Wiring and DCC

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Wiring a model railroad isn't difficult, until you begin to desire more than just back and forth or round and round operation. These pages may help you to solve some of the mystery surrounding reverse loops, multiple train operation, and Digital Command Control (DCC).

Definitions:
Transformer - A device used to change the voltage of AC current.
Powerpack - A device used to change the voltage of AC current AND convert it to DC AND regulate the output voltage.

When your tracks are straight, or simply a circle, you need only to connect one powerpack lead to one rail, and the other powerpack lead to the other rail. To control the direction of your train use the direction switch on the powerpack.

When you start adding turnouts to your layout things can get more complex, particularly when your track turns around and comes back upon itself. This is called a reverse loop. It is used to reverse the track polarity without interupting the trains forward (or reverse) direction of travel.

Inorder to do this, we will need to provide a means for separating a section of track within the loop from the rest of the layout (mainline). This is done using insulated rail joiners at each end of a section of track within the loop. In addition, electrical switches must be provided to reverse the polarity of the loop and the mainline. It operates like this ... a train is run from the main layout into the separated section of track, the polarity of the mainline is reversed, the train is run out onto the mainline at the other end of the loop. To re-enter the loop at the original end the polarity of the loop must be reversed. When the train is to re-enter the mainline at the completion of the loop, the mainline polarity must again be reversed.

Notice that if the loop is powered directly from the mainline, when the polarity of the mainline is changed, the polarity of the loop section will change also! A means to separate the mailine polarity from the loop polarity must be provided. This is done by using two DPDT (double pole double throw) electrical switches; one to control the mainline , and one to control the loop.

The powerpack is connected to two DPDT electrical switches. The direction switch on the powerpack will then change the direction of the train in both sections, while the DPDT switches control the polarity (direction) in each section(mainline and loop). The DPDT's are wired so the power is put onto one pole and crossed over to the other poles. The wires going to the track are connected to the center poles. This allows for the polarity to be reversed in each of the two electrically isolated track sections. You will need to do this when using DCC also, however, DCC has devices that will do this automatically, but the rails will still need to be isolated with insulated rail joiners.

Shows reverse loop set to receive trains from lower mainline.

Shows mainline set to receive train from return loop.

What is DCC? DCC is an acronym for Digital Command Control.

When using DCC to control your trains:
* a serial digital signal is transmitted on the track to a receiver in each locomotive
* Each locomotive has a unique address.

Many advantages can be realized by this system:
* a constant source of 18 volts is available to the locomotive
* Each locomotive can be instructed as to speed and direction, entirely independant from other locomotives
* Switches can be controlled directly from the track and the information it carries, thus simplifying wiring.
* Locomotives with dissimilar operating characteristics can be made to run smoothly together
* Lights and sounds can be operated uniquely on each locomotive.
* a computer can be used to program your layouts operation, including starts and stops, route assignments, and train schedules.

The following pictures show a homemade DCC system which was built according to the plans provided by Tillorps' Mekaniska. It allows for train control from keyboard, handheld thottles, and a TV IR remote. The system cost less to build than most commercial DCC systems. The construction did require some learning and patience, and a little design work to get a nice setup, but was well worth the effort. The system utilyzes an older PC(486). The system is based upon Micheal Brandt's which has proven to be reliable and easy to build. This system is actually Chuck Heller's reduced chip count system. The plans for this system are on the Tillorp's site. I chose it because I could build it without making an etched printed circuit board. As you can see, the card was built with point to point wiring and uses many solder jumps to reduce wiring connections. There are only about a dozen, or so, actual wires.

Shows all items in system, without computer and TV IR remote. The 'black boxes' are the power supply on the bottom, and the Booster Station on top. The Chuck Heller reduced chip count DCC-MB card is in the card edge connector and also carries the TV IR remote receiver circuit. The rainbow ribbon cable connectors carry the parallel and RS-232 serial signals to the computer. A Radio Shack "wall wart" power supply is used to supply + and - voltage to the TV IR remote circuit. I have only two throttles at this time, but the Sound Blaster 16 card that I am using is capable of four. I have found that two, plus the keyboard, and the IR Remote keeps me plenty busy.

The following pictures are close ups of the main circuit board. This card contains all the serial and parallel port interface components. It also carries the TV-IR Remote receiver. The command control signal generated by this card is fed to the Booster Station by a 5 pin DIN.

	Components where first layed out on a copier print of prototype board. When a 'logical' layout became apparent the connections were penciled in with colored pencil. Each component layout was double even triple checked.

	The "RR Buss" is simply a serial port, a parallel port and some power supply connections.
	The Booster station contains the wires to adapt handheld throttles to the joystick port. On this modules motherboard are the H-Bridge MOSFETs and a small regulated power supply. Power from the main 4 Amp Power supply enters on a 5 pin DIN. This voltage is regulated by an LM338 and used to drive the H-bridge and the power supply for the interface card.
	The power supply station takes the house current (line) and turns it into 24 volt AC. This AC current is converted to DC with the two diodes. It is then smoothed (filtered with the capacitor bank) to 18 volts DC. Power from this 4 Amp DC power supply is taken to the booster station with a 5 pin DIN. This voltage is regulated in the Booster station by the LM338 and used to drive the H-bridge and the 5 volt power supply for the DCC-MB interface card.