After this tedious step, he designed a PCB that hosts an Arduino Nano to accept input, two MCP23017 GPIO expanders to give it enough outputs, and CD4066BE CMOS switches to trigger the connections.

An Arduino Uno (CH340G clone) reads temperature and humidity from a DHT11 sensor and computes 10+ environmental metrics (heat index, dew point, enthalpy, humidex, vapor pressures, etc.), outputting ...