Kato uses three kinds of lightboards in their designs, which I have labeled "Narrow", "Wide", and "Short", for lack of better terms. The narrow-style board is extremely common in their North American outline models, but it is only used in one Japanese model, the DD51—all of these are rather narrow diesel locomotives. The short-style is relatively new, showing up in the North America NW-2 switcher, and a new release of the C62 steam engine.
I suspect that the upcoming DE10 release may use this board as well.(nope, it takes the "Narrow" style!) The wide-style board is used extensively in everything else (including some European HST locomotives).
Wide:
DF50, DF200, EF58, EF60, EF63, EF64, EF65, EF66, EF81, EF200, EF210, EF510, EH200, EH500, ED75, ED79, E851
Narrow:
DD51
DE10
Short:
C62
| Short | Short | Wide | Wide | Wide | Wide | Narrow | Narrow | Narrow |
| DN123K3 | K3D3 | K0D8 | #0001664 | N12K0a | DN163K0a | #0001642 | K1D4 | DN163K1d |
| Manufacturer | Digitrax | TCS | TCS | MRC | NCE | Digitrax | MRC | TCS | Digitrax |
| Price | $30 | $35 | $?? | $35 | $30 | $35 | $35 | $35 | $36 |
| Functions | 2 | 3 | 8 | 2 | 2 | 6 | 2 | 4 | 6 |
| Advanced Consisting? | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ | ◯ |
| Loadable Speed Table? | ◯ | ◯ | ◯ | ✕ | ◯ | ◯ | ✕ | ◯ | ◯ |
| Dimmable Lights? | △ | ◯ | ◯ | ✕ | ◯ | △ | ✕ | ◯ | △ |
| BEMF? | ◯ | ◯ | ◯ | ✕ | ✕ | ◯ | ✕ | ◯ | ◯ |
| Fancy Momentum? | ✕ | ◯ | ◯ | ✕ | ✕ | ✕ | ✕ | ◯ | ✕ |
| Transponding? | ◯ | ✕ | ✕ | ✕ | ✕ | ◯ | ✕ | ✕ | ◯ |
| RailCom? | ✕ | ✕ | ◯ | ✕ | ✕ | ✕ | ✕ | ✕ | ✕ |
| Max Current (cont. func.) | n/a | ? | ? | n/a | n/a | 500 | n/a | 50 | 500 |
| Max Current (peak func.) | n/a | ? | ? | n/a | n/a | ? | n/a | ? | ? |
| Max Current (cont. total) | 1250 | 1000 | ? | 1000 | 1000 | 1500 | 1000 | 1000 | 1000 |
| Max Current (peak total) | 2000 | 2000 | ? | ? | 1250 | 2000 | ? | 2000 | 1250 |
Functions
Two functions are the minimum: One for each set of headlights. Two more functions are even better: One for each set of markerlights. Of course, the Kato locomotives that these decoders will fit don't actually
come with markerlights, but they do come with clear red lenses and space to fit a small LED. Some frame milling may be required, but nothing extensive. Two more features and…well, I'm not sure what those buy you. I don't see any reason why you could wire the markerlights to two function outputs simultaneously to allow a broader range of effects.
Advanced Consisting
If you want to consist locomotives, Advanced Consisting is the way to do it. The hard way is to assign each locomotive in the consist the same address, but then you cannot operate their various lights prototypically—each locomotive will have its headlights on, for example! Advanced Consisting allows each locomotive to keep its individual address by adding a secondary address. Consisting is only activated when an address is programmed into this secondary slot. Moreover, decoders with Advanced Consisting give you the option of setting up alternate programs for the various functions, allow prototypically-correct lighting control during consisted operation. If you are going to consist a locomotive or two with an EMU or DMU, make sure that the decoders you use in the MU also support Advanced Consisting.
Loadable Speed Table
All decoders today support the three-step speed table. This table maps voltages two the lowest non-zero throttle setting, the middle throttle setting, and the highest throttle setting. But many locomotive models do not have a linear response to increased voltage, and indeed, neither do the prototypes. A 28-step speed table, also called a loadable speed table, divides the throttle into 28 regions (instead of just three), giving you more control over the models response to throttle changes.
Dimmable Headlights
As in the United States, Japanese rules of operation require trains to dim their headlights when passing or standing at passenger stations. Although a subtle feature, many modelers enjoy prototypical lighting effects in their trains. Typically, a decoder that supports this feature will dim the lights when F4 is pressed. Any function decoder that supports "Rule 17" operation of the lights will support this feature.
Digitrax's implementation of Rule 17 lighting is not as flexible as other manufacturers. One option for Rule 17 lighting is to dim the headlight opposite the direction of travel, so both headlights are on. This is called "opposite dim" by Digitrax and TCS, and is not prototypical for Japanese locomotive operations. Unfortunately, Digitrax decoders do not allow you to disable this aspect of Rule 17 operation—headlight dimming and opposite dim are all-or-none in Digitrax decoders.
BEMF
Back EMF (BEMF) is a method for regulating the motor speed for smooth low-speed operation, and maintaining constant speed up and down inclines. It works by inferring the motor's speed by measuring the amount of feedback generated by its rotation—called back EMF—and adjusting the voltage up or down to maintain a constant speed. This feature is critical for low-speed operations, including smooth acceleration and deceleration from and to a full stop.
Fancy Momentum
All the decoders surveyed offer basic linear acceleration and deceleration, but some manufacturers go a step further. TCS offers 3-step acceleration and deceleration curves for non-linear momentum. This feature is nice for simulating smooth and realistic-looking station stops and starts.
Lenz and ESU offer a feature called "constant stopping distance", which, when active, varies the deceleration term to bring the model to a stop within a fixed distance, regardless of the speed of the model. This is great for automating station stops, because you will know the distance from the station throat to the stopping point, but you might now know just how fast a model is traveling when it enters the station throat.
Bidirectional Communications
RailCom and Transponding are two different systems of bidirectional communications over DCC. Normally, DCC is a one-way signal: From the command-station to the decoder. There is normally no method for DCC decoders to respond. RailCom and Transponding are methods for the decoder to send a response to the command-station. This is really useful for automated control of a layout, but is not a necessary feature to implement basic block occupancy detection, although both methods require a block occupancy detector detector to work. I won't get into a discussion of the advantages or disadvantages of each system; you can read more about those elsewhere on the Internet.
RailCom is an
open standard developed by Lenz and
adopted by the NMRA as a Recommended Practice for DCC. That is, it is now an official, if optional, part of the DCC specifications. RailCom responses can be detected by a Lenz
LRC130 RailCom detectors and reported to a computer via the Lenz
LRC135 RailComBus USB adapter.
Transponding is
Digitrax's proprietary standard for bidirectional communication, and is currently only implemented in Digitrax decoders and Kato decoders designed by Digitrax. Transponding responses are detected by a Digitrax
RX4 detectors, which must themselves be attached to a Digitrax
BDL168 block occupancy detector. Transponding events can be communicated to a computer via the Digitrax
PR3 LocoNet USB adapter.
Maximum Current Ratings
The current rating of a decoder tells you the largest load you can connect to the decoder. Each light, motor, speaker, etc., draws a certain amount of current; attaching too many will cause the decoder to overheat and perhaps even die.
A manufacturer often lists two or more different current ratings. A current rating is either for
each function individually, or the
total current for all functions combined. Moreover, a current rating is either a
continuous rating or
peak rating.
Continuous Current per Function is the amount of current a decoder function lead can handle over an indefinite time period. For example, if the literature claims a 125mA continuous function current rating, then you can attach a lamp that draws up to 125mA to that function, and leave it on as long as you please.
Peak Current per Function is the amount of current a decoder function lead can handle for short bursts. Incandescent lamps, when they first turn on, have an inrush current that is ten times the current draw of that lamp. For example, a lamp that is rated as drawing 50mA will actually draw
500mA very briefly when it is turned on. So this rating is important to know when you are using incandescent lamps. LEDs do not have a significant inrush current.
Continuous Total Current is the total amount of current that the decoder can supply for
all functions combined over an indefinite time period. The sum of the current draw of all lamps must not exceed this amount. This may limit the number of lamps or other loads you can attach to the decoder.
Peak Total Current is the total amount of current that the the decoder can supply for
all functions combined for short bursts. This is particularly important for motor decoders, where the stall current of the motor (the amount of current the motor draws when it is stalled or locks-up) must be less than this number. Unless you will be using a large number of incandescent lamps (see above), this number is relatively unimportant for function decoders.
A heavily editorialized version of this review can be found on my blog:
http://akihabara.artificial-science.org/dcc/dcc-decoders-for-dcc-ready-kato-locomotives/
