Everything from the DCC basics to computer control.

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Sunday, February 10, 2008

Wiring a crossing for DCC

There can be few layouts which get by without including a diamond crossing at some point, mine included. And for those of us using electrofrog trackwork and DCC that raises the question of how to wire it.

My first assumption was that it would require some complex wiring and a DPDT switch, but I chose to search the internet first for a definitive answer. I found rumours about using a revering loop module but nothing in detail. I couldn’t see how a reversing loop module would work, but then I don’t understand how they work as reversing loop modules, but I figured it was worth some experimenting.

Below is the technicolour diagram of what I ended up with.

The blue and green wires show the normal ‘two wires’ from the command station/controller. These are wired to either side of the crossing as they would be normally with blue to one rail and green to the other.

The short red lines show where an insulating joint is needed either side of the crossings frogs.

The inputs of the reversing module (I’ve shown a Lenz LK100 here, but another make would work equally well) are connected to the ‘two wires’ from the command station. It doesn’t matter which wire connects to which terminal, the module will switch them as necessary.

The outputs from the LK100 are in turn connected to the crossings frogs. Again it doesn’t matter which output goes to which frog, just as long as the frogs are insulated from neighbouring rails.

With my crossing wired as above when I run a train over the crossing there is a ‘click’ from the relay as the LK100 switches polarity and the train runs across the track completely unhindered.

PS. The diagram assumes that both the crossing tracks have the same orientation, ie neither is part of a reversing loop or figure of eight style layout. If so you’ll need to make some modifications, I suspect putting another reversing loop module over the other rails of the crossing (and inulating them) or on one or more approach roads.

Posted by Mike on 02/10 at 02:57 PM
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Sunday, July 22, 2007

Farish HST DCC Conversion

Bachmann/Graham Farish have recently re-released the HST with a completely new chassis. This chassis is of a similar design to that of the class 66 and revised class 57, but they have taken a slightly backward step as far as DCC conversion goes by not including the marked solder tags (and they still haven’t managed to make a DCC plug-and-play chassis, but that’s another article). However, this new chassis is much easier to convert than the older ones.


The body is easy to remove - insert a thin screwdriver or finger nails either side and the chassis just drops out. You will now see the circuit board atop the chassis. We will do the conversion by removing the two coils (labelled L1 and L2) and soldering the decoder in their place. There is space to put the decoder in the guards compartment (on the right in the photos).

Start by removing the two coils with a small pair of clippers.  Remove the yellow, blue and white lighting wires from the decoder and cut the other wires to length, the red and black being the shorter pair (see the photos). Now solder the red, black, orange and grey wires as shown in the photos.

All that’s left is to place the chassis on the programming track to test and programme as usual.

Posted by Mike on 07/22 at 01:30 PM
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Tuesday, August 08, 2006

Conversions and Being Converted

For a while now I’ve wanted to add some more DCC conversion instructions for the site and in the last week I’ve been making a start on them.

The conversions are for the class 08 and a pair of Farish steam engines - a West Country class and a 4MT. As far as I know all the steam engines (except the recent V2) use the same or similar chassis, so it should be easy enough to adapt the instructions for other locos.

Progress so far has been to strip down the locos to extract the parts necessary for sending to Gerry Spencer in exchange for his modified parts. When these come back I will be able to finish off the conversions - and the instructions.

Those of you who have been following the site will know I’ve been writing my own DCC control software, but progress has been very slow with a few difficult to fix glitches in the block detection code and, frankly, not enough time to devote to writing software.

So I’ve taken the decision to convert to using Freiwalds TrainController.

It will be a shame not to be writing my own software - I always like the way custom software enables me to get exactly what I want - but using a commercial solution will allow me to get things running much faster. I also felt that using custom software wasn’t helpful for people who wanted to follow along and create their own computer controlled layout. Anyone reading these pages can get hold of a copy of TrainController and use techniques I post here.

So far I’m having a play with the trial version to see what it can do. Sadly it won’t let you drive trains for more than about two minutes before telling you to buy the full version, but I’m looking forward to playing with the layout designer.

Posted by Mike on 08/08 at 04:28 PM
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Tuesday, March 28, 2006

Graham Farish Diesel DCC Fitting

Most Graham Farish diesels sold from the early 2000s use two variations on the same Bachmann chassis. This article shows how to fit a DCC decoder to the chassis fitted to the Co-Co locomotives (in particular a class 50), but the procedure for the Bo-Bo chassis is very similar. I’ll detail any differences as I go.

I’ve done Co-Co conversion on classes 37, 47, 50 and 52 (Western). I expect the same chassis is used for classes 40, 44, 45, 46 (Peaks), 55 (Deltic), 56 and 57. The Bo-Bo chassis I’ve converted are classes 31 and 33 (note that the 31 uses the Bo-Bo chassis, rather than the Co-Co). I would expect that the class 25 also uses the same chassis. The 158 and probably other DMU classes also use the same or similar chassis.

Classes 08, 20 and 66 (and any later models except the ‘peak’ classes 44, 45 and 46) use a very different chassis and are not covered by this article.

See the end of the article for extra notes on particular classes.

The Principles

Graham Farish use what is known as a ‘split chassis’. This means that the chassis is split into two halves, each being kept electrically separate from the other. Power from the pick ups is routed through each chassis half to the motor contacts which directly touch each chassis half. As with any DCC conversion we need to break this power route, in this case by milling away some of each chassis half where the motor contacts it. The motor wires from the decoder can then be soldered to the motor contacts. The track power wires get electrical contact with the chassis by being held under the screws which secure the chassis halves together.

The Conversion

Start by removing the body of the locomotive. This is held on by two clips each side of the bodyshell. The easiest method I have found is to hold the loco upright over something soft and slide a fingernail between the body and chassis on each side at one end. Give a little shake and the clips should come apart. You can then either repeat for the other end or gently pull on the undercarriage (be careful not to pull on the bogies). You also need to remove the undercarraige using the small screw underneath (on the Bo-Bo it just pulls off).

Take a look at the chassis from above. Note the black plastic bogie spacers at each end. These are used at the factory to vary the bogie spacing between models. Take a note of which notch on the chassis they are positioned in. Also note which end has the small dimple, since this also varies the bogie spacing.

Now remove the two screws holding the chassis halves together. The chassis should now just pull apart. Remove the plastic spacers (note the one which is positioned underneath the motor for holding the undercarraige in place) and extract the motor.

Each chassis half can now be milled to remove the part that contacts the motor, as shown in the before and after comparison shown above.

(If you’re unsure about milling, or don’t have the tools, a possible work around I’ve used successfully is to superglue a small piece of plastic on the chassis where it contacts the motor, but note that this may lead to increased pressure being applied to the brushed which could wear out faster).

You now need to solder the orange and grey wires to the terminals on the motor. It doesn’t matter which way round the wires go, but make sure they both head upwards from the motor (note that the motor will fit either way up - which direction is upwards is entirely arbitrary). I like to attach the wires to the motor with the motor out of the chassis and later route the wires between the two chassis sections. Others wire the motor in situ and run the wires outside the chassis. It’s entirely up to you, but I feel that with the outside method the wires have to squeeze uncomfortably between the chassis and the body.

You’re now ready to re-assemble. At this stage some people like to apply some insulating tape inside the milled part of the chassis to prevent any accidental electrical contact with the motor.

Pop the chassis spacers back in place. If using the Co-Co chassis I like to swap the spacers over on one end, so that one screw goes in from each side (this makes attaching the track power wires easier), but on the Bo-Bo chassis the screws will only fit one way around. Lay one half of the chassis on it’s side. You can now position the bogie spacers and lay the bogies in place, taking care to put the drive shaft in the motor and the locating pin from the bogie spacer in the hole in the top of the bogie tower. Don’t forget, also, to put the undercarraige mount back in place on the Co-Co chassis.

Attaching the other chassis half can be somewhat fiddly. Lay in on top in the correct position and you’ll probably find it helpful to slightly push the bogies downwards to help the chassis slip over them, but take care that the bogies don’t slip out from the bogie spacers and motor. If you get problems look from the end to check that the bogie spacers and bogie towers are correctly positioned on the chassis halves. With the Bo-Bo chassis the bogie power pick ups contact the underside of the chassis. Take care that they do not get trapped between the two chassis halves.

Once the two halves are together insert the screw or screws which are accessible from that side before turning the chassis over for the other side. When turning the chassis over try to keep it ‘top-down’. If you hold the chassis ‘bottom-down’ the undercarraige mount will probably fall out and you’ll have to start reassembly again (after finding it).

You’re now ready to attach the track power wires of the decoder. This is done by running them under them under heads of the chassis joining screws such that they are held in place when the screws are tightened (For the Bo-Bo one side needs to be secured on one of the plastic securing piece on the other side of the chassis since you can’t reverse the screws. You’ll find it best to tin the ends of the wires before attaching them (tinning means applying a small amount of solder to the bare wires to keep the bare strands together). To make attaching the wires easier, run them around the screws in the appropriate direction so they’ll be ‘pulled in’ as you tighten the screw.

It’s now time to put the complete chassis on the programming track to check all is okay and program in any required settings (including, of course, the decoder address) and give a quick test run on the layout.

The decoder can now be secured in place on it’s self adhesive mound, the function wires can be removed or wrapped in insulating tape ready for later modification (trim them to different lengths first, so they don’t short) and the wires can be held in place on the top of the chassis.

To provide room for the wires on top of the chassis it’s also necessary to file away a small notch on the inside roof of the body, as shown in the photo.

Reattach the undercarraige and put the body back on (note that it will only fit one way around) and everything’s complete.


Class 158 (and probably the class 170). Before dismantling this model make a note of which way around the bogies are fitted, since they are different at each end. The chassis on this model is very slightly different than described above with two screws holding the undercarraige and two extra plastic lugs inserted between the chassis halves to attach it. It’’s nice to note that these lugs have been redesigned and are less likely to fall out during reassembly. The roof moulding can be removed by inserting a couple of finger nails into the gap between the roof and body and pulling. This will reveal that the body moulding has a solid roof with limited space above the chassis. To create space for the decoder it is necessary to cut a hole in this solid roof. I also recommend cutting the wires as short as is practical since any obstructions in the roofspace will prevent the body from sitting snigly down on the chassis.

See also: Soldering

Posted by Mike on 03/28 at 05:37 PM
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Tuesday, March 21, 2006

Farish Class 66 DCC Fitting

(For fitting instructions for other Bachmann/Graham Farish diesels see here).

At the time of writing the Bachmann/Graham Farish class 66 is unique among N gauge British outline models in being the only one which has a chassis that was designed with DCC in mind. It therefore seems like the ideal candidate to use as the subject of a first DCC conversion. Full instructions for conversion are included with the model, but this article should prove of use to anyone who has yet to purchase or who has lost their instructions.

The body is attached by a clip at each corner. The best way I have found to remove it is to hold the chassis each side of the buffer beam with one hand, gently grip the cab sides with the other and wiggle the body free. Repeat this at the other end.

Remove the small screw at each end of the circuit board and lift it straight upwards. Be careful not to damage the motor power clips underneath the board (see the next photo).

The decoder wires are soldered to the connectors marked 1-8 on the board. Remove the two ‘DC clips’ from the circuit board, then solder the wires in the following sequence:


(Note that the connector numbers are out of sequence on the circuit board and the above listing is from left to right).

Attach a small piece of insulating tape to the top of the chassis under where the connectors will go to prevent any shorts and screw the board back on.

The decoder can now be secured onto a self adhesive pad in the recess to the right of the connectors. Normally the decoder would fit underneath the lighting wires, but I managed to cut the wires a little too short and have fitted it above them, as shown.


Reattach the body and put the loco on the DCC programming track to set the decoder address and any other settings you want to change.

Pop the loco on the main track and off you go. Select function 0 to turn on the directional lighting…
...and at the press of a button…

Posted by Mike on 03/21 at 03:22 PM
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Saturday, March 04, 2006

Debugging feedback blocks

Last time I mentioned I was having problems with the software forgetting which train was in which block.

Closer investigation showed that there was a problem with one particular block. The train would leave the block and the ‘occupied’ light would go out, but shortly afterwards the occupied light would come back on and stay on.

I checked the wiring but there where no faults there, so I ran a test train over it at slow speed. For testing I’d hooked up a loco to a rake of coaches. Normally for block detection you would wire a resistor across a wheelset at the end of a train, otherwise you would just detect the presence of the engine. But I hadn’t got around to installing any resistors on the coaches.

So the block would read empty while the coaches where still occupying it. I didn’t think this would be a problem for some simple testing. However, occasionally one of the wheels on the train was making an electrical connection between the two block segments and the Lenz LB101 block sensor would be detecting the presence of the loco in the briefly linked block. And for some unknown reason it would fail to register the block as empty once the connection was broken. My assumption is that there is a fault in the Lenz LR101 feedback sensor when there is only a momentary signal on the input.

Later I’ll add some extra code to the software to double check the LR101 status when such a spurious signal arrives.

I removed the carriages and testing with one loco now worked flawlessly.

I added a second loco and again all worked fine - the trailing loco successfully stopping at the entry of the previous section whilst it waited for the first loco to exit. But I did notice on a couple of occasions that the LR101s would fail to successfully report that a section was empty. Usually this was corrected when a loco entered or left another section using the same LR101 (the LR101s report back the status of a block of four feedback items at one go).

That was until the lead loco simply refused to enter a section which was shown as being empty.

This afternoon I added a lot of extra code to the software to log the state as it gets updated by locos entering and exiting blocks. I’ve left two locos trailing each other around for over an hour waiting for the problem to recur but, as sods law often dictates, everything ran perfectly.

Posted by Mike on 03/04 at 05:26 PM
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