Most Powerful Open Source ERP

How to build a rPLC Coupler

Step by step process of building an open source and open hardware Coupler running OPC-UA
  • Last Update:2026-07-10
  • 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 (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. 4 x 40mm M3 (female-male)  and 4 x 15 mm M3 (female-female) hexagonal spacers from stainless steel
  6. Micro SD card with recommended  capacity of minimum 16Gb
  7. LAN cable
  8. (optional) external battery
  9. (optional) DIN rail bracket (1 piece)
  10. Screws (Phillips type): 4 pieces 3.5mm x 40 mm, and 4 pieces 3.5mm x 10 mm
  11. Screws (and nuts): 4 pieces M3x12mm
  12. Spacers: 4 pieces 35mm M2.5 (female-male)

Print with 3D printer needed cases

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 bracket and battery

Please add 4 bottom 35mm M2.5 (female-male) spacers into the four corners of the case and optionally add a battery as shown below.

Also if you need to add bracket for installation on DIN rail. Please connect the bracket using M3x12mm bolts and nuts 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.