How to detect which DCC loco is in a block?

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fpmacko

New Member
My modeling so far as been only large scale outdoor so I'm still learning about DCC. I'm building a small indoor HO layout using NCE BD20 DCC block detectors on each of my 10 blocks. Not sure if I'll be using JMRI or something homebrew as a control system. I understand how block detection works but I'm drawing a blank on how to discern "which" of my two locos has entered a block so that I know which loco to stop if the next block is showing a stop indication.

Any help greatly appreciated!

Frank Mackowick
Annapolis MD
 

Iron Horseman

Well-Known Member
My modeling so far as been only large scale outdoor so I'm still learning about DCC. I'm building a small indoor HO layout using NCE BD20 DCC block detectors on each of my 10 blocks. Not sure if I'll be using JMRI or something homebrew as a control system. I understand how block detection works but I'm drawing a blank on how to discern "which" of my two locos has entered a block so that I know which loco to stop if the next block is showing a stop indication.

Any help greatly appreciated!

Frank Mackowick
Annapolis MD
What you are looking for is Digitrax Transponding or the Lenz RailComm. The NMRA DCC standard is RP S-9.3.2 "Bi-directional Communication". The Lenz is NMRA compliant. The decoders in each locomotive have to be so equipped to report channel, speed, and direction back to the command station.

Now having said that. One can work around this with enough software to layout interfaces. At the museum, we set the control software at the start that says loco 123 is in block 7 and its direction. So when control software sees the next block in that direction go occupied, it moves loco 123 to that block. The issue is obviously two trains facing each other and the intermediate block goes occupied, which one is it. Our control system looks at the turnouts to see which side is aligned to that track. Our control system will also not allow two occupied sidings to be aligned to the connecting track at the same time. When one thinks about it there are more scenarios that can be problematic, but more blocks yield fewer situations. For example we have a block just for the turnout. So it is easy to detect which train is headed for that connecting block. ETC. The layout has run on automatic control every Sunday for over 9 years now without a collision. The museum runs nine trains simultaneously, so for just two loco's I would think it could be much simpler.

No, I have not used this on my personal layout mostly because I don't have one :-(
 

tootnkumin

Well-Known Member
Staff member
When you say you are building a small HO layout and that is has 10 blocks, or as they are called in DCC jargon "power districts", just how small or big is this layout? Can all of it be seen from 1 viewing position, or is a lot of it distant or obscured from view?
 

PowrCab

New Member
Funny ! I was just about to ask the very same thing as Toots (above) !!
Or, is it so that you can part of the time act as dispatch in a far off tower watching a control panel instead of solely being an engineer ?

Toots..I think you are off a tad:
'Power district' refers to splitting huge model layouts electronically, so that if one district is shut down by a short, other district won't be affected. Whereas, the 1:1 scale's signal system of train occupancy is what 'block control' is in the hobby (if not the 1:1's term as well).
 
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tootnkumin

Well-Known Member
Staff member
Toots..I think you are off a tad:
'Power district' refers to splitting huge model layouts electronically, so that if one district is shut down by a short, other district won't be affected. Whereas, the 1:1 scale's signal system of train occupancy is what 'block control' is in the hobby (if not the 1:1's term as well).
Thanks for straightening that out. I'm also a club runner and whereas it was originally DC (still is if so desired) and blocks are what it's method of keeping trains apart relies on is where my confusion originates from.
 

tootnkumin

Well-Known Member
Staff member
Funny thing happened. When I was shopping on Thursday, I went to my local Newsagents. Browsing the mags on the shelves, I spotted a lonely Model Railroader mag, a September issue (we do get them about a month later here unless you subscribe), on the bottom of the cover was an article announcement, 'DCC block detection for signaling p54' with lots of info about using Digitrax gear. There was a section talking about detecting locos and rolling stock in a block too using responders TL1 or TL4 fitted to them.
 

fpmacko

New Member
When you say you are building a small HO layout and that is has 10 blocks, or as they are called in DCC jargon "power districts", just how small or big is this layout? Can all of it be seen from 1 viewing position, or is a lot of it distant or obscured from view?
Ok, you got me. :) Power Districts it is. The layout is 16' long by 6 at one end and 4 at the other. Everything will be clearly visible from one position, at least for now. The reason why I want to know which loco is where is that I'm planning a totally automated layout. I'm using DCC only for cab control and I'll be using DCC block detectors. I want to control all switches and signals using discrete I/O with Raspberry Pi's and my own software logic.
 

fpmacko

New Member
What you are looking for is Digitrax Transponding or the Lenz RailComm. The NMRA DCC standard is RP S-9.3.2 "Bi-directional Communication". The Lenz is NMRA compliant. The decoders in each locomotive have to be so equipped to report channel, speed, and direction back to the command station.

Now having said that. One can work around this with enough software to layout interfaces. At the museum, we set the control software at the start that says loco 123 is in block 7 and its direction. So when control software sees the next block in that direction go occupied, it moves loco 123 to that block. The issue is obviously two trains facing each other and the intermediate block goes occupied, which one is it. Our control system looks at the turnouts to see which side is aligned to that track. Our control system will also not allow two occupied sidings to be aligned to the connecting track at the same time. When one thinks about it there are more scenarios that can be problematic, but more blocks yield fewer situations. For example we have a block just for the turnout. So it is easy to detect which train is headed for that connecting block. ETC. The layout has run on automatic control every Sunday for over 9 years now without a collision. The museum runs nine trains simultaneously, so for just two loco's I would think it could be much simpler.

No, I have not used this on my personal layout mostly because I don't have one :-(
(sigh) Thanks much for this info. Obviously I have a lot to learn about this stuff despite 45 years as an EE. DCC has a lot more to offer than what I was exposed to years ago. I took a look at these two systems and it sure seems like they're closed systems. This is a joint "Hey, what's this do?" project with a couple of software weenies. They want to embed as much functionality into their software as possible and minimize dependence on outboard systems, so they're talking about building a high resolution geolocation system for the layout.

Are you referring to the NMRA museum in Sacramento or the Toy Train Assoc. museum in Strasburg, PA?
 

fpmacko

New Member
Funny thing happened. When I was shopping on Thursday, I went to my local Newsagents. Browsing the mags on the shelves, I spotted a lonely Model Railroader mag, a September issue (we do get them about a month later here unless you subscribe), on the bottom of the cover was an article announcement, 'DCC block detection for signaling p54' with lots of info about using Digitrax gear. There was a section talking about detecting locos and rolling stock in a block too using responders TL1 or TL4 fitted to them.
Classic example of serendipity. I dropped my subscription to Model Railroader a while back when they bought Garden Railways magazine and subsequently disappeared it. But the trains.com unlimited subscription looks too good to pass up because it includes other mags that I've wanted but didn't want my magazine overload to worsen. So I just pushed the button. Thanks for the tip!
 

dave1905

Well-Known Member
Also the systems will tell you which train is in a block, but not where it is in the block. If the block is 8 ft long, the engine could be on the east end or it could be on the west end or it could be in the middle. All the transponding system will know is it's in the block.

If the goal is to stop the train at the signal at the exit from the block, you will need something that can detect the location within the block.

Just as a note, even the prototype dispatching systems don't know where a train is in the block, it just knows the train is in the block. Of course the prototype systems aren't controlling the train, the engineer is.
 

fpmacko

New Member
Also the systems will tell you which train is in a block, but not where it is in the block. If the block is 8 ft long, the engine could be on the east end or it could be on the west end or it could be in the middle. All the transponding system will know is it's in the block.

If the goal is to stop the train at the signal at the exit from the block, you will need something that can detect the location within the block.

Just as a note, even the prototype dispatching systems don't know where a train is in the block, it just knows the train is in the block. Of course the prototype systems aren't controlling the train, the engineer is.
Figured as much. For now I'll keep the consists short and worry about that later on. And we're looking into how we can do geolocation within the layout so that we don't have to deal with transponders. We like to tinker.
 

Iron Horseman

Well-Known Member
What a lucky guy to be able to work at that fantastic HO layout.
It is truly an honor they let me help there. I just wish I would have gotten in on the initial construction. They didn't call on me until after it was built and they realized they needed experienced operators to train others and bring it to life.
 

trailrider

Well-Known Member
If you want to know where the train is in a block (presuming you know which way the train is heading in the first place, you might consider infrared (IR) detectors that would illuminate lights on the control panel, or signals on the layout, or both. Azatrax has electronics like that. You could put IR detectors near each end of a block, plus one in the middle to show its progress. As the train enters the block, on light would light up on you panel. As the train progresses, the next one would light, etc. When the rear of the train clears the first detector, the light would go out indicating the train was clearly in the block. You might have it wired so if the front of the train was triggering the circuit on that end of the block, but the first one indicated clear, signals in the following block would indicate stop, or at least Approach-Slow, be prepared (for a following train) to Stop. If the middle detector showed clear, but the front end of the block indicated part of the train was still in the block, the signal in the following block might show yellow over green or Approach Medium, or somesuch. Just a thought...
 




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