// the take
A C server that bridges OPC-UA and Modbus, exposing Modbus RTU/TCP devices as OPC-UA nodes configured via a JSON file. Aimed at industrial automation scenarios where you need to integrate legacy Modbus hardware into an OPC-UA-based supervisory system.
The JSON-driven configuration is genuinely useful — you can map Modbus coils, holding registers, and input registers to OPC-UA nodes without recompiling. Support for both RTU (RS485/RS232) and TCP Modbus in one server is practical for real-world mixed environments. The byte-order field on float registers ('abcd', 'badc', etc.) shows awareness of the endianness mess that actually bites people with Modbus floats.
The build process requires patching a fork of open62541 to add a custom API (`UA_Server_writeWithoutCallback`) — if that fork diverges or goes stale, you're stuck, and it already has since the repo hasn't been touched since 2022. The entire project is a handful of C files with no tests, no CI, and no release artifacts, so you're on your own when something breaks. Error handling is minimal — if a Modbus device goes offline, it's unclear how the server recovers or signals the fault to OPC-UA clients. At 3 stars and 4 forks, there's no community to debug with.
We read the README, the directory tree and a key source file in July 2026. Nobody pays to be listed. How we judge →