Humidity control circuit using NAND gate and transistor

An RC self-excited multivibrator is composed of two NAND gates
Di, Dz, resistor Rz, capacitor Cl, etc., with an oscillation frequency of 2.5Hz and an oscillation amplitude of 4V. Humidity resistor RS is used as the temperature detection element. The control circuit is composed of transistors VTi~VT4
.
    When the humidity drops to the set value (can be adjusted by the potentiometer RPi), the relay KA2 is released and the power supply of the dryer is cut off;
at the same time, KAi is closed and the power supply of the humidifier is turned on. When the humidity rises, the RS resistance decreases, and when the humidity reaches the set value.
KA2 closes and repeats the above process to keep the indoor humidity near the set value.