I watched a 2015 video from Andreas Schiffler the other day, where he set up LinuxCNC to send status information to the MQTT broker IBM Bluemix. As I also use MQTT for graphing, it occured to me that a generic MQTT LinuxCNC component would be useful and I set out to implement it. Today I got the first draft limping along and submitted as a patch to the LinuxCNC project.
The simple part was setting up the MQTT publishing code in Python. I already have set up other parts submitting data to my Mosquito MQTT broker, so I could reuse that code. Writing a LinuxCNC component in Python as new to me, but using existing examples in the code repository and the extensive documentation, this was fairly straight forward. The hardest part was creating a automated test for the component to ensure it was working. Testing it in a simulated LinuxCNC machine proved very useful, as I discovered features I needed that I had not thought of yet, and adjusted the code quite a bit to make it easier to test without a operational MQTT broker available.
The draft is ready and working, but I am unsure which LinuxCNC HAL pins I should collect and publish by default (in other words, the default set of information pieces published), and how to get the machine name from the LinuxCNC INI file. The latter is a minor detail, but I expect it would be useful in a setup with several machines available. I am hoping for feedback from the experienced LinuxCNC developers and users, to make the component even better before it can go into the mainland LinuxCNC code base.
Since I started on the MQTT component, I came across another video from Kent VanderVelden where he combine LinuxCNC with a set of screen glasses controlled by a Raspberry Pi, and it occured to me that it would be useful for such use cases if LinuxCNC also provided a REST API for querying its status. I hope to start on such component once the MQTT component is working well.
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