I modified a Kawh 8586D hotair soldering station to us the A1321 Thermistor heater (50W) instead of the original A1322 Thermocouple heater (30W).
I have reversed engineered the Soldering Iron op-amp circuit for measuring temperature using A1322 thermocouple going to micro controller. Op-amp is LM358 going to ST8L152 micro controller, both using 3V3 suppy.
To modifiy it to use A1321 Thermisor heater add a 10K resistor in parallel with R17 (6M8) and a 4K7 or 10K resistor in parallel with R20 (27K).
Cal needs adjusting after doing mods. Set to 400C and adjust Cal until LED reads the same value as Tip.
Heats up now in 45 sec instead of 2 minutes and 45 sec.
I dont understand why the circuit is using a 22uF capacitor before it feeds the micro controller? Other similar circuits dont have this capacitor or if they do its only 0.1uF. I also ended up changing the 22uF to 0.1uF.