Digital Command Control

Analog DC power for HO railroads

Since its inception, HO railroads have been run using DC (direct current) motors, typically around 12 volts. Power is routed from the transformer to both tracks. Increasing the voltage makes the train move. Reversing the voltage between the two rails causes the train to move in the opposite direction. Increasing the voltage and the train moves faster. Turn off the voltage and the train stops and all lights on the train turn off.

There are two obvious weaknesses to this scheme:

  1. Turning off the lights when the train stops is not very prototypical. You would like the lights to remain on.
  2. Only one train can be on any section of track since putting two trains on a single track would cause both of them to always move forward and backward in unison.

The classical solution was to break the track plan into separate sections, called blocks, with a switch to determine which transformer controlled a specific block. Before a train entered a new block, the switch on that block would be set to that transformer. By manipulating these block controls, several trains could operate on a single large track plan. Needless to say, this was quite cumbersome and you were also limited by the number of transformers you had available.

Digital Command Control

In 2013, the Riderwood Railroaders converted its layout to Direct Digital Control (DCC) using a system sold by Digitrax. Beginning in 1989 several companies began working on a digital solution to the problem. With DCC, a computer chip is installed in each engine and each engine is given a unique number. A throttle is plugged into a receptor, called a Loconet, and the engine’s number is set on the throttle. A constant 14 volts is applied to the track. As you increase the speed on your engine via the throttle, the command is sent via the Loconet to a central controller, called the command station, and then a signal is set along the tracks that contains the engine number and a command. Only the specific engine addressed by the command responds to it. Theses signals are similar to the packets that drive the Internet, and it is fascinating to see a similar technology used in model railroading using the tracks as the digital circuit.

In this way, as long as each engine has a unique number, each can be individually controlled. There is no problem in putting multiple trains on a single track, and due to the constant 14 volts always on the track, lights on trains remain on even if the train stops. There is no need to bother with block controls, and with 9999 available numbers, we will never run out of addresses to put in each engine.

The only limitation is that the current Digitrax command station running the Riderwood railroad can only handle 22 engines running simultaneously – more than enough for our operations. We also need multiple throttles, one for each engine. But these are not unduly expensive.