# Designed my own CDU w/LED display



## Hutch (Dec 19, 2012)

I couldn't find anything I liked on line so I made my own circuit and it works great. Here it is if anyone is interesred in building their own. I don't have any idea what the component cost will be but I don't expect it would be more than 10 or 15 dollars if you don't have a junk box full of stuff like this.


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## gunrunnerjohn (Nov 10, 2010)

Looks like it'll do the job just fine. The two parallel 1k resistors are a little confusing, why not just use a 470?


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## Hutch (Dec 19, 2012)

If you're talking about R6 and R7, dang, I knew someone would point that out. I'll change it to a single resistor.:laugh:


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## Hutch (Dec 19, 2012)

Oh wait a minute, I see what you may be talking about. The ones next to the dividers at the bottom. I could probably get rid of them.


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## Hutch (Dec 19, 2012)

Yup. Thanks John.


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## Hutch (Dec 19, 2012)

Update.


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## Hutch (Dec 19, 2012)

Since I have 2 more NOR gates on the chip, I may as well have the ability to control 2 turnouts. I edited it to show the correct values for the dividers.


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## gunrunnerjohn (Nov 10, 2010)

Now you're talking!  Good idea tossing in another turnout.

Another dumb question. Now that you took out the two parallel resistors, the values are different, 1k instead of 500 ohms. It doesn't appear that it affects circuit operation, just curious why you had them in the first place.


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## Hutch (Dec 19, 2012)

I started out with the flip circuit and then added the dividers after I got that working. I didn't realize I was paralleling them until you pointed it out. Now that I think of it, the divider, though it works is still wrong. I want 5V not 6V. Good thing the IC is a little tolerant of the input overvoltage. 1500 on the top will get me close enough with a litlle head room.


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## gunrunnerjohn (Nov 10, 2010)

HCT, I think that's good to about 7 volts if I recall correctly.


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## rkenney (Aug 10, 2013)

They look good, I was never much for reinventing the wheel though.

Don't know if you've seen these. They are 12v dc units designed by a guy named Ken Stapleton. They work great. My feelin' was by the time I acquired the parts I didn't already have and assemble it on a universal perfboard I would be wastin a lot of space. It would be mine but it wouldn't be very elegant.

He'll sell you just the board, a kit of parts, assembled units or you can get the schematic off his site for nutin.

Very compact. Not exactly surface mount small but gettin there.


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## Hutch (Dec 19, 2012)

That Looks good. I found it and the price is right!! http://www3.sympatico.ca/kstapleton3/751D.HTM


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## gunrunnerjohn (Nov 10, 2010)

Nice find Bob, those look great and as you say, they're really dirt cheap!


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## Hutch (Dec 19, 2012)

I checked out the schematic and quickly wired up the front end to see what it looks like on a scope and was very impressed. Fewer components than mine and smaller caps. If I build my own I'll use his schematic. Thanks for posting that.

BTW, I had a lot of fun reinventing the wheel and I'm not opposed to doing it once in a while. That being said, I have no problem at all accepting a better design and going with it. I have all these components so it's just a matter of how much fun I'm having wiring up the entire circuit on a perf board. I'll make them as I need them.


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## rkenney (Aug 10, 2013)

Hutch said:


> BTW, I had a lot of fun reinventing the wheel and I'm not opposed to doing it once in a while.


My hat is off to you there, sir.

In all honesty most of my story is just mental laziness. I recall in high school they said I was a 'mental loafer.'

They had a few other choice words of wisdom for me from time to time, but I didn't think much of them either.


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## Nuttin But Flyer (Dec 19, 2011)

This site might as well be in Latin....for a non-electronic boob like myself, what are these and what use do they provide?


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## gunrunnerjohn (Nov 10, 2010)

They're CD discharge switch controllers with position indication.


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## Nuttin But Flyer (Dec 19, 2011)

I was right...it is in Latin. I'm sorry but that went over my head, as usual.

The train sets I'm familiar with are the vintage American Flyers from the 50's and 60's. Will these switches do anything to improve operation with these? If so, you will need to explain it to me....in second grade terms, please.


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## rkenney (Aug 10, 2013)

gunrunnerjohn said:


> They're CD discharge switch controllers with position indication.


CD here does not stand for 'compact disc'. It stands for 'capacitive discharge.'

Basically a capacitor stores a charge and it delivers that charge as a burst to the turnout motor when the switch is thrown. Prevents turnout motor burnout by holding the button (there is no button) too long and provides a more positive turnout action (no drag as voltage builds up in the coil.)


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## rkenney (Aug 10, 2013)

Nuttin But Flyer said:


> I was right...it is in Latin. I'm sorry but that went over my head, as usual.
> 
> The train sets I'm familiar with are the vintage American Flyers from the 50's and 60's. Will these switches do anything to improve operation with these? If so, you will need to explain it to me....in second grade terms, please.


These CD units work with DC voltages. So if your AF turnouts will operate on a DC voltage, your first going to have to supply a DC source.

I have a lot of Marx turnouts that operate just fine with these units, I have a diode bridge installed across my KW 14v terminals to supply DC voltage. I also use the DC to operate relays that connect and disconnect my track blocks.


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