PC-controlled layout to NMRA-DCC standards


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"With DCC you run the train - not the track"

Some tips

When the decision is taken to go DCC you have several choices.The first question is whether you want to control your layout from a computer (PC / Mac) or a digital central unit with traditional trottles. Next choice is homebuilt or a turnkey system from any of the model railroad suppliers.
The turnkey systems includes lots of accessories and follows the NMRA DCC standard with respect to mobile decoders for locos but individual solutions for stationary decoding for turnouts, signals etc.- i.e. not compatible. Most new systems based on a central unit have the option to use a PC. The market offers a large variety of software for model railroading - mostly in Windows environment.

If you decide to build a digital system by yourself you will as allways save some money and also have great fun. With basic knowledge in electronics and soldering it is not that complicated. You will find several alternatives in literature on the internet.
Rutger Friberg`s NMRAF- solutions of boosters and stationary decoders is a very good example.

I started to build my layout based on analog technology with block sections and four trottels controlled from a panel with LED's and switches.
I took the first step towards digital control in the beginning of 1996 by looking for  PC-software.

My choice fall on Winlok 2.1 and I started to run the free demo version downloaded from internet. I recommend to define all functions on the layout and run the software in simulation mode to test your ideas before buying or building the digital hardware. Unfortunatelly Winlok is no longer supported and the development is closed. A better choice today is Train Controller from RR&Co that I use for my layout.

Today I have replaced most of my homebuilt decoders to Lenz LS 150 and Digitrax DS 64 with a lot better functionallity. The mobile decoders used are Lenz and Tran. Ss centralunit and other controllers I use the Lenz digital system.

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How does it work?

Short description of digital (DCC) model railroading

The central unit with a trottle (alternatively PC) transmits via a booster a stream of digital pulses to the track. The output includes both power and data.

All mobile loco decoders on the track receives the pulses and decodes the information. Each loco have an individual "address" and only one locomotive responds to the actual address followed by data for loco control. Several locos on the same track can with this technique be individually controlled from the central unit. A rectifier in the mobile decoder separates power for the motor and data for control of various functions in the locomotive.

The NMRA DCC standard defines a long list of functions included in the decoder registers.
Most mobile decoders will only take care of the basic functions in the locomotives.

Forward / Reverse   -    Start level   -   Speed   -    Acceleration   -   Retardation   -    Light on / off

The speed is controlled by 14 to 128 steps depending on type and manufacturer of the decoder.
More advanced functions like smoke, sound and couples can be operated from some decoders or more than one decoder installed in the locomotive. A real challenge for the N-scale model railroader.

The choice of decoder depends on the available space and current for the loco usually not more than 0,5 Amps for the N-scale locos. If you measure the "stall"-current before you install the decoder you will be safe by knowing the maximum loco current for any situation.
Connect a DC-amp instrument between the analogue voltage supply and the track. Hold the loco locked to the track and turn the trottle to maximum and read the current.Don’t forget to add the loco lamp current to obtain the total max current.

You can find suitable N-scale decoders from various vendors.  Lenz, Digitrax, Tran and others have a good assortment in small size. The new DCC handbook by Rutger Friberg and Stan Ames have a complete list of decoders with all data.
I have used the Lenz LE 030 and 040 with EMF-technology. This facility with feedback of motor load to the drive logic’s in the decoder will keep the loco to a constant speed independent of load from the wagons or going up or downhill.

The block diagram shows an example of a DCC system controlled from a PC with a feedback from block sensors to obtain a live presentation of all train movements on the PC-screen.  The software Train Controller is used in this layout.
Separate boosters for track and stationary decoders connected to individual power supplies minimizes any interaction between the control of trains and switches. 

The PC transfers the commands to the central unit (lenz) that generates the DCC-signal powered from an internal booster. 
The output from the block sensors indicates if the actual section is occupied or not - connected to a Lenz feedback unit. The software Train Controller is prepared  to indicate the status from the layout. 

The layout can be easily switched from digital to analogue to give the loco`s not yet modified to digital a chance to show up and still use the ability to be indicated on the PC-screen from the feedback from the block sensors.

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Screen view of  Train Controller 

The use of a computer to run the layout is often missunderstood.

" I prefer to run my trains by myself and not let the computer take over"

A limited view of computer technology – it is your decision - manual or automatic.Trottles are available on the PC-screen controlled from the mouse or the handheld controller attached to the central unit..
With Train Controller you design a copy of your track layout on the screen including switches, blocks and signals as active elements bound to real events on your railroad model.
Before you start your train - a route is activated that will define the status of involved switches, blocks and signals. Several routes can be defined simultaneously sharing common tracks and switches with interaction between the trains to different priorities.

The feedback from block sensors indicates the position of the trains indicated on the PC-screen. All active functions can be operated by a mouse click on screen by pointing on individual switches, blocks or routes etc.

Train Controller also have the ability run your trains fully automatic in sessions without programming knowledge. 
Complicated? – No, all functions are defined in a standard Windows environment with straight forward instructions and help menus with the result stored in a database linking all data in a logical scheme.

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Booster NMRAF 8

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A large layout will take several boosters appointed to different sections. Some turnouts like PECO takes a lot of current that will need a separate supply not to interfere with other devices. The main booster integrated in the central unit is used for the track (trains) and other functions on the layout is driven from the booster NMRAF8.
This booster consists of a data logic and a power distribution circuitry. Multiple boosters can share the same data logic on a master connected to the central unit expansion port and the slave boosters only having the power output mated from individual transformers or separate windings from one transformer.
 The NMRAF 8 is be equipped with an overload protection (Polyswitch).
Schematics and instructions are found the                                        in "Electronics for Model Railroading edition 5" by Rutger Friberg.
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Stationary decoders -  Digitrax DS 64 and Lenz LS150

A stationary decoder used for solenoide turnouts must be able to supply a short pulse to the turnout not to burn the coil. I have used 
Lenz LS150 capable of  6 turnouts like TRIX / ROCO
. The PECO turnout coils works with  LS 150 but because of the AC pulse supplied it sounds terrible with a high "buzzing" sound and the turnout will suffer from this in the long run.

A very good
alternative for PECO`s turnout solenoides is Digitrax decoder DS 64 including a "CDU" (Capacitor Discharge Unit) that supplies a short DC-pulse to the solenoide and the PECO-turnout is switched with a silent "click".

For static functions (no pulse) on a layout like trainsignals and streetlights  Littfinski decoders is an exellent alternative.



Lenz LS 150 for 6 turnouts Digitrax DS 64 for 4 turnouts Littfinski LS-DEC for 4 signals
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Block sensor connected to computer

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Why block control with DCC? - a DCC layout will operate the loco`s individually without any block sections!
The beauty by having block sections running DCC is to follow occupied tracks. A nice feature with indications on the layout displayed on the PC-screen alternatively used in the software to keep track of the trains in "ATC" mode.

The described hardware above can be operated by any DCC PC-software capable of supplying a DCC-signal following the NMRA specifications.
The  DCC pulses are brought to the track through the diod bridge D2 giving a signal to the block sensor D3 if there is a load on the track section caused buy a locomotive or a lighted wagon - moving or parked.
The outputs from the block sensors are connected to a feedback module attached to the central unit.
The diode D4 and capacitor C1 ensures a stable sensor signal from the transistor T3.

Simplified block sensor

A blocksensor can be stripped to inlude just a rectifierbridge and a optocoupler. This simplified sensorboard is connected to the central unit via a feedbackmodule. A blocksensor without filtering will force either the feedbackmodule or software to stabilize the blockindication.
The program Train Controller "TC" have functions inbuilt for such filtering to achive a stable blockindication.
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 Loco- decoder installations

To install a decoder in HO-scale loco or larger normally doesn't give and problems as space is not an issue. N-scale or Z is a challenge and demands lots of preparations and a good portion of patience.
There are no standard solutions for the mechanical adaptation - every locomotive has to be taken care of individually
I will in following show a couple of examples of decoder installations with detailed information's for the Fleischmann "Rc4" and "Du" N-scale loco`s. The decoders used follows the established NMRA-DCC standards.
The NMRA standard in
cludes a communic
ation protocol and definition of decoder registers with respect to content and functions. Most decoder installations will only use the basic functions. I recommend to study the Rutger Fribergs book no. 5 and the new  DCC book by Rutger Friberg, Stan Ames and Ed Loizeaux to get a deeper knowledge of the DCC standards.

Decoder installation in swedish Rc4 - loco

dek_RC4-gold.jpg (50118 bytes) The RC4 is an example of a N-scale locomotives with extremely good analogue run characteristics that gets even better with a DCC modification.
The decoder used is the "Lenz mini Gold" LE 10410 decoder . Alternatively LE 040 or Digitrax smallest fits also into the RC4.
The measured "stall"-current is 300mA, that's ok with good margin for above decoders.

Start to prepare the loco both electrically and mechanically and check for running with no problems from an analogue supply. Very important if anything fails during the installation. Open the loco and remove the connections to the pantographs.

The locomotives normally include a printed circuit board (PCB) bringing the wheel connections to motor and lamps. Disconnect the motor from the PCB and remove coils, capacitors and the rectifiers to the lamps.(hidden at the lamp connections)

  "Mini Gold" decoder  in RC4                                     RC4 printed circuit board                          Alternate installations of bulbs

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The "Lenz mini Gold" decoder is placed from underside in the space between the boggies after removing the pantograph switch. Solder the decoder wires to the PCB and cut the PCB etches (x) as shown in the figure. Check all connections from the drawing. Use a thin soldering iron and follow general rules for ESD protection.
Make sure the motor poles are only connected to the orange and grey wires. Other connections like the wheels may destroy the decoder. Secure the wires with "loctite"

Some loco`s like the RC4 have the left or right wheel tied to chassis in connection with the common lamp pole. This doesn't give any problems except for half rectified supply to the bulbs with less light that could be compensated by a alternate choice of lamps. The blue decoder wire is left disconnected in the RC4.

Decoder installation in the swedish Du-loco.

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This N-scale locomotive have a  limited space for a decoder installation. I am using the LE 040 for the DU-loco. A mid part of the PCB is removed (cut off) to give some room for the decoder. The chassis has to be cut down 3 mm, see figure. The LE 040 is fixed by dual glue tape.
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The DU-loco have as standard dual cable connections to the wheels on both sides where one pair will loose the connection to the PCB when it's cut off. Extra wires have to be soldered.
Both left and right wheels are isolated from the chassis so the blue wire connected to chassis is used as common pole for the lamps. The wires from the decoder is soldered to the PCB as shown in the figure. Follow the same procedures as for the RC4 loco.

Ready to program the loco`s

The moment have come to give the loco decoder the four basic parameters. Address,
start level, acceleration and retardation.
Do always use a separate programming track apart from the layout - preferable an oval of minimum
1 meter of diameter for final adjustments of the parameters.
If the programming by mistake takes place on the ordinary layout all locos will pick up the same parameters and the old erased. 

The DCC central units have a special programming mode and  when running from PC a loco programming software are available. Some handheld controllers attached to the central unit can be used for loco programming. The decoder supplier tells the default setting at delivery and how the parameters can be altered. Test the loco with the default values before any changes.

Give the loco a free unique address. Tandem coupled loco`s are given the same address with individual parameters depending on each locomotives characteristics. The startlevel can differ a lot depending on motor and friction. A certain voltage level is needed to get it moving.  The first step shall be tuned to give a smooth slow start and the rest of the steps distributed up to top speed. Acceleration and retardation is programmed to give a realistic movement - run the test track!
Keep in mind that hundreds of tons don`t stop in 10 meters. 

The DCC technique can be treated as "AC" (alternating current) giving a lot more tolerance against dirt and oxide. A general problem for the "2R" railroader. Some locomotives without boogies are difficult to run smoothly even with DCC. I have tested tandem coupled locos to extend the connetion to the track. Permanent coupled wagons is another solution to extend the number of contacts to the track.
This method could be the only alternative to modify a Z-scale loco to DCC by having the decoder in a wagon with wires to the motor in the loco.

Steam locomotives with a tender is an excellent example where the decoder can be installed in a coupled unit. The above solutions are just example on individual installation used for small scale locomotives.

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Per-Ake Jansson, email: