Zmodell Digital Decoder for Märklin 87210 Entertainment Car

Greetings to all,

I would like to introduce one more digital solution for Z scale passenger cars. At the same time, it is one of the most interesting and complex developments in my assortment – digital decoder for Märklin 87210 Entertainment Car (or "Gesellschaftswagen" in German). Surely, original disco lighting will work in digital mode too (without ability of turning off), but I thought it was worth to pack this unusual passenger car with more interesting features, like its “big brother” in H0: www.maerklin.de/en/products/details/article/43868/. Additionally, I find original blinking lights feature executed a bit primitively.

So, here is this decoder:

Like most of my other circuit boards, it is based on Doehler & Haass FH05B function decoder. As you can see, the population of components is very dense, and the circuitry is extremely complex. It was really hard to trace this circuit board; I was in a one step to switching to the triple-layer design. However, I tried my best and managed to trace manually everything that did not trace automatically.

Taking into account a big number of functions that consume higher current in total, I increased capacity of the buffer even more – it is as much as 2200 µF here (using 22x 100 µF/16 V X7R MLCC), and tests show that it helps extremely well.

Now here are some details about the main function of the wagon – disco lights. As I already wrote above, original blinking lights feature executed quite primitively, and one of my goals was to develop a better implementation of this function. First, I thought about adding a special light effects chip and to control a chain of color LEDs with it (like in Christmas tree lights), but this was questionable due to a very small available space. Standard flashing LEDs weren't a good solution either, as I would get a similar primitive blinking effect with fixed color, like in the original board.

After some research, I found a superb solution – a very special kind of full-color RGB LEDs that consist of three individual LEDs (red, green and blue) and a control chip in a single package that equals to 0807 SMD size. A distinctive feature of these LEDs is that the color in them switches smoothly, and not discretely, as in the original LEDs. Additionally, the flashing sequence is quite long, so that you won't even notice that it plays repeatedly. It includes both fast and slow beats, as well as short flashes and smooth transitions – just like real disco lights.

Another potential problem I was concerned of – is that all these LEDs would switch simultaneously, at the same speed, and as a result, visual effect would not be too attractive. I connected several LEDs in parallel on the test bench, and I made sure that this problem does not exist – the flashing sequence of the each LED starts at the random point, and the speed is slightly different too, so several LEDs together look really nice and overall effect is very attractive.

But even an Entertainment Car should have normal interior lighting. I added it too. And I did it in a bit more interesting way: the lighting is divided into two separate sections – bar and restroom area at the ends of the car, and central area with dancing parlor.

As a result, now we have three different lighting functions that can be combined in any desired way. Furthermore, I did not forget about red tail lights – outputs for them are also present at the both ends of the circuit board, and can be fitted with special ultra-small circuit boards with red LEDs.

Here is the bottom side of the circuit board. Different LEDs are combined here – warm white SMD 0402 and full-color RGB SMD 0807 models. And once again, you can see a very complex circuitry on this side too:

For such a variety of functions, I had to use all available outputs of FH05B function decoder – from AUX1 to AUX4 (only except optional AUX5/6). For normal warm white interior lighting, I reserved non-amplified, logical AUX3 and AUX4 outputs. As warm white lighting consumes a very low current (all 10 SMD 0402 LEDs consume around 6-7 mA in total), I connected it directly to the logical outputs without additional transistor switches.

Doeher & Haass claims that their logical outputs can provide up to 20 mA each, which is more than enough in this case. The only point to consider – are the voltages of logical levels. Low level is actually not equals to 0 Volts, it is around 1 V, but it is Ok for warm white LEDs, as they start to glow at only about 2,5 Volts. The high level stands at around 5 Volts accordingly, so the only measure to take is to use a different resistor. I used 2 kOhm for this (for comparison, I use 10 kOhm resistors for normal, amplified outputs).

The only downside of unamplified outputs is that they are not dimmable. It means that the brightness of LEDs cannot be adjusted. However, I chose resistors with an optimal value here, so the brightness of warm white interior lighting is not too high. Adding adjustable resistors was not possible too, as there was not enough space for anything more on the circuit board.

Now let me tell about even more interesting function that I decided to add to Gesellschaftswagen. What is one of distinctive features of H0 variant? Right, it is music! So why does Z scale should be worse?

Of course, I have to tell that this part is a development announcement. A lot of R&D work has already been done, and the same amount is waiting yet – honestly, developing a super-compact MP3 player complying to all strict limitations of Z scale is not a trivia. However, a working prototype was already built on a test bench.

The sound module will be on a separate circuit board that will be connected to the main decoder board via brass poles. I have already prepared appropriate holes for them on the main PCB.

Here is a list of planned features:

– Sound module will be available as an option for digital interior lighting board for Gesellschaftswagen, as well as a separate item;

– It will be equipped with 128 Mbit (or 16 Mbytes) Flash RAM that can store up to approx. 15 minutes of 128 Kbit 44.1 kHz 16 bit MP3 stereo audio or approx. 30 minutes of 64 Kbit 44.1 kHz 16 bit MP3 mono (which have the same quality as 128 kbits stereo). An MP3 decoder chip I plan to use limits the maximal volume of storage to 16 Mbytes. Manufacturer claims that bigger volumes can be supported theoretically, but it is not documented. By the way, the same 16 MB Flash RAM chip is used by Doehler & Haass in all their sound decoders.

– USB connectivity. Instead of complex programming of sound decoders, you will be able to copy any audio content to the sound module via USB from PC, laptop or even a smartphone, as most OS will detect it as a conventional USB flash drive. Micro USB connector will be fitted directly on the circuit board.

– Sound module will be compatible both with digital and analog mode. It will be equipped with rectifier and 5V voltage stabilizer (device will start from approx. 4 Volts).

– Sound module will be equipped with small 13x8 loudspeaker with built-in transparent soundbox.

– Planned size of the circuit board – 68 x 8.7 mm.

I had to reject the idea of using a MicroSD card as a music storage, because all variants of MicroSD slots are unfortunately too big to fit into any kind of Z scale vehicles. Therefore, I switched to a built-in Flash RAM in my development.

Now let’s return back to what is already produced. The installation of digital circuit board is more than easy – just remove the roof, unscrew original circuit board and install a new one in its place:

Look at the next picture. Original construction from Märklin raised some questions to me. First, I believe it was not optimal to make separate brass poles and spring-loaded contacts from the trucks. Flat metal parts could come into contact with brass poles at the bottom, and then electricity could be transmitted through these poles:

For me, the reason is quite obvious – it is an economical matter. Märklin already used such springs in their other passenger cars equipped with interior details and lighting. They simply used them here too instead of developing a new part, that would increase production costs.

Original black circuit board has empty pads for additional LEDs. It looks like Märklin intended to add more LEDs for more interesting effects, but later they decided to give up this idea. The only mention about it was left in the product description on their official website: “…red, yellow, green, blue, etc.” What was meant by “et cetera”?

www.maerklin.de/en/products/details/article/87210

And surely, there is no current buffer here at all, unlike it was specified in product description as well. If you look at the previous picture, you may notice empty pads on the left part of the top side of circuit board too, right after four rectifier diodes. These pads were intended for filtering capacitors, but only one capacitor is installed instead of three. It is sad once again, as all three capacitors in parallel could serve as a current buffer as well.

Now the new digital circuit board with big current buffer and many other “bells and whistles” is installed in its place:


As usual, nothing is visible through the windows:

After installation of decoder circuit board, the car weights 18 g. I estimate that around 3 more grams will be added after installation of the sound module.

Now let’s see the results of all these efforts. First, here is a list of functions:

F0 – Directionally controlled red tail lights (not shown in this video)
F1 – Disco lights
F2 – Lighting of entrance area
F3 – Normal lighting for dance area
F8 – Sound (only with optional sound module)

F1:



F1+F2:





F2:



F3:



F2+F3:





Of course, it is possible to turn everything on, but I think it will be too much. Here is how it looks when you turn on F1+F2+F3 at the same time:





I also prepared a short video demonstration:



One of the obvious advantages of full-color RGB LEDs used here is that we have any possible colors thanks to the smooth transition of the light tones, unlike in the original circuit board that has only four fixed colors that blink at constant speed all the time.

Note: due to the automatic exposure of the camera, brightness of interior lighting may seem to be too high. In real life, the brightness is adequate.

I expect the sound module to be ready somewhere in the next year. I will make a separate announcement about it.

Zmodell digital decoder for Märklin 87210 Entertainment Car is available directly in the USA here:
www.zscalemonster.com/zmodell/

Best regards,
Alex