This page is intended to explain a little about the DCS control system and what you can do with the remote handset(s) and Track Interface Unit(s) with Protosound equipped locomotives
Firstly it may be as well to explain what you can expect if you already have an electric power-supply/controller
All MTH Ho gauge locomotives can accept a constant voltage DC or rectified DC supply. To obtain a reasonable maximum speed and power the supply should be capable of a minimum of half an amp at 16 volts. If you like multiple unit lash-ups, double heading or whatever you might want to consider a 2A supply. On a conventional resistive or variable voltage supply you can get forwards and reverse motion, lights and small library of default sounds including start-up, running and shut-down sequences along with smoke output. The upper volume of smoke and sound can be limited by switches or potentiometers on the locomotives.
The Protosound 2 and 3 decoders fitted to the larger MTH O gauge and gauge 1 locomotives are able to be powered by either an ac or dc supply which should be capable of providing at least 18 volts with a 2 to 5 amp capability per locomotive under power. Under analogue dc control the default digital effects will be as for the Ho models whilst under ac MTH locomotives are able to react also to coded a/c power pulses to reverse the locomotive, sound the horn or bell or loosen the couplers. A DCS controller will of course provide access to all the digital effects whether ac or dc.
If your power supply generates a high frequency "chopped" output then the power pulses may be interpreted as illogical DCS commands and for this reason "chopper" controllers are simply not recommended.
So what can the TIU-handset combination do? Let us consider the general specification of the TIU:
The TIU has four power inputs and four power outputs. Two of the input/output units can only be used to control DCS equipped locomotives. These outputs are effectively fixed voltage with command signals being sent down one of the rails. Just for your information it is the central rail on 3-rail and right hand side of 2-rail Protosound 2 locomotives that picks up the signal so if the locomotive does not seem to respond try swapping the power leads over (this will also need to be attended to if you have a reversing loop).
The other two outputs are factory ready to be used as either independent "fixed output" DCS control mode or for conventional (variable voltage a/c output from fixed ac input) control. The addition of simple bridge rectifiers to these two outputs allows the TIU to control normal dc locomotives via variable voltage rectified dc. The features that are available depend on whether the the motor in the locomotive needs an ac or dc supply. If you happen to already have a conventional dc transformer/controller then the TIU can "pass through" a variable voltage but will not act as the voltage controller itself.
Each output controls a "loop" or section of track. These track sections must be electrically isolated from each other and common-return wiring is not an option. Under DCS control more than one locomotive can operate on each track section, either as a diesel lash-up, double heading, push-pull helper or independent trains as long as the total power drain of 10 amps per output is not exceeded. Whereas with gauge 1 models it is possible to find a locomotive that has a 5 amp peak drain it would take a fairly impressive Ho system with dozens of locomotives operating at maximum power to even approach 10 amps. Obviously the TIU cannot provide more output power than it is supplied with and each of the outputs in use will need an adequate supply on the input side. If you tend to operate only one locomotive per output then a 5 amp supply shared between the inputs will most likely suffice for general Ho purposes whilst a 20 amp supply would most likely cover half a dozen gauge 1 or ten O gauge locomotives running simultaneously. With gauge 1 and O gauge operation MTH recommends that a 15 amp quick-blow fuse is used on each of the TIU inputs, to protect against the possibility of damage if there is a short on the track, but for Ho this can sensibly be reduced to just exceed the normal continuous load that the power supply can support on each input. The TIU can be connected to a chain of Accessory Interface Units and also to a computer to allow new sound files to be loaded into locomotives. It should be noted that there are no manual controls on the TIU itself (other than an emergency stop panic button) it can only be controlled by the remote handset.
Should you have a number of very high current requirement locomotives that could exceed the 10 amp per output internal rating of the TIU it is possible to connect the TIU to the track in "passive" mode where the main power supply is connected directly to the rails and the TIU is fed either from an auxiliary power supply or from the track via TIU output port 1. In this mode the TIU does not have to handle a high amp current but merely adds the DCS control signals to the rails. In theory, if your power supply is up to the job, you can keep going until the rails start to glow.
The handset is powered by AAA batteries and has a free uninterrupted range of around 50 feet. Remember that the range is not from the handset to the locomotive but from the handset to the TIU. The handset has a two-line lcd display, a central thumbwheel and an array of pushbuttons that give immediate control over the bell, whistle/horn and coupler without you having to remember the code sequence for these particular features. MTH locomotives that are on controlled sections of track are first detected and then logged on to the handset's memory. The selected locomotives can then be controlled for speed, direction, sound and smoke volume, all the bells and whistles and other sundry sound effects that the locomotive has been programmed with plus the uncoupler for those recent locomotives that have this feature. The handset can be set to one of five frequencies should you want to operate layouts in close proximity at an exhibition. If you want to control more than four track sections with further TIUs they can be set for common control, in this instance each TIU will broadcast the control signals and it will not matter which section the chosen locomotive happens to be on. It is also possible to have two operators, each with a handset, controlling through the same TIU. In this instance, if there is a conflict in operator intentions, the locomotive(s) will obey the most recent valid instructions.
If there is a remaining bugbear with DCS it is that the controller only puts out command signals on one wire and that Protosound 2 locomotives only pick up the command signals on one rail which means that it is possible to have the power leads or the locomotive on the track "the wrong way". 2-rail Protosound 2 locomotives have a polarity switch to overcome this but, if you have a reversing loop, you may want to fit a dpdt switch to the track feed or simply swap the power leads if such a basic solution is acceptable. In a perfect world the next generation of TIU would send signals down both rails and also provide variable dc control straight out of the box. [please note that DCS was developed around an O gauge 3-rail heritage where the control signals could be confined to the central rail. The newer Protosound 3 decoder, as developed for the 2 rail Ho locomotives, does not need a polarity switch as it can receive control signals from either side]
The TIU and handset tot up to around two hundred pounds and might not look like a bargain in the first instance. I would however suggest that you look at the pricing of just one conventional transformer-controller that can actually manage a 10 amp output and you may find that you are looking at anywhere between one to four hundred pounds. If you then consider that the TIU needs just a simple 16 to 22 volt supply, that it can control up to four separate outputs and gives you full access to all the DCS control features then it seems a far better deal in comparison.
I would also draw your attention to the DCS Commander which, if it's single 5 amp maximum output is sufficient, may provide a cheaper option and also the more recent DCS Commander Remote (which is even cheaper but which does not operate all the minor controls).
It is worth remembering that the TIU is the only interface device produced so far that can be used to download new sound files to Protosound locomotives, neither the DCS Commander nor the Commander Remote can do this.
For further notes on the TIU regarding capabilities, wrinkles and potential pitfalls and solutions regarding lengthy track sections or outdoor tracks and suchlike I would suggest taking a look at the information kindly supplied by Rayman4449 .
Here is an extra page for those that would consider using their DCS systems in alternative ways.