Sensor type: HR202 (resistive)
Measurement range: 20-95%
Sensor accuracy: ±5%RH

Operation:
In the circuit, the HR202 resistive humidity sensor acts as part of a voltage divider, the resistance of which varies depending on the relative humidity of the air. The voltage of the divider is compared by an LM393 comparator with a reference voltage set by a potentiometer, thus determining whether the humidity falls above or below the set limit. The comparator output controls a transistor, which pulls or releases the relay, thereby automatically switching an external device (e.g. a fan or humidifier) ​​based on the measured humidity.