The first thing I did was choosing the components:

I started with the soldering iron tip, I came across a model that has integrated heating element and thermocouple inside the metal body. My previous soldering station had detachable tips that can be replaced, that is convenient if you exchange the types of tips frequently but the problem I identified is that the heating element is not contacting the metal body of the tip perfectly so the contact area is small and the thermal transfer has to be low, as such the tip is not heating as good as it could be.

The T12-D16 model of tip that I selected has the tip, heating element and thermocouple all integrated in the body as such it makes a compact part and resolves many of the problems from the beginning. It is also very light and got me to think that the final product may be portable! The disadvantage of this model is that it has only two external electrical connections, by making elegant the manufacturers imposed some engineering challenges to make this work. (I kind of like it).

The next thing that comes is the precision, more exactly the thermocouple amplifier that reads the extremely small voltage produced by the thermocouple and amplifies it. I chose the MAX31856 as is the most precise (19-Bit, 0.0078125°C) I found and has an integrated ADC, cold junction compensation, input protection, 50/60Hz noise rejection (very important since the wires that connect to the tip assembly pic up a lot of EMI) and such removes a lot of overhead from our part.

For testing I chose an Arduino board as it's enough processing power, for controlling the temperature I will include a PID library, the controller will have a OLED display to clearly show the temperature and have a few setpoints in memory that we can choose from. A rotary encoder will be the input interface.