DCC basics

DCC stands for Digital Command Control. This is a very popular way to control model trains in the smaller scales. It is used less often in G scale.  DCC is a somewhat quirky control method as it provides both power and communication to a locomotive via the track pickups.  In this regard, DCC is both power and a network communications protocol.  It works by modulating a digital signal over the track power. The ‘decoder’ inside of the locomotive separates the communication from the power and uses the commands to control various locomotive functions including the throttle, sound and lights.

DCC is a free open protocol design maintained by the NMRA (National Model Railroad Association). It is widely supported. Detailed information on the electrical and logic connections and commands can be found Here

The DCC commands are divided into 3 main categories. Throttle commands, Function Codes and CV messages. The throttle commands sent by BlueDCC are all 128 step commands. For historical reasons, DCC decoders can also accept 14 step and 28 step throttle commands. While the BlueDCC board has that capability it is not used in this release. Function codes are commands sent to do things like turn a light on, trigger a horn or whistle, make a coupler/uncouple sound, etc. CV messages are sent to setup and program the board. For example to set the kind of engine sound or select a particular horn sound or setup a momentum/brake value, things like that.

One of the main features of most decoders is that since you are controlling the throttle with the decoder, it can do ‘smart’ things like sense the amount of current flowing to the motors and adjust that in real time for a more realistic locomotive operation. It can also use the ‘sense’ to control the various locomotive sounds- if you are pulling a large load up a grade, it can sense that and change the engine sounds accordingly.

In the smaller scales, this is quite a good system. It also works well in the larger G scale world except for the fact that many G scale layouts are outdoors. While it will work fine outside, it does require very clean and reliable track work. Since the track must carry the signal and power, it also precludes the use of aluminum track to some extent. Typical wiring problems also come up, reverse loops, switch frog wiring, etc.

I don’t particularly care for track power, it requires a bit too much work for my tastes and is not actually very prototypical. This is the main reason for my design. It gives you most of the benefits of DCC- great sounds, lighting control, prototypical momentum and braking- without any wiring or track issues.