Trigger events How?

Depends what you are trying to accomplish. Accessories are triggered in the same manner,no change. I recommend relays for a lot of reasons.  

Train routing involves transmitting codes which are proprietary. To do that you have to backwards engineer. Im sure some brainy people have done it but it would be involved. If you cut power in TMCC command the train loses its memory of its last state,so conventional methods do not work as far as collision avoidance. . DCS engines can be stalled to stop by reducing voltage,then assume original state when voltage is restored. I have done this for a few DCS users to stop a trolley at a crossover. Not for the squeamish. 

Dale H

Dale, TMCC engines can be handled the same way, if you maintain enough voltage to keep the electronics alive, they do exactly the same thing.

Can the control electronics be kept alive with an on-board trickle supply (say from a capacitor or battery) while the propulsion power is dropped for an application such as proposed by the OP?

Gunner, I was hoping you would jump in.  How would I go about doing that?  And Dale, I use relays all the time now that I have finally learned how.  What I am considering is something that lets one train enter a return loop activating the train in front of it to appear on stage for a trip around the layout.  This would have to be in the TMCC world for now, DCS is not present on my layout and probably will not be for now.  Not because it is bad or better, just because my stable of locomotives are all early version command control from Lionel, Atlas or enhanced WBB.

I'd suggest you try and experiment with a command locomotive.  Try simply reducing the track voltage running in command mode until the locomotive just stops.  Then leave it for 20 seconds or so, and slowly increase the power again and see if it simply picks up where it left off.

I just did that using the MTH remove on a variable channel.  I tried both a DCS locomotive and a TMCC one.  Neither did it reliably, in both cases I could get it to work at times, but the threshold voltage was VERY tricky, and different for each locomotive.  Also, the sound cut out on the TMCC locomotive, though a battery in the tender fixed that issue.  The DCS locomotive would sometimes shutdown and go dark.  The next time at the same voltage setting, it would stop and idle.

I think this is probably not the way to go.

The way I'd probably look into doing this, given the idea of doing some mod to the locomotive, is to work a way to shutdown the motor circuit while keeping the track voltage up.  This would work for locomotives that don't have cruise control, but the ones with cruise control would be chomping at the bit, and when motor voltage came back, they'd jackrabbit out at full speed for a brief spell.  However, a non-cruise TMCC locomotive would simply sit with the same motor power applied until the motor load came back.  If it came in slowly, it would have the same motor power leaving.  One issue might be that in order to get the consist moving, you might need a "boost".

I don't know of any "clean" way to do this, anything I can think of requires significant alterations.

One way is to use Legacy locomotives with the IR transmitter and the new Lionel LCS Sensor Track.  You can program the individual locomotive or any sensor equipped locomotive to follow the canned program.  You could expand this to other TMCC/Legacy locomotives when the sensor track rolling stock that Lionel is working on comes out.

To stop a train in a block,assuming what John says is correct,(I have no experience with TMCC or DCS for that matter but it works reportedly with DCS),you could use a SPDT relay. Feed in 8 volts or whatever thru the NO contacts to keep the direction state and memory and stall the train. When the stop is over, I use a timer so the reaction is not instant ( hate automation that is obviously mechanical) ,the full 18 volts goes thru the NC contacts. The voltage can be provided with 2 transformer taps,the relay keeps them separated depending on the layout configuration,or use voltage dropping diodes. PW transformer hot taps must not be cross connected.

I made a couple of these circuits up for DCS users who wanted to stop a trolley crossing a track and it seemed to work. You have to adjust the voltage just right. Too much it does  creeps through the crossing. Too little voltage and it looses it's memory. All this trouble could have been avoided with a better board design. Here is a conventional method for 2 or more trains on a loop. Perhaps it could be adapted for command. 

LINK1

Passing siding

LINK2

Dale H

Thanks Dale and Gunner.  I think this gives me a place to start the experiment.

If you are working with a single engine, you can probably fool with the voltages to achieve the result desired.  OTOH, if you're trying to do this for any train that comes to the siding, I can't see the reduced voltage trick working, there's too much difference between different units.

You can even out units with the diode trick in the engine.  You can adjust them to all stall at the same voltage on a test track. A real PITA but probably it could be done.

LINK

Dale H

For non-cruise locomotives, the diodes would probably be a solution.  However, for cruise equipped locomotives, they just keep pouring on the power until they reach their speed or run out of power.

If there is only 8 volts or less there is no power to pour other than 8 volts ,which I think is held in reserve and blocked by the diodes. . It would affect the top speed. Not sure without trying it. Ps2 locos in conventional don't start under 8 volts in my experience. Easy to try,put a loco in command and reduce voltage until it stops.

Dale H

I did that, which is why I suggested he seek alternate solutions.

John

What voltage does it stop at?

Dale H

It actually stopped at 5 volts, and then it promptly went through it's shutdown sequence and was silent. 

Obviously, this is a sample of one, but if one has a problem, I'm not going to dig out the twenty or so DCS engines to find maybe one or two that it will work with.

I had better luck with the TMCC, but I did have to put a battery in the RailSounds to prevent that from flaking out at the low voltage.  However, it did resume running after I brought up the track power as desired.  The locomotive did NOT have cruise control, I doubt it would have gone so smoothly if it did.

I don't really have a dog in this fight, so I don't plan on doing any more experiments, I've got a full plate right now.

The sticking point is starting up a cruise equipped locomotive without it taking off at a leap until it figures out it's running again.  That would seem to require an internal connection to the board.

Well, this is all just talk (I know your plate is full or else I'd be imagining how easy it would be...) but here's my thinking.  Obviously the simplest is a relay which is normally closed letting the motor control voltage go to the motor...and cutting it off when the trigger is detected.

So yes, this would lurch/leap if full-track voltage is suddenly applied.  But if the cut-off switch from electronics to motor is a power transistor, it could be re-enabled slowly (over a few seconds) by ramping up the transistor biasing so that you don't get a sudden full voltage.  In practice, this ramping would probably be implemented by PWM'ing a FET to maintain efficiency.  A proper design should have no problem handling a PWM of a PWM (assuming modern engines use PWM on the motor drive).

Now the fact that power should be present on the motor drive wires means this imaginary electronics module could get its power from the motor electronics so 2-wires go into the module and 2-wires go out of the module to the motor.  So I think it could be a 'clean' connection for a DC drive without having to tap into the existing circuit boards.

It would be more work to handle bi-directional operation using transistor switching so maybe this would only work for forward-operation.

Anyway, all this is just forum talk and the only solution on the table is some variation of the stalling method.   I hasten to point out this comes up not just for station stop 'automation' but to stop command engines when approaching a lifted-bridge, or general block-signal traffic control, etc..  The frustrating thing is it would be so much easier if the engine manufacturers would simply include this capability in the first place.

Like I said, the LCS sensor track to the rescue!   Even if I had time to design something like this, I certainly don't see it being a volume item, and it would be no use to me, so any incentive for me to do one is pretty much gone.

The method I use is called RFID. Same as what is used for EZpass. I stick a TAG under an engine and when the engine passes near a reader it gets an ID number from the TAG. The reader then sends this number to a circuit which then generates TMCC engine commands for that engine. I have them hooked to my Atlas signals so that with a red indication the train will come to a stop. On the signal going green the train starts up. I also blow the whistle with the proper stop or start sequence

TAGS are about the size of a nickle and cost about a buck. Readers are more expensive at $25 and are about an inch square.

Gary, your scheme assumes a ton of specific expertise, and only a handful of folks here could duplicate that.

• I sold a lot of those circuits  But actually you dont need a ton of expertise. The readers can be connected to a PC for control instead of a specialized circuit board. Besides I'm sure folks would like to know about "schemes" whether they can do it or not. I know I do.

I agree that it's good to know about them, but I was just pointing out that knowing about something is not the same as being able to implement it.

Even if you connect those RFID readers to the PC, who's going to write the program to control them that is specific to a particular layout?

I think John's got the right idea...the LCS sensor track was the first thing that popped into my head when I  read your original post. That said, I think it demonstrates that to really make the most out of Legacy you need to be all in and that includes Fastrack, at least for portions of the layout. 

Actually if you're going to use a pc for control it would be easier not to use RFID. You could just use simple block detection such as isolated rail and have the program track the trains as they move from block to block. The RFID is nice for a stand alone kind of thing - station stop, grade crossing whistle sequence, etc. I only have 2 installed more for show and tell. 

So to your point about exchanging ideas, what would the OP need?  As I understand it, you'd need a $1 tag fastened to each engine.  Then two $25 readers - one at the stopping station, the other at the location where the approaching trailing engine triggers the stopped engine to leave the station.  So it sounds like you sell/sold specialized circuit boards which gather the reader data and send out address-specific commands?  How much are these boards and what kind of and how much programming required? 

Same questions as above.  A 5" LCS sensor track is $94.99 (MSRP).  Would the OP need two of these for the application described?  Then since he has TMCC engines can these be modified/upgraded to put out LCS infrared signal that apparently comes out of Legacy/Vision engines?  How much is that?  And, as with the ID Tag method, what gathers the sensor data and issues the commands?  What kind of and how much programming is required?

I SOLD a circuit board with a reader and 2 TAGS for under a $100. Been awhile and I don't recall exactly. It was a stand alone circuit - no programming required just option selection. You could select grade crossing whistle sequence, a stop sequence where a a ground on an input pin would stop the engine. Such as the DOUT (detect output) from the Atlas signal. Removal of the ground would restart it. An option would apply sounds. One toot before stopping, brake sound and 2 toots before starting up. A station stop would need something to supply a ground like a timer.

I used ID Innovations ID-12 reader from Sparkfun. Google that for info. Its about 1" X 1" X 1/4" so I would cut a section out of 2 ties and mount it under the center rail.

The operative word is sold, do you still sell them?  Obviously, the OP would want to find something that's available today.

That's why I emphasized sold. I retired for the umteenth time. Although I do have some readers and tags left over that I would let go cheap. But they wouldn't be useful unless you have some way to interface them.

So it as I see it, not much has changed in the 20 years or so that command control engines came out,  The only practical method for implementing station stop/go automation for command engines is  some variation of the stalling method. This means lowering the track voltage to some magic value where the motor stops but the digital electronics stays alive.

Methods to detect the position of specific engines and use the command signal to perform the automation remain in the realm of the tech-savvy DIYer or those with deep-pockets.  Considering the conventional control technique of isolated-rail switching could perform this automation for "free" I suppose it is a pretty high bar to reach.

A couple of problems. You not only need position detection but engine ID in the block. The supermarket scanner accomplishes this,assuming the train is not moving too fast.  To a point this could also be done with just relays. Assuming the engine could broadcast it's ID when crossing a proximity switching device. . MTH often bragged about 2 way communication but it does not use it for this application.  Collision avoidance has to be reliable. Next you have to have something that broadcasts the command to the specific engine,assuming more than 1 is on the loop. . Gary E has done this apparently,the scanner thing I understand,but  I would like to know what he uses to send the command. Does he alter a hand held device,or make a whole board in the command language of the system? Would be interested in the details,not that I want to do it but just for the fun of knowing.

Perhaps there is a way to alter the boards,so it remembers the last command state when power is removed and restored. I have a TV on a wall switch. When power is cut off and restored the next day,it continues to play the same channel I was watching. I dont see why this could not be done with a model train or at least have been incorporated in the original design. A slide switch could turn the feature off.

Dale H