LM-3S-21 Module compatibility with different manufacturers

[rdickson]

Hello,

Somewhat new to the group and just purchased RPK-2 starter kit. I'm assuming that the simplest way to go for install is look at locomotives with DCC / sound ready. After reading through several threads i'm getting the impression that Scale Trains might not play so well with Rail Pro, is that correct?

Any recommendations on what manufactures integrate well with RP?

Sorry if this have been covered before but I couldn't find any threads about this topic. Thanks for any advice.

 

[Smoke]

I just installed an LM-3S-21 in an Athearn Genesis MP15AC — no issues at all, and I’m able to access all the functions without a hitch (headlights, ditch lights, ground lights).

As far as I know Scaletrains is the only manufacturer that doesn't 100% work with 3rd party 21 pin modules/decoders. Here is a link to more info on the Scaletrains issue with the LM-3S-21: https://rpug.pdc.ca/index.php/topic,1666.msg11645.html#msg11645


I’m planning to install more LM-3S-21 modules in Rapido and Walthers locomotives soon, and based on my understanding, I don’t anticipate any major issues there either.

[rdickson]

Appreciate the reply Smoke, thanks for the information.

Bob

[KPack]

Scaletrains definitely does not integrate well with 3rd party 21 pins.  It's a known issue between ST and other DCC boards.

I can report that Rapido is a direct drop in for the LM-3S-21.  Plugs right in and has access to all functions, as well as the built-in Rapido keep alive.  Couldn't be any easier.

[G8B4Life]

Scaletrains definitely does not integrate well with 3rd party 21 pins.  It's a known issue between ST and other DCC boards...

There was a lengthy discussion about this over at Model Railroad Hobbyist awhile back (Link, look for Yarons posts on page 76-100 and 126-150). What it really boiled down to was all the other decoder brands aren't fully NMRA compliant and lack the required function outputs from the standard to work with Scaletrains; there wasn't anything non standard about Loksound or Scaletrains motherboards at all.

Now, the LM-3S-21 does have the required function outputs so why doesn't it apparently work in place? Mystery!

- Tim

[rdickson]

Great information, Thanks.

[gregeusa]

Love to read that discussion, can you supply the link?

Interesting, the first paragraph says that the decoder is fully NMRA compliant so it's not their fault

The second paragraph then asks why the RP does not work, since it had the function outputs...

So, I'd love to read about this, so link please?

[Smoke]

Tim posted the link to the thread above (Link), but here are direct links to the posts by Yaron he mentioned:


Yaron Post #1

Yaron Post #2

Based on my understanding of the thread, the LM-3S-21 should offer full 21-pin functionality, including access to the ST functions. However, as Kevin’s testing has shown, certain features currently appear to be inaccessible. I wonder if there is there an update planned from Ring that would enable full functionality? That enhancement would be a significant selling point for RailPro (On top of the already great selling points).

[G8B4Life]

In the below, when I say others I mean North American manufacturers directly competing with ESU's Loksound v5 in the marketplace, this means Soundtraxx and TCS. This is pretty much the situation summarised:

• ESU makes its 21 pin Loksound v5 decoder with all outputs on the 21 pin connector available in the standard, available . The others do not. Scaletrains apparently sometimes makes use of those extra outputs.
• ESU makes its 21 pin Loksound v5 decoders in line with both the NEM and NMRA standard ^*. The others do not. ESU's decoders contain 4 amplified outputs on the 21 pin connector (Front/Rear headlight, AUX1 and AUX2), The rest of the outputs are logic level. The others decoders are all amplified outputs. The two types of output are not interchangeable for directly hooking up lighting.
• Scaletrains motherboards are designed for ESU Loksound and therefore are designed for NEM / NMRA standards compliant decoders.

* ESU also makes the 21pin Loksound v5 with more amplified outputs on the 21pin connector but this decoder is specifically designed for Marklin models.

The LM-3S-21 according its the documentation also follows the NEM / NMRA standard with which outputs are amplified and which are logic level, and all outputs available on the 21 connector in the standard are available. Now, as to why the LM-3S-21 is not working in place of a Loksound v5 in Scaletrains is a mystery that I can't put my hand to as I don't have any LM-3S-21's (too expensive until the exchange rate radically improves) or any Scaletrains stuff.

I feel Scaletrains has been dealt an unfair amount of bashing over this, when they were the ones compliant all along.

- Tim

Edit: Grammar

[gregeusa]

yep, thanks for the details gents!

one niggle: a "normal" output on a decoder is an open collector transistor which conducts to minus (most people would say ground)
this "output" is either open circuit/high impedence or connected to ground

(clearly this is why the LED common is positive voltage)


a logic level output is positive when true and negative or ground when false.

open collector "outputs" can sink reasonable current, 100 ma is typical

logic level outputs can only handle a few ma, most are under 10...

but in no case would I call normal open collector outputs "amplified" they are merely a controllable switch to ground when "on"

just trying to clarify something that could be misconstrued.