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Connect model railway train detectors and layout automation devices to a computer via USB

Why choose USB for your layout automation bus?

USB A to B cable
USB type A to B cable
• USB has 1,000 X faster data rate than DCC power bus
• Avoid getting locked into a single vendor's DCC Control Bus
• Keep your accessory circuits when you replace your DCC system
• USB - a standard, robust communications channel that is already in your computer

 Azatrax infrared (IR) train detectors with USB interface

  • Proven pulsed infrared detection is independent of room lighting, works in tunnels and hidden track areas
MRD2-U Dual IR train detector with USB interface
• Senses trains at two locations
• Timing data can be used to calculate train speed and direction
• Powered by the USB bus, 25 mA required  more details...
MRD2-U dual detector   MRD2-S Dual IR train detector with switch control and USB interface
• Senses trains at two locations
• Track switch control:
  ° Automatic, triggered by IR sensors
  ° Computer via USB
  ° Manual push buttons
• Powered by the USB bus, 80 mA required, or by separate accessory supply  more details...
MRD2-S dual detector

Get ready for the future. More and more, computers are being used to coordinate the control of model train layouts. Put your layout sensors, train detectors and accessory actuators on the computer's USB bus, and leave the DCC system to do what it does best, controlling the trains.
DCC architecture
Model railroad DCC architecture
The basic DCC (Digital Command Control) model railroad system looks like the diagram at left. Individual Cab Controls (also called 'throttles') connect to a Control Bus that funnels data from the cab controls to the Command Unit.
The Command Unit takes the input from the cab controls and formats it into a DCC data stream.
This data stream is fed into the Booster, which combines the data stream with raw power from a power supply (not shown) and sends encoded power over the Power Bus to the track. Locomotives with DCC decoders receive their power and control commands from the Power Bus via the metal rails of the track.

Users often add automatic layout controls to their railroads to operate signals, track turnouts and similar devices. At first it is convenient to connect these accessories to the DCC system. It is a digital communication system already in place. Accessories can be connected to the Control Bus or to the track Power Bus. But there are disadvantages to this approach:
  • The Control Bus is proprietary, it is not standard. Each DCC manufacturer has their own control bus. Examples are Cab Bus®, XPressNet®, LocoNet®, RocoNet® and others. Accessories generally are not interchangeable. If you change to a different DCC system, you also have to change all of your accessory circuits.
  • The track Power Bus, on the other hand, is a standard format. That is why you can use decoders from different manufacturers on the same layout.
    But - as a layout grows with more locomotives and more accessories (stationary decoders), the track Power Bus becomes a data bottleneck. By nature the Power Bus is noisy and has low bandwidth (slow data rate). As more decoders compete for 'talk time' the response time gets slower. Train control suffers.
DCC system with computer
Layout control via USB,
train control via DCC

USB is an easy to use reliable data path with shielded cables, sophisticated error correction, widely available hardware, and it has over 1,000 times more data capacity than the DCC power bus. This higher bandwidth will be critical as accessories become more complex, sending more data to the computer.
And, when you replace your DCC system some day, all of your layout control functions can stay in place.
USB does not lock you into one manufacturer's products. Anyone can build a USB accessory. Microcontrollers with built-in USB ports are available from several chip manufacturers.
Nor does USB lock you into one computer system. Linux, Mac OS and Windows all work with USB devices.
Deepwoods Software's Model Railroad System is a model railroad software package that supports Azatrax USB train detectors.
Do you write your own software? These libraries provide generic access to USB devices:
  •, a library of C routines
  •, a library of C routines, similar to libusb
  •, a Java interface to the libusb functions.
    Azatrax does not supply software for these devices.
    Want to learn more? Use our contact page to send us your questions or comments.

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