The first and simplest method was the use a simple variable transformer as introduced by Lionel in 1906 to lower the Alternating Current [AC] voltage from the wall to a lower, safer value and allow the user to control the speed of a model electric train by changing the amount of AC power applied to the track. In the 1920's, Lionel included remote control reversing switches to allow the user to control the direction of the model train.



When Direct Current [DC] powered trains with permanent magnet motors were introduced, a different standard was developed for most two rail train tracks where the direction of trains were controlled by the polarity of the DC track power applied to the track.

In the late 1940's Lionel added a new concept of applying DC on top of the AC track voltage to turn on and off an on-board whistle by remote control. This concept of high frequency transmission was introduced in the Lionel Electronic Train Control. This system supplied ten different signals that would control ten different remote control effects. The different high frequency signals were superimposed on the standard AC power when selected buttons were pressed at the control center. Each remote engine or rail car was equipped with a receiver unit that was tuned to the individual frequencies. When the correct high frequency signal was transmitted, the corresponding receiver would toggle or turn-on some remote effect.

These high frequency signals increase the ability to remotely control various effects but they had other problems. Transmission losses were usually high and it was critically important to keep the track, the track joints and the wheels of the receiving car or locomotive extremely clean. However extra feeder wires to different parts of the track were used to prevent signal losses and placing capacitors across the track joints and adding inductors at the power supply and on each accessory being used assisted in reducing signal loss and in ensuring that all components of the model train layout operated properly. All this additional equipment however added to the cost, the complexity, and the maintenance for the model train operator.

Model train manufacturers have, over the years, introduced different methods of applying high frequency signals to the model train track to increase the remote control capabilities including independent train control which means that the operator can control the speed, direction and features of a number of different engines all on the same powered track section. With most DC and AC systems however, the biggest problem is that there are only a limited number of remote control signals possible and their application is slow by modern digital standards.

The application of digital technology uses remote control signals to carry digital signals to decoders in the engine for digital command control of locomotives and other accessories.

Digital Command Control (DCC) is a method of controlling individual engines, rail cars and accessories by transmitting digital remote control signals down the track to on-board digital receivers and decoders in the locomotives, wagons and other rolling stock and accessories.

DCC has been around since the 1970's but had not received wide acceptance because of the limited technology at the time and the difficulty and expense of installing receivers in each engine. With developments in digital technology these problems have diminished and over the last ten to fifteen years major model train manufacturers have produced several different versions of DCC. So many that unfortunately customers have been confused about which system is best.

Fortunately, in recent times, the National Model Railroad Association [NMRA] has established a preferred method of transmitting and receiving digital transmissions on model train layouts, based on the Lenz system developed in Germany and this is recognized as the accepted standard for DCC.