Zmodell digital decoder for AZL Alco RS series locomotives

Alex_dn Apr 30, 2021

  1. Alex_dn

    Alex_dn New Member

    2
    9
    4
    Greetings to all,

    I am a small series manuafacturer from Kiev, Ukraine. Although I registered already several years ago, I was not active here (I am active mostly on AZLforum.com and German ZFI forum - f.z-freunde-international.de). I have a big number of developments for Z scale to show, and I would like to start from the newest one - digital decoder for AZL Alco RS-2/RS-3/RSD-4/RSD-5 diesel locomotives.

    In this new model, AZL switched to a different chassis, and standard drop-in decoders from Digitrax and TCS do not fit to it anymore. There were numerous reports about manual digitizing these locomotives using small decoders like Doehler & Haass PD05A, but all of them required irreversible modifications of the original circuit board and a lot of manual wiring; therefore, I decided to develop a professional, easy to use drop-in solution. I also managed to pack it with some bonus features that is almost impossible to implement in a different way.

    Unlike most other variants of digitizing based on the D&H PD05A – a decoder with limited set of functions, my digital circuit board is based on the full featured D&H DH05C decoder that supports analog mode and many other options not available in PD series. As a bonus, my circuit board features a good 600 µF power buffer and interior lighting for driver’s cabin.

    So, here is the circuit board, bottom side:
    [​IMG]

    Top side:
    [​IMG]

    I thought a lot about how to add interior lighting to the driver’s cabin. At first glance, it looked to be very simple – just to add a LED on the top side of the circuit board. However, such approach led to some issues. To let the light from the LED come into the driver’s cabin, the main body should be drilled from inside, as the driver’s cabin box is a separate part mounted on the top of the main body. I considered drilling as a risky and unwanted operation for two reasons – first, it kills all advantages of drop-in installation; additionally, there is a risk of overdrilling and damaging the cabin’s roof, as removing of the cabin box is too difficult and may damage the locomotive too.

    Furthermore, the light would have come from the wrong side – from the bottom (instead of spreading from above), which is also incorrect. Thus, I decided to use a different solution – to solder a separate LED with flexible wire outputs to the circuit board. I used a smallest SMD 0402 warm white LED for this (only 1x0.5 mm size). I have to admit that soldering such small LEDs manually is a hell. 25 mm pieces of high-flexible ultra-thin multi-stand wire with PTFE coating were used for wire outputs.

    Here is a comparison of the digital circuit board with original analog one. My PCB is a bit wider; however, it still fits inside without any problems:
    [​IMG]
    [​IMG]

    This is how the decoder looks when installed onto the RS-2 chassis – nice, compact and elegant:
    [​IMG]

    As you can see, nothing touches the chassis, despite the circuit board populated with relatively bulky elements like SMD 1206 ceramic capacitors:
    [​IMG]

    However, I still recommend isolating area marked with red using a piece of adhesive tape for additional safety:
    [​IMG]

    7x9 mm piece will be enough:
    [​IMG]

    Installation of external LED is also quite easy. First, wire outputs should be bent like this:
    [​IMG]

    Then, the LED should be carefully threaded into the gap between the main body and the driver cabin’s box using precise tweezers. It is important to pick only wires, and never pick the LED itself with tweezers. Small SMD 0402 LEDs are very brittle and can be easily damaged by any metal tool.

    I have two Alco RS locomotives in my collection and I successfully digitized them all using these digital circuit boards.

    Union Pacific RS-2:
    [​IMG]
    [​IMG]

    Chesapeake & Ohio RSD-5:
    [​IMG]
    [​IMG]

    All together on my test loop:
    [​IMG]

    The brightness of both headlights and interior lighting is separately adjustable. Due to the automatic exposure of the camera, brightness of interior lighting may seem to be too high on the pictures. In real life, the brightness is adequate.

    Based on the test results, I like very much how combination of D&H DH05C decoder and small AZL coreless motor with flywheel works. I like it better than Digitrax DZ123Z0 decoder that installed in the most AZL locomotives in my collection. Furthermore, you get everything you can ever imagine in programming options with DH05C and that is unavailable with Digitrax.

    About availability and price: I expect my RS-2 digital decoder to be available at selected dealers in the USA in the nearest observable time. Unfortunately, it is impossible to sell electronic items in EU officially without a certification. Such certification requires significant investments – this is not what I would like to spend money for at the moment. Furthermore, in combination with import tax that is inevitable for products from outside EU, the final price will be simply too high.

    Otherwise, I can always produce and sell any of my decoders privately with direct shipping worldwide. I did not calculate the final price for RS-2 decoder yet; however, I estimate it to be similar to the price of standard digital locomotive decoders from Velmo. I will disclose further details as soon as I know more.

    Best regards,
    Alex
     
    Last edited: May 1, 2021
    ddechamp71, Moose2013, Kez and 5 others like this.
  2. ZFRANK

    ZFRANK TrainBoard Member

    920
    463
    24
    Nice approach, actually a small decoder piggyback on a loco compatible circuit board with embedded buffer capacity to overcome the track current drop outs.
     
    Alex_dn likes this.
  3. mrp

    mrp TrainBoard Member

    21
    3
    11
    What are the dimensions of this decoder?
     
  4. Alex_dn

    Alex_dn New Member

    2
    9
    4
    The size of the board is 61 x 6.6 x 2.1 mm (LxWxH). The height is measured at the thickest element (SMD 1206 ceramic capacitor that has its own size of 3.2 x 1.6 x 1.6 mm).

    Greetings,
    Alex
     
    Kurt Moose likes this.

Share This Page