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Introduction to Computer Controlled Signaling

You don't have to use a computer, but it seems everyone wants to use JMRI. Probably the main reason is that people want to use it as a control panel. That's a good enough reason, but there are a few others. It is more flexible than most hardware implementations that do not use a computer and it is probably easier to debug your signaling system. So I will assume you, too, have decided to use a computer and most likely, JMRI as well.

Whenever I hear from someone who is building their first DCC layout, they have a lot of entusiasm and want to put in signaling. That's great, but there are some serious considerations before doing so.

When you put a decoder in a locomotive, you hook up the track wires and hook up the motor. Try it out. Good! Then hook up the lights. Try it out. Still good! Set the locomotive's address and you are done!

When you build your layout, you hook up the booster to the track. Put on a locomotive and try it out. Things are looking good! Now you can enjoy your trains. Life is grand!

Signaling is another animal altogether....

Serious Consideration #1:

Signaling will likely cost you more than your total investment in DCC to date.

For many people, this is all they need to hear to have second thoughts about signaling and scrap the idea. It isn't that signaling hardware costs so much. The problem is it takes a lot of hardware to implement DCC signaing. Rather than just needing a booster or two and a handful of sound-equiped locomotives to get started, you will need a block detector circuit for every single block you will need to detect. You will need a module to send the output of the block detector to the computer. You will need to hook up this same module to send your turnout positions to the computer as well. You will need a computer interface for your signaling system. You will need modules that will drive your signals. And, of course, you will need the signals themselves. For more than a small layout, all this hardware will add up. For my 1100 square foot (about 120 square meters) layout, I have spent about $3,000 USD and have about $2,000 more to go.

Serious Consideration #2:

You will need the help of someone with an electrical or computer engineering degree.

Signaling wiring is simple in concept; at least to an engineer. So what's the problem? The problem is getting all the stuff to work together. Everything needs to work for a single light to go from red to green. There are a lot of things that can go wrong. So you need someone or a team of people who understand the whole system and who has some serious troubleshooting skills. In the end, it will be a wire that came loose or a bit in JMRI that isn't set right. But finding that problem is much more difficult than figuring out why your locomotive decoder isn't working right. If you are new to DCC and don't have significant electrical and software skills, you will probably need a lot of help implementing signaling. If you have trouble getting a decoder in a locomotive working, you had better start sucking up to someone that has the skills you don't.

Something Else to Think About:

The number of years since I started my railroad and the present was longer than I would have liked. When the railroad was started, I started installing block detectors. Since progress was slower than I would have liked, I stopped installing the block detectors. I figured, probably like you, that I can install them later when I get around to installing signals.

Now that I'm going back and installing those block detectors, I'm wishing I had done a better job of documenting where they would go. Worse, remembering where I had put those perfectly concealed insulated joints between blocks is difficult and finding them is worse.

So if you can't afford the cost of installing the block detectors now, make flawless maps of your layout and under your benchwork of where your blocks are and where the block detectors need to go.

Good news! Current transformers used for many block detector systems are now about $1 each and all you have to do is slip a wire through them. So I suggest that you install these devices now when you start your railroad. You will still need the circuit to utilize the output of these devices, but you can definitely add them later. For now, get your current transformers installed. You will still need to carefully document where they are located, what block they go with, and exactly where that block starts and ends. Having the current transformers installed now will help you know later of where to hook up the rest of your signaling system.

And Now for a Non-Electrical Tip:

Before I planted my first signal mast, I worried about how I would do so to avoid damage when track is cleaned or when someone reaches to uncouple a car. I tried to think of breakaway connections. Nothing I thought of excited me.

Then my friend, Ken Klaviter, introduced me to an adhesive called Aleene's Tack-It Over & Over. You buy it at craft and hobby shops. This is a re-usable adhesive. He uses it to install decoders. You can use to to stick two surfaces together, pull them apart, and then restick them together. This may be just what I was looking for. I'm hoping someone can knock over a signal and simply put it back in place. I don't know how many times you can do this and how many years resticking will be possible, but for now, the prospects look good. We installed our first signal this way a few months go. Time will tell if this is the solution to the breakaway problem.

Circuits for the following signals have been contributed by Don Vollrath.
Ask Don a question on the Wiring for DCC Q&A Forum.

Indicating Polarity of Reversing Section

Use this circuit to indicate if a reversed section of track is at the same or opposite polarity from the mainline track.

This first circuit is for use of a 3-lead bi-color LED or two separate LEDs.

Signal Reverse Track 3 lead

This second circuit uses a 2-lead bi-color LED.

Indicating Turnout Position

Use this circuit to indicate the position of your turnout. This clever circuit works on DCC because DCC has a constant voltage on the track.

This first circuit is for use of a 3-lead bi-color LED or two separate LEDs.

This second circuit uses a 2-lead bi-color LED.


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