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Test Track Project


Electronics

Layout Wiring

All wiring from the layout (track power, turnout controls, lighting, etc.) was connected to terminal strips under the layout as shown in the photo below. Also shown in the photo are two small circuit boards that contain circuitry to control the emergency vehicle flashing lights. A 25-wire cable was used to connect the layout wiring to the electronics drawer wiring.

Layout Wiring

Note: The 25-wire cable was a standard computer communications cable that had been cut in half to make two cables, each with a connector on only one end. The connector ends were plugged into each other, while the cut ends were connected to terminal strips under the layout and in the electronics drawer.

Electronics Drawer Wiring

Wiring from the layout was connected to the electronics drawer through the cable shown at the bottom of the drawer on the left side (photo below). The cable was connected to the terminal strips along the left side of the drawer. From there, signals were distributed to the CTI control modules, etc.

Note: the power supplies were located externally and were connected to the electronics through the color-coded (yellow, red, green, and blue) connectors along the top edge of the electronics drawer.

Electronics Drawer

Control Modules

CTI Electronics produces a comprehensive line of control and sensor modules for computerized model railroads, and they produce programmable software that communicates with the modules.

The test track used 8 CTI modules as shown in the photo below. The modules were located in the drawer that slides out from under the layout.

CTI Electronics Modules

Four of the CTI modules communicated directly with the controlling laptop computer. Those modules (from lower left to lower right in the photo) are:

  • TrainBrain

    The TrainBrain has 4 heavy-duty SPDT controllers and 4 adjustable sensor ports.

    The test track used 1 controller for track switch (turnout) control and 1 controller for track power control. The remaining 2 controllers were spares. One sensor port was used to detect train derailments. The remaining 3 sensors were spares.

  • Switchman

    The Switchman has 16 medium-duty SPST controllers.

    The test track used 4 controllers for track switch control and 5 controllers for scenery light control. The remaining 7 controllers were spares.

  • Sentry

    The Sentry has 16 nonadjustable sensor ports.

    The test track used all 16 sensors for detecting train location and direction.

  • SmartCab

    The SmartCab is a programmable throttle that is used to operate the train.

The remaining 4 CTI modules (small modules near the center of the drawer) are dual current sensors. They sense the location and direction of the train and send that information to the Sentry module described above.

Power Supplies

Four standard DC power adapters provided power to the test track as follows:

  • 9 VDC unregulated, 1000 mA: CTI module power

  • 12 VDC regulated, 1300 mA: Scenery Light power

  • 12 VDC unregulated, 300 mA: Turnout power

  • 13.5 VDC unregulated, 1000 mA: Track power input to throttle

Overload Protection

The 9-volt and 12-volt power supplies were protected by standard fuses. Because overload conditions (short circuit, etc.) for these power supplies are rare and usually mean that there is a problem, standard fuses were acceptable.

The 13.5-volt power supply was protected in a different way, because overload conditions are common. This power supply provided track power, and every time a train derailed, there was likely to be a short circuit created between the rails. Since derailments were common, the 13.5-volt supply was protected by a computer-controlled resettable breaker.

The protection circuit for the 13.5-volt power supply is shown below:

Under normal operating conditions, very little current (approximately 0.1 amps) is required to run the train. Under these conditions, the 12-volt lamp has insufficient current flowing through it to illuminate it. When there is a short circuit (e.g., a train derailment), the current increases dramatically, and the lamp lights up. When it is illuminated, the lamp actually limits current flow sufficiently to protect the throttle from damage. However, I wanted to make sure that all track power shuts off when there is a short circuit.

The mechanism that I used to shut off the track power consisted of the 12-volt lamp, a photo-darlington transistor, a normally open (N/O) relay, and some software code.

Under normal operating conditions, the CTI relay (in the diagram, above) is active, so the normally open contact is closed, thus allowing track power to reach the track. When the lamp illuminates, the light-sensing transistor activates the sensor port, which activates the software code. The software code deactivates the relay, thus disconnecting the shorted track from the throttle. This, in turn, shuts off the lamp and deactivates the sensor port. The train cannot run again until the operator "resets" the software—presumably, after rerailing the train.

The photo, below, shows the 12-volt lamp and the photo-darlington transistor. The transistor is under a light-proof cover that has a small rectangular opening in it, facing the lamp. The cover prevents the transistor from being triggered by ambient light. The cover, by the way, is the removable cap from a cheap ball-point pen. It may not look pretty, but it works.

Oh yes, and when the computer turned off the track power, it also turned on the flashing lights on the layout's emergency vehicles. After all, there has been a train wreck, so the emergency vehicles should respond.

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