Connecting Siemens PLCs to the Cloud with Snap7 and Node-RED

Connecting Siemens PLCs to the Cloud with Snap7 and Node-RED

In this course, you’ll learn how to extract data from Siemens S7 PLCs and send it to the cloud using a Raspberry Pi-based gateway with Node-RED.

Requirements

• Raspberry Pi with Docker, Node-RED, and Python 3.7+.
• Siemens PLC with Ethernet connectivity and network access.
• Python libraries snap7 and paho-mqtt.
• Available MQTT broker (local or cloud).

S7 Protocol and Addressing

• Data block (DB) structure and tags in Siemens S7.
• Addressing: DB#, offset, and data types (BOOL, INT, REAL).

Reading/Writing with Snap7 in Python

import snap7
from snap7.util import get_real, set_real
from paho.mqtt.client import Client

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

plc = snap7.client.Client()
plc.connect('192.168.0.100', 0, 1)  # IP, rack, slot

# Leer DB1, offset=0, 4 bytes -> REAL
data = plc.db_read(1, 0, 4)
value = get_real(data, 0)
mqtt.publish('plant/area1/s7/temperature', value)

# Escribir REAL en DB1 offset=10
buff = bytearray(4)
set_real(buff, 0, 55.5)
plc.db_write(1, 10, buff)

Node-RED Flows

1. Install S7 nodes (node-red-contrib-s7) and MQTT.
2. Configure PLC host (IP, rack, slot) in the S7 node.
3. Design a flow:
   • Read tags and publish to MQTT topics.
   • Subscribe to MQTT commands and write to the PLC.

Practical Project

• Extend your gateway (Python or Node-RED) to:
  • Read multiple data blocks and publish metrics.
  • Control PLC variables via MQTT.
• Test with PLCSIM or real hardware.