Every time I migrated to the new version of openHab I had huge problems with launching the MCP23017 bindings. Recently I switched to openhab 2.5.10 and the problem appeared again (Cannot start MCP23017 binding for openHAB 2.5.10-1). I said enough and wrote a small program MCP2MQTT for myself. The method of operation is simple, data from MCP inputs are sent to MQTT topics and what is supposed to go to MCP outputs is also received from MQTT topics. The program is very simple and adapted to my needs but can be a starting point for people who have similar problems.
In rules you can use like this:
-output Switch WtrValveFront <water> {mqtt=">[mosquitto:mcp23017/20/A/output/0:command:ON:1],>[mosquitto:mcp23017/20/A/output/0:command:OFF:0]"}
@Michal_Szymanski thank you very much for sharing your script. You are right, there are a lot of problems with the MCP binding and I am not sure if it will ever works with OH3.
For my needs your solution is much better, because I can put some logic into the script easily. Before I had to solve it with a lot of rules in OH.
Thank you very much
I do want even check it That is why I decided to write my own program. Program is limited to my case but after small modification everyone can customize it.