DC, DCC, LCC, JMRI, and the Alphabet Soup!

I've been involved with electronics for nearly as long as I have been a model railroader. When I was in my teens (back in the mid-1970's) I wanted to add signals to my parent's layout. I started with relays and Grain of Wheat lamps but soon discovered these new-fangled LEDs and 7400-series TTL. The bug bit hard, and my career has been centered around technology ever since.

That first layout was DC - a simple power-pack driving a single engine. When I bought a house and built a small layout in the basement, it was again DC, but this time with "Cab Control" allowing each block to be connected to one of three(!) controllers. This also brought in "advanced" technology in the form of transistorized throttles that implemented electronic controls to simulate momentum and braking.

Some time around 2002, I took the leap into DCC and sound-equipped locomotives. I learned about J/MRI to make configuring the decoders easier and eventually build some automation into the layout.

In 2021, we relocated in anticipation of retirement. A basement with room for a good-sized layout was a priority, and I now have a 16x30 room with benchwork filling 25' of that space! (see my personal web site for info about my layout.) Since this layout has room for 4-5 operators and a dispatcher, I thought I would document the journey through the electronics and acronyms.

DCC - Digital Command Control

I have used the Digitrax system since the beginning of my DCC operations, and while I will reference their parts, the concepts should apply to most DCC products. DCC, or Digital Command Control, can control decoders that are in engines (mobile), cars (function - often for sound and lighting control), and accessories such as turnouts and signals (stationary). There are a limited number of devices (addresses) that can be used in DCC, so I made the decision to use DCC to only control my engines and cars. I would use a newer technology - LCC - to control the accessories. The main difference is that DCC requires a central controller to manage everything while LCC allows one device to send a command directly to another device. This allows one device to monitor the state of push-button switches and send commands directly to the device that controls the turnouts.

I will delve into the details in a later post, but for now I will introduce some of the core components of a DCC system and their functions.

• Power Supply - a filtered DC power supply that provides 15Volts and sufficient current (amps) to drive the layout. I purchased a 20A power supply from an electronics supplier, which would be plenty for my planned needs.
• Command Station - this is a device that takes the DC power, listens to a control buss for commands from a controller, and then transmits the commands by modulating the data on the rails. The command station also provides current protection for (part of) your layout. I use a Digitrax DCS-210+ as my command station, which can deliver up to 8A of current.
• Booster - A device similar to the command station but without the intelligence. It uses a separate power input and listens to the command station and repeats the signal on its output. A booster allows you to increase the power output to your layout by dividing the layout into sections. I use a Digitrax DB-210 as my booster, which delivers a second 8A of current to a different section of the layout.
• Power Controller - a form of electronic "circuit breaker", it takes the power from a command station or booster and creates independent "Power Districts". It does not add power - if the command station outputs 5A, the combination of all power districts cannot exceed 5A. The primary benefit of this is the ability to divide the layout into electrical sections so that a short-circuit in one zone won't suddenly shut down the entire layout.
• Computer Interface - Usually a device that interfaces with a PC via a USB port and connects to the control buss of your DCC system. Some command stations (like my DCS-210+) have a USB interface built-in. While this isn't a requirement, loading the J/MRI software on the PC will make configuring the decoders and setting addresses much easier.
• Control Buss - the cable and connection technology that allows the command station, booster, controllers (throttles), and computer interface to share data. Many systems use telephone or computer network cables to connect devices together. My Digitrax system refers to this as "LocoNet" and uses a 6-conductor telephone-style flat cable to connect the devices together.
• Throttle - A device, usually hand-held, that allows an operator to control a train and often other accessory devices. Throttles can be wired (tethered) or wireless. Some throttles allow control of multiple trains concurrently - my Digitrax DT602 series has two separate throttles in a single unit, while my UT600 has fewer buttons and a single throttle. Wireless throttles can use radio or infra-red (IR) technology. IR throttles usually need multiple receivers to function well, while radio throttles only need a single receiver. 
• Decoder - the electronic "receiver" that accepts and interprets the commands from the DCC system. These are most commonly installed in engines to control the speed, direction, lighting, and (optionally) sound. Other decoders might be placed into non-engine cars to control lighting (caboose and passenger car interiors and marker lights), provide special sounds like the refrigerator engine in a mechanical reefer or cattle in a stock car, or "transponding", which can report which block specific equipment is located in. Other decoders that control turnouts, signals, and other non-moving devices are called "static" or "stationary" decoders. These often receive their DCC commands from the Control Buss and not through the rails.

LCC - Layout Command Control

The core concept of LCC is that it can generate (called PRODUCE) an event in response to a condition and broadcast the event. Other devices listen for that event code and respond (called CONSUME) the event and perform an action. In the simplest form, an LCC device can be configured with an input and an output port. The input port checks the status of a toggle or push-button switch, and the output port drives a turnout motor. In this case, the same device can Produce and Consume the same event! No central controlling device is needed to process the events, making the system very expandable and flexible. The "network" uses the well-established CAN buss, used in most automobiles and was introduced over 40 years ago!

LCC uses standard RJ45 connectors and CAT-5 network cables for communication. This "network" provides the power and the data signals to devices. Some devices that drive turnout motors obtain their logic power from this network but require an additional power connection to drive the turnout motors. The power on the network is limited to 0.5A per segment.

• Power-Point - a device that injects a DC voltage onto the LCC network cable. Power Points usually have two RJ45 connections and can supply a total of 1A of current - half to each port. It's important to track the power that LCC devices (nodes) consume and balance them across both connections. It might also be necessary to use an additional Power Point.
• USB Interface - an LCC node that interfaces to your PC using a USB cable. This interface is used for initial programming and configuration of LCC devices but is not required for basic operation of the automation. A JMRI system can consume events and produce events to create complex capabilities.
• Terminator - A small device that plugs into the last node port at each end of the LCC network. This device prevents the signals from reflecting back and causing interference or data corruption. 
• Node - This is a generic term for an LCC smart device. Nodes can perform input or output and often provide a combination of these actions in a single node. A typical node has 16 unique I/O ports. Nodes operate at 5VDC for input output and require additional modules to connect to other devices like turnout motors. There are several types of commonly available nodes, including:
  • General purpose I/O node
  • Signal Control node to drive trackside signals
  • Turnout Control node with special power drivers for servo, solenoid or slow-motion turnout motors
  • Power Status node displaying voltage and current
  • Real Time/Fast Clock node that broadcasts time data, allowing time-based actions such as dimming room lights and turning on layout building lights
• Module - a generic term for a device that converts the logic signals on a Node's Input or Output port into levels that can drive devices with higher voltage and current requirements, such as lamps, servos, and turnout control motors and solenoids. Some common modules include:
  • Current Sense module for track occupancy detection
  • High-current output drivers for stall-motor turnout control
  • Servo drivers for turnout control, signals, crossing gates, and other animated devices

By combining DCC and LCC, you can leverage the strengths of each system. LCC eliminates the address limitations of DCC and allows it to focus on driving the trains while LCC automates the control of accessories.

J/MRI - The JAVA Model Railroad Interface

J/MRI is a computer program written in JAVA, which allows it to operate on all common platforms, including Windows, Apple Macintosh, and Linux! The software is free and will easily run on most old and low-cost computers. Note that if you do use an older computer, it should not be connected to the Internet for security purposes, other than for brief times to obtain software updates!

J/MRI actually consists of several separate programs.

• Decoder Pro - creates an inventory of your decoder-equipped engines and rolling stock and the configuration settings for each. This makes configuration and programming of these devices as simple as filling out a form on the screen!
• Panel Pro - allows you to design and operate control panels. These communicate with DCC and LCC (and other) components to reflect the real-time state of the layout. You can also use these digital panels to control the operation of the layout.
• Operations Pro - Operate like the prototype! You can define your car and engine inventory, businesses, and the products that they receive and ship. Operations Pro can generate trains, manifests, switch lists, and more to give your train crews a realistic experience.
• Dispatcher Pro - This is actually a sub-component of Panel Pro and allows you to leverage a centralized dispatching method and even automatically control trains. A neat concept is having Dispatcher Pro run a local passenger train on the mainline on a timetable basis, stopping at stations, all while you are running a local freight and trying to switch industries. 
• LCC Pro - provides tools to configure LCC nodes using the traditional J/MRI interface. You may need to update your JMRI software to the latest version for LCC Pro to function properly and support all of the current devices.

You can use any or all of these applications in your layout. They all share configuration data so you only need to configure things once. 

Since J/MRI is an Open Source application, many sophisticated users are constantly improving and enhancing the software.

Summary

This should provide an overview into the terminology used in an automated model railroad. In the next post, I'll dive deeper into setting up the DCC system to control the trains, including the use of a booster and two power controllers, wiring of the various power districts, and how I will prepare for using LCC to control other accessories. I'll post about LCC down the road a bit.