Between 2018 and 2020 I wrote the control firmware for two industrial units, an air purifier and a humidifier, both on PIC24 microcontrollers. The units and the company that made them belong to the client, so this page only says what the code does.
All of the firmware is mine, from the sensor readings to the user interface. On the purifier it reads the sensors and controls the fans, and the user sets everything through a menu on a display with two text lines. The same work includes pressure sensors, PID control, alarms and Modbus RTU, which lets a larger system talk to the unit.
The humidifier firmware is similar. It uses a different set of sensors, and it can humidify the air in two ways, ultrasonically or by heating water.
I put both units on one page because it was one job for one client, on one family of microcontrollers.