Based on comments in the original thread, some questions on requirements.

1. Does it need a bleeder path to apply some TBD minimum voltage to keep the E-unit from cycling into neutral?  Or can we assume the engine is locked-in-forward?

2. Is soft-start like the AF station a must-have, nice-to-have, or don't care?

3. Given thermostatic replacements (Lionel #132-44) appear to be $25-30, are there any cost/size/complexity guidelines that, if exceeded, would nix the project?

4. As brought up in the other thread, there are layout-level off-the-shelf control systems with station stop/start capability and many additional features.  Is the focus here is on just a single-station?

Background material:


I can't find it now but while hunting for 132 info I think I read the Nichrome wire has a nominal resistance of 60 Ohms (or something like that?).


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Dale K posted:
trainman129 posted:

Try using one of these modules from the bay.

DC 12V LED Display Digital Delay Timer Control Switch Module PLC Automation K2

Can you please provide the name or specification of this circuit board so I can look it up on the internet, or a link to where it can be found?



I put "time adjustable relay module" in the eBay search box and got a lot like the one pictured here; but not this one exactly. Try that.

Thanks for the replies - I have found one of these circuit boards on eBay too now.  But I do have some additional questions about wiring it for a stop control on a traditional AC, 3-rail layout:

1. I assume this circuit board relay will be activated by connecting an insulated ground rail in the stopping track section to the black terminal marked GND.  If that's so, will I need to install a rectifier on that terminal as well as the red +12V connection (which will be connected to a 12V AC accessory power source), since this is a DC relay?   

2,  What would I connect to the green "control switch" terminal?

3. I assume one of the blue "load power" terminals (probably the NO terminal) would connect to the insulated center rail section, to feed power to the stopped engine once the timer has expired - correct?  

4, Would the other blue "load power" terminal with the circled X (COM) be connected to the AC power ground?

5. I assume this circuit board would have no voltage "leak by" like the 132 station's nichrome wire coil does?  As stated in an earlier part of this thread, that coil still passes a small amount of voltage (about 2.5V AC in my case) as the coil heats up, which doesn't completely stop the newer MTH trolley that I am operating on this loop.  

All your help is appreciated!  




Dale: These cycle timed relay modules are generic in that they are not made specifically for model railroad applications. The module suggested by @trainman129 back in 2016 may do the job but I have no idea what his plan would have been. It could be done but it would take more than just this module to make it happen.

I will try to address your questions as best I can:

1. No. As you say this is a DC relay module. The DC+ and GND terminals supply power to the module. The GND does not connect to an insulated rail section.

  My standard answer for DC power is to use an AC to DC buck converter that allows you to use AC accessory voltage as an input and get DC voltage out. You can set the output voltage to what you want with a built-in potentiometer. The DC+ and the GND would connect to the buck converter outputs.

Other possible sources of DC power are DC power supplies (like an ATX computer supply) or a wall wart. To see an example of the buck converter I recommend, copy and paste this number into the eBay search box:


2. The green "control switch" terminal on the board is the trigger. You would need to have the module setup in one of the modes of operation as outlined in their description (which is not easy to understand):

Working mode: 
P1 mode: after the signal is triggered, the relay conducts the OP time and then disconnects. During OP time, do the following
P1.1: signal triggering again is invalid
P1.2: signal triggers again to retime
P1.3: the signal is reset again, the relay is disconnected, and the timing is stopped
P-2: after the trigger signal is given, the CL time of the relay is disconnected, the OP time of the relay is conducted, and the relay is disconnected after the timing is completed
P3.1: after the trigger signal is given and the relay turns on the OP time, the relay disconnects CL time, and then the above actions are repeated. When the signal is given again in the cycle, the relay disconnects and the timing is stopped. Looping (LOP) can be set
P3.2: there is no need to trigger the signal after power is on, the relay conduction time to OP, the relay disconnection time to CL, and cycle the above actions; Looping (LOP) can be set
P-4: signal holding function if there is a trigger signal, time clearing, relay keeping on; When the signal disappears, time the OP and disconnect the relay. During the timing, another signal, the timing clear.


You see what I mean. Anyway, one of these modes should turn the relay on after the timing cycle has been triggered for the specified delay time. And then the relay should turn off (I'm not sure what mode does that).

The trigger could be done with an isolated rail section, or an ITAD (infrared detector) or an opto-isolator or I would use something like GRJ's track sensor available online from Hennings Trains. It works with the insulated rail section to trigger a small relay. That could be used as a switch to trigger the timed cycle.

3. Yes. The outputs from the relay go to power the stop section of track. One side (NO - normally open) connects to the isolated center rail of the stop track and the other (COM - common relay connection) goes to the track power AC.

4. No. See 3.

5. Right. No leaks to keep the E-unit engaged in the forward direction. This would only work if you have the E-unit switched to lock it in forward.

I have used a microprocessor and relay to stop a train, toggle the E-unit into neutral, then reverse, and back to neutral so that the train is stopped with the lights on for a period of time and then proceed. If you like that idea, let me know and we'll start a new thread on how to use an Arduino to control a stop block.

As I understand it, you already have a #132.  This of course has an isolated center-rail section to starve track power to the trolley...but does not use the insulated-outer-rail for triggering.  If you don't want to mess with cutting/modifying the track section to install an insulated outer-rail, you can place a 10-cent magnet on the trolley(s) and then a 25-cent reed-switch in the track bed on the approach to the station.  The reed-switch would then trigger the timer module to shut-off center-rail power via the relay for however many seconds.

OTOH, if you do use the insulated outer-rail method to trigger you may run into a so-called race condition which can create false/multiple triggers.  See if this makes sense.  The trolley arrives to the station section that has been modified with an insulated rail trigger.  The trolley triggers the relay which stops the trolley.  But the trolley is now sitting on the insulated rail.  So when center-rail power is restored, the trolley instantly re-triggers the timer and maybe jerks for a fraction of a second and then stops again!  Lather, rinse, repeat.  So maybe you cut an insulated rail section that is only 1" long (or whatever) so that the trolley triggers the timer but rolls by the 1" trigger section under its own momentum before stopping.  As you can see this technique is fraught with peril! 

So to dig further down the rabbit-hole, what you could do in this situation is use 2 timers; you could have the insulated rail section the same length as the stop section.  Both timers are triggered together but one is set to 10 second and the other is set to 15 seconds (or whatever).  Power is removed from the center-rail for 10 seconds...but the outer-rail trigger section is disconnected from the timer triggers for 15 seconds.  This gives the trolley 5 seconds to leave the station and roll out of the trigger section since the triggers have been disabled for 5 seconds when power is restored.  Timer modules are only a few bucks so not really much of a penalty.  The 2nd timer essentially duplicates the nichrome thermostatic switch delay in the 132 accessory.  That is, when the trolley leaves the station it takes several seconds for the nichrome switch to cool down which gives time for the trolley to leave the station without instantly re-triggering the stop.

Separately, if you go with the insulated outer-rail trigger you probably want to use a wall-wart to supply the 12V DC power for the timer modules.  The AC-to-DC converter module that Leo shows cannot be used as-is for most train transformer systems.  That is, it creates a "new" DC- output voltage that does not play well with the AC common in most layouts.  This has to do with the bridge-rectifier in the AC-to-DC voltage converter.  We can get into the technical details of mixing AC and DC commons if interested, but a 12V DC wall-wart is only about $2-3 on eBay.

Clete posted:

you probably could use the timer from the 253 Block signal. It provided the same delay operation as the 132 stop station. 

Does it use the same nichrome thermostatic switch?  If so, I'd think it would have the same voltage "leak by" that Dale says would not work for his MTH trolley.

The nice thing about the relay method is you could then choose to present 0 Volts to the center-rail to truly stop the trolley in its tracks...or some non-zero voltage that mechanically stops the trolley but also keeps the lights on so the passengers can safely load and unload.  I don't know which MTH trolley Dale has, but on the newer Protosound trolleys with speed-control there is a defined voltage range where the engine will not move but the electronics (e.g., the lights) will stay on.  

Thanks for all the great input, guys.  The trolley I'm using is a 2005 MTH RailKing 30-2581 NFL Steelers Bump-n-Go Trolley.  It's pretty basic - no Protosound.  It really has to have 0 volts to stop, and I'm afraid the poor passengers are going to have to get off the trolley in the dark!   I think I'll get one of the relay circuit boards and then just play around with it, trying some of what y'all suggested.  For about 4 bucks, even if I can't get it to work the way I want, I'm not really out much...


When I last "researched" the original Nichrome switch (e.g., in this thread) they were $25 or so, re-furbished, and potentially difficult to find.  Clearly a drop-in replacement would be the easiest, but my understanding is it nevertheless would not work in Dale's application because of the voltage "leak by" since the switch is really a ~100 ohm resistor when in the stopping mode.

I think it could be done for $5-10 using eBay modules (e.g., relay, timer, voltage regulator).  But it would require DIY'er persistence, wiring, and the like. 

6-30v relay module with optoisolated DC trigger

There are many suitable timer relay modules that I think will do the trick.  In the video below, the station stop zone is the single track section with the white-paint.  This is just a proof of concept - a station stop zone would no doubt be much longer.  I didn't have a trolley to play with so just used a powered motorized truck (co-opted from a twin-motor diesel) with a bridge-rectifier to convert track AC to motor DC; the motor is locked-in-forward so to speak.  There is also a white LED on the truck to show when power is applied to motor.

In this example, the timer module shown above is set to Mode P-2, CL time of 7 sec, OP time of 3 sec.   Normally there is no track power in the station zone.  When trolley enters the stop zone, the timer module is triggered.  This starts a 7 second (CL) delay which is the station stop time; the relay is OFF.  Then the relay is ON for 3 seconds (OP) which powers the station zone so the trolley can leave the station and reach the powered track.

lionel 132 alternative

Note that if the station stop zone is too short and/or the trolley enters the station too quickly, it can coast through the unpowered station zone and reach the other side and continue on without stopping.

The key to this method is tying the DC common that powers the DC-timer-relay module to the AC common that powers the track.  

If there is any interest, I can provide additional details and comments.


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That's an insightful question. 

Tying AC common and DC common together can seem like black magic or something untoward!  But here's what's going on.  Remember we are starting with two isolated circuits...the AC circuit which has the track power and the DC circuit which has the timer/relay power.  These two circuits are isolated because they are operating off separate transformers.  Hence they are not aware of each other's existence in an electrical sense.

As you know the term "circuit" itself implies a to-and-from.  Connecting one wire between two isolated circuits does not create a new circuit or electrical interaction because you only have a "to" and not a "from".  Hence the two circuits behave independently as if the other was not two ships passing in the night.

So that's what we have when with the shared AC and DC commons.  The AC circuit can have a bell and/or whistle DC offset, it can drop to 0V on the track (for direction change) or even jump to 100V AC or whatever and blow up the engine, etc. … but the DC circuit is completely isolated and ignorant of this action!

I don't know if this made any sense at all but that's how I think of it...

Well that makes some sense but what about the bridge rectifier on the AC to DC buck converter unit? How does that change the picture? And what if you had an old transformer driven power supply with an adjustable voltage regulator that takes 110 VAC as input? I believe it also has a bridge rectifier; but after the secondary coil. How is that different?

dc ac common

In the top case, you have an AC-transformer (e.g., brick) feeding ONLY an AC-to-DC regulator module that has a bridge rectifier.  Or the transformer and AC-to-DC regulator can be combined in a wall-wart.  When you tie the DC common to the AC common of the track transformer, there is only this single connection so you do not form a "circuit" between the two power supplies.  So this configuration is OK.

In the middle case, you have the AC-transformer feeding the AC-to-DC regulator module from the Accessory AC (e.g., 12V, 14V, 16V) output.  Accessory AC common is typically internally tied to track transformer AC common for multi-output train transformers.  Or even if using a separate transformer for Accessory and Track power you typically tie the two AC commons together so that, for example, you can use Accessory AC to power turnouts and other accessories that are triggered by an insulated rail.  The problem is now you have 2 connections between the AC circuit and the DC circuit and this forms a new circuit between AC and DC systems which wreaks havoc as they "fight" each other.  What practically happens is a diode inside the bridge rectifier explodes and game over.

In the lower case, the AC to DC conversion is performed with just a single-diode rather than a 4-diode bridge rectifier.  Doing the AC-to-DC conversion this way allows the DC common and the AC common to be one and the same which means there is only 1 connection (no circuit is formed) between the DC and AC systems.  In this case you only need a DC-to-DC converter module which does not have a bridge rectifier.  There are practical considerations to single-diode (a.k.a. half-wave) AC-to-DC conversion.  But for a trolley application with only a single, or at most a few, DC timer/relay module(s), it should be straightforward.

No doubt there are better ways to explain the problem of shared DC and AC commons!


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Thanks Stan! The pictures help. The circuit/no circuit idea makes sense to me. But I'm not seeing where they exist and don't. That's OK though as I think this is the reason that I shy away from mixing AC and DC in the first place.

I'll remember that you can run both AC and DC through the same conductor/wire/track and that you have to be cautious about how they are powered. These examples will help with that. Are there other common examples that might be tempting to use but may be hazardous to the life of a diode?

I'm approaching this from a practical standpoint.  I don't want to see the math in this case. I'm sure it would be over my head. Tracing current direction also gets my head spinning.

Agreed.  Tracing currents between power systems is tedious at best.  But based on your comments I think I've stumbled on the root-cause of the confusion.

ac ac common

Since day 1 O-gaugers have used the isolated rail trigger method to activate accessories and what not.  In other words, the idea of sharing commons is NOT the issue.  For example, as shown above, you might have a separate Accessory AC transformer to power turnouts, uncoupling tracks, and so on.  The commons between the Accessory AC and Track AC power sources are shared which makes insulated-rail triggering possible.  

Even layouts that don't use insulated-rail triggering routinely share the outer rail for, say, block-power configurations where there may be a handful of train transformers.  As an aside, for anyone following along, the often discussed issue of "phasing" multiple AC transformers in a multi-block system is related in that when a train straddles two blocks it is adding the "dreaded" 2nd connection thereby creating a to-and-from "circuit" which is bad.  Phasing is a technique to demote the effect of this undesired new circuit.

Thus, shared commons are routine and not the issue.  Instead, I believe the confusion stems from how AC voltages are converted to DC voltages.  That is, we have been conditioned to expect the SAME AC common when regulating or adjusting AC voltages to another AC voltage in a train transformer.  For the most part, AC-to-AC circuits in modern train transformers use the semiconductor triac to chop the AC waveform to lower the voltage.  This method preserves the common between the input side and output side.

On the other hand, when converting from AC-to-DC, the bridge rectifier rears its ugly head by breaking the sacred bond between the input common and the output common.  In other words, there is no longer a "common" common!   Terminology such as "return" or "ground" or "minus side" etc. are frequently used in an attempt to distinguish this.  But I think the average user has become so accustomed to the idea of a universal common (that resides on the outer rail) that it's hard to put one's arms around the idea of multiple commons.


So leaving the world of shared commons, your question about other diode examples.  I have a good one!  Lots of guys have been converting rolling stock lighting from bulbs to LEDs.  In many cases they are using bridge-rectifiers to convert track-AC to DC as needed by LEDs.  But this breaks that sacred bond between AC input common (the outer rail) and output common (DC- to the LEDs).  The practical gotcha is you can no longer use the frame or chassis of the rolling stock as the DC common.  I seem to recall several threads where this was the burning (literally) issue!   As with my example for the station-stop, you can preserve the AC and DC common by using a single diode (half-wave rectification) instead of a 4-diode bridge rectifier.






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I never thought that a bridge rectifier could cause so much trouble! The key is that as long as you don't have a connection from the track AC common to the accessory common, the bridge is okay to use. You string the AC out through the DC converter (with the bridge) and don't look back. That means that you can not use the accessory posts of the same transformer with the bridge because they are connected internally. Hmm...

Well Stan, running DC through the rails to trigger block detection and accessory activation seems like a distinct advantage as you have demonstrated repeatedly. If I ever attempt this myself, I will pay attention to the multiple commons problem that comes up when using a bridge rectifier to convert AC to DC.

In the meantime, my interest for block detection with the isolated rail method centers around the use of AC optoisolators. That seems like a good choice as long as you are planning to design a circuit board to hold the darn things.

Thanks again for all of your shared insights and experience!

  -- Leo

Here's another less-than-$5 alternative for the 132 thermostatic switch that DOES NOT use the insulated-rail trigger.  In other words, you can use the existing 132 stop section which has "continuous" outer rail power on both outer rails.  You don't have to mess with cutting the outer-rail or using track pieces that can be configured for insulated outer-rail joints.  Also, the the insulated rail method can by problematic for trolleys (and SuperStreet vehicles) due to potential intermittent outer rail contact to the wheels of light-weight chassis - your mileage may vary!

This method replaces the $25 (and up) hard-to-find Nichrome thermostatic switch with a 10 cent O-gauge 14V (or so) lamp bulb that you might find in any conventional engine or the bulb in a lockon or turnout controller.



So when the trolley or engine enters the stop section, the lamp steals all the track voltage thereby starving the trolley/engine and it stops.  In the thermostatic switch method, the Nichrome heater wire resistance stole the track voltage.

Now, the lamp turns on when the trolley/engine enters the stop section.  In the thermostatic switch method the Nichrome wire started to heat up when the trolley/engine enters the stop section.  The lamp illuminates a 10-cent phototransistor which applies the electrical trigger to the timer module when it sees the light from the bulb.

3mm IR phototransistor 10 cents each

Otherwise, the operation/setup of the timer module is as before.  That is, when the timer module is triggered (when trolley enters the stop section and turns on the lamp) it starts a 7-sec delay where track power is held back from the trolley - the lamp is ON and continues to starve the trolley of any track voltage.  Then the timer turns its relay ON for 3-sec which applies track voltage to the stop section.  The trolley starts up and exits the stop-section reaching the already powered section of track and continues on its way.

132-alternative does not required isolated rail trigger

I realize there is a very limited audience for this but just wanted to document the concept before I dis-assemble my prototype.  Note-to-self: this method allows use of an bridge-rectifier AC-to-DC voltage module to provide DC power from the AC Accessory voltage.  This is because the lamp-phototransistor is itself an electrically-isolated interface (i.e., it's an opto-isolator) which allows a shared DC and AC common (typically not allowed when there's bridge rectifier in the mix).




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