Model railroad signal design

Andrew’s been in touch with an excellent ‘how to’ on model railroad signal design:

“Hi Al

Firstly, I must compliment you on a stunning site full of the most useful tips and instructables.

But I don’t want to be a taker and not offer something in return, however, modern technology and I don’t always sit comfortably around the same table so I am unsure as to how to submit my little offering.

Living in South Africa with a most unfavourable exchange rate makes the railway hobby more challenging than it is for our counterparts in Europe or the Americas so necessity becomes the mother of invention and we have to find affordable alternatives.

So being old school and not following the DCC trend, my objective has been to develop cheaper methods to achieve similar ends within affordable limits.

Model railroad signal design

We tend to spend our money on mostly locomotives because that is what gets our hearts pounding and then we scrimp on the accessories regarding them as being very expensive for what we get.

Yet we are surrounded by sources of low cost items that can be easily converted to reasonable facsimiles with a bit of effort and very little expense.

A great source of components is old/broken CD/DVD drives which many computer shops are willing to give away at no charge. Strip them down and here are some of my offerings for model railroad signal design :


From the main board there is (sometimes) a duel LED holder, normally both green but simple to remove and replace one or both with either red or amber LEDs. Then with the purchase of a few other items, follow these steps:

Model railroad signal design

If you have purchased the items rather than strip down the DVD drive, the item in figure 1 is available off the shelf with a red and a green LED.

Start by carefully bending the legs of the LED up so that they point straight out the back of the plastic holder as indicated in figure 2 and then gently ease the LED’s out of the

Increase the size of two of the diagonally opposite holes as indicated in figure 3 with a 1.5mm diameter drill being careful not to drill into your fingers.

Model railroad signal design

Model railroad signal design

The purpose of this is to accommodate the thickness of the wires to be used and I use one of the pairs of wires from inside a CAT5 network cable which is readily available in suitable lengths.

Un-twist approximately 25mm of the pair and push each one through the enlarged holes. You may wish to strip off about 3mm of insulation on each one and tin it first. Put it one side and now on each of the LED’s, trim the anode leg (the longer one) down to approximately 3mm and tin it using flux. With a light touch, solder one wire to the anode of each led.

Be careful not to apply the soldering iron for too long as this will cause the insulation to melt away with the risk of a short. The use of flux here will allow the bonding to occur quickly.

Model railroad signal design

Model railroad signal design

Re-insert the LED’s into the holder through the original holes and carefully bend the wires from the LED back to their original positions as indicated in figure 5. Cut a piece of 2.5mm diameter brass tube to ±90mm long and using a drill bit.

Remove any burrs from where the tube was cut……you don’t want to nick the insulated wires after the previous effort.

Thread the 2 wires down the inside of the tube.

model railway signals

Cut the 2 remaining LED contact so that the project beyond the holder by approximately 3mm. Bend the two LED contacts so that they fit snugly on each side of the brass tube and once the LED holder is positioned “on top” of the pole in the desired position, solder these 2 legs onto the top of the pole.

All you need now is a ±800Ω resister to be soldered to the inside of the tube base, a touch of paint and voila!

For a suitable circuit diagram, please see below where an RC helicopter servo motor can be used. For the purpose of this topic, I have displayed both the LED 2 aspect signal and a semaphore signal. The micro switch is another component “rescued” from that broken DVD player.

signal wiring diagram

In the above circuit diagram, a servo motor is used as the point motor and is reasonably inexpensive from eBay coming in at around R30.00 apiece. In order to obtain the functionality, the circuit board inside the motor is removed and the two wires from the motor are connected directly to the DPDT switch (Make sure the switch is a centre-off, non-latching type). The micro switch from the DVD drive is a 3-pin type which is spring-loaded centre-off.

In the event that a manual semaphore signal is to be activated, this is connected to the arm of the Servo motor by means of a stiff wire (piano or spring steel) and then via the crank, can activate the semaphore signal.

The servo motor is mounted directly below the turnout with a stiff wire fixed vertically through a hole in the base board to the centre of the turnout draw bar.


Admittedly, the electronic components below have been sourced at one outlet only and you may have a preferred supplier or even other items that you can strip for components. Feel free to modify the circuit diagram if you want to adapt the circuit for your specific model railroad signal design.

For example, you may wish to install a 3- aspect signal and for this you would need to modify the LED header as they are only available in combinations of 1, 2 or 4 LEDs. The easiest would be to purchase the 4-LED header (part no L-934SB/4SRD) and cut away the top LED position. No big deal as you will score an LED for future use.

Also, the sub-micro switch configuration would have to change and maybe the installation of 2 SPDT type switches will do the job (I will figure it out and revise the circuit diagram).

Of course, you don’t need to install the servo motor system and if you are using manual or built in turnout control, it would mean that you would have to position the sub-micro switches a little differently, maybe on top of the baseboard and then hide them behind other scenic items.

At the end of the day, considering that to purchase a turnout motor and a multi aspect signal could cost you well over $25.00, this provides you with the means to produce the same for just $5.00 with the added advantage that you could connect multiple 2 or 3 aspect signals to the circuit.

model train signal

Here is my circuit diagram to simulate block occupancy where the “trigger” could any one of a number of methods depending on your preference. I have illustrated it using the micro switch method illustrated above.

Thank you once again for your superb contribution to the hobby and may it continue for years to come.

Kind regards


And now on to Hall of Fame member, Rob:

“I have purchased many signal heads and thought I could build my own for about 1 tenth the price I have been buying them.

I tried it and it worked so then I thought building one with the camera running might interest others.


Latest ebay cheat sheet is here.

A huge thanks to Rob and to Andrew for sharing his model railroad signal design- if you’ve ever thought of cobbling together your own signals, I hope today’s post has helped.

There’s also this post to help with the wiring:

Model railroad signal wiring

That’s all for today folks. Please do keep ’em coming.

And don’t forget the Beginner’s Guide is here if you want to get going on your own layout.



5 Responses to Model railroad signal design

  1. Gregory Jeffries says:

    Good, well written article. Very informative.

  2. Hi Andrew, where in South Africa are you? I am in Pietermaritzburg KZN, and also build my own signals, with route indicators etc.

  3. Tony, Kitty Hawk, NC says:

    Great tips Andrew and Rob- and both very well illustrated and explained. Thanks!

  4. Stephen D Gispanski says:

    This is just what I needed, now time to read this many times so I get this right the first time. Hats off to you on the information.

  5. Alastair Lee,
    Have a question. Am just starting to build a layout, and have recently moved and mis-placed my copy of the beginners guide. So, I am wanting to try the “Pink Foam Board” on top of my layout. What type of glue would be suitable to glue it to the plywood top. Seems like I recall Elmers White Glue is suitable, but not for certain.

    Thank you, Malcom Lee Johnson Central Texas.

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