Online Payment to Trigger Vending Machines PLC to Dispense

Let's dive into the details of using a Raspberry Pi Pico to trigger your vending machine's PLC upon successful payment. We'll cover the GPIO pin setup, server integration, and the complete workflow.

1. Raspberry Pi Pico GPIO Pin Setup

Components Needed:

• Raspberry Pi Pico

• RS485 adapter (if using Modbus RTU)

• Jumper wires

• PLC with RS485 communication capability

GPIO Pin Connections:

• GPIO 0 (TX) to RS485 TX

• GPIO 1 (RX) to RS485 RX

• Ground to RS485 Ground

Wiring Diagram:

Here's a wiring diagram for connecting the Raspberry Pi Pico to a PLC via RS485:

1

2. Server Integration

Step-by-Step Guide:

1. Set Up Your Server:
   
   

• Choose a server environment (e.g., Node.js, Python, etc.). For this example, we'll use Node.js.

• Install necessary packages:
  Bash

npm install express stripe body-parser

• 
  
  

2. Create a Webhook Endpoint:
   
   

• Stripe will send events to your server via webhooks. Set up an endpoint to listen for payment success events.
  
  

• Example code to handle webhooks in Node.js:
  
  JavaScript

const express = require('express');

const bodyParser = require('body-parser');

const stripe = require('stripe')('your_stripe_secret_key');

const app = express();

const endpointSecret = 'your_webhook_secret';

app.use(bodyParser.raw({type: 'application/json'}));

app.post('/webhook', (request, response) => {

  const sig = request.headers['stripe-signature'];

  let event;

  try {

    event = stripe.webhooks.constructEvent(request.body, sig, endpointSecret);

  } catch (err) {

    response.status(400).send(`Webhook Error: ${err.message}`);

    return;

  }

  if (event.type === 'checkout.session.completed') {

    const session = event.data.object;

    // Send signal to PLC

    sendSignalToPLC(session.amount_total); // Assuming amount is RM 1 is

  }

  response.json({received: true});

});

function sendSignalToPLC(tokens) {

  // Logic to send signal to PLC

}

app.listen(4242, () => console.log('Running on port 4242'));

3. Test Your Webhook:
   
   

• Use Stripe CLI to test your webhook endpoint:
  Bash

stripe listen --forward-to localhost:4242/webhook

• 
  
  

3. Raspberry Pi Pico Setup to Trigger PLC

Step-by-Step Guide:

1. Install MicroPython on Raspberry Pi Pico:
   
   

• Follow the official guide to install MicroPython on your Pico.

2. Install Necessary Libraries:
   
   

• Use upip to install the umodbus library for Modbus communication:
  Python

import upip

upip.install('micropython-umodbus')

3. MicroPython Script to Send Signal to PLC:
   
   

• Example code to send a signal to the PLC using MicroPython:
  
  Python

from umodbus.client.serial import ModbusSerialClient

def send_signal_to_plc(tokens):

    client = ModbusSerialClient(method='rtu', port='/dev/ttyS0', baudrate=9600)

    client.connect()

    # Example to write a value to a PLC register

    client.write_register(1, tokens)  # Register address 1, value (tokens)

    client.close()

# Example usage

send_signal_to_plc(10)  # Send 10 tokens to the PLC

4. Integrate with Node.js Server:
   
   

• Update the sendSignalToPLC function in your Node.js server to call the MicroPython script:
  JavaScript

const { exec } = require('child_process');

function sendSignalToPLC(tokens) {

  exec(`python3 send_signal_to_plc.py ${tokens}`, (error, stdout, stderr) => {

    if (error) {

      console.error(`Error: ${error.message}`);

      return;

    }

    if (stderr) {

      console.error(`Stderr: ${stderr}`);

      return;

    }

    console.log(`Stdout: ${stdout}`);

  });

}

Summary

1. Set up Raspberry Pi Pico: Install MicroPython and necessary libraries.

2. Write communication scripts: Use MicroPython to send signals to the PLC.

3. Integrate with server: Ensure your Node.js server can execute these scripts to communicate with the PLC.