It used to be hot air soldering gear was exotic, but not anymore. There are plenty of relatively inexpensive choices. Many of these appear to be the same despite having different brand names and model numbers. One that is common and inexpensive is the 858D. These run about $50. [Gabse] has one and decided to upgrade it using some open source controller hardware and software. There wasn’t a complete guide, so he created one himself.
According to the original GitHub page, the controller will work with the Youyue-858D and any clones. However, there are others like the Atten 858D that use a different controller. In addition, there have been several variants. [Gabse’s] guide is for the latest version. Information on other versions and brands might be on this discussion board thread.
The new controller and firmware offer better temperature regulation, a safety feature that prevents the handpiece from heating up if power is applied when the handpiece is not docked, fan fault detection, a cold air mode, a sleep mode, and more. There are PCBs available from OSH Park if you want to attempt it yourself. There are also a few YouTube videos showing the custom firmware, one of which appears below.
In addition to the controller change, [Gabse] shows you some optional tweaks to make the handpiece more robust, change the power plug, and make the cradle sensor more reliable. Worthwhile changes and all well-suited for the processing power of the Arduino.