I tidied up the bean mass probe software a bit. The probe still measures temperature twice per second but only sends it to the Raspberry Pi when requested.
I added some code that will identify local minimum and local maximum temperatures. The local minimum temperature corresponds to the point in the drum rotation where the bean mass thermocouple is buried in the beans. I also fixed the temperature synchronization problem.
This Guatemala roast shows a once-per second reading of the bean mass probe — lots of fluctuations due to drum rotation.
The chart below is the same roast but only plotting the local minimum temperature from the bean mass probe. Works like a charm.
Check this out — according to Sweet Maria’s information on “Using Sight to Determine Degree of Roast”, first crack should start at about 9:20 at a temperature of 401F. First crack in this roast started at 13:19 at a temperature of 401F. I think that this is a pretty good sign for the bean mass probe. The current roast profile I am using controls outlet temp at 510F — I could increase this and achive a faster roast. Might be worth a try to see if I can match the 9:20 target.