Locomotive Simulator Projects

Control Systems

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All switches, contacts and controls in the cab are monitored through the Cab-to-PC interface. For example, every circuit including items such as the step and crosswalk lights have an input to the PC interface. Although current PC simulators may not support most of these controls, the simulator platform is ready if and when simulators are capable of supporting them. The Control System Overview is shown below is taken from my simulator electrical schematics. It provides a high level overview of how all of the controls interface with the PC.


My cab is not yet tailored to any specific PC train simulation software. I built my cab to be a generic simulator platform. This concept allows me to apply my controls to the multitude of simulators available today and in the future. Since many of the controls in my simulator are not supported by currently available PC simulators, I require a Cab-to-PC interface that is extremely flexible and capable of handling a variety of both digital and analog inputs and outputs. I also needed a method that supports all functions in the cab whether or not the PC simulator supports them. Initially I considered building my own interface until I came across the EPIC by R&R Electronics. The EPIC is considered the industry standard flight simulator PC interface. The EPIC provides all of the functionality I required, without forcing me to spend all of the time and effort to develop my own system. Please follow the EPIC Control System Overview link for details on the EPIC capabilities.


In a nutshell, the EPIC interface allows me not only convert the “typical” controls to keystrokes and mouse movements, but through the EPIC Programming Language (EPL,) the EPIC allows me to activate controls in my simulator that may not be supported within the PC simulation program.

Control System Overview
Click to See Fullsize

Click Here for EPIC Interface Description

In my cab, most devices operate at their designed locomotive voltages. For example, most locomotives use #44 6-volt indicator lamps powered by 74 vDC control circuits. As in a prototypical locomotive, these circuits require voltage reducing resistors wired in series with the indicators to provide the proper operating voltage for the bulbs. Although I could have used 6 volts to drive the lamps directly, the 74 vDC allows me to use the actual dropping resistors and provide the prototypical delay in lamp illumination. It has also enabled me to add devices designed for a locomotive’s electrical system without considerable modifications. For example, I can install a Locomotive Wheel Slip Buzzer to the Wheel Slip indicator circuit without modifying the buzzer to operate on a different or separate voltage.

Original Simulator to PC interface
Will be replaced by an expanded system in the UEC.

While using 74 vDC for the outputs adds a considerable level of complexity to the control systems, it also adds a level of realism to the way the systems are designed. When control panels in my cab are opened, you see a representation of the way real General Electric locomotives are wired; the wiring and labeling methods used are identical to GE’s specifications.


Using 74 vDC outputs also adds complexity when connecting outputs to the EPIC interface. The EPIC interface supports only output loads of up to 50mA at 50 vDC. In order to drive the 74 volt DC loads, I installed relays to protect the EPIC boards from the higher voltages. As well, all inputs use opto-isolators to protect the EPIC circuits. Since an opto-isolator uses an LED to drive a photo-transistor, I can monitor any DC input using an appropriate voltage-dropping resistor to reduce the voltage to an acceptable level for the LED. The phototransistors also provide the required matrix diode for the EPIC input scan functions.


In order to support the various higher voltage loads, my simulator requires a complex system of power supplies and separate power busses. I suggest anyone interested in “just making their controls work,” use either 5 or 12 vDC circuits consistently throughout their controls and eliminate the added complexity of separate power buses. I do suggest using the opto-isolators though, as they provide an inexpensive level of protection for the more expensive, and harder to repair/replace EPIC hardware. They also provide a convenient test point for trouble-shooting.