Need a temporary pulse from an occupied track to flip a semaphore

Maybe if you can tell us more about your situation we could begin to come up with some answers. What type of pulse does this unit expect? Is it high trigger or low? What are you using for block occupancy detection? Do you want to buy something or build something? Could you put together a 555 timer circuit on a breadboard? Where else have you looked?

  -- Leo

try a magnetic reed switch

@Leo - it is a semaphore to signal track occupancy.  there are 2  wires plus a common wire -  momentary contact at 16v to move the semaphore in each direction -- one wire per direction.  So I need to generate a momentary pulse (it moved smoothly with just a momentary contact < 1second when i tried it manually)  when the track is occupied and another when it is clear.   Not sure how to set up a situation where I generate a track cleared pulse, since there is no specific direction of travel on this track.  And yes, if there's something available great! ... otherwise it's wire my own.

@Chainsaw  - Thanks. I'll look into reed switches.  New to wiring triggers, so please forgive my ignorance.

What happens if the pulse lasts longer?  Does it malfunction?

If the pulse is longer, no harm. It just cannot be continuous (because I assume this will burn out the motor on the semaphore).  The not-so-well-written instruction sheet says "temporary contact only".  I had it on for as long as 5 seconds without ill effect.

How about one of the many eBay modules?  eBay: 131608618526 is one example.

Panel Mount Momentary-Switch/Pulse-Signal Control Latching SPDT Relay Module,5V User Guide

I guess I need electronics for idiots.   I can figure AC current and using Diodes to rectify a signal to + or - polarity, but high school electronics ended there for me.

I'm looking at the module and recognizing the individual bits, but I'm not realizing how i can get  a block occupied current (wheels creating contact with the insulated rail) cause a pulse to be sent out by this board off one terminal,   and then the absence of current from the isolated rail to send a pulse out of the board on another terminal. The user guide is confusing at best (I guess it all makes sense if you can read electronic schematics).  I'll study it more to see if i can make sense of it, but any help would be appreciated!

Is there such a board?  

input current --> sends pulses out on port 1  

no input current --> sends pulses out on port 2

I'm sure there probably is, but I've never had the need to go search it out.   My solution if I had a specific requirement like that would probably be to roll my own, cheaper and I know how to do it.

I'm guessing you need something like a non-derailing  switch machine but shuts off after the switch is thrown,,

 Something like a NJ switch machine with contacts to work with that can disconnect the pulse..  I'm guessing there are still a few around.

Once the Semaphore changes position  will it stay in that position without power?  

This idea is kind of a hack job but it might just work. The item shown below is a delay activation relay module with an adjustable timer from 0 to 10 seconds. They're dirt cheap but you would have to wait a few weeks because they come from China. You would need 4 of them for this idea to work.

You would connect them daisy chain fashion so that when a train enters the block, the first module turns on. The relay connection on this first module would connect to the second module through the normally closed (NC) output, turning it on at the same time. The second module is connected to the occupied side of your semaphore using the activated side of its relay (NO). When this relay activates after a short interval, we have the start of the pulse that we need.

    Block Occupied (NO) --> Module 1 (NC) --> Module 2 (NO) --> Semaphore Occupied Aspect

Now to finish the pulse, Module 1 has a time interval adjusted so that soon after the pulse starts, its relay kicks in and removes power to module 2. Module 2 shuts down, its relay deactivates and the pulse is completed.

The other part of this requires that we have an SPDT relay for block occupancy to begin with. GunRunnerJohn has one in the works and I think you could use this. With that, when the train vacates the block, the block detection relay will connect at the NC output to another set of timers to give us the clear aspect pulse.

    Block Clear (NC) --> Module 3 (NC) --> Module 4 (NO) --> Semaphore Clear Aspect

I said it was a hack job. There is a better solution using a 555 timer circuit but that requires component level handling, breadboard connections and eye straining work. I can't tell you what that would look like but I'm sure it could be done. This at least keeps things at the module level with all screw in connectors.

Most semaphores are controlled by a man in a tower  and not automatically activated.

How about  two  Momentary  push buttons... One for clear and the other for stop. 

You'll l have to be the guy in the Tower.

I would recommend using the standard, insulated-rail with a bounce protected relay, set-up. But have it drive individual 555 timers from each of its NO & NC output terminals. When a train occupies the block and closes the NO contact, its 555 sends a single (adjustable) pulse to semaphore wire A. The train can pass through or sit there all day (provided the relay is suitable for continuous operation). When it leaves the block, the relay changes state resetting that 555 and triggering the second 555 from its NC contact, sending a pulse to semaphore wire B. This could also be done with logic level devices, but using the standard relay set-up for the track interface is a robust method, and the 555 end of the circuit is easily configured from widely available designs.

LEO's idea is good if you want a straight relay-logic system.

> There must be some type of latching going on inside the semaphore if it continues to move after a brief pulse, or does it just snap into position?

Dave

I'm curious what kind of 16V pulse it needs, is that actually providing the driving current for the semaphore, or is it just a triggering signal?  I think we need to know exactly what the circuit drives.

Lots of ways to get a single pulse of power for whatever length of time you want from an insulated rail.  I'm assuming you want the pulse to trigger the first time a train bridges the insulated rail, then not to trigger again unless the other insulated rail has been triggered on the other side of the signal.  

Many of the ways to do this all cost about the same in parts, Less than $5.00, but some are more complex than others.  There are also turn-key options out there that cost a bit more, for example I think you could kludge an Atlas switch machine controller to do what you want.  

How much assembly are you looking for?  Is it more important to be easy to assemble or easy to use once made?  Is adjustable timing needed?  Also, if the train is occupying both blocks, what is the desired signaling?  Does the train only ever pass the signal in one direction, or can it approach from either direction?  Depending on what needs to be detected and sent to the signal will affect what becomes the simplest way to do what you want.  

I would likely start out with the "most complex" fix here and use a micro-controler that can be programed to do whatever you want.  For me, this is the least hassle way to do it, and the most flexible, but lots of folks don't want to delve into such things.  

JGL

John, I'd think we need to know what we're driving with the signal,the 16 volts sounds like we're driving solenoids directly.

Scottv, can you provide us with a link to this "semaphore from overseas"? 

You're getting a lot of "How to" suggestions but I'm not clear on exactly What is required.  Measure twice, cut once...

Stan, my issue exactly.  Once we know what we're dealing with, then it would be a bunch easier to suggest solutions.

gunrunnerjohn posted:

John, I'd think we need to know what we're driving with the signal,the 16 volts sounds like we're driving solenoids directly.

I'm expecting as much, but a 99 cent relay module takes care of it well enough.  I'm expecting parts to include a relay module to power the signal, a micro, probably a Nano or similar, to compute the logic.  A ac-dc buck converter to power the micro and relay board, and some discrete components to make the input from the insulated rails.  One could use relays, But I'd probably go with optocouplers triggered with a power resistor and zener diode on the input side.  all told about $6 out of china.

stan2004 posted:

Scottv, can you provide up with a link to this "semaphore from overseas"? 

You're getting a lot of "How to" suggestions but I'm not clear on exactly What is required.  Measure twice, cut once...

Knowing exactly what the signal does, and knowing exactly the desired operation would be needed before anything could be really worked out, of course.  I think, however that even in a worse case scenario a solution would not be hard to find.  

JGL 

Guys - sorry for the delay....   been working nights and weekends and it's taken me away from this.  The online documentation might be somewhere for the Viessmann product line but I can't find it. However here is what i found:  the semaphore is operated by a solenoid. separate circuit for lights on the semaphore vs. the solenoid movement power (totally separate ground and throw contacts). So essentially the throw mechanism is like a 3-contact solenoid switch.

Armed with that knowledge, I found a circuitboard that works very well from Azatrax.  http://www.azatrax.com/dual-train-detector.html    The documentation on these boards is awesome, simple to understand, and includes several examples of operating mode implementations.  You know, "when Train A is eastbound and Train B is westbound.... when will grandma's cookies be ready?" LOL.         Seriously check it out if you have any such needs. 

Dtrainmaster posted:

I would recommend using the standard, insulated-rail with a bounce protected relay, set-up. But have it drive individual 555 timers from each of its NO & NC output terminals...

Upon further clarification of the requirements, I think you nailed it! 

And LEO identified 0-10 sec delay-on relay modules that have the 555 timer functionality built-in.  So if a picture is a thousand words:

The bounce-protected relay on the left uses a resistor and capacitor to filter out the intermittent wheel-to-track bounces.  The NO and NC contacts steer Common to one of two 555-timer delay-on relay modules.  The delay-on module is set to 1/2 sec so when powered it waits 1/2 sec then activates.  By using the NC output of the delay-on module, a 1/2 sec pulse is generated and then goes quiet for as long as the delay-on module stays powered.  When the bounce-protected relay changes the same 1/2 sec pulse action occurs on the other delay-on module.  Lather, rinse, repeat...

So there is some Lego-like assembly required and surely not as sophisticated as the Azatrax board.

OTOH only $1 shipped on eBay for the relay module, $1.25 shipped on eBay for a delay-on relay module, 25 cents or so for a resistor and capacitor.  A 12V DC wall-wart goes for less than $2 shipped though these seem to lurk unused in the attic or garage.