the sorcery of copper
this is about replacement sensor module I designed for the Aplatec DH 10 dehumidifier.
here pictures of the dehumidifier:
here pictures of sensor modules (not mine, but also not an original):
the sensor modules kept failing. my guess for the reason is that the IC and passives are right next to the cold and humid metal radiator, and the plastic separator isn't enough to protect it.
the sensor module uses an unidirectional pulse-width modulation protocol (similar to Infra-Red protocols used by remote controls):
the replacement modules I designed implements this protocol in an STM8S003 micro-controller, and gets the humidity measurements from an AHT20 sensor over I²C. the parts are placed on the front side of the PCB, less exposed to the cold humid metal plate.
here is the schematic, fabrication output, hardware source files, firmware source code, firmware binary