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    How to build a rPLC Coupler

    Step by step process of building an open source and open hardware Coupler running OPC-UA
    • Last Update:2025-11-04
    • Version:006
    • Language:en

    Agenda

    • Purchase required hardware
    • Print with 3D printer needed cases
    • Assemble coupler
    • Power up devices and connect peripherals

    Requirements

    • a 3D printer
    • USB keyboard and mouse
    • basic assembly skills

    Goal

    This how to explains how to build yourself a rPLC coupler from scratch which you may use in automation projects.

    Purchase required hardware

    Purchase list
    1. STMP157-OlinuXinu-LIME2-EXT (the coupler's main board)+ power supply
    2. STMP15X-SHIELD (an expansion top on SOC board)
    3. MOD-IO + power supply for it
    4. UEXT cable
    5. Micro SD card with recommended  capacity of minimum 16Gb
    6. LAN cable
    7. (optional) external battery
    8. (optional) DIN rail clips (4 pieces)
    9. Screws (Phillips type): 4 pieces 3.5mm x 40 mm, 4 pieces 3.5mm x 25 mm and 8 pieces 3.5mm x 10 mm
    10. Metal stands

    Print with 3D printer needed cases

    Two cases need to be printed each with a top and bottom part. This makes overall of 4 different parts.

    Below you may find links to .stl files which can be used with proper transformation with any 3D printer.

    1. rPLC coupler bottom case
    2. rPLC coupler top case

    Recommended 3D printer settings:

    1. Material: PLA
    2. Nozzle: 0.4 mm
    3. Infill Density: minimum 50%
    4. Support : Yes
    5. Shell thickness: 0.8 - 1.0 mm

    Assemble rPLC coupler

    Step1: Install the micro SD card first into the coupler

    The first thing we need to do is to insert the micro SD card into the designated slot as show in the picture below.

    Step 2: Add supports and optionally DIN rail brackets and battery

    Please add 4 metal supports into the four corners of the case and optionally add a battery as shown below.

    Also if you need to add brackets for installation on DIN rail. Please do make two holes for each DIN rail bracket using the designated hole marks on bottom of the case.

     

     

    Step 3: Connect coupler to its bottom case

    The second step is to connect the coupler bottom case with board from step 1. For this we use 4 screws (4 x 10mm) as shown in picture below. In case you use optional battery please connect it to the appropriate pins.

    Step 4: Connect the shield

    We need to connect the shield board by placing it on top of the case and board from step 2. Mind to properly match all the pins as this potentially can lead to an electrical damage.

    Step 5: Connect the UEXT cable

    As later one we will close the case we need to install the connecting cable (UEXT) to MOD-IO now. Please connect to UEXT1 slot.

    Step 6: Put MOD-IO board

    Please put the MOD-IO box on top of metal holders and connect the UEXT cable accordingly.

    Step 7: Put top cover

    Please put the top cover of the case. The rPLC coupler is ready.

    Power up devices and connect peripherals

    Please follow the following procedure:

    1. Connect a 5V  power supply to the coupler.
    2. Connect a 12V power supply to MOD-IO
    3. Connect an USB keyboard and a mouse
    4. Connect the coupler to the local LAN

    Success

    Now you have all needed hardware up and ready. Next step is install OS on the coupler.