So we're on the same page, I believe you're referring to this OGR thread from 2013, and this short video clip from that thread albeit of a trolley as I don't have a subway set:

So what exactly is your setup?  Have you settled on where power comes from, quantity and spacing of LEDs, etc.?  Are you comfortable working at the tiny-component level (e.g., resistors, capacitors, diodes), soldering, digital meter measurements, etc.?

As to the delay idea.  My first thought is a DC-powered relay timer module.  These are just a few bucks and can be programmed with 0.1 sec digital precision. When triggered, the relay turns on or off after some settable time interval.  I figure something like this could be the core component of a delay mechanism - obviously i's to dot and t's to cross.

Note that if you search for "delay timer module" on eBay or Amazon or wherever I'd say 99% of these timer modules have a relay output.   This can be somewhat annoying that the relay is clicking multiple times every time the subway passes; of course the relay sound is likely drowned out by the train itself but just saying.  The particular timer module above is also available in a solid-state, non-relay version that operates silently.

If this approach looks like something that might work for you, I can expand on the idea.

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Separately, as to the randomizing effect, if you use the delay method it seems to me you could get in a situation where the behavior becomes consistent/repeatable.  For example at some speed, when the subway comes around to the sparking circuit it will always trigger on the leading wheel axle.  Then the delay kicks in blocking the next 3 axles on the lead car, so the leading wheel axle on the 2nd car sparks, the exact same delay kicks in blocking other axles on 2nd car, and the leading wheel axle of the 3rd car sparks, etc.

So this is one of those measure-twice, cut-once situations.  Best to experiment as much as possible with the effect you're trying to create before boxing yourself in.  I mentioned the 0.1 sec precision of most of these low-cost timer modules since this allows you to do-the-math for your particular subway setup.  That is, you know the wheel axle spacing and can plan out exactly how far apart multiple spark sites are located. 

For example, these timer modules can be programmed to cycle on/off...say 1.0 sec ON, then 2.0 sec OFF forever.  Suppose your LED circuit was powered like this.  This would also be a form of randomization as the axle would only spark when crossing the trigger IF the timer happened to be ON.  This would allow the case where the leading axle on the front car might not spark!  This could be a more interesting effect.

Or, using multiple timers, you could only activate the sparking when the train speed exceeds some speed.  I'm speaking from ignorance but I'd think there would be less sparking at slow speeds(?).  Also, this qualified sparking could address the 0 MPH (stopped) situation that was discussed in the linked thread.  I'd think you wouldn't want the LED steady-on if the subway comes to rest with a wheel on the trigger section.

We are 100% on the same page bro.

My idea was to make "isolated islands" by cutting the track with a Dremel, much like you and others have done. I have several LED'S sitting around from various projects from Evans Designs, so using track power is easy without a lot more work. I set-up a mock version and realized right away that over time I would want two things to happen; #1) having the ability to turn the track sparking system off in case I was running something else like an Aem-7 on that part of the layout and #2) to be able to somehow make the spark more random/realistic.  #1 is easy, #2 takes some thinking

In watching videos of RL CTA trains I don't see any big difference in "speed" effecting spark as you asked about and in some situations it appears that the spark happens with some actual regularity at certain points in the track. Sometimes there is a spark one after another for a car or two, then nothing. At other times there is a spark and then nothing until another spark 3-4 cars later or all the way at the end of the train.

My trains will all be short (4 car consists) for the most part with maybe an occasional 6 car consist. I still have to "think" about the approach, but your ideas are always welcome. Thank you so much!

-Todd

"... in some situations it appears that the spark happens with some actual regularity at certain points in the track."

My experience from riding the NY subways is that the sparking occurs most often where the third rail shoe breaks contact with the third rail, which is usually at switches where the third rail stops to make room for the diverging track.

I was thinking about that after reading one of the earlier posts of the week.  If it is location based, the flicker might be installed below the rails instead, giving you the feature on whichever loco cars you like (reed sw. & magnet could basically ID which and when.)

Aren't there random timing boards on the bay?  It was often as easy as an IC swap or clock jumper wire on the timer boards I used to work with to get a random number generated.... I mean; they seem to have everything else.

My understanding is that 3rd rail arcing is location based. The arcing gradually destroys both the shoe and the rail, and so is something to be avoided as much as possible. But at the points where the third rail stops and the shoe leaves the rail, there seems to be no way to prevent it.

Not meaning to divert the discussion but I noted the post about the trolley.  Doesn't the sparking on trolleys occur on the overhead wire, not the track?

Yes, but the guy who put that video together doesn't run any subways, so he just used a trolley...

@Dick Malon posted:

Not meaning to divert the discussion but I noted the post about the trolley.  Doesn't the sparking on trolleys occur on the overhead wire, not the track?

It could occur on either really, but the overhead is more visable.  Some didn't use Canterbury wire either. But overhead wire and safety won out.

Canterbury?.... that's Goofle spellwreckfspellwreck at it's best again!

LOL.  

Do ALL subway cars in a consist have 3rd rail shoes (or whatever it's called)?  That is, with the proposed method of sparking when the wheel rolls over trigger section, you get four triggers/sparks per car (4 axles).  Do cars really have 4 shoes?  Might some trailing cars have high-power tether cables bringing lighting/ventilation power rather than having their own shoes and power system? 

Since this appears to be in the planning stages, perhaps another homework assignment is to imagine, say, 1) sparking where it actually occurs on a powered car (rather than at the axles), 2) sparking only occurs for cars that have 3rd rail shoes (if indeed some kind of tether system is used), etc.

I can only speak for NYC subways, and generally, each car in a NYC subway train has two 4-wheel trucks, both of which are powered, and each truck has two third rail shoes, one on each side. I don't think that every shoe on a train would arc when it leaves and rejoins the third rail. From what I've seen, the arcing appears almost to be random. Maybe it depends on the condition of the shoes.

I found the section of track that I used in previous thread - it has isolated "islands" each with an LED. 

To generate the random effect, I used the solid-state cycle-timer module I showed earlier.  The timer module was programmed to cycle on-off with 2 different "duty-cycles". 

In the first demo, the module cycles 50% ON, 50% OFF every second.  So 0.5 sec on, 0.5 sec off, repeating forever.  So when an axle sits on a trigger island, the LED will blink 0.5 sec on, 0.5 sec off.

In the 2nd demo, the module cycles 10% ON, 90% OFF every second.  So 0.1 sec on, 0.9 sec off, repeating forever.

So when all's said and done, the 50% ON should "spark" 5 times more often than the 10% ON.  The module is programmable so you can mess with the ON-OFF ratio to adjust the effect to your liking.  It is not a truly "random" effect but might be good enough.

In the measure-twice, cut-once category note that the left trigger island is maybe 1/2 the length of the right trigger island.  This is also an adjustable parameter as a longer island has a greater chance of triggering...but obviously it's easier to re-program the timer module than to re-cut islands!

If this approach shows promise, I can draw up wiring instructions.  Let me know how many trigger islands you plan to have, and any other electrical related info such as track voltage, power available, LED components you're looking to use, etc.

Hi Stan, first off THANK YOU! You da man! I left a comment on YouTube, it was funny, the wife and I took a walk and I saw your video by chance when we came home, before you ever posted here. I am still in the planning stages and I have ordered several of the components that you recommended from eBay. For laziness I will use the "all encompasing" lazy man's leds from Evans designs. I think if you want to share the diagram of what you have going on here, that would suffice for now. I am going to have a few different spots on the layout with the arc/spark effect. I will experiment with the parameters until I am satisfied with the visual results. I will also include a switch to be able to turn the whole spark system on/off, because an aem-7 shares the track at times, and it obviously wouldn't arc, at least not from the track wait, an arcing overhead...task for later on

Thanks again, have a nice day!

-Todd

Should be able to click on image to expand.

Here's an approach using the solid-state cycle timer module shown earlier.  This method requires a DC-output wall-wart power adapter.  It has to do with isolation of the AC track voltage for subway operation and the DC voltages for LED operation.  You might already have a suitable DC wall-wart lying around; it will power both the timer-module and any LEDs.  The module requires 5-36V DC.  IIRC the Evans AC/DC LEDs accept something like 10-20V DC.  Or the wall-wart cupboard is bare, these are inexpensive and widely available; I do recommend a female connector adapter which converts the barrel-coax plug into screw-terminals so you don't have to splice into the wall-wart power cable itself.

Example above shows a 2 Amp wall-wart but even a 1 A wall-wart is more than enough to power the cycle-timer module and a dozen LEDs.  It doesn't have to be 12V either... since the timer module supports a wide voltage range, it's the Evans LED that defines the DC voltage that will work.  You only need one cycle-timer module to support dozens of LEDs.

I don't recall seeing the guts of an Evans AC/DC LED but I believe it would have at least a diode and resistor as suggested in the diagram above.  So this would be for those working at the component-level.

Wherever you bought the timer module should provide programming instructions using the mini-pushbuttons.  The first time is always a challenge ... may take, say, 15 minutes with possible loss of hair (as in pulling your hair out!).  But once you get the hang of it, less than 1 minute to adjust the ON OFF timing.  In case not obvious, the module itself has an on-board red LED that flashes when ON.  The numeric display also counts like crazy.  I believe you can actually turn off the display if annoying though the module is probably hidden under the layout. 

I wonder what flickering LED's would look like in the same scenario?

Good question.

Not sure what color(s) of LED Todd has settled on, but here's a U.S. eBay seller of a flickering BLUE 3mm LED - pre-wired for 12V DC operation.  Less than $1 a piece!  I'm pretty sure that's less than what Evans charges especially considering free-shipping. 

Now that I think about it, I'm wondering if WHITE flickering LEDs are "common" as are flame/candle colored LEDs... and what applications they'd be used for.

I think I have ever color of flickering LED except white, don't think I've seen those.  FWIW, a flickering or blinking LED requires filtered DC as there is a small circuit in the package that provides the animation, they won't work with unfiltered DC.

I've been messing around with white or white and blue, I think either look good.

All the above info is appreciated greatly. The above image looks good. I will post something once I get far enough to do so.

Thanks guys!