# How to convert a SPST to pulse a switch



## rreiffer (Jan 14, 2009)

Hello all,

I was wondering is someone has an electronic circuit that converts a SPST switch connection to be able to "pulse" a switch machine, I.E. Open turns the switch machine one direction and off turns it the other. 

Thanks all,


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## Greg Elmassian (Jan 3, 2008)

google "555 timer circuits", you will certainly find one. 

Regards, Greg


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## chuck n (Jan 2, 2008)

Rich, I would think that you could buy one at Radio Shack or some other electronic supply house that is spring loaded. I had some years ago for operating the solenoids on my HO switch throws.

Chuck


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## rdamurphy (Jan 3, 2008)

I believe Electronics Projects for Model Railroaders, a book by Kalmbach, had several methods to do that. I've always just used those cheesy Atlas switch controls, hey, they work! 

Robert


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## Axel Tillmann (Jan 10, 2008)

Rich: 

Alternatively use a switch machine that has a built in limit switch.


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## toddalin (Jan 4, 2008)

Why would you not use a regular momentary spdt (or dpdt) like most everyone else? Push it one way and let it go for positive pulse. Push it the other way and let it go for a negative pulse. Is it that you want the visual indication of the toggle handle to one side or the other?


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## Axel Tillmann (Jan 10, 2008)

There are two good reasons why you wouldn't


The position of the switch (up or down) indicates the current position of the turnout
You can wire up a dual color LED to to give you lighted optical feedback of the turnout's position


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## toddalin (Jan 4, 2008)

Posted By Axel Tillmann on 07 Jan 2011 05:51 PM 
There are two good reasons why you wouldn't


The position of the switch (up or down) indicates the current position of the turnout
You can wire up a dual color LED to to give you lighted optical feedback of the turnout's position

And he's going to do this just using a spst (on/off) toggle?


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## Jerrys RR (Jun 28, 2010)

This is about the easiest and cheapest circuit to build:










I have forgotten where I got the diagram but I have built dozens of these circuits and they work perfectly.

Jerry


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## Greg Elmassian (Jan 3, 2008)

I guess I'm the only one to answer the question. 

It can be done easily. 

Greg


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## Axel Tillmann (Jan 10, 2008)

Posted By Greg Elmassian on 07 Jan 2011 09:08 PM 
I guess I'm the only one to answer the question. 

It can be done easily. 

Greg 
Yes Greg - You are the man. Actually on second thought my answeres for the valid reasons don't even work with SPSTs, you need DPST for that but with your 555 timer you could probably even add extra ciruits to generate the optical feedback as well.


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## Greg Elmassian (Jan 3, 2008)

I'm not being snotty, I'm trying to encourage him to find the circuit and buy the $5 worth of parts and play around. Basically you want to have the 555 work as a latching relay. 

It would be simpler with a spdt switch, and way simpler as you mention with a dpdt... but it's fun to take a challenge and find the exact solution. 

The 555 timer is a versatile and inexpensive component. 

Googling it will give you tons of circuits... 

Hint: you might use a 556 dual timer (2 555 timers in one chip) and make one pulse when the switch is closed, and make the other pulse when the switch is opened. Using a 555 timer to make a pulse is the most fundamental use of the circuit. 

You will most likely want to use the 555 timer outputs to relays to give enough current to the switch motors and guard from inductive "kickback".... this can also be done with "transistor current amplifiers", but I assume you want to keep it simple. 

You can use the spst switch itself to power the "position" leds... 

Regards, Greg


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## toddalin (Jan 4, 2008)

Posted By Greg Elmassian on 08 Jan 2011 11:16 AM 
I'm not being snotty, I'm trying to encourage him to find the circuit and buy the $5 worth of parts and play around. Basically you want to have the 555 work as a latching relay. 

It would be simpler with a spdt switch, and way simpler as you mention with a dpdt... but it's fun to take a challenge and find the exact solution. 

The 555 timer is a versatile and inexpensive component. 

Googling it will give you tons of circuits... 

Hint: you might use a 556 dual timer (2 555 timers in one chip) and make one pulse when the switch is closed, and make the other pulse when the switch is opened. Using a 555 timer to make a pulse is the most fundamental use of the circuit. 

You will most likely want to use the 555 timer outputs to relays to give enough current to the switch motors and guard from inductive "kickback".... this can also be done with "transistor current amplifiers", but I assume you want to keep it simple. 

You can use the spst switch itself to power the "position" leds... 

Regards, Greg 



Actually, finding the "right" 555 circuit is not quite that easy. Sure the 555 can be set up as a "one shot," but eventually it will "time out" and if the "switch" that activates the circuit is left on, once it "times out," it will re-trigger until it "times out" again. Yes it can be done, but it may not be beginner's fare. Someone would probably have to research the proper circuit for the OP. Greg??? 

I could do it with "relay logic" but it would involve at least a few relays.

My thought is that the OP already has these switches and it trying to make them work for the application (which is why I asked of the intent). Better to go back a step and use switches that will more easily do the job (e.g., momentary spdt or dpdt).


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## George Schreyer (Jan 16, 2009)

depending on what switch motor he uses, the "latch" is the motor itself but you need TWO timers, one for each way. See similar circuit at 

http://www.girr.org/girr/tips/tips3/interlocking_tips.html#wireless 

2nd schematic, outputs D and E. 

Alternately, you can make you own latch with a flip flop 

- gws


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## Axel Tillmann (Jan 10, 2008)

Posted By Greg Elmassian on 08 Jan 2011 11:16 AM 
I'm not being snotty, ......................
Regards, Greg 

Nobody said so, at least not me







But the DPDT works with switch drives that have a built in limit switch. Then it is simpler than the 555 scenario and even offers optical feedback if desired. 

As far as easy or difficult of the 555 - I rememeber reading that poeple struggled with these babies in two ways:

1. They triggered once and never again (until power down)
2. They triggered over and over again due to the current feedback from the user (here switch drive) - I guess George was hinting at it. I remeber a customer calling that tried some form of gondola autoreversing circuit with 555 and gave up after the nth attempt.


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## Greg Elmassian (Jan 3, 2008)

No, was not directed at you Axel... was figuring I would get feedback from my first post: Google it... 

When I do that, many people say I'm not being helpful.... but if you want to build a circuit and maintain it... then it's my opinion you should understand it... 

Otherwise, do it a simpler way, or pay someone to do it... 

The 555 is pretty simple, but people having problems may go back to sentence #2 above! 

Regards, Greg


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## noelw (Jan 2, 2008)

Posted By rreiffer on 07 Jan 2011 11:52 AM 
Hello all,

I was wondering is someone has an electronic circuit that converts a SPST switch connection to be able to "pulse" a switch machine, I.E. Open turns the switch machine one direction and off turns it the other. 

Thanks all,
Not sure what you are using for a switch motor. If it an Aristo or LGB sw motor it easy. But looks like you are trying to turn the point with a spring loaded coil Mach.? 
Flip the bat handle one way to put power to the switch coil. and then move the bat handle to off position to move the SW points bad to normal again. Is this what you are doing trying to do? 
We use Cap. control cir. in our Ho track switch's with one shot push buttons. We played around with these cir. and they will oper. The Aristo sw.motors due to they have a stop switch on ea end of the throw. and with diodes for motor rev. 
These work well with a Cap Discharge cir. by using Single throw/Two Pole switch and leave the bat handle in position you want left to show the direction of the throw. Also, with a Dbl throw/Dbl pole you can use the other set of pole for LED showing direction on a panel also.
Here is some cir.
I used some going back to my Ham days for my Ho layout.... 
Take a look and see what may work for you..

Switch Track Cir.

I tryed a one shot 555 and dbl. up 4 cir. with 556 chip and still not quite enough power to throw a Aristo or LGB track switch with out getting to a amp cir. that is more conplex to build.
Hope this help some.. 
Realy ...Jerry R.R. has the best all around cir. to use and can get SW.Motors that accesory contacts with them like LGB has on some. That can feed back the direction of the Switch Machine to a panel light or LED.


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## Jerrys RR (Jun 28, 2010)

One problem with switches (turnouts) is that they frequently do not throw the 1st time. Often it takes several pulses to get the switch to throw.

A DPST switch can be used as per the lower image here:










but you are still left with a repeat pulse for a sluggish turnout.

Here is another SPDT and a dual SPST circuit.










Here is LGB's 5175(0) schematic:










A better solution with capacitors for a more positive pulse is:










There are many reasons why turnouts do not always throw the 1st time (tarnished switch contacts, friction inside the switch machine, conductor size, length of wiring, quality of connections and components, impulse voltage, dirt or grit inside the switch machine etc. etc. etc.). 

The main problem is that a turnout that fails to throw completely often results in a derailed loco/train. 

A SPST circuit can work but it might not be the best solution (and maybe it might be). It all depends on your preferences and circumstances.

Jerry


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## rreiffer (Jan 14, 2009)

Hey thanks all for the many different ideas, etc. The primary reason is that I have a several 12 channel remote controls that have SPDT output's (not just SPST - sorry), push the remote once and it closes, push it again and it opens. I have run outdoor underground phone cable (I picked up a 1000' ft spool that has 6 pair in it with the protective jel - it's designed for 75 years underground for $10) to every switch and to where I will want buildings throughout my entire layout. These all come back to a central location and I will be putting the master receivers at this location. Basically all of my switches have direct physical connections back to my central location. I will build an indicator panel at this site that hopefully will show me the state of every switch. I will also put the circuitry to control these in this common location.


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## rreiffer (Jan 14, 2009)

One other side note, the outouts of this are relay based but they latch and are not momentary contact based.


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## toddalin (Jan 4, 2008)

Posted By rreiffer on 09 Jan 2011 02:21 PM 
One other side note, the outouts of this are relay based but they latch and are not momentary contact based. I can show you how to create the + and - pulse using a best case of two or worst case of four dpdt relays per turnout (depending on what turnout motors you use and how you intend to power them). However, the pulse would be very short and may not be long enough to ensure that the turnouts throw all the way every time. The length of the pulse can be altered to minor extent by putting a capacitor across the relay. The value of the capacitor would be dependant on the relays selected and may require some experimentation on your part.

However, this pulse can easily be used to "one shot" a 555 without doing anything but the most basic 555 function. (As I previously noted, for most circuits, if you trip a 555 for a one shot, it will continue to one shot until the "trip" is removed.)

What is your comfort level in basic relay wiring and experimentation?


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## Jerrys RR (Jun 28, 2010)

Posted By rreiffer on 09 Jan 2011 02:18 PM 
I have run outdoor underground phone cable (I picked up a 1000' ft spool that has 6 pair in it with the protective jel - it's designed for 75 years underground for $10) to every switch and to where I will want buildings throughout my entire layout.


One other side note, the outouts of this are relay based but they latch and are not momentary contact based.. 


Hi Rich,

At best you have a marginal wiring situation. I would guess that at best your phone wiring is 24 AWG which can work but is marginal for electric turnouts (and probably insufficient for turnouts with mechanical switches attached to control sidings etc.). Unless you are using LED lighting for your houses 24 AWG may be too small for the current you will need.

This is based on my personal experience as there are well over 150 electric LGB turnouts and over 100 lighted buildings on my layouts. This is a drawing that is several years old (before several modifications/expansions to the layout):










Actually I used a LOT of telephone wiring on my layouts and many times it worked/works just fine but every turnout is somewhat unique in terms of how easy or hard it flips.

I also use a combination of LGB, Aristo, home made and other switches (with and without capacitors) to activate the turnouts. 

If you use the phone wiring (and I am not suggesting that you cannot) you may need to double up on some of your connections (two conductors per contact) as needed.

I always use the cheapest solution when it comes to wiring. Often telephone wires work but sometimes I need a heavier gauge. While you start with an AC voltage to the switch boxes you end up with DC voltage to the turnouts and DC voltage is more affected (I believe) by the length of a run in terms of the amps it can carry.

Your mention of latching relays concerns me as the turnout motors are definitely NOT designed for a lengthly pulse. A latching relay sounds to me like a good way to burn out your turnout motors. A long pulse will not work as a substitute for multiple momentary pulses but then too a very quick pulse may not work either.

Many things can be done that are not done in the "conventional" way. Many things work for me that others have said would never work but just be aware when you are stretching the conventional way of doing things that there can be consequences.

Good luck,

Jerry


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## Jerrys RR (Jun 28, 2010)

Posted By rreiffer on 09 Jan 2011 02:18 PM 
I will build an indicator panel at this site that hopefully will show me the state of every switch. 

This suggests that you will need switches on your turnouts (to put out a signal showing which way the turnout is flipped) such as the LGB 12070 EPL Supplementary Switch, Type 2. This requires extra current to throw the turnout but it takes a lot less push than the older LGB version.

Additional variations that may affect your results include the voltage input, mechanical smoothness of individual turnouts (they can vary a LOT) and whether you are feeding a half wave (through a single diode) or a full wave pulse. Greg or George (GWS) can give you more help here. Another big factor is how well your switch motor is connected to the turnout (it must be perfectly flat - in relation to each other - and sometimes some work is needed to find the best fit for the smoothest throw).

Then too I don't know how many turnouts you are planning for or how long your circuits will be.

Jerry


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## rreiffer (Jan 14, 2009)

All, 

Thanks for the many updates. I do have 6-pair of 24 gauge going to every switch so I should be covered from that aspect. Now I was hoping that I could make something easy but I see Aristocraft just released their 5-switch module for the Revolution and street price has it at $80 each. This equates to about $16 per switch to control (still need to buy the transmitter but I am headed that way anyway) and I don't think I can create a solution for $16 per switch! I did come up with a circuit that would create the right pulse AND change the polarity (it took a combination of two relays and a timer circuit - the first relay controled the polarity and the second was used to distribute the "pulse" required to the switch), however my cost was going to be about $30 in parts per switch (before the labor) to put it all together. Well if you have quite a few switches it doesn't take long to realize that you can buy the transmitter and the remote switch controls from Aristocraft and be ahead. 

Now I did find an interesting control device on eBay. This device is based upon 12V and then controls a 4PDT switch. This might be an interesting way to "buffer" the output of a switch control machine especially if you are making a double-slip crossing. Here is the link to them: 

http://cgi.ebay.com/Two-DPDT-Signal...824?pt=LH_DefaultDomain_0&hash=item1e5e02fc38


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## rreiffer (Jan 14, 2009)

A couple of other notes: 
- I am very comfortable with building my own electronics and in fact I have scratch built computers and programmed them with assembler and TTY output (dark ages for anyone under 40 !). 
- I am using 100% LED lighting as I don't want to spend my life replacing bulbs! 
- I expect to have 1 - double slip (4 switches), 2 cross overs (double switches), a yard with about 6 sides in it (using about 8 switches) and several other misc switches throughout the layout (another 6 switches)


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## toddalin (Jan 4, 2008)

Posted By rreiffer on 11 Jan 2011 03:12 PM 
A couple of other notes: 
- I am very comfortable with building my own electronics and in fact I have scratch built computers and programmed them with assembler and TTY output (dark ages for anyone under 40 !). 
- I am using 100% LED lighting as I don't want to spend my life replacing bulbs! 
- I expect to have 1 - double slip (4 switches), 2 cross overs (double switches), a yard with about 6 sides in it (using about 8 switches) and several other misc switches throughout the layout (another 6 switches) 



Using Internet surplus, you could do it for about a 1/4 - 1/3rd of that, but it may not be as ellegant as the AristoCraft unit nor would it be "ready to go." In it simplest form, you can actually do it with just two SPDT relays with a pair of diodes to give the pulse the proper polarity. If the duration is not long enough, then you would need the caps on the relays or the 555 chip. If its of interest, I can talk you through it. (But it sounds like you've figgured a way to do it also.)

I do pulse my turnouts with relays driven by 555 chips in those cases where the operation would be normally be triggered by a reed switch ala LGB. This way I can drive two turnouts for ~3/4 second regardless of how fast the magnet passes over the reed switch and not worry about the reed switches arcing open/closed as they can because it no longer carries any real current.


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## toddalin (Jan 4, 2008)

Posted By Jerrys RR on 10 Jan 2011 07:05 AM 
Posted By rreiffer on 09 Jan 2011 02:18 PM 
I will build an indicator panel at this site that hopefully will show me the state of every switch. 

This suggests that you will need switches on your turnouts (to put out a signal showing which way the turnout is flipped) such as the LGB 12070 EPL Supplementary Switch, Type 2. This requires extra current to throw the turnout but it takes a lot less push than the older LGB version.


Jerry




Actually, I don't think that this is what you would want to do. This would require that you run extra sets of wires out of the panel, along the layout, to the turnouts, and back just to turn on a light on the panel. Its easier and cheaper to just put a latching relay or pair of relays wired to latch when the turnout is toggled right in the panel and avoid the external wiring. Furthermore, the relays would be far cheaper than the LGB (or PIKO) EPL DPDTs.

Plus it alleviates that extra drag that you note.


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## Jerrys RR (Jun 28, 2010)

Posted By toddalin on 11 Jan 2011 05:02 PM 
Posted By Jerrys RR on 10 Jan 2011 07:05 AM 
Posted By rreiffer on 09 Jan 2011 02:18 PM 
I will build an indicator panel at this site that hopefully will show me the state of every switch. 

This suggests that you will need switches on your turnouts (to put out a signal showing which way the turnout is flipped) such as the LGB 12070 EPL Supplementary Switch, Type 2. This requires extra current to throw the turnout but it takes a lot less push than the older LGB version.


Jerry




Actually, I don't think that this is what you would want to do. This would require that you run extra sets of wires out of the panel, along the layout, to the turnouts, and back just to turn on a light on the panel. Its easier and cheaper to just put a latching relay or pair of relays wired to latch when the turnout is toggled right in the panel and avoid the external wiring. Furthermore, the relays would be far cheaper than the LGB (or PIKO) EPL DPDTs.

Plus it alleviates that extra drag that you note.

Every situation is a little bit different. I try not to recommend what someone else should do because I don't know what is important to the other person. I can only say why I do what I do in a given situation.

In my case many of my turnouts will not have been thrown for many months (perhaps over a year). Since I cannot see the actual turnouts I always press the switch the way I want to throw the turnout at least 3 or 4 times to allow for tarnished contacts etc.

In a few situations (where a mis-thrown turnout will run a train into the back of another train) I have used the LGB LGB 12070 EPL Supplementary Switches to activate warning lights at my operating station to alert me of the danger. 

In another situation I use the 12070's on passing sidings so I know that I am not putting a 2nd train on the same siding that another train is parked on. In that case I wire the 12070 to an overhead signal bridge to illuminate the proper lights to identify the siding the train will be directed to. In that case the 12070 not only activates the proper light but it also directs power to the track the turnout is pointed to.

Part of the problem is that I believe all turnouts are hand assembled and even with LGB turnouts it is not uncommon to find a turnout that throws very smoothly as received from the factory yet has a significant bind when the turnout motor is removed and reinstalled on the opposite side. I have had a few that could not be thrown at all when the switch motor was put on the opposite side while others would work but with a significant increase in the pressure needed to throw the turnout. In many cases the installation clearances dictate which side the switch motor MUST be installed.

Personally I would be hesitant to trust a relay to correctly indicate the position of a turnout as the relay could change the indication even when the turnout failed to flip.

A lot would depend on what the consequences might be if the lights did not accurately show the turnout position. Sometimes the lights are more for show than for confirmation.

In some situations I turn to closed circuit TV to visibly monitor what a loco is doing when it enters a turnout.

For others my concerns and precautions may not be relevant.

Jerry


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## Greg Elmassian (Jan 3, 2008)

Wow, Rich (original poster), did you get an answer you can work with? 

Todd is the "king" of wiring stuff like this, IMHO. 

I was under the impression you needed to have this function to work with an inexpensive existing remote control. 

Just curious after 2 pages. 

Regards, Greg


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## rreiffer (Jan 14, 2009)

Greg,
Thanks for the followup. I guess I got my question answered (by going out a doing some research elsewhere). It involved two relays and a two 555 circuits. One relay is used to control what polarity is presented to the second relay which controls the duration of the pulse. The two 555 timer circuits would be triggered by a single push button with one circuit set up in a flip-flop mode (to control the polarity relay) and the second 555 timer controled by the same push button is used to create a "hold" pulse that would keep the second relay closed:









This should work with little or no problem. In fact I found a module that has two DPDT relays on it for $10 on ebay (see earlier post). I should make it very easy and I could put indicators off from the second set of poles to indicate where the switch state was located. Very open to additional thoughts, etc. 

I was really getting ready to proceed down this path when I opened my latest Garden Railroad mag and Aristocraft has their switch control module (handles 5 switches) for a street price of about $80. This device can handle the "instant" switches and switch machines both (which my above circuit should be able to do by changing the duration of the "pulse" coming out of relay two). 

I know I can use these handy little remotes (12 channels) for lighting up my buildings in any sequence that I want so they won't go to waste. I guess the real question is if I want to spend the time building it for the fun of it or just buy the commercial version?


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## Greg Elmassian (Jan 3, 2008)

That's great news and glad you got a solution. Radio shack sells the 556, which has two 555 timers inside. 

Let us know how it comes out! 

Regards, Greg


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## toddalin (Jan 4, 2008)

This shows how to generate the pulse using two relays, two diodes, and two caps. The important thing here is to see how easily one relay can be used to generate the single pulse while the other stays shut. In actuality, the relays could be of any voltage with minor changes. The duration could be lengthened by placing a cap on the left relay (that pulses). The cap would have to be bi-polar (use two polarized caps) as shown because the relay could receive either a positive of negative voltage.


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## rreiffer (Jan 14, 2009)

Thanks for this latest one. It is VERY interesting. Now with the module I list above the entire thing comes pre-assembled for only $10. All I would need to do is add the caps and the diodes. This is an interesting diagram!


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## rreiffer (Jan 14, 2009)

P.S. Where would you put the cap exactly? Just to make sure!


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## toddalin (Jan 4, 2008)

Posted By rreiffer on 15 Jan 2011 03:57 PM 
P.S. Where would you put the cap exactly? Just to make sure!  

The capacitor would be in parallel with the coil of the relay on the left (top) that pulses for a "split" second. Because this arrangement could receive either positive or negative voltage to activate the coils, this capacitor must be "bi-polar." You can find information on putting a bi-polar capacitor together at Dave Bodner's web site. There is a recent thread on installing a bi-polar capacitor into an Eggliner or L'il Critter to get it over turnout frogs that provides a link to Dave's site.

These guys have lots of 24 volt relays that may work. They even have one that only draws 8.4 milliamps (with a 1 amp capacity). At that draw, a moderate sized capacitor should hold it open for a while. But there is a caveat. Many of these DIP relays are designed to be driven by semiconductors and include an internal diode such that they must be connected one way only and that will not work in this particular case. I don't know if that is the case with this relay.

All Electronics Relays 

24-volt, 8.4-milliamp relay

But the circuit could easily be modified so that the relays continally receive the same polarity using their own power source of any chosen voltage (got a wall wart lying around?) and you could use a regular electrolytic capacitor across the relay. The capacitor charges up while the upper relay activates and this charge holds the relay open a bit longer so that it ensures that the lower relay throws all the way prior to cutting the voltage to the upper relay (which shouldn't be a problem even without this capacitor) and, hopefully, long enough to ensure that the turnout throws all the way. 

Some experimentation would be in order.


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