Yes, you're thinking of thread drift - I suppose I should just be thankful that a couple of people understood the meaning of the phrase "Track circuit" (as applied to railway use) and have answered the original question...
No not thread drift, more where someone steals a thread for their own slant on the topic.
cheers, Simon
simon wrote: [...]
[...]AIUI, OP is just wondering if DCC, with its AC at a constant 20V on the track, would cause a problem with occupancy detector circuits. Answer (as with all things electronic) is "It depends."
HTH
Like I asked, how do you propose to do that for the decoder connected to the track? Are you proposing digitrax decoders with transponding or Lenz et-al with Rialcom? Either way it's a totally OTT suggestion when you might just as well fit such decoders in the locos.
MBQ
DCC is "always on" so you always have something to work with. Even a stationary loco will draw some current that can be detected, if it's not enough then the old trick of a resistor connected across the pickups will do. Ideally you want galvanic isolation between the traction power and your track circuiting logic. Since DCC is (barring pedantry from some) AC, a current transformer is ideal for this purpose.
MERG have at least one circuit and kit of parts.
MBQ
to that stage. Hopefully will be able to use own software, may be an interesting bit to add on.
Cheers, Simon
Like I asked, how do you propose to do that for the decoder connected to the track? Are you proposing digitrax decoders with transponding or Lenz et-al with Rialcom? Either way it's a totally OTT suggestion when you might just as well fit such decoders in the locos.
MBQ
from your reply it would seem I didnt explain the idea very well. But not to worry, got all the info I need now. Thanks, Simon
Would I be right in assuming that the above (most snipped) is in effect "Loco/Train reporting", rather than just indication that something is causing section occupancy, if so I can see a use for it as a means of allocating - from a time table held in computer software - a train reporting number (aka Head Code) to the motive power used to pull the train and feeding this to track diagrams etc. Or have I got completely the wrong grasp on this?!
As what I wrote was snipped :-)
The basic occupancy detection with Loconet bits and pieces (or equivalents from other makers) reports that something is on that block section. The detection itself could be current draw (DCC chip, even on idle, resistor over wagon wheel, etc), or could be optical or magnetic switch. That far can drive a simple block diagram which can indicate occupation or clear on sections. The diagram could be on a computer or a stand alone "traditional" display panel (eg. CML Electronics do a Loconet board for this purpose). Combined with signalling and turnout control, this could give a prototypical interlocking signalbox, and drivers of trains would be "commiting offences" by deciding to drive past signals at red (just like a real railway before any form of automatic train control). I think its possible to introduce "automatic train protection" where a signal passed at red causes an instruction to be sent to shunt down the train on the section in question (essentially an "all trains in section stop" instruction).
If the computer monitors turnout settings, which trains are driven, which blocks are occupied and released, it can (if detection locations are well designed) work out where trains have moved to. This can then display train numbers (etc) on a track diagram, or operate a layout to a timetable. But, as the system involves dead-reconing, a weak design could get things wrong. Railroad & Co (commercial software) does this job, and its ability to do it well is one of the makers main claims as to why their software is superior to alternatives.
The more advanced forms of train reporting require transponding where information comes back from the locomotive to the control system. Digitrax do their own system which requires their block detectors and their chips in locos (they sell a transponder chip which can sit alongside another maker's loco control chip). The Digitrax system has been around a while and has mixed views (even on the Digitrax owners forums) as to how well it really works. Digitrax themselves have said that transponding has been a technology seeking a practical use, and that application might be the new track-side surround sound system from SoundTraxx (source: AJ the owner of Digitrax at a recent conference, video available on the web). Lenz have a different system (Railcom), but to date there isn't much you can actually do with Railcom (lots of promise and neat ideas but few actual products).
- Nigel
My current flow based track circuit detection has no problem detecting an idle DCC decoder. It's a circuit of my own design, so I can't say whether all of the commercial offerings manage the same feat, but it's certainly possible. I would say that if you adopt a reasonably modern digitally-based approach it's not even difficult.
The transistor- and relay-based circuit shown there probably won't spot a DCC decoder with all of its outputs turned off.
I use the four diodes and optocoupler trick. It's very sensitive and gets the cost and component count per block right down. I rely on firmware in my microcontrollers to debounce with the `present-absent' oscillation caused by the fact that the circuit only detects on one half of the DCC waveform.
In my system I don't bother with any loco-to-computer transmissions.
The computer knows where all the trains are and can detect their presence as they enter new blocks. It can therefore compute which train must be occupying a particular block: it's the one from the adjacent block which it just told to move in that direction.
Just like the real thing! Very prototypical ;-)
Cheers Richard
How do you cope with the hand of god moving a train when the layout is turned off? How do you introduce a new train to the system?
MBQ
How do you cope with the hand of god moving a train when the layout is turned off? How do you introduce a new train to the system?
MBQ
If hand of god tries to move locos then he gets knuckles wrapped. Time stands still when the layout off - its as though the universe doesnt exist. You keep sending decoder address requests ...... :-) Theres also the problem of what happens when the layout is created.
Cheers, Simon
If the hand of god moves a train, the train must be placed in its designated start spot. And if there's another train already there it will also have to be moved by the hand of god, etc.
This turns out to be less annoying than one might expect. If it gets too bad I might provide a function on the computer screen to specify where some train is, or to allow the computer to know more accurately the exact length of a goods train, the but I haven't found it necessary yet.
The system knows about all the trains that might be on the layout and I have to update the computer configuration to introduce a new train. But that's really trivial compared to the effort of selecting and purchasing it, fitting the decoder, etc.
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