rule of Thumb – Feeder wires are usually 1 to 3 ft in length and are usually  3 to 6 ft apart.  The following table depicts the feeder bus wiring vs scale used.

Direct Current (DC) and Alternating Current (AC) Differences

If a locomotive is of the Direct Current (DC) variety it will likely use 2 rails instead of  3 as used with the Alternating Current (AC) Lionel Trains.

The table below provides a breakdown of locomotive AC/DC power requirements vs scale.

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

Refer to the following for additional information associated with Digital Command and Control units for model trains for every scale such as HO, O, N, and G :



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