Bookshop

At the other end of the row of Vollmer houses that has the Butcher shop at one end, there is a bookshop (bookstore, Buchhandel). I designed some interior furniture to take advantage of the large windows.

The building is a mirror of the butcher shop so I was able to reuse the parts I had designed to even out the interior walls with the window frame, etc.

I designed a desk with cash register

and some bookcases filled with books of random sizes.

I spent some time painting the books!

I embedded four white LEDs in the ceiling to provide good lighting in the shop.

and added some lights for the rooms above too...

Using LEDs in buildings

LEDs are now the standard method of adding lights all over the layout, including buildings.

They are small, cheap, and don't get hot, making them ideal in modelling. There are a few things to consider when using them within a building. Here is my list of items to keep in mind:

1. Make sure the light cannot leak out through joints in the building or even directly through the walls or roof. Nothing looks more unrealistic than a glowing house. You may have to add a paper mask inside, or between the light and the roof and walls. Test in a dark room.
2. Don't make the light too bright. Modern LEDs can be very bright. LEDs are usually run at about 20mA and this may be way too bright for a building. You may want to design your electrical circuits so that the LEDs run between 5mA and 12mA.
   
   I usually recommend a 12V DC bus to power all your lighting. This lets you power up to four white LEDs in series in each circuit at around 10mA with the following resistor values:
   
   1 LED, use a 1000 Ohm resistor
   2 LEDs, use a 680 Ohm resistor
   3 LEDs, use a 390 Ohm resistor
   4 LEDs, use a 120 Ohm resistor
   See this page for all the details on the electrical side of things.
   
   One can also place a pulse width dimmer on the 12V bus so that you can dim all the lights at once, but it will act on all of them which is not very useful. If you want to vary the brightness one can also control the maximum brightness of individual LEDs by running them from a RemoteSign ESP at 3.3V and a 120 Ohm resistor. Once the building is complete, you can then experiment with the brightness to determine the best value.
3. Place the light where it would normally be inside the building. Typically, lights are placed overhead in each room, so placing them on the underside of the ceiling is a much better choice than placing it on the floor. When the lights are placed high up, the light coming out of the windows falls down to the ground in a natural way and adds much more realism.
   
   
   
4. Pay some attention to the color of the light. Use cool white LEDs for rooms that would likely be lit using fluorescent lighting. Use warm white for spaces that are likely lit using incandescent lighting, but be aware that many LEDs sold as 'warm white' are more like yellow. I sometimes add a bit of yellow acrylic paint to a cool white LED to give it a warmer color.
5. Take care with lighting effects. These days there are numerous products that will create special lighting effects such as the flickering start of a fluorescent light, welding, fades, etc. (For example RemoteSign ESP). If you are using startup sequences, take care not to connect all the lights in the building to the same output that creates the effect. I once saw a video of a train station where the lights of every platform all flickered into life in perfect unison, which spoiled the whole effect of having some lights flicker on startup.
6. Some lights are on all the time. Don't feel it is necessary to be able to switch every light on and off, or have them going on and off at random times. Places such as station platforms are typically lit from dusk to dawn, so a single switched circuit can handle all those lights together. Other spaces such as station buildings and offices are lit all day, so those can all be powered by a circuit that does not have independent switching. Lighting that is not too bright can also be unnoticeable during the day, and can simpley be left on all the time. See farm lighting experiment.
7. Not all rooms are lit at the same time. Depending on the type of building, you may want to mask some windows off to simulate rooms that have their lights off. Consider which windows would be part of a single room though, you don't want to make it look like each room only has one window.
8. If the windows of your building are clear, illuminating the room will enable the interior to be seen. This then suggests you should also add appropriate interior details.
   
   
   
   If you don't want to add interior details, then consider adding curtains or some window decoration so that the light shines through, but we can't see in.
   
   
   
   
   
   
9. Think of where the wires will run. You don't want thick wires to create shadows or large visible 'pipes' if one can see through the windows. Wires can be collected into small tubes (E.g. a straw) or carefully glued into a corner of the room. You can now buy the small surface mount LEDs already soldered onto 'Litzen' wires which are thin as hair.
10. It is best to include the LEDs when you build the kit. Access is better, and one can drill holes for wiring, add masks, etc.

Changing Intellibox firmware

The Uhlenbrock Intellibox is a groundbreaking device that came out in the 1990s. Not only does it support three different track protocols (Motorola, DCC, Selectrix) at the same time, it also supports LocoNet and the IC2 bus, s88 sensor input and Märklin boosters. It provided two speed controllers too.

It was also upgradable, so when Uhlenbrock made improvements we could load updated firmware.

When I got my Intellibox it had version 1.203 installed. I found it incredibly stable and bug free. I read about updates over the years but never felt compelled to make any changes, since all the updates did not affect how I used my Intellibox. 

Recently I managed to short my Intellibox and I substituted another one I had obtained a few years ago in case of such a situation. This second device was running version 1.55 which is the latest version that was available for free. I was having some problems and I was not sure if the problems I was seeing were due to the newer version. I therefore decided to see if I could downgrade it to 1.203 to answer that question.

I had saved some of the update programs over the years but have never used any of them. The older update programs required us to create a bootable floppy disk, which would start the computer up in DOS, precluding anything else from running in the background. This is because the firmware update could not be interrupted in any way or the update would fail. I found one old PC with a floppy drive, but it does not have a serial port, so I could not use that to load the firmware.

Later, Uhlenbrock also released a CD image that could be burned onto a bootable CD. This CD created a RAM drive and copied the 1.55 update file into the RAM drive. This ensures that the program could read the file without any interruptions. 

I tried to modify the ISO image file to add the older firmware files and I made numerous CDs but the files copied to RAM only included the 1_55.IB file, never the additional files I was trying to add. Once booted, I was also not able to switch to another CD to access and copy additional files. So I eventually gave up trying to make a bootable CD.

I had also downloaded a more up to date Windows program from the Uhlenbrock site that is used to update to version 2.0 called IBUpgrade. I installed that and selected the 1_203.IB firmware file but it declared that to be an invalid file.

I wrote to Uhlenbrock asking if they could perhaps create a CD image with all the free versions so we could select the firmware version. After numerous mails they directed me to use their windows update program at https://uhlenbrock.de/de_DE/service/download/software/I0011930-001.htm and they also sent the firmware files I was interested in.

Of course I said I had already tried that and at that stage they said, I am using IBUpgrade and I should be using IBUpdate. See the difference?   They have two programs that look identical, and only differ from each other in names that are synonyms of each other! Update vs. Upgrade.

So, I uninstalled IBUpgrade and downloaded and installed IBUpdate. I was able to select the 1_203.IB firmware file and start the process.

Finally I could load different firmware versions and test to see if the older version made any difference.

It did not make any difference. As soon as I connect a Märklin booster and switch track power on, the s88 bus gets filled with garbage data. You can read about that saga here.

An electrical disaster (A geek tragedy)

This is how I managed to destroy an Intellibox (IB) and two boosters at once. Well OK, it is still somewhat of a mystery, but here is the story...

I have 4 power districts on my layout, powered by my Intellibox and three boosters.

Everything shares a common ground, including other small devices around the layout that run on 16VAC or 5VDC or 12VDC. I run using mixed Motorola and DCC protocols.

One of those devices is a turntable which takes 16VAC and rectifies that to drive the motor using DC. There are six contacts that go to the turntable:

• Track center rail
• Track running rail #1
• Track running rail #2
• Motor positive
• Motor negative
• Solenoid

The track connections are digital, i.e. a square wave AC signal.

The turntable motor connections are all about 20V DC 

I was trying to resolve a contact problem and I was measuring the voltages on the contacts shown above and I may have measured the voltage between the turntable power contacts and one of the rail contacts. A voltmeter should not be able to conduct much current between its probes.

The next thing I noticed was that the IB screen was dark. It had blown the 3A fuse on its power supply line. I replaced the fuse. The Intellibox complained of a short and then presence of an external voltage. After that it would no longer power on. I attempted a repair of the Intellibox.

After placing another Intellibox (running version 1.55) in service, I found that the sensor bus was reporting nonsense, and the last booster in the chain of boosters was making trains in its section move, and lights flicker. I traced the problem to the first and second Märklin 6015 boosters! Once I removed them, trains in the last power district worked normally and there were no spurious sensor reports.

I obtained a used Märklin 6017 booster and tried that, and I got the same result. No matter which of the three Märklin boosters I connect, I get s88 interference and trains start running even when the IB is in STOP mode. It is as if they are putting analog current out.

I have an old Modellbahn Ott 100W booster and I connected that in the same place as the Märklin boosters and it does not exhibit any problems.

Update 2024-01-05

I obtained another Märklin booster - a 6015.

This one does not send bad output to the tracks, but when rail power is on, I get the junk s88 readings. This is now making me suspect that there is something wrong with the s88 bus of the Intellibox. Track output seems to be leaking into the s88bus, but only in the presence of a Märklin booster. I will be retesting to see if I can locate a defective s88 module, however I believe this is not the case because with the Ott and Power 3 boosters, they all work fine.

Special Option 901 = 3. This controls the asymmetry of the digital signal, and a value of 3 is recommended when using 6015 and 6017 boosters.

Here is a summary of the behavior of each of the 6 boosters I have:

A = Märklin 6015

B = Märklin 6015

C = Power 3

D = Modellbahn Ott 100W booster

E = Märklin 6017

F = Märklin 6015

IB 1.203   IB -> A -> B -> C. Everything was OK

IB 1.55   IB -> A -> B -> C. STOP: flickering and trains moving  GO: s88 garbage

IB 1.55   IB -> A.  STOP: flickering and trains moving  GO: s88 garbage

IB 1.55   IB -> B.  STOP: flickering and trains moving  GO: s88 garbage

IB 1.55   IB -> C.  All OK

IB 1.55   IB -> D.  All OK (See update 2024-01-11)

IB 1.55   IB -> D -> C.   All OK (See update 2024-01-11)

IB 1.55   IB -> E. STOP: flickering and trains moving  GO: s88 garbage

IB 1.55   IB -> F.  STOP: OK  GO: s88 garbage

Update 2024-01-06

Sometimes, when one of the Märklin boosters is connected, I can select a loco address if the track power is off. If the track power is on, then an attempt to select any loco is met with the message "Error" in the loco address area. 

(Note the irony in that the error message has German style hyphenation on an English word! I noticed this error is not in the IB control though.)

I wrote to Uhlenbrock support and described this problem and they replied saying this error occurs if the Loconet is corrupted and that the Intellibox is in need of repair. (See below on an update on this.)

Update 2024-01-11

We have found that if we disconnect the connection (red) to the rails, from a Märklin 6015 booster the corruption of the s88 bus stops, and returns as soon as it is connected again.

My son and I spent a day disconnecting everything from the red feed in one of the power districts (all trains and K83 / k84 modules) and it makes no difference. To me this now suggests that there is electromagnetic interference occurring between the bundles of s88 sensor wires and the track power lines. The s88 bundles are all shielded cables and have never given any problems in 20 years.

We also found that if we waited long enough, the Modellbahn Ott booster does indeed also precipitate false s88 changes, but way fewer than with the working 6015 booster we have.

If we connect the Power 3 Booster to any of the 4 power districts, no corruption of the s88 bus occurs.

I now believe that the IB is not defective in terms of a bad s88 bus port or booster output. I also think the corruption of the Loconet is because the IB gets overwhelmed by the number of s88 changes. This explains why the loconet goes haywire when track power is on, as that is when the false s88 messages come flooding in.

So despite the IB working perfectly with Märklin boosters for decades, a 6015 no longer works with this IB. The only difference I know of is that this IB is running a newer version of the firmware (1.55). If version 1.55 really did not work with Märklin boosters I am sure that this would be a well known problem though.

Uhlenbrock now maintain that the Märklin boosters do not work well with DCC signals. This is strange because they have worked fine in the past and there is a special option (901) which specifically adjusts the symmetry of the digital signal to support them. Uhlenbrock recommend using Power 3, Power 4 or Power 40 boosters instead.

The difference in behavior of my original 6015 boosters (A & B) plus the 6017 (E) I bought on eBay compared to the 6015 (F) I bought on eBay, make me believe that both my original boosters died and the 6017 I bought, also suffered a similar fate before. That booster (E) has now been returned.

I am now looking for Power 3, Power 4 or Power 40 boosters.

I am also going to test with sending only motorola packets to rule out DCC as being the issue, and I am also going to get an old computer going that will allow me to load an older firmware version to see if that resolves the problem.

Update 2024-01-14 

I got rid of all DCC signals by setting the following special options:

SO 6 = 1

SO 12 = 0

SO 22 = 6

SO 25 = 2

SO 901= 1

SO 904 = 28

SO 907 = 1

SO 909 = 198

SO 931 = 1

As expected, the Märklin booster still causes corruption on the s88 bus.

Update 2024-01-28

I managed to downgrade the firmware of the IB to 1.203 - which is what my original IB was running.

It behaves the same. So it is not the firmware version.

I have some second hand Power 3 boosters on their way from Germany. I hope they resolve the problem.

Resolution

After replacing the Märklin boosters with Uhlenbrock Power 3 boosters and adding a fourth booster instead of using the IB output, everything is working again.  The nature of the failure is still a mystery.

Upgrading the Märklin 7286 turntable

My Märklin 7286 turntable was not moving so it was long overdue for a service. While I did that, I also decided to do some upgrades to make it work better than before.

I describe here how I carried out the following upgrades:

• Improved rotation
• Improved electrical contacts
• Added lighting to the control shed
• Added control desk direction indicators
• Added an operator in the control shed

Improved rotation

The turntable was designed to work with analog layouts. Track power is provided to the running rails and the center rail from below, and there are contacts at both ends of the bridge to transfer this power to the current spoke track. This allows one to only power the spoke track one is using, allowing locomotives to be left on other tracks unpowered. On a digital layout, all the tracks can be powered all the time, making all these contacts superfluous. Not only do these contacts add resistance to the rotational movement, they also make clicking noises and they even cause short circuits between the center rail contact  and the running rails of the spokes. I had previous defeated the connectors around the edge of the turntable by jamming them in. I decided it was time to take it a step further..

The center rail on the turntable has two metal plates that lie between the running rails. I cut the ends off both with hacksaw, filed them smooth and painted the ends black.

On the underside of the bridge, at the end of each rail was a small contact. I cut all four off with some small side cutters:

This results in a much smoother and quieter rotation.

Electrical contacts

The turntable bridge pivots about on a central support ("Königsstuhl") which has some concentric contacts. These contacts needed cleaning so I rubbed them with a very fine sandpaper and also cleaned them with some contact spray applied with a cloth.

I also cleaned the finger contacts on the underside of the bridge that ride along on the contacts:

Despite good contact on the supporting side, I could not get one of the running rail contacts to work, despite bending the finger downwards to apply more pressure, so I gave up and soldered a wire between the two rails.

Control shed

It always annoyed me that there was no light in the control room, so it was time to fix that. The shed unclips from the bridge providing good access to the interior. The glass windows are made from a single translucent piece that has a small dimple in the ceiling, a perfect size for adding a surface mount LED.

First I looked closely at the LED with a magnifier to determine which wire was connected to the end with a small dot. This is the side that has to be connected to negative. I tied a small knot in the other end of that wire.

I taped the LED into the top and ran the fine wires to the the corner of the building .

I then inserted the glass into the shed, keeping the wires between the glass and the outer frame at the corner so they cannot be seen.

There is enough room in the hole that the building clips into, to pass the two wires through to the underside of the bridge without having to drill a hole.

I decided to power the light using the power from the track as I did not want it only going on when the turntable was moving. Since the track contains the digital signal, it is AC and thus needs a diode to only allow the current to flow in one direction, plus the usual protection resistor.

The rails provide one side of the power source for the light, so I needed to get power from the center rail. I soldered a wire onto the small contact that conducts the center rail current to the parts between the tracks:

I drilled a small hole next to where the contact sits:

and threaded the wire though and soldered it to a 1N4001 diode.

The other wire was soldered to a 2K Ohm resistor soldered to one of the running rail contacts.

A quick test showed the light worked well.

Control desk direction indicators

I thought it would be nice to put red and green LEDs into the control desk so that when the bridge moved one way, a green light would go on, and the red LED would indicate the other direction.

I drilled a very small hole in the middle of the control desk.

I then connected the two LEDs in antiparallel. (I did not have a green SMD LED so I used a red SMD and a much bigger green one)

This illuminates the red LED when the current flows in one direction, and the green LED when the polarity is reversed. These were then inserted into the hole on the underside and one side was soldered onto a 2K Ohm resistor.

The pair of LEDs then had to be connected to the motor terminals, so that red will indicate one direction and green the other. One motor terminal is easy to connect to, but the other required a contact to be temporarily removed to solder a wire on.

It works:

however, the control room light is too bright for them to show up well. I need to increase the size of the resistor on the room light.

Operator in the control shed

I found a person that looked suitable and glued him in front of the control desk.

MDOS

 A blast from the past....

I came across some old archived files from April 1992 which included a copy of my program for controlling trains with a Märklin 6050 interface. The program was started in 1988 and demonstrated publicly in 1989 at the University of Natal Winterfest.

The executable file is just 43K in size!

Here is the description file:

In my spare time I over the last five years, I have been working on a Turbo Pascal program for the Märklin digital system.

I have used earlier versions to demonstrate the Marklin digital system at the ComputerFest held at the University of Natal in Durban, South Africa in 1989 and also at a modelling exhibition in Durban in 1990.

I have uploaded the file MDOS.ZIP containing my program in its present form as well as MDOS.DOC which is a brief description in ASCII format. MDOS.DOC is also contained in the MDOS.ZIP file.

System requirements are minimal. No graphics card is required. Colour is nice but not required. An 8088 is adequate.

Future plans include complete automatic control, full crane and turntable support, digital sound output, graphics layout diagrams that can be built up from tiles, wagon lists that enable automatic train lengths and speed limits etc. Given sufficient incentive, I may contemplate other digital systems as well.

Although I live in Germany my mother tongue is English but I invite comments in either German or English.

D M Schultz

Here is the content of the MDOS.DOC file:

Brief description of MDOS (Maerklin Digital Operating System)

The program is a test version only and is NOT FINISHED. I invite feedback and suggestions as to possible methods of distribution. Shareware ?

MDOS is a control program for the Maerklin Digital Interface. The following can be controlled independently:

     80 locomotive addresses

     256 electro-magnetic devices

     496 switches can be monitored.

It should run on any PC compatible machine and is written in Turbo Pascal 5.

The program detects the type of display adaptor and sets its colours accordingly. The colours are fixed at present.

Locomotives run at SCALE speeds. E.g. 120 km/h not 'level 9'

Any number of the locomotives an be linked together allowing multiple heading. A circular linkage is not possible.

Each locomotive accelerates properly according to its power, mass of the train and in addition the acceleration will not exceed that which would be possible given its axle loading and number of axles applying tractive force. i.e. maximum tractive effort, before wheel slippage occurs. Train mass is divided evenly between all locos pulling that train.

Forward and reverse speed limits can be set for each loco.

At present the layout diagram is very rudimentary and is made from ASCII files. The layout diagram can be scrolled. Up to 10 magnetic devices can be allocated to any key. Eg. key G can set 10 of the 256 possible devices.

Redundant command are not sent. The program hooks for automatic travel have been built into the program but are not yet implemented.

During normal use of the program, the program is never in a wait state. i.e. all accelerations are being monitored and the respective commands are being sent out.

The interval between the reading of all switches via s88 modules can be specified.

Any s88 module can be tested. A schematic view of an s88 module is presented and can be read, decoded and displayed at 28Hz on a 386/25.

The setting of every locomotive can be resent at a specific time interval or on demand by pressing f9. This is useful if a loco did not receive a command due to a bad contact or was not on the rails at the time.

At program start up, all locomotive addresses are set to stop.

The special function if the 6080 decoder can be switched on and off independently of loco speed.

Additional functions have been temporarily programmed as follows:

   function 1     key f5
   function 2     key f2
   all off        key f6
   function 1 & 2 key f7

this is for the testing of a digital crane. f7 thus allows the boom to be raised and swung simultaneously.

At present, a loco cannot be deleted from a file.

Decoder DIP switch settings are shown when you set the decoder address.

USING MDOS

MDOS looks for a configuration file called MaeRKLIN.CFG. If this file is not in the current directory, you will be prompted for configuration information.

Once the program is running you are presented with one or more odometer scales.

f1 gives help on the key commands available. ESC pauses the system and pops up a menu that will allow you to alter the configuration, loco information, test an s88 decoder, alter points settings etc. If you have more than five locos defined, use PgUp & PgDn to move through screens of five locos at a time.

IMPORTANT

If you do not have a Maerklin Digital Interface connected, set the Serial port to Zero (0). This will allow the program to run but all commands will be sent to the NUL device. You cannot test an s88 module if the port is set to zero. You also cannot specify the number of s88 modules that you have unless you have a valid port number.

If the .LAY file cannot be found, MDOS will create one from the. .ASC file which must be an ASCII file. If you want to change the  .LAY file, edit the .ASC file and delete (or rename) the .LAY file.

Locomotives can be chained together by specifying the loco number (not the decoder address) of the next loco to be controlled, in the loco configuration screen. Eg if loco 1 is linked to loco 3, all commands issued for loco 1 will be repeated for loco 3.

For correct Double-heading, the locos should be correctly calibrated.

Automatic calibration can be carried out by selecting B from the 'Change loco info' menu option. This ensures that correct scale speeds are achieved. Calibration is carried out by sending the loco in question up and down past two track switches having a known distance from each other and measuring the time delay between the two switches. This is then converted to the correct scale speed and is saved to disk along with the rest of the information for the loco. For automatic calibration one naturally needs an s88 encoder. Calibration speeds can also be entered manually via the loco configuration screen.

The file MDOSDEMO.LOK defines 8 locos of varying type, mass and power.

Locos 6, 7, 8 & 3 are linked. When controlling linked locos, the maximum speed for the set will be the speed limit of the slowest.

You will notice that the acceleration for the different locos will be in accordance with their axle weight and mass of the entire train.

If you find the start up screen too time consuming, press any key.

This version of MDOS allows the selection of either English or German (in the configuration menu). All keystrokes are however still language independent.

DISCLAIMER

D M Schultz does not accept ANY responsibility for incorrect operation of the MDOS files or any equipment damage that may arise from using the program.

D M Schultz

If you have an old PC that runs DOS, you can download the program.

Repairing the output stage of the Intellibox

After 23 years of use, I managed to burn out my Intellibox!

I think it happened when I was measuring the voltages of my turntable and I must have touched the track center rail contact with one of the probes. The 3A quick blow fuse on the power supply line to the Intellibox blew. I replaced that and then the Intellibox (IB) complained about a short. I disconnected things and tried a few times and then it said "Attention Extern. voltage".

I disconnected everything from the IB and all it would display was the same error.

This is how I went about repairing it. Though unsuccessful, the method of doing the work may be useful to others.

I recalled online discussions from years back that one had to drill out the plugs on the underside in order to open the IB case. I did so (but used a drill bit somewhat oversized) and opened it up. Nothing  could be seen to be destroyed, but the obvious candidates are the two power output transistors. These were BD535 and BD536.

I could not find replacements online and I asked in the IBX online forum for suggestions and also emailed Uhlenbrock support. As usual, J.J. McVeigh was extremely helpful and said that he had successfully replaced the transistors with NTE152 and NTE153, and that their 4 Amp rating would not be a problem since the IB output is limited to 3A. I ordered some online and started removing the old transistors. Uhlenbrock replied that they replace these with BD911 and BD912 (Also not readily available in the USA.)

This comprises cutting their legs off and unscrewing them from the heat sink:

and pulling the pins out the underside while melting the solder from the top:

To get the solder out of the holes I used some flux paste and some copper solder wick

I then cleaned up the flux with some alcohol.

One of the transistors tested to be bad, so I was confident I was replacing the correct items.

The new components arrived:

and it was pretty easy to solder install them. After careful cleaning, I used the existing insulation pads, screwed the new transistors in place and then soldered the legs in. The effect of the heat sink meant that the middle legs called for a 700°F soldering iron.

I reassembled all the parts and tried it out, and sadly I still get the same error. Something else in addition to the power outputs appears to be damaged. I may need to ship the IB back to Germany for repair at Uhlenbrock.

How the Märklin turntable (7286) works and how to control it digitally

I needed to understand the internal working of my turntable so that I could optimize its digital operation. I have documented what I found below.

The Märklin turntable (7286) is a rebadged Fleischmann product and adapted for 3-rail running. It is a very nice prototypical looking turntable and has 48 possible track positions at 7.5° intervals.

It can be controlled manually on an analog layout and digital control is also possible, but not out of the box. (More on that later.)

Both ends of the turntable bridge have contacts that make connections with tracks around the edge. This allows transfer of power from the turntable to spoke tracks, ideal for analog layouts, but it can cause a problem with digital layouts due to contacts shorting to the always powered tracks as it turns.

To remove the bridge, unscrew the screw between the rails in the middle. Lift up the screw and a contact clip and the two metal plates that make up the center rail.

Two edge slots, three slots apart, have to be removed from around the perimeter in order to lift the small end of the bridge out. 

The bridge sits atop a set of six concentric contact rings. Below the turntable they are connected via a ribbon cable to a small interface board. Some of the connections are bridged with capacitors on the underside.

The contacts are as follows:

Contact ring	Label on Interface board	Function
1 (center)	B	Center rail of bridge
2	2	Motor - positive for clockwise movement
3	3	Motor - negative for clockwise movement
4	1	Relay - negative to turn it on
5	0 (near 1)	Rail adjacent to shed
6 (outer ring)	0 (near end)	Rail opposite the shed

On the underside of the bridge is a motor mechanism. The entire mechanism can slide a short distance along the length of the bridge. This allows a driving gear at the outer end of the motor mechanism to engage with, or be disengaged from, the teeth around the side of the turntable pit. A small hand lever can be pushed towards the center of the turntable to disengage the mechanism, allowing the turntable to be freely repositioned. A small spring reengages the motor mechanism when released.

The motor mechanism has a relay which is connected in such a way that when the relay is energized, it will close a switch in the motor circuit. In addition, the relay is mechanically connected to the main drive gear so that the switch is held closed except at 4 positions of the main drive gear, 90° apart. Thus, the motor circuit switch is closed and operable, if either the relay is energized or the drive gear is not at one of its 90° positions. 90° of rotation of the drive gear corresponds to 7.5° of rotation of the turntable bridge. There is also a third way the motor circuit switch can be closed, the hand lever that disengages the motor mechanism can also be pushed towards the outer edge of the turntable.

Rotation of the turntable bridge is achieved by energizing the relay and applying a voltage to the motor. To stop at the next turntable position, the coil is de-energized. The bridge continues to turn while the mechanical latch holds the switch closed. When the drive gear reaches one of its 90° positions, the latch is pushed into a notch on it by a spring, which opens the switch in the motor circuit, stopping the turntable. It is locked in place until the coil is energized and voltage applied to the motor.

To stop at a specific track beyond the track adjacent to the starting track, the coil must remain energized until it is within the last 90° of rotation of the drive gear. There is no feedback mechanism to know the speed of the motor so control systems using this setup have to rely on a time delay before de-energizing the relay.

Negative voltage on coil (4) will engage the relay if either motor line (2/3) is positive.

If the motor switch is closed, a positive voltage on 2 (and negative on 3) will drive the turntable clockwise and a positive voltage on 3 (and negative on 2) will drive the turntable counterclockwise.

The wiring schematic in my turntable is as follows:

Note that there are numerous versions of the turntable sold through various companies, and the wire colors and connection labels vary. The principle of operation is however, the same.

Inputs to control the turntable

Electrical input is direct current (12 - 16 Volts DC). If you want to use readily available 16VAC you should convert it to DC using a bridge rectifier (there is one you can use in the manual controller that comes with the turntable).

Controlling the turntable using a K84 type module.

One can use 3 addresses (A, B & C below) of a k84 module to control the turntable. Here is an example:

Connections

Turn clockwise

Port/ring	Voltage	K84s
3/3	Negative	A Green
2/2	Positive	B Green
1/4	Negative	C Green

Set port 1/contact 4 to positive (K84 C = Red) to stop at the next position

Turn counterclockwise

Port/ring	Voltage	K84s
3/3	Positive	A Red
2/2	Negative	B Red
1/4	Negative	C Red

Set port 1/contact 4 to negative (K84 C = Green) to stop at the next position

Immediate halt

Port/ring	Voltage	K84s
3/3	Positive	A Red
2/2	Positive	B Green
1/4	Positive	C Red

Multiple position movements

In order to move a specific number of positions (for example 24 positions to move 180°) automatically you will need to time how long your turntable takes to move one position, and multiply that by the number of positions you want to remove, and subtract one half period, to determine when to set port 3/contact 4 to negative. For example, say it takes 2s per position, to move 5 positions you wait for 2s x 5 - 2s/2 = 9s.

Note that turntable speed can vary with temperature and even direction of movement.

Order of k84 commands

If the K84 commands are sent in the order C, then A, then B, no unexpected movements will take place. Note however that with an Intellibox at least, there is no absolute guarantee in the order in which K84 commands are carried out.  This is because if the Intellibox turnout buffer happens to fill up, some commands are not accepted and the software has to resubmit them, and that may result in them being executed out of order. Other systems may be similar.

Other control methods

A number of third party companies have produced control systems. The most sophisticated I have read about is from the DSD2010 Digital-Bahn but you do have to modify the mechanism extensively. It also provides lighting for the control room and outputs for signals, and an option for a sound module.

Märklin used to sell a digital controller (item 7687) but early versions were very unreliable, and a number of people have opted for the k84 approach instead.

To get reliable turning to any specific track position, there has to be feedback from the turntable as relying on timings is fraught with sources of error. One approach I am considering is placing 48 reed contacts, connected to a single sensor, in a ring on the underside of the turntable and mounting a single magnet under the bridge. As the bridge moves, successive reed contacts will be closed and software can count the slots traversed and know how far the bridge has turned.

Bw

In my layout control software I can define turntables as follows:

And then it looks like this when running:

Red on a track indicates that it is occupied.

I can optionally display radio buttons to select any track directly, or even any slot that is 180° away from any track.

If the turntable is not motorized, the software makes a voice prompt to move the turntable to the required position.

Upgrades

I have done some upgrades to the turntable.