Hey there! I totally get your situation - trying to bring modern IoT sensors into a legacy PLC-5 system can feel like trying to teach your grandpa to use a smartphone! The good news is there are several practical workarounds that don't require ripping out your entire control system.

First up, protocol converters are your best friend here. These are standalone hardware devices that act as 'translators' between your PLC-5's older protocols (like DH+, DH485, or DF1) and modern IoT protocols (like MQTT, OPC UA, or Modbus TCP/IP). Companies like Red Lion, Prosoft, and UCONNECT make converters specifically for AB legacy systems.

For PLC-5 systems, you'll often need a DH+ to Ethernet gateway. These convert the PLC-5's Data Highway Plus protocol to Ethernet/IP or standard Ethernet, which then connects to IoT gateways. The 1785-ENET/B module is one option, but there are also third-party solutions that offer more flexibility.

Another approach is using IoT edge gateways with built-in protocol conversion. These devices can connect directly to your PLC-5 via serial or DH+, convert the data, and send it to cloud platforms using modern protocols. They're like adding a modern brain to your old system without touching the PLC logic.

Software solutions like Ignition or Open Automation Software can also bridge the gap. They run on a separate industrial PC, connect to your PLC-5, and provide modern interfaces like OPC UA or MQTT for your IoT sensors to communicate with.

The key is to think of it as adding an 'adapter layer' rather than replacing the whole system. Start with a small pilot project to test the waters - maybe just connecting a few sensors to monitor temperature or vibration. Once you see it working, you can scale up gradually.

What specific types of IoT sensors are you looking to integrate, and what's your main goal - monitoring, predictive maintenance, or something else?