Someone has remaked "Your "precise" temperature control is far from anything a decent solder station would do. You basically have a comparator that compares the set point and the feedback it gets from the thermistor. That thing overshoots, I guarantee it. A decent solder station needs a carefully tweaked PID control loop, whether it is analog or digital."
This is nonsense. Can you "guarentee it"?
Show me any video or any data to back up your claim for absolute need for a "carefully tweeked PID control loop,,or that other "Professional" soldering stations maybe hundreds of times more expensive are not also showing this behavior?
Having a "carefully tweaked PID control loop' implies a critical need that a competent soldering station has been equipped with a microcontroller and carefully tweaked software. I haven't yet to see even the uncommon use of any MCU in any soldering station schematic I've ever seen.
There is only reason for MCU's not being used, they are not necessary to achieve good temperature control.
First of all it is not necessary to control the temperature of any soldering iron within few degrees, soldering is a much an art as a skill and learning how to use the tools you have makes all the difference in using any soldering tool.
Even with the crudest of soldering tools, learning that soldering technique is a "touch and go" situation that can be learned as a skill, and having this skill can allow even a cigarette lighter heating a ball-point pen clip to be used to successfully solder/unsolder tiny SMD components. It does take a little practice.
Having any feedback loop, such as the very simple comparator circuit I've shown is in comparison, is a thousand time more able to stablize temperature and can rival the soldering ease of the most expensive stations.
The temperature of the tip of a soldering stations varies, it varies, with many factors, most notably, the thermal mass it is applied to, the power available to heat the heating element and the distance/thermal resistance from the heating element from the sensor and the tip and the thermal conductivity of the object being soldered and the surface it is soldered to, the time that tip is applied to the object to be soldered..etc. It is not constant.