Adding a small circuit for exact temperature control to a modeling iron
I disassembled the iron and started choosing the controlcircuit and a fitting thermistor.
Since thermistors ready for 300°C are rather expensive I chose one with 150°C limit.
An alternative solution seemed to use an existing thermostat from an baking oven, but they are too big for my purpose.
I chose the circuit of Oliver Pering:
I had a nice time calculating resistor values for the voltage dividers used to switch the heating via the OpAmp (the good old workhorse, a historic LM741 ;-) )