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Thank you again to those of you that saw and commented on my post requesting information on how to create a clone of a FasTrack switch remote controller.

Now I have a question on the other end.   For background I'm creating a test set that allows me to debug a control panel, switches and the wiring between them independently .  The controller can be used to diagnose the switch end, now i am looking to diagnose the controller end.

To do so I need build a circuit that uses the four wires appropriately.  Yellow presents the problem in that it uses +4.5v and -4.5v to indicate thru or out.   The question is how does one create a circuit that delivers -4.5v (from either 18v track voltage or a dedicated ~5v power supply)   While likely a basic question for many of you I just don't know how. 

Thanks Jim

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Jim, maybe I'm missing something in your wanting to test the controllers without using a remote turnout (switch).  What I do to test the controllers is just connect them to a known good FasTrack switch.  Would this work for you?  If not, it might be helpful to know what you're trying to accomplish by not using the switch to test the remote controllers.

Thanks Steve ... I do that now.   Problem is manifold ... its large and inconvenient and represents a $100 investment that I would rather have on the layout than on the bench.   My goal is to replace the switch/power track arrangement with a dongle of sorts that will indicate momentary switch position and switch position ... just need to know how to generate the -4.5v.

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  • switch test rig

Thanks for the schematic Steve ... I had thought about that as a solution but believe that the ground is used by the RSC and wonder about it being +5vdc when the switch controller is thrown ... that's the puzzle in my head :-)   The confusion for me is that the momentary switches on the RSC end (i assume but will verify) connect red with black or green with black to send the signal ... the switch machine manages the details and provides led talk-back via yellow.   I'm wondering (and will experiment) on how that can work if the black wire floats between ground and +5v.

The 5V wall wart Chuck mentioned is what I had in mind.  It has a transformer that electrically isolates the secondary (5VDC source) from the other transformer powering the switch machine, and in your case the test dongle.  If you connect the wall wart's output one way you get 5VDC and if you swap the connections, it becomes -5VDC.  Because it's electrically isolated, it doesn't care if one of it's legs is tied to the track power common (black wire on turnout), which is what needs to be done.

The other point you make about the switching for the turnout, yes that switch is a momentary SPDT.  Electrically, what it does is make a brief short between the black ground and either the (Red -  Out or the Green - Through) turnout's terminals to activate a throw of the turnout's position.

Last edited by SteveH

The black wire will not float between 0 and +5, the black wire is ground in the switch and will remain at ground. The isolated 5 vdc power supply will float between + or - 5 volts.

Oh sorry, I was writing at the same time as Steve. He already answered your question...

Last edited by cjack

If trying to simulate the switch, I'd think you'd want to simulate it in the entirety (all 4 wires taken together).  I agree $100 is a bit steep to that end.  But what about something like a latching relay that flips one way or the other (and stays) when triggered by the respective momentary switch wire.  The output of the relay selects between +5 or -5V DC to send out on the yellow wire.

If you "manually" select yellow wire voltage using a mechanical toggle switch, it seems to me this divorces the switch-machine action from the feedback.  Of course this may be exactly what you want. 

Steve -  every idea is worth exploring ... and you offered a workable solution.   I had thought about a bistable or latched relay ... in the world of components I can find a 12v triggered latching component or a 5v bistable single channel (pole) component ... its never simple :-)    My concern was with the ground.  and so I'll  plan to use a latching relay to emulate the points and respond to red/green and use yellow to signal position ... i can use the relay outputs for this ... my concern was using the ground to reverse polarity *and* as the "return" for red/green momentary signals.   Part of the fun of this Hobby for me is solving problems ... so thanks for weighing in

Last edited by LIRR-Jim

fastrack switch machine simulator

Right.  I think it is beneficial to use a single ground/common/black.  So the proverbial black-box above is powered by AC on the left.  It generates +5V and -5V DC using 5-cent diodes, 10-cent capacitors, and 25-cent voltage regulator IC chips.  A $3 "dual-coil" 5V latching relay is set or reset by the momentary RSC (red or green) wires.  And the relay output contacts steers either +5V or -5V to the yellow wire.  Obviously there's soldering and messing with small electronic components...

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  • fastrack switch machine simulator

EDIT: I originally thought that a Latching Dual Coil DPTD circuit using a single 5VDC power supply might be possible and tried to conceive one that would work.  After discussing it offline with @gunrunnerjohn, the design I had would have been problematic in providing switched power to the relay coils.  He has a better solution than mine using a Boost Converter with + and - 5VDC outputs from a single 4.5VDC power source.  His solution is a couple replies down the page.

Last edited by SteveH
@SteveH posted:
I'm wondering if a small electrolytic capacitor push-pull pair might be a good idea in this circuit to ensure the relay coils are energized long enough to fully change state, and if so, the resistors would limit capacitor discharge current.

The relay should change states in a few milliseconds, I see no reason that you'd need a "boost" to make that happen.  The K.I.S.S. principle clearly applies here.

From the data sheet for the EC2/EE2 series of relays.

Sure seems fast enough to me.

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  • mceclip0
Last edited by gunrunnerjohn

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