I'm making my own PID controller for a soldering iron using an Arduino, and as a first step, I'm going to try to control the iron that comes with the Hakko FX-888D station. I was able to get a cheap knockoff for $11.
The manual says that the thermistor resistance at room temperature will be between 43 and 58 Ohms, but there's no mention of what the resistance is at higher temperatures. I am going to hook it up with another resistor in series and hook it up to 5V and then measure the voltage across the therimstor. Since the Arduino can only read a max of 5V with a 5mV resolution, I need to know what other resistor to choose to get me a nice range of voltage values across the normal temperature range of 300C to 450C.
With regards to the heating element, does it exhibit the same rise in resistance? Typically how much current is passed through the element?
Thank you in advance.