Thank you for the pics and diagram! That sounds like a great project for me
I have a spare iron and tips for mine as I never expected the actual controller to fail.
Opening the soldering station I was shocked at how simple it was - just an OP-AMP driving a Triac.
Mine is a K type Thermocouple so this sounds like a great replacement, rather than $150 to replace the soldering station with a new one and not being able to use the spare iron etc.
How did you find the Automatic PID calculation go? Did it work well? Or did you end up entering values manually?