Making Signals

One of the main reasons I put so much effort into electronics is to give the layout signals and lighting.  For signals, I’m creating an automatic block signaling system that is visibly active wherever you  look on the layout.  So I need a fair number of signals.

Not Many Choices On Market

In N Scale you are faced with the twin dilemmas of a paucity of working signals on the market, and the challenges of creating signals at that scale. NJ International makes working N Scale signals that are fine, but their available styles are limited and availability is a big problem for their products.

NJ International Signals on the test loop.

Atlas offers N scale signals with little availability and stylistic choice.

Recently, some inexpensive “traffic light style” signals showed up on Amazon. I have not handled one, but while not fine scale models they look pretty good. They come in 2 aspect and 3 aspect versions.

That’s pretty much it for N Scale.

UP995 at Signal 34 on the test loop. Dual Searchlight Signals, Scratch Made with BLMA Signal Heads.

I have a few NJ International Signals, but what I wanted was target style heads, and for that there are no working models [I note that NJ International is listing target style as TBA, but there is no further information on the website.]

Creating Signal Heads

BLMA has offered an etched brass kit for creating target style signal heads. To make them work, all you have to do is add LEDS. Simple as that, right?

I’ll show you what that involves.

BLMA-1000 Signal Heads

I have to mention that since I started building the layout, Altas bought the BLMA product line and, as far as I can tell, have discontinued these little etched brass models. I’m not sure what I’ll do when my stockpile runs out; I guess I’ll have to fabricate something from scratch.

As you can see (the squares are 1/2″) its a very small model, with the target about 1/4″ in diameter. To illuminate it you need 0603 (.6 mm x .3mm) chip LEDS. In the first dozen I made, I used three chip LEDS (1 ea red, green, yellow), tying them together on the Anode side. It was difficult to do and I probably lost 50% or more of my attempts.

Multi-color LEDS to the Rescue!

Kingbridge RGY LED. That is what 1.6mm square looks like.

I found an RGY (red, green, yellow) LED from Kingbright, and it is a vast improvement over what I used to do. Its about the same size as three chip leds together — 1.6mm x 1.6mm — about 10 scale inches square in N Scale, which is about right. The LED has four contacts on the back: a common anode plus red, green and yellow ground connections.

Note the Polarity Mark on the bottom of the chip for identifying connections.

Using Magnet Wire

First, I have to give credit where credit is due: I learned the basic techniques for using magnet wire with SMD LEDS from ngineering.com. I have also purchased a few of their special effects boards and use them with my Arduino gear.

If you want to attach wire to tiny contacts a fraction of a millimeter wide, or slip wire through tubes or other small spaces, you need to use magnet wire. #38 magnet wire, available from ngineering.com, is very thin and difficult to work with because it has lacquer insulation and it tangles really easily. But it works well in small scales where concealing things is difficult; and it works very well attached to LED’s.

To work with magnet wire, it helps to have a temperature adjustable soldering iron, like the Hakko FX-888D. It also helps to have a magnifying lamp of some kind.

Step 1: Prepare the Wire

Cut four lengths of magnet wire. I use painter’s tape to hold the wires and prevent tangles. If possible, use two different wire colors: one to mark the anode and the other for the LED grounds. Or you can mark magnet wire with a Sharpie or similar permanent marker.

My Hakko Soldering Station set for burning off lacquer.

The lacquer insulation burns off above 800 degrees (Fahrenheit). So I set my Hakko for 850. When the iron reaches temperature ( a few seconds ) I melt a bead of silver solder onto the tip of the hand-piece.

Then, I dip the ends of the wires into the hot solder bead for about a second. On one end of each wire, you’ll dip a tiny bit the size of a pin or needle point as shown below. This is the end that will be soldered to the LED.

The tinned wire end is no bigger than the point of a pin.

On  the other end of the wires, draw a 1/4″ / 5mm or longer length through the bead to make an end you can connect to a terminal.

Try not to leave the wire in the hot bead for more than a second. Heat tends to make the wire brittle; the the effect is worse the longer you leave it in the hot solder bead. About a second seems to be right.

Step 2: Prepare the LED

The next thing is get the LED securely into a holder. I use a self-closing tweezer for this. My tweezer has a blunt end; for this purpose the blunt end holds more securely than a pointed end tweezer. I line it up using the polarity mark; the top right terminal is the anode.

At this point I turn the soldering iron down to 450 degrees.

The next step is where I go a different way than others. Bear in mind that SMD parts are designed to handle a certain amount of heat for a brief time. If you attempt to solder a prepared wire to a terminal at this point, it will not adhere reliably every time without additional flux or solder. As a practical matter, it is hard to hold two pieces together for normal soldering without risking overheating.

My solution is unconventional but works every time: pre-tin the LED contacts. The technique is simple: melt a tiny bead of solder onto the handpiece then just brush the wet tip across the terminals. So long as the SMD part is clean, it will pick up light coat of fresh solder easily. You have to apply solder immediately after melting or oxidation will set in and prevent adhesion.

Step 3: Solder the First Pair of Leads

Now, attach the magnet wire leads one at a time. To to that, straighten the wire so you can lay it on the tweezer/led combo and control placement. Let the prepared end of a wire rest on the target terminal; the little side notch helps capture the wire. With your iron set to 450 degrees (f) or lower, touch the terminal with the wire end briefly to remelt the solder and join the pieces. I like to anchor the wire securely on the tweezer with a finger then drag the iron tip across the LED joint.

The first two leads are attached. The red wire is soldered to the chip anode.

As you can see, its a tiny connection and you’d be right if you think its easily broken. It is, so careful handling is essential for the next two steps, after which the assembly will be reasonably stable.

Step 4: Solder the Second Pair of Leads

Gently bend the first two leads back so they are pointing up and are out of the way. Holding the leads, release the LED from the tweezer, turn the LED the opposition direction, then grab the LED with the tweezer again.

After reversing the LED, I grab it with the tweezer and hold it a little lower in the jaw than before. This helps protect the first two connections. I pre-tin these terminals before attaching wire.

After resetting the LED as shown, solder the next two leads, this time holding the wire with one hand, resting the prepped wire end on the pre-tinned LED terminal and brush across it with the soldering iron tip.

After soldering the remaining two leads, gently bend those up, parallel to the first two wires. Gather the wires into a single bundle; holding the wires in one hand, gently twist the LED a few turns to lightly twist the wires .together.

After soldering, the wires are lightly twisted together.

At this point it is essential to test the connections and make sure the LED lights up. Re-solder any connection that seems flaky (I rarely have to do this, but it happens).

Step 5: Protect the Assembly

With the LED tested, the next step is to stabilize and protect the connections. For this step I use Crystal Clear Gallery Glass, available from Amazon and many craft and hobby stores. Gallery Glass creates “stained glass art”, so it is very useful for simulating various kinds of glass.

Here I’m using it to create a clear coating around the assembly that helps hold it together during handling, and also creates a pseudo lens for the LED.

I dipped the assembly in Clear Gallery Glass, gently shook off excess, ending up with a nice ball of material surrounding the LED and its connections. I hang it pointing down to dry.
The Gallery Glass is just about dry. Notice the subtle lensing effect on the LED.

At this point, the LED assembly can be stored for future use. I try to make 4 to 6 at a time.

Step 6: Build the Head

The “box” part of the BLMA signal head is the large, complex shape in the etched brass sheet. The first step is to carefully cut away the tiny tabs holding it in place. Next, fold the box parts per the instructions.

Here I’ve folded the main box and used a tiny amount of CA glue to hold it together. Then I bend the middle tabs around a make-shift mandrill to created the curved top.

It takes patience an steady hands to fold the brass without breaking the tabs that hold the parts of the main box together. But if they break, its not a disaster; it just means you won’t have the tabs helping with final positioning.

Use tiny amounts of CA, applied with a micro brush, to fix box parts in place as you complete folds.

Completed signal boxes

Once the box created and secured with CA glue, I use a #60 drill in a pin vise to punch a hole into the back of the box for wires. Next I cut out the target and hood parts (the center and right-hand parts above) — with my make-shift mandrill (the handle of a round, steel micro-file), I bend the hood into a U shape, insert it into the target and CA glue it in place,

Now I have the 3 assemblies needed for a signal head: the LED, the box and the target/hood.

I start assembling the head by threading the LED wire through the other two assemblies in order.

With the LED wire threaded, I bring the two brass assemblies together, fitting the back side tabs on the target inside the box. Using a micro brush, I apply CA to the back of the target where it meets the box, being very careful to use the least amount possible and void excess.

Pulling the LED into the head. At this point in the process I pause to fill the box with clear Gallery Glass.

Now its just a matter of gently pulling the LED into the box. With the LED pulled until just outside the box, I stop and fill the cavity with more Crystal Clear Gallery Glass. Then I pull the LED into the box, embedding it in the Gallery Glass material.

After the Gallery Glass dries, the head is ready to paint and use.

At this point, head assemblies can be stored for future use if you are not ready to make the signals.

Step 7: Build and Test a Signal

A signal bridge with 5 heads on the L&NC.

The heads can be mounted on a bridge, pole structure or any other appropriate place. For this example I’ll make a simple pole-mounted single-head signal, using brass tube and styrene parts.

Two sizes of brass tube, a piece of square styrene tube, and a piece of thin, round styrene (comes with the BLMA kit) that provides the mounting pin for the head.

Whatever mounting structure you choose, pull the wires and glue the parts together.

I design these signal poles so that there is a 1/2 inch of brass tube at the bottom of the pole that gets inserted into a brass tube receiver on the layout. That makes mounting the signal on the layout easy.

Testing is a must, of course, to make sure nothing has happened to the wires and connections during construction. I have a simple platform with receivers to temporarily mount signals for testing.

Two signals undergoing tests.

For testing I use the same electronics I use on the layout: a duinoNode port device attached to a prototype Layout Control Node.

Since this only temporary, I use blue painters tape to corral the magnet wire and keep it from tangling.

Coming Soon

There are quite a few items on my agenda right now. Its time to return to Layout Control Nodes. Having described the essential components, its time to discuss methods for multi-node communication via nRF24l01+ radio.

Also, I haven’t talked about managing control panel inputs, like buttons and switches, in quite some time. Since control panels are an important part of every layout, it seems appropriate to look at methods and tools for trouble-free control.

Until then, Happy Model Railroading!

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