Simple and Inexpensive CTC Signal Control for Your Layout

CTC versus ABS SIGNAL CONTROL

Centralized Traffic Control, or CTC, is a control system in which the signal aspects are controlled manually by a central dispatcher.
Absolute Block Signaling, or ABS, is a control system in which signal aspects are controlled automatically by a block occupancy detection system.
Prototype CTC systems include block occupancy detection, and the occupancy status of every block is displayed on the CTC control panel. Most of these systems have signals which are controlled manually by the dispatcher – called Absolute signals – and other signals which are controlled automatically by the block occupancy system – called Intermediate signals.
Intermediate signals are usually identified by a number board affixed to the signal mast. Absolute signals have no number board, or they may be identified by the letter A on a board affixed to the mast. (The D&RGW used the term Permissive signal instead of Intermediate signal.)
On my layout, I affix a number board to every signal mast, and those numbers are unique. In theory, that makes them intermediate signals, but I treat all signals as absolute signals. I justify this deviation from prototype practice by the fact that the unique numbers allow my guest operators to easily identify the signals.

WHY CHOOSE CTC?
I chose CTC for three reasons:
First, there is a fair amount of infrastructure required to implement block occupancy detection on a model layout. Infrared detection requires less infrastructure, but it only senses rolling stock at points where the infrared detectors are located. With blocks that are five, ten, or even fifteen feet long, this is a drawback to infrared detection. Current sensing detection requires electrical isolation of the blocks, current sensors on the power feeders to every block, and resistive wheelsets on every piece of unpowered rolling stock.
Second, I have a very small layout – less than 50 square feet, with a mainline run of just over 25 feet – and so I could fit, at most, five blocks into my layout. This didn’t seem to justify the effort and expense of installing automatic block occupancy detection.
Third, since ABS control does not protect against head-on collisions, it makes more sense to rely on CTC control in situations where you might have trains traveling in opposite directions on a single track; and my entire main line is single track.

ADDITIONAL RESOURCES
For an explanation of common cathode versus common anode wiring, see this video:    • Building   and Controlling   Dwarf Railroa...  
For a thorough explanation of the Aruino code, see this video:    • C++ Classes Part 2: Class Hierarchies  

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Links to items mentioned in this video. (Note: I am NOT endorsing any particular product(s), nor am I compensated by or connected to any of the companies mentioned.) I do NOT guarantee that these links will give you the best available price! Consider these links to be a starting point for your search.

The Fritzing designs and Gerber files for the three-aspect signal controller and for the six-light signal controller are available on my GitHub page: https://github.com/RJW496/DRGW-HO The Arduino scripts for four aspect control and for the Canadian Rail signal aspects are also on this page.

You can upload a Gerber file for manufacture at JLCPCB: https://jlcpcb.com/

PCB Components: Be sure to buy components with 2.54 mm pin pitch!

Screw Terminal blocks: search Amazon.com for “hxchen screw terminal pcb mount”. You should have a choice of 2-pin, 3-pin, 4-pin, 6-pin, 8-pin and 10-pin. You’ll need both 2-pin and 4-pin.

DPDT switches: search Amazon.com for “WMYCONGCONG 2 Position DPDT”

SPDT switches: search Amazon.com for “Chanzon SPDT Mini Micro Slide Switch 1P2T”

Female 40 pin header blocks: search Amazon.com for “40 pin female header block”

SP4T rotary switches: search Amazon.com for “uxcell 1P4T rotary switch”

SP3T switches can be found on Digikey – see, for eaxmple: https://www.digikey.com/en/products/d...
You’ll need to buy the knobs separately: https://www.digikey.com/en/products/d... BE SURE THE KNOB FITS THE SWITCH SHAFT.

I buy my Nano clones either from Amazon:
https://www.amazon.com/gp/product/B07... (These cost about $6.50 each.)
Or from AliExpress:
https://www.aliexpress.us These cost about $1.60 each if you buy 10, but you have to solder the pins to the boards yourself.

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This video was edited using Shotcut for Linux. Video footage and still images were recorded using a Galaxy A10e phone and a Nikon D7100 camera.