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Hi All,

I have a fairly eclectic collection of 3-rail O scale model trains that I am planning to run on a future layout.

For signaling I am going to use CMRI connected to JMRI

Switching is up in the air but im considering using tortoises or Z stuff for the machines connected to either the DCC system or also CMRI (I'm having trouble finding info on how to connect the z stuff switches to CMRI, some of the switches I'd want to be faster than the tortoise machine since I am aiming for a modern layout)

Where I'm a bit stuck is, I want to use DCC but I also want to make sure all of my locomotives are compatible, in the case of the older locomotives I don't plan on running more than one on a layout at a time but the key is that it all goes into JMRI or is wifi enabled and I can use a tablet.

Let's assume that price is no object, and I don't have any qualms about buying and daisy chaining multiple different proprietary systems as long as it eventually feeds into JMRI or a Mobile app

These are the types of engines I am looking for the system to support:

Lionel conventional (postwar)

Lionel Legacy

K line conventional

Lionel VisionLine (i think also runs off legacy)

MTH Protosound 1, 2, and 3

All engines I want to run are AC only

Any advice would be appreciated, I've tried searching DCC systems before but I'm just left scratching my head, I'm a software developer but I'm having trouble understanding what works with what



Last edited by DashingDanLIRR
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DCC is DCC.    It is a standard signal protocol licensed to the NMRA and is their standard.     It is only the signal on the rail that is standard, not how the signal gets there, so a bunch of systems are available to broadcast and control the signal.     The major ones I am familiar with are Digitrax, North Coast Engineering (NCE), Lenz, CVP products "EasyDCC", and MRC.     The control system components are not interchangeable. 

However, all DCC COMPLIANT decoders can work with any system and utilize all the features of the system.    Some decoders over the years have only used some of the DCC protocols, such as MRC, and MTH; these were compatible, not compliant.     I don't know if this is still the case.

All those locos you mention need a DCC decoder to operate with DCC.    Some of them may have things in them that work with DCC, and some may not.     You may need to install new electronics in them to work with DCC.  

The system boosters are rated by current they can support - number of Amps.    Most have light weight 3 amp systems, and medium 5 amp.    NCE has 10 amp boosters, and Digitrax has 8 amp boosters at the high end.     You need one command station to generate the control signals and run the layout, but  you can have multiple boosters connected to it.   I have a friend who I think has 15-20 on an HO layout.  

Decoders are also rated by amperage they are capable of handling.   Most called "HO" are 1-2 amps with 1 and 1.5 being most common.    NCE, Soundtraxx, and digitrax at least have decoders rated at 4 amps and higher.     You to measure the amperage draw of the locomotive under load and select a decoder capable of handling that amperage. 

DCC is AC square wave power on the rails.   However that does not go directly to the loco.    The signal is imposed on that and the decoder gets the signal and then converts the AC to DC for the motor.     However, most stuff build since 90s and maybe even earlier really has DC motors, and some sort of electronics to convert from AC.

If you are asking is there a DCC system that can run all the locos you listed, the short answer is no.  MTH PS3 locos are the only out-of-the-box locos that support DCC.  All other locos would require a DCC decoder to be installed (if DC motor equipped).  Your asks are not really compatible with each other.  DCC cannot run concurrently with either Legacy/TMCC or DCS.  The most common combination set up is probably Lionel Legacy and MTH DCS, which can be run concurrently. Both systems have apps that can be used with them.  It is certainly possible to have all 3 systems on one layout, but it wouldn't work quite the way I believe you are asking.

MRI works with TMCC/Legacy; not sure about DCS.   Signaling can be separate from the control system so CMRI with JMRI should be no issue.


As a primarily OGauge modeler, what is your rationale for using DCC which is the basic control system in HO and N gauges? This question is not rhetorical. As a result of my support work for companies that provide DCC compatible systems, I have become completely involved with DCC and have studied it thoroughly. My conclusion so far is that it is one of the most complete and capable loco control systems and has a great deal to offer OGaugers who are interested. The key question being worked on at this point is workable implementation of DCC in the OGauge world.

@BOB WALKER posted:

As a primarily OGauge modeler, what is your rationale for using DCC which is the basic control system in HO and N gauges? This question is not rhetorical. As a result of my support work for companies that provide DCC compatible systems, I have become completely involved with DCC and have studied it thoroughly. My conclusion so far is that it is one of the most complete and capable loco control systems and has a great deal to offer OGaugers who are interested. The key question being worked on at this point is workable implementation of DCC in the OGauge world.


In your opinion as DCC exists presently what's unworkable for 'O'?


Last edited by Mellow Hudson Mike

So ultimately my end goal is to have everything feed into JMRI, I'm a java developer by trade so if I want to extend the implementation of whatever is necessary I can always customize it myself or contribute to the JMRI open source project. I also want to be able to control everything (lights, switches, motors) from one location and/or remote which I know I can do that using JMRI.

DCC and CMRI are fully open as far as protocols go, and are relatively seamless when it comes to JMRI integrations. I spent a good amount of time testing and playing around with CMRI as well as super imposing it on the 3 rail tracks to ensure I can do signaling.

For switching I haven't tested that yet, I know tortoise can be connected to CMRI, and I've seen some guides on connecting z stuff too but I haven't confirmed either.

Where I'm a bit stuck is on the train control, I saw that TMCC is sort of supported through JMRI via serial but there is a loss of features, and I saw the PS3 engines could be switched to DCC but I didn't know which DCC platform would actually be supported for 3 rail o gauge because what I read suggested most would burn out (keep in mind I have close to zero knowledge about DC vs AC this was just reading blog posts for awhile).

The conventional trains I inherited from my father after he passed back in 2011, and he inherited them from his grandparents so for the conventional locos if there was a way just to control track power from JMRI via DCC or some other control system that would satisfy my requirements, if I run a conventional consist on the layout it would be the only train on the layout anyway. But I wouldn't want to attempt adding a decoder unless there was a fairly painless way of doing it for those older engines.

The rest of the engines (PS1/PS2, lionel legacy's) I'm sort of at a loss on how to handle them, I'd ideally like to run multiple engines on the layout at once but it sounds like I'd need a legacy remote, DCS remote and then also the JMRI for the signaling and switching.

How difficult is it to install a decoder in some of these locomotives and what are the risks involved in doing so? I've soldered circuits before for the CMRI boards, but overall (as is probably obvious) electrical engineering isn't my strong suit.




3 Rail 'O' Gauge locomotives (Lionel, MTH, etc.), whether traditional-sized or scale-sized, have traditionally been powered by AC through the track (except for a few outliers made in the late 1970's or early 80's as cost-cutting moves).  Early on they all had AC motors inside them as a result.  In the last 30 years DC motors have come to dominate, but are still powered by AC from the track in order to retain compatibility back to the 1930's.  DCC bucks the trend here significantly.

2 Rail 'O' Scale locomotives on the other hand mirror what you find in 'HO' or 'N', or any of the other scale-proportioned sizes (which collectively we call HONGZ).  DCC is quite appropriate here.

For most older 'O' Gauge locomotives including the older ones you've inherited , which we call 'conventional', covering roughly 1930's through 1995, and some later than that even, you can't easily add a DCC decoder within the engine to accomplish what you want, because the motors are presently AC powered and DCC is built upon DC power.  It can be done but is expensive and makes the locomotives unusable to most people in the hobby except you.

Most newer 'O' Gauge locomotives can be run conventionally, but have many more features (DCC-like) available which are unlocked under what we call 'command control'.  Unfortunately 'O' Gauge command control is incompatible with DCC, and in fact interferes with it if imposed on the same track.  These newer models are more easily converted to DCC because they have DC can motors driving the wheels.  Just as above however the conversion leaves them orphans.

The only reasonable conversion, thus the one that takes place most often, is to convert them from 3 Rail to 2 Rail, at the same time DCC is installed to replace command control.   Now your collection has more utility because it's no longer filled with orphans.  However, this type of conversion is usually only employed with scale-proportioned 3 Rail stuff, and not traditionally-sized engines, because it's expensive.

A better alternative may be to consider constructing data gateways between JMRI or CMRI and the native command control protocols.  All of these native protocols are accessible within the native equipment that operates the various flavors of command control, through serial interfaces (RS-232 based).   In fact one of these gateways (to/from TMCC) may already exist.

Lionel's TMCC protocol is open-source and works with Lionel locomotives fitted with TMCC, generally made from 1996 onward.

Lionel's Legacy protocol is not but has been published.  It also would have to be licensed.  It is a superset of TMCC offering more functions for Lionel locomotives fitted with Legacy, generally made from 2008 onward.  Legacy engines will respond to TMCC (but with reduced features), and Legacy equipment will also transmit basic TMCC for older locomotives to use.

MTH's DCS (PS-2 and PS-3) has been reverse engineered but also has not been published.  It would also have to be licensed.  It's completely different from TMCC and Legacy.  On the other hand many PS-3 locomotives are already fitted with a subset of DCC to use as an option, selected via a switch on the underside of the locomotive.

Using data gateways would save the expense of hardware conversions on all of your locomotives and eliminate orphans.

But the gateways suggested above will not work with conventionally controlled engines, all older Lionel (before 1996) and MTH's PS-1 for example.

These would use a power gateway instead, several of which already exist, for example Lionel's PowerMasters, fed by command control data and adjusting voltage levels to the track to provide motion, direction, whistle/horn and bell in the conventional way.

While the data gateways facilitate communication to command control engines, and such engines can run anywhere on your layout, conventional engines must be segregated to 'blocks', or switched sections of track.  Each of these typically has a power gateway, and each is switched to follow it's engine around the layout, in order to prevent multiple engines on different areas of the layout from responding identically to the voltage sent by a single power gateway.  CMRI and JMRI can be used to accomplish this switching.

JMRI and CMRI will work with existing 3 Rail 'O' Gauge command control stuff but it will take some effort to get it to do so.

So which do you prefer?  Hardware conversions or gateways?


Last edited by Mellow Hudson Mike

Hi Mike,

Definitely the gateway route, I saw that the TMCC via serial exists with communication to JMRI, I also saw that theoretically you can link a legacy to a TMCC base and then use that to control the legacy.

In regards to MTH PS3 DCC what gateway would I use that would work with 3 rail o scale? I understand getting the signal/commands from JMRI to the com port, but where I'm lost on this one is the com port to the loco

When it comes to the conventional power gateways seem to be exactly what I'd be looking for so that solves the Lionel conventional, K-Line conventional, and MTH PS1 support.

The DCS on MTH PS2 locos is where I'm sort of stuck. I've seen some attempts to reverse engineer the signal but most are thorough but require custom hardware like this suggestion from a previous post

When it comes to the hardware I would prefer off the shelf with a digital interface (like the TMCC base w/ serial)

Would one option be building the bridge suggested here ->

connect that to the Legacy which is then connected to TMCC which is then connected to JMRI?

Ultimately I was hoping there'd be a way to connect everything to the PC com port in some fashion but it look's like I might need some arduinos to support the DCS <-> Legacy/TMCC connections

UPDATE: for DCS I think I found exactly what I'm looking for ->

So from a hardware perspective which gateways would be best?

For DCS Id need the TIU

For Lionel would the new lionel cab 3 be enough?

and for the conventional's I would use the LCS block power controls?

Final update I think...

I can purchase this

Then use the mobile DCS app on my local network, I can probably skim the commands going to the unit and then replicate them, my guess is they are probably standard REST calls, and this unit looks like it would support all the engines, including the conventional block zones, so I think this could work.

What do you think?

Thanks again for your help,


Last edited by DashingDanLIRR

........These are the types of engines I am looking for the system to support:

Lionel conventional (postwar)

Lionel Legacy

K line conventional

Lionel VisionLine (i think also runs off legacy)

MTH Protosound 1, 2, and 3

All engines I want to run are AC only

I don't believe that's correct.

-  Postwar Lionel locos ran fine on DC -- you just had to disconnect the horn.  If you did a little more modification one had directional control by polarity.  But the key point is the motors ran on DC as well as AC.

-  MTH PS3 locos certainly can run on DC, and under DCS, too, if necessary.

If you are going to rip out the OEM electronics where installed and replace with DCC receivers, you are a lot closer to an All-DC fleet than you think.


With one exception, DCC in its present configuration is track signal based and is DC powered. Adding DCC into a layout in the presence of Legacy and DCS presents a number of system conflict issues which have been cited in previous posts. (Exception is MTH PS3 which has inboarded DCC).

Adding DCC to an existing OGauge layout could benefit from some unique approaches:

A potential solution to the signalling conflict issue is wireless.

A potential solution to the track power issue is battery power.

I have experimented with both of these with excellent results.

It was also previously mentioned that prewar universal  motor equipped engines will perform well on DC power, which I can attest to.

Kudos for going in your own direction on this.  IMO your biggest challenge (besides the dollar cost) will be the postwar Lionel locomotives.  Everything else has DC "can" motors which can easily be tamed by a DCC decoder.  Conversely, the postwar locos have series-wound "universal" motors which will run on DC, but there will be challenges.  In some cases you may have to isolate the field coil ground from the loco's frame.  Also, the current draw will likely be much higher on these than any can motor.  So you'll probably have to look for high-amp decoders designed for G-scale.  Finally, you're still left with a 3-pole motor and very tall "toy train" gear ratios.  So even if you manage to get them running under DCC, the performance may be underwhelming.  IMO you would be better off finding modern-era clones or surrogates.  Most, but not all postwar Lionels have been reproduced during the modern era with can motors.

Look forward to reading about and/or seeing examples of your progress.

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