Over on Hackaday.io, user [Tomasz Jastrzebski] has designed a tidy-looking custom controller for driving temperature-controlled soldering irons. The design is intended to be general purpose, capable of operating with irons rated for different voltages and probe type, be they thermocouple- or thermistor-based. Rather than integrating a power supply, this is handled by an external unit, giving the possibility of feeding this from a variety of sources that are not necessarily tied to the grid.
Hardware-wise, we’ve got the ubiquitous STM32 microcontroller in charge of the show, with a nice front end based on the INA823 instrumentation amplifier, referenced to a REF2030 precision voltage source. The input stage is configured as a versatile Wheatstone bridge input circuit, giving plenty of scope for tweaking.
There are a few extra features in the design that aren’t necessarily needed for a soldering iron driver, such as RTC support, complete with supercapacitor backup, but then this doesn’t have to drive a soldering iron, it could drive any DC heater with temperature feedback. With a change in firmware, this could serve other tasks. One potential feature that springs to mind — have the unit automatically power down at a certain time of day in case it was left on accidentally.
The schematic has a lot of relevant detail — in that many parts have a good list of alternatives, presumably because of the semiconductor shortages — which is a good habit to get into if you ask us. Many of us involved with manufacturing have been doing this for years, as it makes sense to give the assembly house the extra options, but this really is basically mandatory practice now.
Firmware for the STM32G0 series microcontroller is based on the STM32 HAL, keeping it simple, with a Visual Studio Code project provided for your convenience. All hardware (KiCAD) and firmware can be found on the project GitHub.