Working on the same thing - already have running hardware and 80% software in place :-)
From what I see, the characteristic of the Thermocouple is quite close to a Type S thermocouple. The voltages are much lower, as the ones, that you'd get from a Type J/K thermocouple.
What I really wonder about, especially seeing other projects... The cold junction compensation is something, which cannot be done really well.
The cold junction is within the hand-pieces of the soldering iron (copper cable used from iron to connetor, but also the cartridge contacts seem to be of the same metal type.
Kind of proove of this theory:
I've dipped the iron into hot water. Initially the voltage was going up to 450uV, while then decreasing slowly to a much lower voltage, allthough the water was pretty constant at 83°C.
For that reason I concluded, that it'll not make a lot of sense to implement sophisticated cold junction compensation within the controller board.
Agree?
Or is there a mechanism present, on top of the thermocouple? e.g. measuring the heater resistance?