Connecting Allen‑Bradley PLCs to the Cloud with pycomm3 and Node‑RED

Requirements

• Raspberry Pi with Python 3.7+, Docker, and Node‑RED.
• Allen‑Bradley PLC (ControlLogix, CompactLogix, or Micro800) accessible over EtherNet/IP.
• Python library pycomm3 installed.
• MQTT broker available locally or in the cloud.

EtherNet/IP and pycomm3 in Python

from pycomm3 import LogixDriver
from paho.mqtt.client import Client

mqtt = Client()
mqtt.connect('broker.local', 1883)

# Connect to the PLC
with LogixDriver('192.168.0.50/1/0') as plc:
    # Read a tag
    tag_value = plc.read('Sensor_Temperatura')
    print(tag_value.value)
    mqtt.publish('plant/area1/ab/temperature', tag_value.value)

    # Write a tag
    plc.write('Setpoint', 75)

Node‑RED Flows

1. Install the node-red-contrib-cip-ethernet-ip and MQTT nodes.
2. Configure the EtherNet/IP node with your PLC’s IP, slot, and path.
3. Design a flow that:
   • Reads tags and publishes them to MQTT topics.
   • Subscribes to MQTT commands and writes them to the PLC.

Practical Project

• Extend your gateway to:
  • Monitor multiple PLC variables.
  • Control operations via MQTT (e.g., start/stop motors).