Review

Dear Jeff,

In no particular order of preference:

- "Practical Electronics for Railway Modellers" by Roger Amos....
(Old skool, but analog + fundamental + reliable)

https://www.biblio.com/book/practical-electronics-railway-modellers-book-1/d/1314354835

- "Model Railroad and Misc Electronics" website by Rob Paisley
(both optical and track-current detection --> signal driver)

http://www.circuitous.ca/CircuitIndex.html
http://www.circuitous.ca/CircuitIndex.html#Current
/> http://www.circuitous.ca/CircuitIndex.html#Light

- Dr Geoff's "Differential Light Detector" circuit here on MRH (Optical detection --> drives Arduino "brains" --> signal-head)

https://model-railroad-hobbyist.com/node/26133

- the classic "Twin T" 2x transistor track current detector by Linn Westcott

- the Optical Detector + signal smarts offered by the Legends at ISE...

https://www.iascaled.com/store/ModelRailroad/BlockDetection

Hope this helps..

Happy Modelling,
Aim to Improve,
Prof Klyzlr

Thanks Prof Klyzlr. Jeff

Thanks Prof Klyzlr.

Jeff White

Logicrail

I'm a fan of the LogicRail Signal Animator. You can get the photocell or the Infra Red detector that mounts between ties (HO is easier than N!)

Logic Rail

I like the simulation that drops the signal to red as the engine passes, then times out to display yellow, then green after the last car has cleared. It works independently of track power so DCC is not a prerequisite. I can override the detector if, say a turnout is thrown against traffic or if you are running against the current of traffic.

The SA-2 runs about $25-30. Most of my signals are kit built using Oregon parts but I have several Tomar and NJ International, too.

Good Luck, Ed

DC Signals

Jeff

The following is what makes sense to me - don't know if there is some sort of standard or RP on this. Each railroad and railroader is different, so YMMV.

There is not much difference from signaling a DC vs DCC layout as it is all about block protection. If there is some sort of classification yard, split the plan into electrical blocks at least a little longer than the longest train that will fit in the yard's A/D track(s). The longest train pretty much also decides the minimum passing siding length assuming that there will be opposing train movement.  

Each block will need some sort of detection of which that logic will set signal aspects of the detected block, and let adjacent blocks and dispatch panel know the status and set aspects accordingly. You can decide on ABS or APB and then CTC over the top of that if wanted.  There is a wealth of information out there about those.

To keep things simple, each train should have some sort of end of train detection; lit caboose, active or passive pusher, or an EOT device. Besides electrical detection, each control point ( siding, junction, diamond ..etc ) should have optical detection as there could be a non-detectable car in/on it. To expand: If no EOT and the train spans 2 blocks, there is no detection in the previous block and sh.t could happen. I choose not to add resistors to wheel sets for this as that drags down the operating current. On a DC system, probably not an issue, but DCC on the other hand - geesh.

Hope this helps a little!

Detector and signal options

The Twin-T detector mention above was revisited by Geoff and might be better than the original as it works for DC and DCC.

SMA26 Revised TwinT Block Detector for DC and DCC Train Detection

Once you have detection out of the way then you can look into the signal control. I think something like the LCC products from Dick Bronson of rr-circuits would be good, another alternative is the Atlas signal system. I'm sure the are other stand alone products as well. Then you can DIY things with an Arduino: 

Current detection

The problem people had back in the DC era was that you don't always have voltage on the rails to use to detect current. Of course, not being prototypical isn't really a concern here, as controlling tracks with the DC block control kludge was never prototypical to begin with.

Installing resistors is a PITA, but they don't use much current relative to modern DCC systems with 5A or 8A boosters.

If he's that hell bent on not moving past 1994 in terms of a control system, I'd look at something with photocell sensors and Arduinos, and you could throw something together that's cheap and looks semi realistic for the train to knock the signal down and use a timer to bring it back to approach and clear, spacing trains apart to a degree. You could drive about any signal type with an Arduino, you just program what the aspects are and what logic drives them.

re: Current Detection

I seem to recall this was solved by having a low voltage transformer apply voltage to rails and with the diode drop of the detector the trains did not move, but still were detected.

That issue is probably addressed in this thread:   Build a simple block occupancy detector

Bruce Chubb

had a whole system design and written up in Model Railroader years ago. 

Bernd

Yeah Alex, you're

Yeah Alex, you're misinformed. That situation was generally resolved.

The issue was that as DC motors in the models improved they were able to detect those low voltages, so the circuits had to be further refined, but this is a solved problem no need for optical detectors if you don't want them. 

DC detection

I know there were some ways people managed to hack around the fundamental problem of not always having voltage on the track in the pre-DCC world, but if you can detect a car with a resistor-equipped axle in a block, then you're going to have some voltage potential across the rails, which is less than ideal in DC.

There's all sorts of other things that aren't strictly prototypical but useful in the model world that you could do with signals back in the pre-DCC world like interlocking them with turnout positions or block power toggles in some way.

In 2021, anyone serious about operations or realistic anything is running DCC, for people stuck in the past with DC, simple animated but otherwise not realistic signals based on IR detectors would do the trick of providing some animation and background scenery so to speak while trains run around. The other fundamental problem is that as long as you're controlling blocks of track and not controlling trains, trying to do anything operationally prototypical is an uphill battle. Yes, people had workarounds and workarounds to the problems those workarounds caused in the pre-DCC era, but to fundamentally fix them, you need a constant track voltage and independent control of locomotives, whether through pre-DCC command control systems in that era or DCC now.

DC detection

To detect occupancy, you need to apply a higher voltage to the rails than the throttle can ever produce, with a resistor in series to limit the current. Then the throttle needs to be a type that only sources current, never sinks it, and because it's unipolar, reversing has to be accomplished by a relay per block, not a reversing voltage that comes from the throttle. What gets sensed is the voltage on the track, or whether the high voltage source is delivering current. It requires a fair number of components per block, but it can be done. And then, of course any piece of equipment that you want to detect has to have conductive wheels. 

Rail detection on Analog (Detect when throttle = zero volts)

Dear MRHers,

Um, this issue (detection when analog throttle set to "zero volts") was addressed back in the early 1980s, please see the previously-referenced "Practical Electronics for Railway Modellers" by Roger Amos (ISBN 0-85059-555-X)

Might also be worth taking a look at the documentation available by MERG
https://www.merg.org.uk/download/chapter/10(Detection Overview and examples)

and indeed all of the chapters, just change the number at the end of the URL above to any number from 1 thru 28
(chapter 27, "Pocket Money Projects", may be particularly useful).

Happy Modelling,
Aim to Improve,
Prof Klyzlr

And I would hardly call all

And I would hardly call all of this a hack.

Clearly DCC is easier, but DC block detection is 40 years old, well established and well understood. no hacks required.

Too late for me

Agree with many here about my D.C./ brass Sect. track hobby.

WIshed I would have read the hole book of by Paul Mallery associates.

Chapter #7, pg.26 Independent control of locomotives.

But,  NO,, I had to get in a hurry and build a point to point switching layout.

And with so many engines.

Can still help friends to not over spend if later no longer interested in Model Railroading.

Anyway,  great read.

Boudreaux.

Bayou Crest Express R.R.

Book is an ATLAS Copyright 1958

Detection

Well, that was interesting. On page 16, that chapter off the MERG website features my picture of my work on fitting barcodes to freight cars. It would have been a few years in the past, and I can't remember for sure if anyone did or didn't ask me for permission! As for the current-based detector, the circuit diagram is incomplete and there doesn't seem to be any plan for dealing with the situation where the throttle output is zero.

The barcode setup was fun to play with, and I did get it working quite well, but the labels were a real pain to attach, and I never really figured out how to do it in a satisfactory way. RFID seems like a better plan.

DC block detection

DC block detection is a total hack, as DC is intended to have no voltage on the rails if nothing is moving. DC block control itself was a kludge because it took 15-20 years after ASTRAC for command control technology to become practical, and then no one could agree on a standard until 1994.

Detection

DC block detection can be done for trains moving at any speed, including standstill. It's not a "total hack", just a system designed and built to accomplish a task.