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Discussion Starter #1
http://www.modeltrainforum.com/showthread.php?t=7337

Looking at the diagram and have a couple questions. First I don't need a whistle as the ZW already has it. So I can eliminate that gang of diodes. If I am reading it correctly the switches are normally closed in this case routing power around the diode array. When pushed it breaks contact and directs the current over the diode array.

The why does the route with the switch have 1 diode in it? wouldn't that be rectifying the voltage at the point? Or is it about how many diodes are in series? I'm not clear on why you used so many diodes. I took your counsel on fixing my 4-4-2 and used a bridge rectifier and resistor with the LED and it worked great!

Also, this may be me but I saw more than one thread and I think in one you suggested 3 amp diodes and in the other 6 amp but the diagrams are the same. I assume that has something to do with stepping down the voltage. I would just get a bag of diodes and solder them and test them but my meter had a stroke last time I tried that. Something about feeding it DC piggyback while in AC range, it just couldn't handle it.

Wait a second, you ARE still sending AC because there is one diode on each side! Hmmm.

What if instead of feeding the main power directly through the unit at all times, you created a shunt from the power to the button and diode array and then back to the power line. Use an normally open switch, when closed it allows current to flow through the diode array sending the DC pulse but not interrupting the main current flow.

Code:
transformer-----------------------------------------------------center rail
                       |                                  |
                       |-----[diode array and switch]-----|
I hope that displays right on your monitor.

It seems to my unschooled eye that this is even simpler.

And is there a way to measure the DC pulse piggybacked on AC? Digital and analog meters are about the sum of my test equipment. And I haven't used the analog in ages.

Frank
 

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Yard Master & Research
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10,840 Posts
I originally saw this in another forum. We had so much interest that Gunrunner built one. I have never got to the point to understand it or build one. Somehow it has to pass 3 volts or so of DC to make the horn or whistle work along with the normal track power.

After looking at the picture in your link, I would say the AC is dioded to two DC's and then joined again to form an AC current. The switch bypasses a group of diodes causing a deficient DC of one direction. (.7 drop per diode) At the output this off reading is the DC for the sound.

That makes sense to me now.

My other suggestion is to read all the threads concerned. Use the tag search words at the bottom of the post for starters.

Using diodes makes it more reliable than the discs used in older transformers.
 

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Railroad Tycoon
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24,336 Posts
You have Johns name in the title.

You would think he would have answered? :dunno:
 

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Admin
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I did answer, I don't know what happened to my reply! :confused:

The answer is, you can't remove any of the diodes. If you don't want both buttons, the only thing you can really remove is the button. The diode strings are necessary to properly pass the AC when the function is not being used.
 

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Railroad Tycoon
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24,336 Posts
I did answer, I don't know what happened to my reply! :confused:

The answer is, you can't remove any of the diodes. If you don't want both buttons, the only thing you can really remove is the button. The diode strings are necessary to properly pass the AC when the function is not being used.

Maybe you forgot to hit submit?
Sometimes I do that, then 5 mins later I notice that it is not showing.

I then use the back arrow till I find it and then hit submit.
It helps to hit submit. :p:eek:

Not to say that you didn't. :smokin:
 
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