LED lighting circuits

The topic of LED lighting is a popular one, perhaps because there are always so many answers!

The big question is always how much resistance is needed to protect the LEDs, but this usually leads to other questions: "How bright do you want the LEDs to be and how much voltage will be used to power them?"

Installing signals

I thought I would share how I install my Viessmann signals on my layout. The Viessmann color light signals use LEDs and are of excellent quality.

Viessmann 5210 Signalsteuerbaustein

I use the Viessmann signal modules to drive my light signals from k83 (Viessmann 5211) type modules.

Advantages of these modules are:

• You can use momentary contact decoders (k83) type instead of K84s
• Once a signal aspect is selected, it is latched (held) by the module
• Each module can support two signals (up to a 3 aspect plus a 4 aspect)
• It has the ability to handle the Dunkelschaltung of German distance signals on the same pole when the Hp signal is on aspect 0
• It can use 16 VAC or DC input
• The signal lights fade out prototypically

I find it useful to mount them on Velcro strips as shown below. In this case I needed to drive 3 HP0/1 signals and one Vr0/1/2 signals plus a couple of turnouts so I needed two 5211 modules to do the digital switching.

Connecting a track detection point to an s88 module

The technique of obtaining train location feedback from the train layout is well known and one typically uses a Märklin s88 module or one of the many modules that perform the same or similar service, such as the Viessmann 5217 modules.

Understanding how to connect the length of isolated track to the port on the module is one aspect of the job. Another is the technique of how to actually get the signal from the track all the way around to where the s88 modules are located. This page documents my technique for doing this.

Signal module rack

I attached the rack of K83 type modules and the Viessmann signal modules under the benchwork.

This was mostly to get the rack out of the way as it is a long way off before I will be able to connect any signals...

Arc-welder in HO

I designed and made a welding machine out of thin card

Voltage visualization

I was connecting a Semaphore signal and I decided to try powering the light using the 5.1V DC supply and since it is an LED light I needed to get the polarity correct. My other color light signals also have LEDs and they all have their black lead with the diode connected to the common ground since the Viessmann signal modules produce a negative voltage relative to the common ground. My 5.15V DC supply is however positive relative to ground so the semaphore signal needed to have its yellow wire connected to ground and the brown lead with the diode connected to the positive power supply.

I realized that I needed to keep track of the various voltages I have available on my layout so I created this visualization.

Installing signals

After playing with software for a couple of months I am back to my signals project....

I had to mount my rack of signal modules and their digital switching units - that was pretty easy because I measured where the studs in the wall were before I laid them out so it just took 2 screws and three connections to connect it to the layout.

I inserted cable ties along the lower edge in preparation for the numerous cables that will connect the signals to the module outputs.

Viessmann 5291 kit to build 5211

In order to keep costs down I decided I would buy the kit versions of the Viessmann 5221 module that is used for switching turnouts, signal control modules, etc. It is the equivalent of the Märklin k83 module. The Viessmann item 5291 is a kit containing all the components to build a single 5221 module and is cheaper than the 5221 (which in turn is cheaper than the Märklin k83)

Märklin Digital Crane 7651+7054

Some 14 years ago my wife bought me the Märklin 7651 digital crane. It is the classic rotary crane with a special decoder in the base to allow digital operation.

Preliminary tests indicated a nasty design flaw, the decoder allowed the crane to slew or raise/lower the hook but one cannot do both operations at once! I suspect that since there are two motors, one for each function, they designed it so that only one motor could be active at any one time - in order not to overload the decoder. Gebr. Märklin,  here is a solution:, use a decoder than can handle the load!

Digitising the Märklin turntable 7286

The Märklin digital turntable decoder (7687) is meant to work with the 7286 turntable but it is horrible. The decoder tries to memorize the positions of the connected tracks and this needs to be refreshed periodically and this requires laborious 'programming' to tell it where track positions are. Even then the current that it provides to the turntable seems to be wholly inadequate - causing me to dismantle and service my turntable a number of times until I worked out that it ran just fine using the analog controller. Any disturbance to the movement seems to make the 7687 module go to sleep and it needs to be 'rebooted' .

I therefore decided not to drive my turntable using the 7687 decoder. Since I am using a PC to control my layout I decided that it would be simpler and more reliable to use a simple k84 type module to control the turntable. These pictures show how I did this.

The manual controller that comes with the turntable provides the plug interface to the turntable and a rather pathetic direction knob and on / off button to stop and start the turntable...

Märklin 6015 Booster

I decided that since it is a bit of a pain to get decent size wires into the Märklin 6015 booster connections I would make a permanent connection that could simply be plugged in. I found that the harness from an old PC power supply had 4 leads of 18 AWG wire that would make a nice connection. As luck would have it, it also has a red a yellow and two black lines which I can easily treat as brown! I cut the wire a short distance form the plug and twisted the black + yellow leads as well as the black and red leads to reduce electrical interference. After stripping the ends I primed them with solder and inserted them into the booster connections. I then dropped some solder on the ends to help make the best possible connection. The last step was to fasten all four wires to the small plywood base I had cut for the booster so that any tension on the wires would not stress the connections.

I can now screw the base firmly wherever I need the booster and connect with a matching PC  power supply female.

I intend using a female 'Y' that will give me an additional set of wires allowing a nice ground bridge to the IB nearby.