Model Railroad Signals
From My Own Experience
On My Utopia Northern

model train signal bridgeSignal bridge at Underhill North

For the past few years I had been experimenting with adding trackside model railroad signals to my previous HO layout. This involved making my own signals from Oregon Supply kits, scratchbuilding signals and a brass signal bridge, assembling circuit boards and adding all the electrical wiring.

It has also involved learning more about how prototype railroads used signals to control movement of trains. 

I started by installing some commercial circuit boards from Logic Rail that use photosensors in the trackbed to detect passing trains. Not being completely satisfied with that setup (because the signals would time out after 30 seconds) I "graduated" to using current transducers (CTs) to detect the presence of trains and lighted rolling stock, ie, anything that draws current from the rails. I have been using Bill Hudson's circuits and he has been guiding me through the process. More recently (2015) I have been experimenting with signal logic based on Paisley's circuits being developed by friend John Houghton for his N gauge layout.

If you're interested in adding model railroad signals and are a DIY kind of modeller and are prepared to do a lot of the work yourself, use this page as a starting point to my various and sundry projects.

Signals are time consuming and complex and take a lot of wiring, but they're fun. It's great to see them changing even if you and your operators don't always follow the rules and "run a red" once in awhile. At least, my operators ignored them half the time.  My layout was still in the testing and learning stage so I didn't mind.

John, who alternated ops sessions with me before the Utopia Northern was dismantled for a house move, has done a lot of electronic work in building his N scale layout. We operate his layout with our iPads and tablets and jmri operations. Another modeller had contacted me about the detection system I am using. John has designed his own and agreed to reply to the email with information about what he has been doing. I share it with you in case you are also interested in doing your own circuits. John is open to helping others and even selling his boards to recoup some of his costs so he can buy track! Here is his email:

model train detectorsTrain detectors on John's workbench

"My layout is N Scale with Digitrax, Tam Valley servo controlled turnouts, Tam Valley Power management system and in the process of connecting to JMRI through OpenLCB or NMRANet using TCHTechnology boards. I have been experimenting with detection over the past year and I started with Paisleys circuits for IR detection, Transformer current detection and signal control. I modified most of his stuff and finalized on a dual comparator circuit for my detection system. Reason is that I have a comparator stage that is common to all my detections and all I need to do is alter a few parts on the input for either IR detection or current detection.

I have drawn the circuits and created the boards in Eagle 6.4. I then got 3 each of IR reflection, IR cross track trip, current detection and signal control, from OSH Park PCB . This is a unique way to get PC boards for cheap. My detector boards are about 1"X2". The price at OSH Park is $5.00 per sq. in. for 3 boards so each of my detector boards costs just over $3 unpopulated. Parts for each is in the $3-5 range so pretty cheap. 

Because my system is specific to my needs, and I am connecting to OpenLCB, everything runs from 5V DC only. The output from the dual comparator is open collector and is TTL compatible for sinking, very limited source current. I can turn on an LED with sink current. 

The current detector is Paisley's front end transformer and 2N3404 transistor into an LM2903 dual comparator. I got the transformers TM-57P1822 from Surplus Sales of Nebraska. With 1-1/2 turns through the Transformer, they will detect an N scale loco  at idle with 1 LED headlight. Also, a wet finger will trip the current detector. The detectors must be mounted close to the road bed at the wire drops. I will not be using resistor trucks so I cannot current detect cars. To do additional detection I am going to use my IR detection system. Same LM2903 Dual Comparator but using IR detection. My between the rails reflective detector will recognize a light colored car at 1-1/4" distance. For black locos and under frames, I have had success with white painted strips and metal furnace duct tape strips. My cross track trip IR detector works well up to 3". I am using T-3 sized IR LEDS and detectors so for N Scale, I need to be creative in hiding the LEDS above track. 

I also got ok results with a Vishey SMD photo detector Mouser # 782-TEMD7100X01. I intend to match this up with an SMD IR Emitter Osram Mouser #720-SFH420Z for really tiny reflective between the rails detection. Yet to play with this setup, but if it works, for N Scale it will fit on a rail tie. 

Paisley's CT Detector circuit will work with the systems that you and Bill are using, and with the LM 556 output there is lots of umph to output a long run to your detection location. His circuits are geared to work on 12V DC. You are also welcome to experiment with my circuits if you want. I can send you the Eagle files and you can bread board some experiments. If you are not into that much creating, if you are interested I can work up a real price for my stuff, populated."

Send me an email through my Contact page if you want to get in touch with John.  Since I posted this John has added signals to our travelling club layout.  Check them out on the Nottawasaga Model Railway page. Anyway, here are some other ideas for you to consider.



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Go from "model-railroad-signals" to Building your own signals.

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