DC polarity trigger for Kato turnouts

[defor]

I have a need to toggle a turnout based on the polarity of the rails leading into a kato turnout.

This seems like it should be a VERY simple circuit, but I'm having trouble trying to wrap my head around how to trigger only on leading edge of the polarity change.

Is there an existing circuit or product for this.

Note, I'm NOT trying to achieve a reversing loop- this is for single track island platform operation.

 

 

Thanks!

[Kiha66]

Will the track voltage be a constant or varied? 

[defor]

It will vary from NC through +/- 12v (normal N scale operating range)

Edited April 18, 2019 by defor

[Kiha66]

A capacitor discharge circuit should work, the harder part is designing the sensing logic. 

 

The kato turnouts can also be used as spring points, where a train can run through the points even if set against them then spring back to the previous routing.  Would that work for your station?

[Kiha66]

If the spring switch doesn't work, a voltage comparator opamp feeding a capacitor discharge should should work.  Let me know if youd like me to try to come up with a circuit diagram.

[defor]

16 minutes ago, Kiha66 said:

spring back to the previous routing.  Would that work for your station?

not for the design in mind.

 

I'm actually poking at a second idea that may be even more extensible (I'll have to pen and paper some simulations) using an IR turnout control, but with a polarity based blocker on each end of the platform if no one has any easy answers- cost will skyrocket a bit for all of this however per module...

Edited April 18, 2019 by defor