QR-Payment Vending Trainer — PLC, HMI and IoT Gateway

Problem

Students learn PLCs on boards of lamps and switches. Real machines on the street now take QR payments, report online and send alerts — and none of that is on the lamp board.

The university wanted a trainer built around a real machine: a coin-operated washing machine that also accepts QR payments, so students can follow one payment from the phone to the motor.

My role & scope

I led the controls side of a small team:

Bill of materials and the datasheet for every device
Electrical drawings: wiring diagram, single-line diagram and the energy-monitoring panel
Automation architecture
FX5U PLC program and GOT2000 HMI screens, step-function flowchart and I/O tests
Lessons for the course: PLC basics (I/O and data types), basic commands, and GOT2000 screen design

Teammates built the 3D layout and the payment front end. The trainer is a mobile aluminium frame holding the machine, the control panel and the payment hardware.

Approach

Coin acceptor · buttons · motor ──► FX5U PLC ◄──► GOT2000 HMI
                                       │
                                  IoT2050 (Node-RED) ──MQTT──► payment front end · notifications
                                       │
Power meter · CT · temperature ────────┘

Hardware that matches a real machine

24 V DC control power, with a step-down to 12 V for the coin acceptor and the pulse generator. A brushless DC motor on a DC drive turns the drum. A UPS, tower lamp, emergency stop and reset button, and a managed switch complete the panel. A power meter, a 30/5 A current transformer and a temperature transmitter add energy monitoring, so the trainer also teaches metering.

The PLC owns the machine

The FX5U ladder program handles coin counting, the wash and spin sequence, machine status and the emergency stop. The GOT2000 HMI shows the coin count, the wash process and alarm events. The payment side sits beside the PLC and talks to it through the gateway, so the machine logic can be taught on its own before payment is added.

Gateway and notifications

The IoT2050 runs Node-RED: it reads the PLC and publishes over MQTT to the payment front end on a Raspberry Pi 5. The front end is a Flutter web app that also shows the machine’s status; payments go through Opn Payments / Omise with PromptPay QR, and a Node.js back end receives the payment webhooks over a REST API and passes the result on, with data stored over MQTT. Machine alerts went to a chat service; when LINE Notify was shut down, the notification flow moved to Discord.

Delivery

FAT/SAT protocol covering each power supply and device, software installation, PLC and HMI backups, PLC–HMI communication, program download and diagnostics
User manual for the training unit
3-day course: payment concepts, architecture, safety and maintenance (day 1); PLC programming in GX Works3 and HMI screens in GT Designer (day 2); full integration and a live payment test (day 3)
Online course “PLC Basics for Washing Machine Automation” — 10 lessons from wiring to a Node-RED-linked HMI, recorded September–November 2025

Result

A trainer students can follow from QR scan to motor, instead of a lamp board
The same machine teaches PLC, HMI, IoT gateways, payment and energy metering
Documentation that lets the lab maintain it: drawings, BOM, FAT/SAT, manual and videos

Skills used

Mitsubishi FX5U and GX Works3 · GOT2000 and GT Designer3 · Siemens IoT2050 · Node-RED and MQTT · electrical design (wiring and single-line diagrams, panel layout) · BOM and datasheets · FAT/SAT · writing and teaching hands-on PLC lessons.

Highlights