Author Topic: Best N Scale Crossing Protection?  (Read 2699 times)

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OldEastRR

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Re: Best N Scale Crossing Protection?
« Reply #45 on: May 13, 2017, 02:31:30 AM »
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Depending on the LED circuit, yes, it's pretty easy to make them fade on and off.
I have a Berkshire Junction flasher/detector thing  (why didn't you make your own circuit, Max???)
I did it purely brute force.   I just slapped a big electrolytic across the LED leads.  Works like a charm.  When an LED comes on, the cap has to charge with it, so it induces a "ramp up".  Then an LED goes off, the cap discharges into the LED so it "ramps down" instead of going off instantly.   

Yeah, that's what I planned to try when building a flasher circuit -- a big capacitor to smooth out the offs and ons.

mmagliaro

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Re: Best N Scale Crossing Protection?
« Reply #46 on: May 13, 2017, 02:19:31 PM »
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Yeah, that's what I planned to try when building a flasher circuit -- a big capacitor to smooth out the offs and ons.

Just be aware that a simple cap may or may not work depending on the circuit.  Without any other components, the cap will discharge back into the circuit itself as well as into the LED, so it might not give you the effect you are looking for.  But if you add a diode in front of it to prevent it from doing that, it should work great.

Point353

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Re: Best N Scale Crossing Protection?
« Reply #47 on: May 13, 2017, 07:23:48 PM »
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Just be aware that a simple cap may or may not work depending on the circuit.  Without any other components, the cap will discharge back into the circuit itself as well as into the LED, so it might not give you the effect you are looking for.  But if you add a diode in front of it to prevent it from doing that, it should work great.
Curious to see if that suggestion will get shot down - again.

mmagliaro

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Re: Best N Scale Crossing Protection?
« Reply #48 on: May 13, 2017, 07:58:46 PM »
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Curious to see if that suggestion will get shot down - again.

We shall see.. ha ha! 
In my case, I didn't need the diode.  The driver circuit didn't load down the cap during its discharge enough to matter.
But I think your solution is more correct.  The extra diode guarantees that the cap will do what you want.

OldEastRR

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Re: Best N Scale Crossing Protection?
« Reply #49 on: May 14, 2017, 10:48:39 PM »
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So how would I modify this circuit to get the fade-out effect on the LEDs?
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mmagliaro

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Re: Best N Scale Crossing Protection?
« Reply #50 on: May 15, 2017, 02:02:27 AM »
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I think in that circuit, if you wired an electrolytic cap across each of those two resistors, it would do the trick.
The base current to each transistor would have to ramp up as the capacitor charged, and when each side gets cut off by the other, the cap would discharge slowly so its associated LED would fade down instead of going out immediately.

As for what value?   Heck... the base currents are going to be tiny in that circuit.  I'd try 10 uF, and if you don't see any effect, try 100 uF.  I doubt you'll need more than that.  The negative terminal of the electrolytic connects to the bottom of the circuit in that diagram (ground).

I'll be honest... I would want to fool around with this to see if I have this right.  I have not tested the idea.


OldEastRR

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Re: Best N Scale Crossing Protection?
« Reply #51 on: May 15, 2017, 02:19:23 AM »
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Yes, testing is in order. I have lots of LEDs from discarded lightboards and whatnot to use them as Guinea pigs.

mmagliaro

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Re: Best N Scale Crossing Protection?
« Reply #52 on: May 15, 2017, 11:25:20 AM »
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Yes, testing is in order. I have lots of LEDs from discarded lightboards and whatnot to use them as Guinea pigs.

If you build that circuit as-is and get it to work, adding capacitors where I indicated is not going to blow anything up.  Worst case, there is something about how it works I didn't consider and the LEDs either won't flash, won't change their flashing behavior at all, or will flash with an unequal weird pattern.  But nothing is going to burn up (assuming you wire the electrolytics in with the correct polarity ;-)  )

OldEastRR

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Re: Best N Scale Crossing Protection?
« Reply #53 on: May 15, 2017, 08:55:02 PM »
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I assume it will work, since its a published design. Getting fade-out effect is what I need to work on. And getting a 3v power source. Remember the old DC days where there were connections for multiple voltages and even AC on the pack? No such thing today ...

mmagliaro

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Re: Best N Scale Crossing Protection?
« Reply #54 on: May 16, 2017, 12:27:33 AM »
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I assume it will work, since its a published design. Getting fade-out effect is what I need to work on. And getting a 3v power source. Remember the old DC days where there were connections for multiple voltages and even AC on the pack? No such thing today ...

You don't have to use 3v.   Put about a 1k resistor in series with each LED, and you can run it higher.   I was a little surprised there were no resistors in there anyway.  I guess they are depending on the transistor junction drops and the inherent current limiting (from the base resistors) to keep too much current from flowing through the LEDs.  But If you raise the voltage to some convenient value, like 12, you definitely want to put some resistors in series with the LEDs.
 

ski

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Re: Best N Scale Crossing Protection?
« Reply #55 on: May 16, 2017, 10:30:27 AM »
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My son talked me into getting the Kato Crossing.  It is fun and a cool
piece of tech. I wish the arms were flat and there were only 2 signals instead of four. I think a little scenery work can mitigate some of the issues.