# Diode Matrix for Yard Ladder



## Bwells (Mar 30, 2014)

A valued member mentioned in passing about a diode matrix for yard control in another thread. It was regarding twin coil solenoids as the method of point control. I did not want to ask there so hence this thread.. It was interesting and intriguing so of to the drawing board I went. After three failed attempts, I came up with what appears to be functional however I see a big problem. That would be the unnecessarily powering of turnouts already thrown in the correct position. I doubt the coils would be happy for long so there must be another electronic component that would be necessary, possibly a Mosfet or a latching relay however I have very limited knowledge on both. Check it out and let me know what you think. N is for normal and D is for diverging.


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## wvgca (Jan 21, 2013)

Applying momentary power to a turnout switch that is already in the correct position will not hurt or damage it, especially if you are intending to use any style of capacitance discharge switch power supply


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## DonR (Oct 18, 2012)

Valued Member, here. And thank you for the
very kind comment.

The wiring diagram for the diode matrix system
makes it look formidable. It is actually very simple
to create using terminal barrier strips. You just attach
the twin coil wires and the buttons to the strips as
you would for any panel then
interconnect the terminals with the diodes.

I've used the diode matrix system on my two yards
for several years. I power it with a door bell transformer
and a capacitor discharge unit. Since you are, as you
note, powering several coils at the same time you
do need a bit more juice than normal. In addition, a
yard with a large number of tracks might need jumpers
to ensure that the coils at the far end of the circuit
get enough voltage. Each diode will drop the current
a volt or so. Several in series could reduce the voltage
below that required to throw the points.

The system does make switching operations much more
enjoyable and all but eliminates derails due to
forgotten turnout throws. You do have to be aware
of where your train is before you push a button. If
in the wrong place, the points under a car would
derail it.

Don


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## Lemonhawk (Sep 24, 2013)

If you have a locnet DCC system you can use a DS64 and program the routes into it. This would allow you to use momentary panel switches and/or your throttle to throw the turnouts. This method also has the advantage of being able to display on your throttle the condition of a turnout (or in JMRI). A single DS64 supports 4 solenoids or 4 stall motor type switch machines.


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## Bwells (Mar 30, 2014)

Don, you caught that. BTW you're welcome. Although Warren mentioned throwing a coil that is already correct won't damage them, the buzz instead of the thwack may be annoying. I'm still not picturing the use of barrier strips, do you have a picture or a link to how this is physically done?


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## DonR (Oct 18, 2012)

Bwells

The only sound I hear when using my diode matrix
is the simultaneous point throws, then silence since
no further voltage comes from the CAP unit after
I release the push button. No buzz.

Here is one type of terminal barrier strip:

http://www.molex.com/molex/products/group?key=terminal_blocks_and_barrier_strips&channel=products

The screws between each barrier are electrically
the same.

They are available with 2, 4, 6, 8, 10 and possibly
more terminals per block.

You have an IN & OUT screw terminal for each 'wire'.
After connecting the wires TO the twin coils, and
FROM the panel push buttons, I then simply 'jumper'
with the diodes from one turnout coil terminal to the next in the
route, and continue that thru to the last turnout
in the route.

For simplicity, I use a common negative buss that
connects to all turnout commons.

Don


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## wvgca (Jan 21, 2013)

If you run just an ordinary AC transformer with manual push buttons for actuation, you can get some buzz, but not normally when you run a DC supply to power the twin coil switches ..
And if you go the Capacitor Discharge option, the actuation is very positive, and holding the button down doesn't do much after the initial throw, no buzzing


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## santafealltheway (Nov 27, 2012)

oh god, Math!

Good luck lol


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## wvgca (Jan 21, 2013)

You could build it exactly as you have drawn it, using a piece of thin plywood or thicker styrene ... drill the switch holes for push button or momentary toggles as you prefer, and glue solid bare wire horizontal .. with barrier / connector strip at the top .. and then diode with insulated wire soldered vertical, same as your diagram ..
Note: although the momentary current through each diode can be more than one amp, many people use common 1N4000 series diodes with no problems .. should cost maybe ten to fifteen dollars for the parts to do the panel..


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## Bwells (Mar 30, 2014)

Thanks Don and Warren for the info. I think I have given up on the barrier strips and considering building a circuit board. It is all about connecting multiple diodes that I am trying to do. I know my father built a few for different projects and I remember him saying he etched them so I googled it and see that the foil can be etched using ferric cloride(sp). I can get a board with foil from Radio Shack. I'm drawing up a diagram that may suffice but it still needs work. In the link I found says that the etching compound will leave ink so I was thinking of a large felt pen with the traces lined out and throw it in a pan of stuff and see what happens. I also remember a friend of mine's dad built a three track slot car track back in the sixties and I think he used copper foil in a roll for both sides of the slot. No idea how he fastened it down but I think I'll see if there is 3/16" one side sticky copper foil. That would be great. Never done this before but it appears to be a piece of cake, sort of!


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## wvgca (Jan 21, 2013)

There are rolls of 3/16 [or 5mm] copper foil shielding tape on fleabay for a couple of dollars, bottom side is sticky.. and it's [carefully] solderable


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## Bwells (Mar 30, 2014)

Thanks Warren, the stuff I see says stained glass, I assume that is what you meant by soldered carefully! How about the acid etching idea with a felt pen to preserve the foil? Thanks, Brian


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## wvgca (Jan 21, 2013)

I have tried felt pen for resist in the past with mediocre results , turned out blotchy for me most times, using striping or masking tape as the resist gave me fair results, with better results obtained by masking the whole board, cutting the tape out where I wanted the traces and then painting those, and finally removing all tape before etch bath , an alternative etchant is 25% muriatic acid, and 75% hydrogen peroxide, some call that mix a 7-UP etch


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## Lemonhawk (Sep 24, 2013)

If you want to use a PC board try the universal ones for experimenters rather than messing around with trying to etch your own.


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## Bwells (Mar 30, 2014)

I took a look at this one, printed it out and started drawing but I was coming up short on holes that were connected.
https://www.radioshack.com/products/multipurpose-pc-board?variant=20332061381

I think I am going to get one with solid copper on it and dremel out the necessary lines that I don't need. I drew that out and it looks a lot more doable provided the dremel will remove the copper.
https://www.radioshack.com/products/2-sided-copper-clad-pc-board?variant=20332044485
Just noticed that it's two sided, that is a problem. How easy is it to pull of the back foil?


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## Lemonhawk (Sep 24, 2013)

Difficult, you could etch it off. I don't think you looked hard enough on experimenter boards. Try this
https://www.adafruit.com/products/1608


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## gunrunnerjohn (Nov 10, 2010)

santafealltheway said:


> oh god, Math!
> 
> Good luck lol


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## DonR (Oct 18, 2012)

If math comes in, I'm out. I got kicked out of HS
algebra. If HO modelling required math I would
have bought old prewar windup Marx trains.

C'mon guys. The diode matrix is very simple when done
on a terminal board with about 4.00 or so worth of
diodes. How did we get to circuit boards and etching?
My anthill is turning into a mountain. Guess that leaves
me yodelling in the dark.

Don


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## wvgca (Jan 21, 2013)

Glad the 7-UP etchant worked for you, at least it can be safely flushed down the sink when no longer needed, however, where's the pictures??


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## Bwells (Mar 30, 2014)

Well I am making headway but ran into a snag. There was no way I was going to chuck up a #57 (.0430",1.09mm) bit in my 1/2" drill press so I ordered a drill press stand for a dremel. In the mean time I can label it and plan where the holes will go. Heck, I don't even have a yard to use it on! I got the diodes from Radio Shack at .75 a piece and I need 14 for a six track yard. Oh well, it is sort of fun!
P.S. That 7-UP etch was GREAT!!!


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## wvgca (Jan 21, 2013)

If you intend doing more than one PCB drilling project, I would recommend that you look for something like these, carbide PCB drill kit, from#80 to #54 ..
Very tough, and will last much longer than an ordinary metal drill bit on FR4, plus they can be used as a router bit on styrene or wood ..


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## Bwells (Mar 30, 2014)

Okay Warren, just ordered 10 bits .3-1.2 mm. That ought to do it. The #57 I have still looks a little large. These things are "hair-like"!


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## cid (Jul 3, 2014)

I can't say for sure but I would guess that a standard breadboard would make quick work of this project!
And much easier (not to mention more flexible) than jumping thru those PCB hoops. Unless you just want to!


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## gunrunnerjohn (Nov 10, 2010)

wvgca said:


> If you intend doing more than one PCB drilling project, I would recommend that you look for something like these, carbide PCB drill kit, from#80 to #54 ..
> Very tough, and will last much longer than an ordinary metal drill bit on FR4, plus they can be used as a router bit on styrene or wood ..
> 
> View attachment 247409


Looks like you've already broken a few of them.


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## cid (Jul 3, 2014)

A pin vise which can be chucked up in your drill press should be readily available!


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## wvgca (Jan 21, 2013)

gunrunnerjohn said:


> Looks like you've already broken a few of them.


Some are in dremels, some in pin vise's ..
and some broke, not during use, just some smaller ones from being dropped on the floor .. like the first three in the photo nearest the camera


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## gunrunnerjohn (Nov 10, 2010)

Well butterfingers, stop dropping them! 

Where did you get that set?


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## wvgca (Jan 21, 2013)

gunrunnerjohn said:


> Well butterfingers, stop dropping them!
> 
> Where did you get that set?


they're really little, and slippery 
came off ebay a few years back, think they were described as being used and resharpened ... think maybe 10 bucks a box or so?

broken ones are still useable, square the end off with a belt sander, and 1/8" of cutter is tougher than 3/8 flute length


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## Bwells (Mar 30, 2014)

Done deal! I know, it looks like I cut the PCB with an axe but I used a Dremel with a cutoff wheel and it got away from me. Solder joints are a little sloppy so I doubt I will be soldering up any IPhone 7's. It checks out at least with a meter so I guess it is time for a yard, maybe. Measures out at 2 1/4 X 3 1/8, about the size of a credit card.


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## wvgca (Jan 21, 2013)

glad that you got what you wanted


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