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Indusi magnets

I decided to add some Indusi magnets to my layout. You may ask, what an Indusi magnet is...  Well it is not so much a magnet, it is resonance transformer that is located next to the rails of most German train tracks. When activated, these units, reduce the magnetism of a corresponding unit on a passing train, and that in turn triggers a signal in the train that can influence the speed of the train.

Typically these placed ahead of, and at main signals. They are also placed near level crossings. There are three frequencies used, and each frequency indicates a different type of speed check.

The first one encountered is usually at the distance signal, a 1000Hz signal tells the train driver that a main signal is being approached. A tone sounds, and the driver must press a button to acknowledge the warning within 4 seconds. If not, the train is slowed.

Then, about 250m before the main signal, a 500Hz Indusi will trigger a speed check of the train to ensure that it has slowed sufficiently in order to stop at the main signal.

The third one, at 2000Hz, is placed at the main signal. If this one is active when a train passes, then the train is stopped automatically.

This is what they look like, and the top is usually painted yellow:

Indusi mage from Wikipedia
Indusi prototype image by WHell  reproduced under CC BY-SA 3.0


Whole train lighting

Seeing an illuminated model passenger train at night is a magical experience. Installing lights makes the trains seem more alive and presents a project within the building and operating of a layout.

model train illuminated at night

There are many, many ways to illuminate passenger coaches. Some methods are more expensive than others, some are easier to install than others and one can find advantages and disadvantages of every approach.

Each approach is a combination of a number of factors:

  • Lighting technology: Incandescent/LED
  • Battery or track power
    • One, or multiple, power pickup shoes for the train
    • Full rectification of half wave rectification
    • Approach used for anti-flicker
  • Permanently coupled rakes or current conducting couplers
  • Off-the-shelf solution or DIY
  • etc
I have about 40 passenger cars that I wish to illuminate. 
  • Unless one is aiming for a classic toy era style, LED lighting is clearly a no-brainer.
  • The high costs of current conducting couplers rules them out for me
  • Multiple pickup shoes create too much drag on long trains (and they are not cheap either)
I decided to use the following approach for my first train:
  1. LED utilizing cheap 12V LED strips.
  2. Track power to be used
  3. Single power pickup shoe per train
  4. Permanently wired conductors run the length of the train
  5. Full rectification of digital track  power
  6. Capacitor for anti-flicker
  7. Inrush current limiting
  8. DC-DC converter used to set brightness
  9. Twin wires run along the length of the train to each coach
The approach is very economical but of course the biggest problem with a whole train permanently wired together is how to service an entire train, getting it on and off the layout can be tricky. I have solved that problem with a whole train cradle (which will be the subject of another post).

Steps to install whole train lighting

I have now completed an entire train and I report the steps I used to add the lighting.

The circuit I used is described in a lot of detail in the page Modelling with LEDs, particularly in the section on lighting passenger cars.

The train I happened to pick turned out to be rather tricky because the design of the Märklin coaches does not make installation of any type of lighting very easy. The metal weight in the floor of the coaches is used to hold the close coupler guide mechanisms in place, as well as transmit current to the next coupler. The chassis, weight, both couplers, seats and body of the coaches all have to be assembled in a single step and it is rather tricky to get all six components to be properly aligned at the same time, and that is before we start adding wires and lights. Things did get a bit better once I had completed a few though.

The train I selected was made of the more modern models of the Donnerbüchsen such as item 4313, 4314 with goods wagon 4315.

The logical place to start is in the goods wagon as it has space for the rectifier and capacitor. The goods wagon already had some tail lights and a pickup shoe. I used a 2200uF capacitor and added an inrush resistor (1K Ohm), and a 1N4001 diode in parallel to the resistor.

To that I connected a DROK DC-DC converter that powers the strips in the train and the tail lights. I placed it opposite one of the sliding doors such that I can easily access the voltage adjustment screw through the door.  I added an additional resistor to the tail light circuit to reduce their brightness.

Since I was not going to use current conducting couplers, I needed to find where I could pass the wires into each coach. After checking the limits of the coupler mechanism movement, I decided to drill small holes next to the brake pads. For the passenger coaches the holes had to be drilled at a slight angle so that the hole comes up through the end seat.

Once the 4 holes were drilled I opened the coach up and removed all drilling remnants.

Initially I ran the wires out of one coach and ran them parallel to each other into the next like this:

I soon found however that the wires can hang too low so I realised I needed to run them up and over the coupling like this:

I then decided that since I was permanently coupling the train together, I may as well use permanent couplers. Having just recently got a 3D printer working, I designed and printed some couplers and replaced each pair of close couplers with my ones.

(At the time I did not have any black resin so I used clear resin instead.) You can now order the couplers (in black) online at

I was using 30 AWG wires that are very flexible but were rather thicker than they need be. Here you can see how the wires have to come up through the end seats.

I glued in some cheap, seated passengers, and simply soldered the wires onto 10cm of strip.The brass weight held the strip while I soldered onto it.

Since both wires are black and I had to keep track of which was positive, I ensured that I always stripped the end of the positive lead. Only once it was soldered to the positive side of the next LED strip did I strip the negative wire.

On the underside of the roof of each coach is a sprue from the manufacturing process which I cut off so that the LED strip could be mounted through the middle of the car.

Since the peel off backing of the LED strips are completely unreliable, I attached the LED strips to the rooves using 3M VHB double sided tape. The columns used for fastening the shell onto the chassis are less than 10cm apart so the LED strips had to be placed diagonally.

Once the whole train was done and placed back on the layout, I was able to set the brightness of the lights using the adjuster on the DC-DC converter.

The capacitor keeps the train illuminated for a couple of seconds after losing power. It is certainly adequate for momentary power interruptions. The DC-DC converter keeps them at a constant brightness. I will also try a train that uses a resistor instead of the DC-DC converter to see if a slow dimming is preferable.


Modelling with LEDs

Modern modeling uses Light Emitting Diodes (LEDs) extensively. This is because they offer numerous advantages over older technology, such as incandescent 💡 light bulbs:

  • They are small
  • They are cheap
  • They are long lasting
  • They use very little current
  • They do not get hot
  • They are available in many colors (including 'warm' and 'cool' white)
Unless you are trying to reproduce models as they were in days gone by, you are going to be using LEDs on your models. They are not difficult to use but one does need to learn a few simple rules to use them.

The aim of this page is to explain the theoretical side of what is needed to power LEDs, how to connect them and even how to produce good results in moving model trains. I will be starting off with some very fundamental principles and building up to powering LED strips from digital power. The actual installation of lights inside models is not covered here, this is about what has to be installed.

LED packages

LEDs come in a variety of different forms and sizes (called packages in the electronics industry).


Typically round 2mm, 3mm, 4mm or 5mm. Rectangular and other shapes are also available.

3mm & 5MM LEDs
3mm & 5mm LEDs

 Surface mount (SMT)

These are even smaller than the through-hole packages and are usually soldered directly to circuit boards by machines. One can now also buy them with tiny wires already attached and these are ideal for model building.

The different sizes are expressed using a 4 digit code that is made up from the length and width of the LED in tenths of a millimeter. For example a 2835 is 2.8 mm by 3.5mm. 5050 is 5mm x 5mm. Note however for that some LED sizes are expressed in thousandths of an inch instead, so a 0402 SMD LED is is 1mm x 0.5mm. It is so small, it represents an object 87mm x 43mm in HO scale! - smaller than a lightbulb.

0402 LED
An 0402 SMT LED with wires.


White LEDs are also commonly found in long, flexible strips up to 5m (16') long. These are made using surface mount LEDs. They are pre wired and ready for use with 12V (sometimes 24V). One can cut them to small lengths, typically 5cm long. These are ideal for passenger car and station lighting. They often use 5050 or 3528 sized LEDs. They are available in various colors, including warm, and cool white.

LED strip

These strips come with a crummy adhesive backing that will not stick for long, and so should be ignored. They need to be attached with a quality double sided tape such as 3M VHB tape.

Multicolor neopixel etc.

There are components that comprise 3 (R,G, B) or 4 (RGB+W) LEDs which allows the color of individual LEDs in a string to be digitally controlled independently. These fall out of scope of these fundamental concepts.

Electricity fundamentals

In order to understand how to connect LEDs up we do need some very fundamental understanding of electricity. Specifically we need to know a little bit about voltage, current and resistance. It may aid the understanding of these concepts by thinking of electricity rather like water in a pipe. For this analogy:

  • Voltage (V) - think of the Voltage as the pressure/speed of the water in the pipe. Measured in Volts
  • Current (I) - think of the Amperage as the diameter of the pipe. Measured in Amperes (Amps, A or mA. 1A = 1000mA) 
  • Resistance (R) - think of resistance as obstructions to the flow of water in the pipe, such as blockages or mesh grates that slow the water down. Measured in Ohms (Ω)

These three things have a simple relationship between them: V = I x R (Ohm's Law) and this formula is used to calculate things in all circuits, but fear not, most of the calculations have all been done already.

Just like a pipe, where water can travel in both directions, so can electricity flow in either direction along a wire. If the pressure is higher at one end, water will flow to the other end. If the voltage is higher at one end of a wire, electricity will flow to the other end of the wire, so long as it can get out.

Like pipes, larger amounts of current (Amperes) need thicker wires.

Series and parallel

We will talk about connecting things in parallel or series, let's just make certain the difference is clear.

Series connection of two lights
Series connection


Backdrops added behind storage area

My storage expansion is progressing with the upper layer now in place. Upper layer tracks have not  yet been laid (other than some temporary testing) but I have now added the backdrops.

Some years ago I bought some BUSCH backdrops on eBay cheaply. When I decided to add the expansion I realized I could use some of the backdrops to add some depth to the area which is visible from the main station.

At one end I needed to transition from the Faller Obersdorf backdrop, and also pass in front of the electrical breaker box for the house. I had kept the unused piece so it was a no brainer to simply continue with the same product. I glued it directly to the breaker box. I have also constructed a small piece that can be removed in order to open the door of the breaker box. Here you can see the door half open:

The door closed and the removable section in place:

Beyond the breaker box, I have mounted all the backdrops on 1/4" plywood. Some of these pieces needed to be bent into curves so I scored the back with a circular saw. I then attached doubled sided tape to hold them to the concrete wall (previously painted blue).

Onto this curved plywood, I attached BUSCH item 2871 which depicts some distant snow covered mountains.

When I unrolled the next backdrop, I found to my surprise that the content did not match the box (BUSCH 2873), and in fact suited my needs much better - it was in fact BUSCH item 2874 depicting a factory and some multistory urban buildings which would be more suitable for a railyard than the bucolic countryside depicted on the box.

The views from the main station look promising

An overview of the area...

Earlier phases


Märklin 2271 turnout shorted by loco slider

I was running a train one some newly laid track when the layout got shorted out. I have a 3A fast blow fuse protecting the booster and the fuse blew.

Close inspection showed that when the loco moved slowly, (along the straight part,) its pickup shoe would bridge the outer rail, and get the leading edge onto the studs on the far side, and then the rear end would drop down and land on the crossing running rail. This of course created a solid short circuit. Nasty.


Tip when drilling near tracks

I try to avoid getting wood shavings into turnout mechanisms (and tracks in general). Today I had to drill some holes for additional wires and I came up with a simple technique for minimizing the mess produced when drilling holes near tracks.  I got a sheet of transparent plastic and made a hole in it which I then laid over the layout with the hole in the plastic where I needed to drill. While holding the plastic in place I was able to drill the hole with the other hand.


Track laying in lower section of expansion complete

I have now completed the track laying in the lower section of the layout expansion.

The lower hidden area has 9 storage tracks.

  • 7 of the tracks can handle trains 184cm long
  • 1 can handle a train of 201cm
  • 1 can handle two trains of  330cm, and 322cm, or one that is 6.52m long.

(The purpose of expansion area was to store shortish trains, as I have 8 long storage tracks in my existing hidden station.)

Once the trains have passed through the fiddle yard (or bypassed it) they climb at 2% up towards the turning loop area:

Two tracks come out of the lower level, and on the way to the turning loop they run parallel to the two tracks that will go to the upper section. This area will have scenery, and I have mounted the plywood for the backdrop.

All four tracks then come together to pass behind our water heater where they travel along a curved section with safety barriers.

The turning loop, can hold two trains (261cm and 251cm) or a single 5.12m train The practical limit for trains running through the extension is therefore 5.12m.

The turning loop area is horizontal so I added a bit of a valley and bridge to add some interest:

The rear track against the wall will be covered by a mountain so that one does not see a train track doing a 180° turn. The rear track will be accessible from below via the holes in the plywood.

A backdrop is also planned to go behind the mountain and wrap around to hide part of the water heater.

Technical stuff

  • For the fiddle yard I decided to use a 13.5 cm stopping area before the turnouts in each track.
  • I also decided to use 3 sensors per track (instead of 4), one at each end and one exactly in the middle. This allows the middle sensor to be used as the slow down section in both directions. This approach will save the expense of 18 sensors for the project.
  • The new area provides a lot more flexibility in routing trains, so I decided to implement the ability to dispatch trains to a destination, rather than only along specific routes. I can now define an event on the screen that will dispatch any train in a track to a specific destination with a single click. Clicking on any track with a train also lets one pick any destination, or activate specific routes.
  • The long tracks that go towards the turning loop do not allow stopping in the direction of the loop. This ensures that a train already booked into, or already in, the loop cannot get trapped there by trains on the incoming tracks. Stopping is permitted on the way out towards the fiddle yard or on the long tracks.
  • 24 turnouts have been laid, turnout switches installed, and connected to k83 type modules.
  • 44 sensors have been made by isolating sections of track, and connected to s88 type modules, usually via a 36' long Cat-5 cable holding 8 wires, about 200' of cable. (I used cable my dear wife picked up at the dump!)
  • About 436 electrical connections made!
  • The layout now has about 271m of track!

Here is the schematic on my control screen of the lower section and the turning loop. The upper fiddle yard (still to be built) is on the left.

Earlier report:
Backdrops done: