This document discusses the advantages of using a computer-based model railroad signaling system over traditional hard-wired logic circuits. Key advantages include low cost, easy expandability through additional interface cards, and great flexibility to modify the system through simple software changes rather than rewiring. Prototypical railroad signaling concepts can be easily modeled through computer programming.

1. 1
THE COMPUTER ADVANTAGE TO MODEL RR SIGNALING
(Material adapted from Railroader’s Application Handbook – Volume 1 Introduction)
Computer Model Railroad Interface (C/MRI) applications have proven with multi-thousands of applications that the
dream of an easy-to-install and simple-to-use model signaling system is readily attainable. With today’s market flooded
by the rapid advances of the computer industry, the power of the computer is available at bargain basement prices,
frequently free for the asking, for anyone wishing to add computer capability to their model railroad.
As you might expect, prototype signal relay logic can easily be reproduced through basic computer programming. The
result is a flexible signal operating system that is both easy and affordable. By adding an SMINI card to enable your
computer to interface with the railroad, you have the makings of a fully functional signaling system that can be as simple
as the most basic Automatic Block Signal (ABS) system, or as advanced as the most complex Centralized Traffic Control
(CTC) system. If the size of your system needs more than one SMINI then adding an RS485 card supports their
interconnection.
Proper signaling for a layout is more complex than just looking at block occupancy or a simple turnout position and
lighting a signal. To clear a signal properly you must ensure that all turnouts are correctly aligned for the desired track,
that the trackage is clear, that no spurs are unlocked and that no other signal is clear for another train to enter the same
trackage. As you can imagine, such crosschecking requirements quickly become increasingly complex as your trackage
arrangement becomes more complex. Fortunately however, such arrangements are easily handled with software at zero
cost. By contrast, trying to handle even simple interlocking plants via specialized dedicated logic circuitry becomes very
complicated and expensive, as well as non-flexible.
Fundamentally, to truly understand Prototypical Signaling and its application to our models and the impact on their
realistic operations, it is important to understand such terms as:
• Route Signaling • Dual-Control Power Switch
• Speed Signaling • Selector and Hand-Throw Levers
• Absolute Signal • Circuit Controller
• Permissive Signal • Traffic Stick
• Route Locking • Tumble Down
• Indication Locking • Time Locking Value (TLV)
• Time Locking • “Knocking Down” a Signal
• Approach Locking • Signal Running Time
• Indication Code • Vital and Non-Vital Circuitry
• Control Code • Protecting Hand Operated Switches
• Stacking Codes and Code Delay • Automatic Electric Lock
• Dispatcher Requested Value • Controlled Electric Lock
All these terms are explained and applied in-depth in the Railroader’s Application Handbook Volumes 1 and 2.
The underlying principle to prototypical signaling is that it’s very logic intensive. This makes signaling an ideal computer
application. Here are some neat advantages you will receive by using the computerized approach to signaling.
Low Cost
A second-hand computer is essentially a zero cost investment. When used for signaling, the computer freely supplies all
the necessary logic function capability. No special signal logic cards are required. All you need are the signals themselves
and a straightforward interface circuit, such as the SMINI, to connect them to the computer.

2. 2
As an additional saving, the oscillating voltage required to achieve the yellow aspect with the 2-lead 3-color LEDs is built
into the SMINI’s capability, so no additional signal driver circuitry is required. Also, the card is capable of driving a
Tortoise switch motor directly, and reading an occupancy detector directly, so again there is no requirement for any other
external circuit cards.
In addition to the low cost of the computer, the SMINI is an extremely economical way to drive signals and switchmotors.
The low cost of this card places signaling within almost everyone’s pocket book. For example, Do-It Yourselfers
constructing a reasonable size system with quantity discounts can achieve costs of the order $110 per
SMINI. This corresponds to approximately $1.50 per I/O line. This way we are talking a $4.50 total cost to drive a
3-color type D signal or $3 to drive a 2-lead or 3-lead 3-color LED searchlight signal.[1]
Do-It Yourselfers building an even larger system with an assumed average quantity discount of 20 percent can get the cost
down to as low as $75 per SMINI. This corresponds to approximately $1.00 per I/O line or $3.00 for a 3LED signal and
$2.00 per searchlight signal. This makes the cost of all the electronics almost insignificant when compared to the cost
of the signals themselves.
Going the complete kit route and using pricing data effective April 2011 from SLIQ Electronics as an example, we are
talking $120 per SMINI or $1.67 per I/O line. Correspondingly, fully assembled and tested SMINI cards cost $190 or
about $2.64 per I/O line. If your need is to build up a small number of cards, then going the kit route, via SLIQ Electronics
(www.sliqelectronics.com), is the most economical approach. Doing so also saves time from not having to place orders
for electronic parts plus it saves on shipping and handling charges.
However, if you are building up a significant number of cards, then going the Do-It Yourself route, where you purchase
your cards directly from JLC Enterprises, at quantity discount, and then buy your own electronic parts, from the
recommended sources called out in the parts lists, at quantity discount, then you can achieve substantial savings of the
order of 40 percent lower than the kit prices.
Easy Expandability
Each SMINI card can handle 72 I/O lines (48 outputs and 24 inputs). Simply connect your signal devices directly to the
nearest node and that’s it! For example, a single SMINI can drive 48 signal LEDs and read 24 occupancy detectors or
turnout and electrical switch position inputs. Depending upon the size of your layout, a single card may be all you need to
add signaling to your railroad.
For readers requiring large amounts of concentrated I/O, such as at a lever-type CTC machine, simply install an SUSIC
based Maxi-node instead of an SMINI. Each SUSIC based node can support up to 64 of the new 32-bit I/O cards yielding
a maximum capability of 64 x 32, or 2048 I/O lines per node. Because a distributed system can be expanded up to 128
nodes, the maximum interfacing capacity is 262,144 I/O lines, calculated as 64 x 32 x 128.
When more I/O lines are needed, simply distribute additional SMINI cards around your layout to build up to whatever
capability you desire. This way each node is close to the signaling devices being interfaced, significantly reducing the
need for a lot of wire.
Simplicity
The only wiring required between nodes is a single 4-wire cable and this same cable is the only connection back to the
computer. You do not need any signal logic wiring running from one signal logic card to another. There are no relays or
multi-deck panel switches.
_______________
[1] All cost data provided in this Handbook is considered valid at time of publication only and may well vary up or down
as time progresses. In addition, Do-It Yourself cost data is presented as estimates only and do not include shipping and

3. 3
handling charges which can easily amount to $30 when one considers ordering parts from 4 different suppliers. Such
added costs tend to make the prices charged for complete kits more reasonable then they might at first appear. However,
when ordering large quantities of parts to create a sizeable system, the impact of shipping and handling charges becomes
relatively insignificant.
With the C/MRI, you simply connect each signal device, whether it is a pushbutton, a toggle switch, a switchmotor, or a
panel LED or the signal itself, directly to the nearest node. All the complex signal logic is handled by software running on
your computer. You just can’t get wiring much simpler!
There are also many “canned” software packages available so that you really do not need to develop your own software.
The most popular is JMRI as discussed frequently on the C/MRI User’s Group. For those that wish to roll your own, there
is an abundance of software examples to pick from, including those provided in the C/MRI User’s Manual and in this
Handbook and the disks associated with each of these publications. Additional examples are available via the C/MRI
User’s Group.
Flexibility
Low cost and implementation simplicity are usually sufficient to justify going with the computerized approach to
signaling. However another tremendous advantage of the C/MRI approach is system flexibility. Fixed hard-wired systems
using groups of highly interconnected, specialized signal logic cards are difficult to change once they are installed. Alter
your track arrangement a little, add another signal or signal head, or select a different style signal and you encounter major
rewiring.
By contrast, using computerized signaling, even extensive layout changes typically require minimal wiring changes.
Frequently, the total change requirement is simply a few statement alterations in the software. The software is extremely
easy to regenerate and update as needs change.
For example, suppose you decide you want to add approach lighting to all your signals – simply add a few statements to
your program. Should you decide to change that junction with a foreign railroad to use semaphores – simply change the
aspect constant in your software. Perhaps you desire to add flashing signal aspects – simply add a couple of new
statements to your signaling program.
Suppose you decide to add a protected grade crossing in the middle of one of your dispatcher controlled OS sections – no
problem. Simply connect the grade crossing protection device to a spare output line on the nearest node and all the
required logic changes are easily handled via minor software updates. The same is true if you decide to add a second
turnout within an OS section to create a branch line or to incorporate a new major junction somewhere else on your
railroad. Most modelers over time make alterations to their railroad. Having the signal changes imbedded in the software
rather than in the hardware makes life easy.
I have been installing model railroad signaling for over half a century. At age eleven I built my first 10-lever mechanical
interlocking plant to control track switches and signals at a junction on my 0-27 Sunset Valley. In the early 1970s I
authored three articles in Model Railroader explaining the application of relay logic to control signals on the original HO
scale Sunset Valley. Over the years I have gained extensive experience hard-wiring all types of specialized fixed-logic
signaling cards. Every time you want to make a change – even simple layout modifications – the resulting wiring changes
can become a nightmare.
The situation is exactly opposite when using a computer. The most wiring changes you will ever see are adding or deleting
of a few simple I/O connections. All complex logic changes are handled by making easy software modifications. I can
assure you from over 50 years of signaling experience that nothing comes close to the simplicity, affordability and ease of
making changes provided by the computerized approach. It’s a hundred times easier to make a software update than it is
to change the wiring in a hard-wired signaling system.

4. 4
Prototype Fidelity
The higher the level of prototype fidelity you seek the more optimum is the choice for computerization. Prototype
signaling involves all types of specialized aspects, the incorporation of circuit delays and timeouts, specialized
interlocking between all types of levers, buttons and toggles, and for modern signaling even keyboard/mouse inputs. Such
operations are easily implemented by using the inherent power of the computer.
For example, implementing an interlocking plant at a railroad junction, a terminal or at the entrance to a staging area is a
snap with the computerized approach. The system works equally well whether the plant is an early era lever-type plant, an
eNtrance/eXit (NX) style pushbutton plant, a modern keyboard/graphical plant or a fully automated plant. Also, nothing
beats the computerized approach for implementing a dispatcher CTC panel, whether it is the older lever-style or a modern
system using graphical display panels. Why use the computer? Using the computerized approach results in an easy to
use system employing extreme flexibility coupled with prototype fidelity and packaged as a most cost effective
solution to meet every signaling need.
The computerized advantage is independent of whether you desire to achieve a simple but totally effective system or a
full-blown prototypical system using Automatic Block Signaling (ABS), Absolute Permissive Block (APB) signaling,
junction and terminal interlocking plants, and/or a complete implementation of Centralized Traffic Control (CTC). For
readers desiring greater insight into how these different signaling systems function, and how the techniques can be applied
to your model railroad, I highly recommend studying Andy Sperandeo’s article Understanding Railroad Signals in the
December 2002 issue of Model Railroader.
As Andy points out several times, all signal logic is readily convertible to software and such software can be easily
executed by a personal computer. To take advantage of this relationship, we need a simple way to interface the computer
to our railroad’s basic signaling elements. The C/MRI, and especially the SMINI card, provides us with that capability.
For additional information consult the following references:
www.jlcenterprises.net (provider of bare board, selected parts and extraordinary documentation)
easeeinterface@msn.com Don Wood (provider of fully assembled and tested boards)
http://groups.yahoo.com/group/CMRI_Users (C/MRI Users Group)
www.ctcparts.com (provider of CTC Machine components and excellent source of information covering CTC)
“Signaling Made Easier”, a 4-part series published in January through April 2004 Model Railroader. Copies available
directly from Kalmbach and from the NMRA’s Kalmbach Memorial Library
“Using State-of-the-Art Electronics to Enhance Operations” March 2007 Scale Rails. Color photocopies available
from NMRA Kalmbach Memorial Library
C/MRI User’s Manual V3.1, consult the JLC Web site for ordering information
Railroader’s Application Handbook, Volume 1, consult the JLC Web site for ordering information
Railroader’s Application Handbook, Volume 2, consult JLC Web site for ordering information

5. 5
Listing of Chapters and Appendices Included within the C/MRI
User’s Manual Version 3.1
Introduction
Acknowledgements
Chapter 1: Basics for Building a Computer Interface
Chapter 2: Introduction to Software
Chapter 3: Making Basic Railroad I/O Connections
Chapter 4: Super Mini-Node Interface Card (SMINI)
Chapter 5: Using Quick-Basic with DOS and Visual Basic with Windows
Chapter 6: Testing Serial-Based Nodes
Chapter 7: Basic Programming Examples
Chapter 8: Packing and Unpacking I/O Bytes
Chapter 9: SMINI Application Examples
Chapter 10: Super Universal Serial Interface Card (SUSIC)
Chapter 11: Digital 32-Bit I/O Cards
Chapter 12: SUSIC/USIC Application Examples
Chapter 13: Modular Programming Examples – Using Calls
Chapter 14: Distributed Serial Application Examples
Chapter 15: Visual Basic – Programming Fundamentals
Chapter 16: Visual Basic – Programming Examples
Chapter 17: Classic 24-bit Digital I/O Circuits and Test Card (available on CD only)
Chapter 18: Adding Analog Interfacing Cards (available on CD only)
Chapter 19: Power Supplies (available on CD only)
Appendix A: Circuit Board and Electronic Parts Ordering Information
Appendix B: Serial Protocol Subroutines – Quick Basic Version
Appendix C: Serial Protocol Subroutines – Visual Basic Version
Appendix D: Universal Serial Test Program – Quick Basic Version
Appendix E: Universal Serial Test Program – Visual Basic Version
Listing of Chapters Included within the
Railroader’s C/MRI Applications Handbook V3.0 Volumes 1 and 2
Volume 1 – SYSTEM EXTENSIONS
Preface – How it started and the road it took
Acknowledgements
Chapter 1: Introduction
Chapter 2: Track Occupancy Detection Fundamentals
Chapter 3: OD Track Occupancy Detector
Chapter 4: DCCOD Track Occupancy Detector
Chapter 5: Using the C/MRI with Digital Command Control (DCC)
Chapter 6: Using the C/MRI with Non-DCC Command Control Systems
Chapter 7: Prototypical Turnout Control
Chapter 8: Prototypical Grade Crossing Warning Systems
Chapter 9: Making Additional Connections
Chapter 10: Product Availability
Chapter 11: Cost Estimating Your C/MRI System
Chapter 12: Cost Tradeoffs and System Design
Chapter 13: The Computer’s Role and the C/MRI
Chapter 14: Operational Considerations and System Design

6. 6
Chapter 15: Additional Software Information
Chapter 16: Simplified Layout Wiring and Computerized Diagnostics
Volume 2 – SIGNALING SYSTEMS
Chapter 17: Understanding Railroad Signals
Chapter 18: Model Railroad Signaling Fundamentals
Chapter 19: Automatic Block Signaling (ABS)
Chapter 20: Absolute Permissive Block (APB) Signaling
Chapter 21: Poor Man’s CTC – Operation without a Dispatcher
Chapter 22: Centralized Traffic Control (CTC) Systems
Chapter 23: Protecting Hand Operated Switches within Signaled Territory
Chapter 24: Programming CTC Systems
Chapter 25: Example CTC System Program
Chapter 26: Dynamic Track Plan Graphics Using Visual Basic
Chapter 27: Emulating Modern Dispatching Centers
Table 11-1. Comparison of card, parts and card plus parts cost data
(Summary constructed using extensive data provided in Volume 1 Railroader’s Application Handbook)
Column
No.
1 2 3 4 5
Card
Type
JLC Card
& Key Part
Cost [1]
Elect. Parts
Low Cost
Estimate [2]
Elect. Parts
High Cost
Estimate [3]
Do-It
Yourself
Card & Parts
Low Est. [4]
Do-It
Yourself
Card & Parts
High Est. [5]
SMINI 66.00 [6] 22.06 28.11 81.46 94.11
SUSIC 59.00 [6] 12.03 14.49 65.13 73.49
RS485 10.00 7.43 9.37 16.43 19.37
IOMBX 30.00 14.24 24.00 41.24 54.00
DIN32 22.00 10.27 12.29 30.07 34.29
DOUT32 24.00 12.46 15.14 34.06 39.14
TEST32 10.00 8.38 12.68 17.36 22.68
OD 6.00 3.13 4.36 7.91 10.36
DCCOD 7.50 [7] 2.51 3.97 9.26 11.47
ODMB 18.00 3.57 5.37 19.08 21.39
SMC12 20.00 6.38 8.94 24.38 28.94
PGCC 24.00 [8] 12.62 [9] 17.48 [9] 34.22 41.48
Note: Consult Volume 1 of the Railroader’s Application Handbook for extensive system design support and
optimizing system capabilities versus ost including all the backup data associated with Notes [1] through [9].
Source for all bare C/MRI circuit boards, selected parts, User’s Manual and Handbooks:
JLCEnterprises, Inc. P.O. Box
88187
Grand Rapids, MI 49518
616-243-4184 www.jlcenterprises.net
chubbbrucemmr@aol.com

7. 7
Source for fully assembled and tested C/MRI circuit boards:
Donald Wood
4925 Foxwood Blvd
Lakeland, FL 33810
easeeinterface@msn.com
Sources for electronic parts:
Digi-Key Corporation
701 Brooks Ave. South
Thief River Falls, MN 56701
1-800-344-4539
www.digikey.com
Jameco Electronics 1355
Shoreway Rd.
Belmount, CA 94002 1-
800-831-4242
www.jameco.com
Mouser Electronics
1000 N. Main St.
Mansfield, TX 76063
1-800-346-6873
www.mouser.com
C/MRI User’s Group: http://groups.yahoo.com/group/CMRI_Users
A single SMINI provides all the interfacing required to signal a small layout.
However, if more I/O is required, multiple SMINIs can be distributed around the layout. They simply daisy-chain together
using a single 4-wire cable.

8. 8
For areas requiring highly concentrated I/O, such as at a lever-type CTC panel, adding an SUSIC-based super-size node
does the job nicely.
In all cases, all wiring to railroad devices (signals, switchmotors, etc.) simply connects to the nearest node making wiring
easy.

9. 9
For more details, consult the numerous downloadable packages available via the JLC website and the extensive
documentation available via the C/MRI User’s Manual V3.1 and the Volumes 1 and 2 of the Railroader’s Applications
Handbook V3.0.